In the last year or so, home calibration of front projectors has become feasible for the average enthusiast, as the prices of test gear have come down and the quality of the instruments has gone up. I feel that more and more we will see people investing in colorimeters, and much like they have taken on the task of performing some of the more simple calibration procedures, like setting brightness, contrast, sharpness, color decoding adjustments, and convergence, they will begin performing more extensive procedures like measuring and adjusting greyscale, gamma, contrast ratio, black level, and light output.

So I figured this would be a good time to discuss what this data means and how it should be applied to get the most performance possible from your projector. I am not writing this to provide a guide, as I am just beginning on this journey myself, but rather to pose questions that I have concerning charts and data in public forum rather than asking them for myself privately.

And by the way, all pictures of charts and data that I will be posting are actual measurements of my InFocus 7210/Greyhawk (edit - Firehawk, not Greyhawk), using the DVI connection from my Panasonic S-97, measured with a Gretag Macbeth EyeOne Pro spectroradiometer running UMR's i1 Pro DCS calibration software in emission mode.

Ok, let's start with the CIE 1931 Tristimulus chart, a chart which provides the user with an overall picture of the color balance:
http://members.cox.net/snidely/postcaltristim.jpg

The squares are for the primary and secondary colors, but of what? I mean, are the 6 squares representing ideal values for the 6 colors, and not actually the measurements from my projector? Well, that would be my assumption, and I would also assume that regardless of how many times I remeasured and what changes I made, those squares would appear at exactly the same coordinates as they are presently. Is this correct?

Now, I can see that there are 6 triangles, and my assumption is that those 6 triangles are the actual measured values from my projector. The red and the blue seem to be pretty much right where they are supposed to be, but as we can see, green is southeast of its ideal values, and is pulling toward yellow. So what do I need to do with green to make it greener and less yellow? And what do those x and y coordinates represent? It looks like I need to go up .04 and to the left .04 units, but what are those units?

Ok, now let's take a look at the secondary colors. They are all off a bit, though nowhere near as much as green is. But there are no secondary color adjustments in my software - only primary gains and biases. So again my assumption would be, if I can move green so that it is on target as well as red and blue, then the secondaries would be pulled into place as well. Is this sound logic? So how do I get green "on target"?

While I am thinking of it, I have the option to measure using two different color gamuts - HDTV or SMPTE-C. I have read "HDTV is recommended for 720p and
1080i tests and SMPTE-C is for 480p and 480i.". My Panny S-97 is an upconverting DVD player, so the source is 480i (DVD) and it is being upconverted to 720p, so which color gamut do I use?

I know that by posting all of these questions I am showing just how stupid I am, but at my age I really don't care any more...:p I could probably get most , if not all, of these answers offline, but I figured that there would be a lot more people who would read this and learn from it, and they might be more concerned about showing their thorough lack of knowledge than I am. If things go well and other "dummies" post more questions or at least post that they are interested in knowing more and continuing with this, AND some of the more knowledgeable members decide to help out, then I will continue on with other charts and graphs until virtually all of the dumb questions have been asked.

This is the standard CIE chart that most magazine reviews use.

Like a world map - it folds the color wavelengths and their mixtures so they are shown in 2D representation. It is one of many color spaces - but this is the one that video standards are based on.

RGB primaries cannot be changed on most projectors - though you can select the color space on the SP7210 - you cannot edit the colors as those are primarily determined by the color wheel. On the NEC HT1100 you can slide the primaries/secondaries along the triangle to the next color. More expensive projectors you can edit the location of the primaries but you cannot get deeper colors than the color wheel allows.

The RGB gain/offsets are used to edit the mixture of primaries that creates white - which is your target in the middle. From there you draw a line from a primary thru white - and that gets the opposing secondary. If they are off the target or off the line or off the triangle it is not perfect- this can be because your white point is wrong, or your primaries are wrong, or your color matrix is wrong, or your video decoder is wrong, or your tint is wrong. How do you know what is wrong you ask? Years of experience getting it wrong before you get it right....

If you use the 1976 CIE it is a perceptual space (what your brain perceives) - rather than the 1931 which is a physical space (what your eyes see)

You would need to research the DVD player forum to find out what your player does on upconversion with the colorspace. The SP7210 defaults to the HD color space (REC709) - you may need to change it to SD space (REC601) to match your player.

BTW that chart is wrong - the SP7210 has deeper reds than the standards - as does the Optoma H79. ColorFacts has an option called constrain to gamut - maybe similar option here.

Hi Kevin,

Thanks for your help!

RGB primaries cannot be changed on most projectors - though you can select the color space on the SP7210 - you cannot edit the colors as those are primarily determined by the color wheel.

That's kinda what I thought. So no matter what adjustments I make to the RGB gains/offsets, the primaries will not change. Is that correct?

How do you know what is wrong you ask? Years of experience getting it wrong before you get it right....

Yeah, I'm beginning to figure that out...:)

If you use the 1976 CIE it is a perceptual space (what your brain perceives) - rather than the 1931 which is a physical space (what your eyes see)

I don't think that I have the option, though I will have to check with Jeff on that.

You would need to research the DVD player forum to find out what your player does on upconversion with the colorspace. The SP7210 defaults to the HD color space (REC709) - you may need to change it to SD space (REC601) to match your player.

The colors look right...If I needed to change to Rec601 wouldn't it be blatantly obvious that something was wrong?

BTW that chart is wrong - the SP7210 has deeper reds than the standards - as does the Optoma H79. ColorFacts has an option called constrain to gamut - maybe similar option here.

What is wrong? I assume that you mean that the red triangle should be elsewhere on the chart, but where? And what exactly is a "deeper" red? Oversaturated?

My measuring technique is far from optimum yet, as I using the emission mode and reading directly off of the screen, so my readings below 30% are rpobably quite inaccurate. Once my new, taller tripod arrives, I plan on remeasuring using the ambient mode by putting a diffuser on the sensor and measuring directly from the projector, which should allow me to get more accurate readings below 30%, and hopefully a more accurate picture of the color balance.

Look at my review for what I got on the CIE chart.

Usually the SD/HD colorspace issue is most noticeable in greens. I had an email into gregr as I had my accupel set wrong - he explained it pretty good.


Think of white balancing as a painter colors wheel - you have three colors Red, Green, Blue that are you mixing to prime the canvas before you paint the picture (though paint is subtractive color so you actually get Mud, light is additive color so you get White). Think of the video picture as water colors - any color in the canvas will show thru.

Bob,

Is your Greyhawk the regular or the reference version? If it’s the regular, it shifts towards blue by about 500 CCT (correlated color temperature) and you should continue to measure from the screen. In other words, if you calibrate the projector directly for D65, the screen will absorb some red and green and the reflected CCT will be about 7000.

Is your Greyhawk the regular or the reference version?

Oops, did I say Greyhawk again? It is a Firehawk, but I don't know if it is the RS or not. I bought just the material itself, and all it said on the packing slip was "bulk material" and never specified anything further.

This is what gregr said about choosing the wrong color space.

"I think you are seeing the effect of the wrong color decoder that you
selected in the projector. If you decode 601 encoded signals with a
709 decoder then the green amplitude is reduced by 15.5% so it looks
darker, (which you may be interpreting as more saturated - it isn't,
it's just darker) and the red amplitude is increased by about 9% and
about 10% green is added to the red, so it looks lighter and is more
orange (it really isn't less saturated, it's a different hue.)"

Reading and interpreting calibration charts and data for dummies

Im really sorry, I wanted to contribute something to this thread but have to exclude myself.

Oops, did I say Greyhawk again? It is a Firehawk, but I don't know if it is the RS or not. I bought just the material itself, and all it said on the packing slip was "bulk material" and never specified anything further.

I think that there is only one version of the Firehawk. Unlike the Greyhawk, I have not measured it and I don't know if it's D65 neutral.

Bob,

It looks to me like you have extraneous light contaminating your measurements or your light levels are too low. Note how green, yellow and red do not form a line on your chart. That should not be the case. You should be able to draw a line from the primaries and the secondary should be on the line. When that is not the case you need to examine your measurement technique.

It is best to use ambient mode for a front projector and place the instrument very close to the lens. The attached file shows how the color triangle should be shaped.

Im really sorry, I wanted to contribute something to this thread but have to exclude myself.

Sure you can, Alan! I represent the "dummy" contingent, so you can contribute by adding to the knowledgeable posts...:)

I think that there is only one version of the Firehawk. Unlike the Greyhawk, I have not measured it and I don't know if it's D65 neutral.

Actually I think there are 2 versions, but from what I have heard the shift toward blue on the original Firehawk is so small as to be neglible for these purposes.

This is what gregr said about choosing the wrong color space.

Regarding the color space issue of the 7210, I found a menu with 4 settings:

1. Auto (default)
2. RGB
3. Rec709
4. Rec601

My setting is "1. Auto". When I tried unchecking the auto box, the projector was now set to RGB (that was the setting that "auto" had chosen for my S-79 [edit: S-97]). I then tried both Rec709 and Rec601, and either of those settings resulted in a very very very green picture, totally unwatchable in any way, so there was no mistake about it - the correct setting is "RGB". How does "RGB" relate to using either SMPTE-C or HDTV as measurement choices? It would seem to me that RGB probably equals SMPTE-C, right? If I am correct, then I should have measured using the SMPTE-C color gamut and not the HDTV.

It looks to me like you have extraneous light contaminating your measurements or your light levels are too low. Note how green, yellow and red do not form a line on your chart. That should not be the case. You should be able to draw a line from the primaries and the secondary should be on the line. When that is not the case you need to examine your measurement technique.

Thanks, Jeff. I only posted one graph so far, and when I post the other graphs, I am sure that we will see problems in my mearsuring technique become more obvious. At this point my intent is just to discuss the graphs to better understand what we are seeing and what it means, good or bad, and you and KRAS have shown how your experience and trained eyes have spotted that something was wrong just from that one graph alone...;)

It is best to use ambient mode for a front projector and place the instrument very close to the lens. The attached file shows how the color triangle should be shaped.

Yes, and that is my intention. I will remeasure in ambient mode as soon as my new 8.5' tripod arrives...:)

Regarding the color space issue of the 7210, I found a menu with 4 settings:

1. Auto (default)
2. RGB
3. Rec709
4. Rec601

My setting is "1. Auto". When I tried unchecking the auto box, the projector was now set to RGB (that was the setting that "auto" had chosen for my S-79). I then tried both Rec709 and Rec601, and either of those settings resulted in a very very very green piucture, totally unwatchable in any way, so there was no mistake about it - the correct setting is "RGB". How does "RGB" relate to using either SMPTE-C or HDTV as measurement choices? It would seem to me that RGB probably equals SMPTE-C, right? If I am correct, then I should have measured using the SMPTE-C color gamut and not the HDTV.


The four settings above are to match the color processing in the projector to the type of signals it is being fed. Apparently you are providing the projector with RGB signals. The Rec 709 and Rec 601 settings are for YCbCr (or YPbPr) signals, (Rec 709 is for HD and Rec 601 is for SD YCbCr to RGB color decoding), which is why they look completely wrong with your RGB signals. The Auto setting will default to RGB when you use DVI signals, but with HDMI signals it will "negotiate" with the source to automatically pick a format that is common to the source and the display, and that will usually be YCbCr (either Rec 601 or Rec 709 depending on the whether the signals are SD or HD).

Greg Rogers
AccuPel
Widescreen Review

Thanks for clearing that up, Greg! One more question - when I measure it (Panny S-97 720p DVI to IF 7210) with my EyeOne, should I choose the HDTV or SMPTE-C gamut?

Bob if you are upconverting in the Panny such that it send RGB over DVI - that means it did the video decoding (YCbCr->RGB) So you need to know when the Panny upconverts to 720P does it assume SD or HD colorspace in the process? Or maybe it assumes HD colorspace but then does not send a full green so as to represent the max SD green which is less than HD? Or maybe it sends a full green thinking you have a SD display - yet full green on the HD display is different?


There seems to be no consistency on how that is done - but see if the DVD forum knows what your specific player is doing.

Yet another reason I am happy with gregr's Accupel black box - you know what you are getting and what to measure!

Digital interconnects have not made video connections bulletproof at all - it just added yet another layer of variables to deal with!

Thanks for clearing that up, Greg! One more question - when I measure it (Panny S-97 720p DVI to IF 7210) with my EyeOne, should I choose the HDTV or SMPTE-C gamut?

The gamut you select shouldn't affect the measurements (unless you have the measurements constrained to the gamut - forced to be wrong - I have no idea why that option is included). I don't use this software, but I suspect the gamut you chose just changes the reference points on your plots, not the measurements that you take.

But something is clearly wrong on the chart at the start of this thread. The yellow measurement is outside the line between the green and red measurements, and that is physically impossible unless the projector has special processing to adjust the primaries separately from the complementary colors, and the 7210 doesn't have that type of processing.

Greg Rogers
AccuPel
Widescreen Review

Digital interconnects have not made video connections bulletproof at all - it just added yet another layer of variables to deal with!

Ain't that the truth!

Greg Rogers
AccuPel
Widescreen Review

gregr

Any idea why ColorFacts defaulted to 'constrain to gamut' at some point - guitarman and I figured that one out after your H79 review - and never got a response from ColorFacts forum (which is now shut down for transferring to the parent company support forum)

Bob

Actually I have the same perfect hue but oversaturated chromaticity for Yellow - that does not lie on the Red/Green line - see my .sig review CIE chart. It is barely noticeable in the CIE76 chart. There must be something in the spectrum that is confusing the sensors (Spyder2 and Eye One).

I think htprojectors.com has the spectral plots of the SP7205.....yep the lamp has a spike at yellow-green then another spike at yellow-orange - but a dip at yellow. I bet that confuses the instruments that maybe do not sample exactly at reference yellow wavelengths (but that is an Eye-One spectral plot). So maybe it is a matrix translation issue from spectral to CIE?

gregr

Any idea why ColorFacts defaulted to 'constrain to gamut' at some point - guitarman and I figured that one out after your H79 review - and never got a response from ColorFacts forum (which is now shut down for transferring to the parent company support forum)

No idea. I can't even think of a reason that ColorFacts has that option. It can only lead to wrong measurements.

Greg Rogers
AccuPel
Widescreen Review

Mark Hunter says here it is a greyscale vs. primary accuracy option....

http://archive.avsforum.com/avs-vb/showthread.php?postid=2821105#post2821105

Not sure why that would be but that is what he said....

The reason for providing "Constrain" primaries is due to the fact that when XYZ colorspace is converted to xyY colorspace an exact match for the coordinates is not always possible! You may in fact end up with a negative value (which is obviously impossible) which will mean that the primary lies outside the boundary of the selected colorspace gamut. When constraining the primaries you are mapping the displays measured RGB primaries and using them on the CIE graph. Since the actual measured values are being used the primaries will always lie directly at the points of the triangle.

The constrain function also allows the bar graph function to be more precise as the distance from the White target to the primaries changes with the colorspace selected. For example the distance from D65 is diffferent to Green for BT-709 then for BT-601 and to a much smaller degree for the other color spaces. This function would not provide accurate percentage values if you did not constrain the primaries.

Cliff Plavin
Progressive Labs

I presume you mean when converting XYZ to RGB that you can be negative - assuming your actual primaries are out of the xy gamut selected. xy is just normalized XY so not sure how it can be negative. So I suspect Mark's comment about more accurate greyscale - really means more accurate % on the RGB barchart/histogram used to help tune the greyscale - but the actual xy target is still accurate either way.

I always make sure this option to constrain is off - the %RGB does not match any projectors RGB adjustment scales anyways so is of little help in being exact beyond math perfection.

The reason for providing "Constrain" primaries is due to the fact that when XYZ colorspace is converted to xyY colorspace an exact match for the coordinates is not always possible! You may in fact end up with a negative value (which is obviously impossible) which will mean that the primary lies outside the boundary of the selected colorspace gamut.

Not true.

x = X / (X+Y+Z)
y= Y / (X+Y+Z)

therefore x and y are always positive because X,Y,Z are always positive.

The X,Y,Z tristimulus values are always positive because they are the integration of the SPD (spectral power distribution) (always positive for any real primaries) weighted by the x-bar, y-bar, z-bar CIE color matching functions (CMFs). The CMFs are entirely positive values. So there is no way to get a negative x,y value from physical primaries, which is what we are measuring.

Primaries that lie outside the standard color triangle gamuts do not generate negative x,y values (as you certainly know). You are confusing issues. Colors that lie outside the display's actual primary triangle would require negative amplitudes of the primary colors, which is why they can't be displayed. But the actual primaries, which is what we are trying to measure, can lie anywhere within the spectral locus without requiring negative RGB amplitudes.

When constraining the primaries you are mapping the displays measured RGB primaries and using them on the CIE graph. Since the actual measured values are being used the primaries will always lie directly at the points of the triangle.

No, that's exactly the problem. Constraining the primaries means that the display's RGB primaries are not being represented correctly on the CIE x,y diagram. They are being arbitrarily constrained within some selectable color gamut (color triangle). This is obvious when you use the software since it produces totally incorrect CIE x,y values when the display primaries are outside arbitrary selected color gamut constraints.

Mark Hunter acknowledges that the "constrain color gamut" option should be turned off in order to measure the color primaries accurately in the link posted above. This is a well-known operator trap in the ColorFacts software.


The constrain function also allows the bar graph function to be more precise as the distance from the White target to the primaries changes with the colorspace selected. For example the distance from D65 is diffferent to Green for BT-709 then for BT-601 and to a much smaller degree for the other color spaces. This function would not provide accurate percentage values if you did not constrain the primaries.

I'm don't remember exactly what the bar graph function does in ColorFacts. Does it display the relative RGB levels required to produce D65 in order to help the user adjust the RGB gain/bias to calibrate the grayscale? If so, then it should compute those levels relative to the measured values of the actual RGB primaries, not some arbitrarily constrained primary coordinates. There would be no point in calculating the relative RGB levels necessary to achieve D65 gray, using RGB primary chromaticities (or SPDs) that are different than what the display actually has to use. But perhaps the bar graph performs some other function.

Mark says the "constrain color gamut" option should be used to optimize grayscale calibration. I would trust that he knows how his product works.

Greg Rogers
AccuPel
Widescreen Review

Not true.

x = X / (X+Y+Z)
y= Y / (X+Y+Z)

therefore x and y are always positive because X,Y,Z are always positive.

The X,Y,Z tristimulus values are always positive because they are the integration of the SPD (spectral power distribution) (always positive for any real primaries) weighted by the x-bar, y-bar, z-bar CIE color matching functions (CMFs). The CMFs are entirely positive values. So there is no way to get a negative x,y value from physical primaries, which is what we are measuring.Greg Rogers
AccuPel
Widescreen Review

I thought this was a thread for DUMMIES :p !

Anyway, I have a dummy question: Kras, I've read several times where you have pointed out that Infocus sort of "cheats" on its green so that it can produce higher lumens - is that one of the reasons why Bob's green is off or is that something totally different?

therealgeno

As long as a few dummies post - then the subject is still valid :p


Bob's green appears to be way off because he is using the original CIE chart. Infocus is aware of the 1976 chart in which the light colors Yellow, Green, Cyan are given less area (and thus errors are less important) than the dark colors Blue, Magenta, Red which are given more area (and thus errors are more important).

So Infocus does push green towards Yellow - as does Optoma who also seems to have recently 'discovered' you can make brighter projectors this way (as opposed to earlier ones that used an overstated Green and were thus dim - but were noticeably different color). Often marketers confuse 'different' with 'better'....

Now manufacturers try to make their projectors noticeably different (Infocus, Sim, Optoma) by pushing reds beyond the Orangy-Red specified in the standards - since pushing Green just makes it dim. Using the latest CIE chart you can see why this is not a good thing - even if it may be pleasing natural Reds it is much more inaccurate than compromising Green for brightness. Video is not capable of a natural Red - so it does look different when it does have a natural Red!

But using the original CIE chart - you would think Red is fine and Green is way off - but that is not what you perceive! See my SP7210 review for both charts to see the differences (while Bob figures out how he can redo his chart!)

That is why our resident expert gregr is using the latest CIE charts in WSR.

Anyways to add to your OCD - you will be pleased to know that your SP4805 has more accurate SD colors than the SP7210. It is not as bright and is thus higher contrast, the greens are more natural per the spec, and the reds are more orange per the spec. (the attached plot is for the HD spec)

Infocus by krasmuzik (http://krasmuzik.home.comcast.net/Infocus.pdf)

Yes I just threw in a curve ball with new charts!

gregr

It was my understanding that was why Colorfacts has you measure primaries before greyscale - so that RGB% can be computed to the actual projector rather than the standard that is never met. If so the 'constrain to gamut' option is still rather unclear why it exists.

That is why ... gregr is using the latest CIE charts in WSR.

The newer (1976) CIE charts that krasmuzik is talking about are called CIE u'v' diagrams. The idea is to convert the x,y coordinates into perceptually more uniform u'v' coordinates, i.e. the ability to perceive differences between colors is more nearly equal to the distance between the colors over the entire u'v' diagram.

However, the u'v' diagram still doesn't express my subjective reaction to color errors. It does a better job of expressing one's ability to discern color errors, but it doesn't express how much I dislike the color error. For instance, I dislike a discernable red color error more than a discernable green color error, even though the errors may be the same distance on the u'v' chart. And I dislike green errors more than blue errors on the u'v' chart. Put another way, I least tolerate red color errors and most tolerate blue color errors. I believe this is a function of how colors typically occur in real images. I'm most sensitive to errors in skin tones, and red primary errors have the most effect on skin tones. Then I'm real sensitive to objects that I know should be red, but look either orange or crimson. After that, I'm particularly aware of green color errors in landscapes, grass, trees, etc. Of course there are exceptions when you are very familar with a particular object that may be rendered incorrectly. For instance, if your favorite sports team wears a bright blue uniform, you may be particularly upset if it is not rendered with exactly the correct hue and saturation. I think my subjective reactions to color errors are fairly typical of most people, but I've never seen a study on that subject.

So interestingly, despite the fact that the CIE u'v' diagram is perceptually more uniform for discerning color errors, the CIE x,y diagram is sometimes a better measure of my subjective dislike for color errors. (It would take another "uniform dislike" diagram to best capture my subjective reaction to color errors.) Nevertheless, I started using the CIE u'v' diagrams back in Issue #82 of WSR. We are now at issue #102. Over that time I've gone back and forth between the x,y, and u'v' diagrams, and sometimes show both in my reviews. Some readers have objected to the u'v' diagrams. They are not as familar with them and make their own measurements using x,y. So by showing both it helps to increase familiarity with the u'v' charts. Othertimes, I still use the x,y charts when I think they better represent my subjective reaction to the color errors.

Greg Rogers
AccuPel
Widescreen Review

therealgeno

Bob's green appears to be way off because he is using the original CIE chart. Infocus is aware of the 1976 chart in which the light colors Yellow, Green, Cyan are given less area (and thus errors are less important) than the dark colors Blue, Magenta, Red which are given more area (and thus errors are more important).



So if Bob was using the correct charts, then green would be closer, if not dead on EVEN THOUGH Infocus pushes green towards yellow?

BTW, gregr, thank you for your last explanation - I could actually follow that one and it makes very good sense.

Could someone post what the 1976 CIE chart looks like - is it the one Kras just linked? Cause I have no idea what I am looking at when those charts are in front of me :p .

And for another dummy question, what do the x,y coordinates mean? And there has been mention of z, although I don't see any z coordinate on the CIE 1931 chart - perhaps it is only on the 1976 chart.

Oh, thanks for starting this thread Bob! I love TRYING to understand this stuff - so thanks to all the vets for chiming in!

gregr

The delC* and delH* charts is based on u*v* which is u'v' scaled by the lightness (L*) of the colors. This tends to temper the u'v' chart which tends to minimize Green error subjectively too much , but does not overstate Green error as much as x,y.

I think these new charts work because green is lighter than blue so it brings out green error a little more even though there are more blue hues it is darker and less objectionable errors. I've been using these charts a few months now- and they generally agree with my subjective impressions of the displays colors, greyscale and gamma.

I suspect the SP7210 having too vivid reds and pale yellow greens but perfect blues does not align with your likes - I need to check your review to see how different the H79 is - as I think the colors are somewhat similar (aside from factory greyscale and 480i decoding). Maybe slightly more red, more green, less blue?


therealgeno

Read Poynton's color science FAQs - he can explain it a lot better than we can! It is a very complicated science.

In a nutshell - XYZ matches your eyes response curves in the blue, green, red spectra - and xy are normalized versions of that (thus you don't need z). CIE u', v' charts are perceptually weighted versions of the CIE x,y color chart, while u*, v* scales u'v' by the lightness L*, which is a perceptual (gamma curve) version of luminance Y.

http://www.poynton.com/ColorFAQ.html

My SP7210 CIE charts are in my .sig link.... click on the review links marked CIE1931 and CIE1976.

The charts I just posted are new ones that I am developing.....

Yes, many thanks to Greg and Kevin for explaining these things to us!

I'm sorry that I haven't posted recently, as I've been plenty busy, but I have been reading and keeping up with the posts. I wonder if Jeff has been lurking as well and might consider adding CIE 1976 charts in a future release.

The next chart is from the same measurement session, and it will hopefully help to explain some of the readings in the CIE 1931 graph:
http://members.cox.net/snidely/postcaldata.jpg
Here we can clearly see that the readings I took below 30% stimulus are inaccurate. I believe this was due to the fact that my projector was mounted normally in its ceiling mount and the readings were taaken in emission mode off of the screen. AAs I can see it, there would have been two better ways to take these measurements that would have resulted in more accuracy in the low percentage stimuli:

1. Move the projector closer to the screen so that the projected image was MUCH smaller (like around 32"X18"), resulting in much higher ftL coming off of the screen and thus moving the measurements into an easier range for the EyeOne to measure.
2. Leave the projector where it was, use a tripod, put a diffuser on the EyeOne sensor (included in the Beamer package), and then take the measurements in the ambient mode, reading directly from the projector lens from a distance of about 2 feet. This would have a very similar effect of moving the measurements to a higher range like in solution #1, except that any color shift happening in the screen would not be considered. Since I am using a Firehawk, my belief is that this color shift would be neglible, but it is still less accurate (IMHO) than taking the measurements off of the screen.

Please also note that the inaccurate measurements in the low percent stimuli also throws any meaningful CR calculations right out the window, though it appears as if no harm was done to the gamma curve measurement, as no numbers were included in its calculations. I also assume that the color coordinates are being affected, as well as the obvious percentage stimulus errors. My intention is to remeasure in ambient mode from about 2 feet once my new 8.5' tripod arrives here (my current tripod is too short for this type of measuring).

Comments? Further clarifications of what we are seeing here?

Bob

I think your color accuracy of the Eye One is going out the window before your luminance accuracy as it gets darker. Red is a darker color and Blue is even darker - and this is generally where I see inaccuracy with Eye One measurements.

So yes a brighter image which ever way you can manage helps. Also with the firehawk watch your measurement angle -if you are right at the screen you are avoiding the sensor shadow you are probably at a severe angle.

I like to use a 2' wide image size - as it makes the lumens math easy (2.25sqft) my Spyder2 can take the 300-400ftL this gives me. ColorFacts has a training mode - the idea is you read a white screen with the EyeOne to find the color error of the screen - then read from the projector with a correction factor for the screen.

As far as I can remember, all DLPs have shown green being towards yellow to one degree or another in the CIE charts I've seen reproduced, so I was assuming this was a technology issue rather than a preference from the manufacturer. I've also seen the measured triangle to show red slightly more saturated as well as the green towards yellow so thought that this was down to the displays colour replication being skewed in that direction, and having moveable primaries would fix it perhaps. Or am I missing something?

If the CIE 'shark fin' is the colour gamut visible to the human eye, will we benefit from being able to reproduce the colours that exceed the triangles of PAL, NTSC, HDTV? Some say the colours (such as red) are over saturated if they are measured outside the system gamut, yet it's still someway form the maximum range of the visible gamut (or is it just exceeding the syatems gamut range and crushing maybe?). Why don't we realise the currently constrained gamuts aren't the full gamut or is the eye/brain easily fooled and readily acceptable to this 'trickery' so believes the colour range to be 'true color'?

Sorry for all the questions but these are a few that I've been meaning to ask for a while now - I want to learn this stuff and even when I think I'm getting to grips with just a small part of it the experts quickly show me there's so much more to know. Keep it up guys!!

Gary.

therealgeno

Read Poynton's color science FAQs - he can explain it a lot better than we can! It is a very complicated science.



Excellent link - thank you very much.

Gary

Wide gamut HDTV is actually discussed in Poynton's HDTV book that I have - but I would imagine until we get laser displays that no manufacturer wants to implement. What we have is a manufacturing compromise - the original NTSC green was a much deeper forest green and was replaced ages ago.

It is not so much a technical issue that DLP Green is often Yellow - the JKP Samsung is correct and some others have a deeper Forest Green (Optoma H30). The problem is lumens - luminance is primarily composed of Green - so the brighter green you have the brighter your display. Since nobody wants to market a display less than 1000 lumens (even though calibrated they are always less except Infocus ScreenPlay) - that really is not possible to do with displays that have Forest Green. So does the market want an accurate display - or do they want a 10' widescreen that works in the daylite?

I thought the HT mag review of the JKP Samsung was rather tepid solely because the brightness and contrast was nothing special - even though the colorimetry, greyscale, and gamma, and video decoding were perfect.

So until the market gets focused away from the marketing numbers and into the real engineering numbers - I don't think things will change. Once they do get it - maybe then wide gamut HDTV will become a reality because the market will clamour for it. But that will require an all new source cheap.

Why do dogs eat dogfood? Because it is what we give them!

The delC* and delH* charts is based on u*v* which is u'v' scaled by the lightness (L*) of the colors. This tends to temper the u'v' chart which tends to minimize Green error subjectively too much , but does not overstate Green error as much as x,y.

I think these new charts work because green is lighter than blue ...

Green is also much lighter than red, so I'm not sure it wouldn't overemphasize green errors compared to red errors. But I'll try some plots to see how it maps to my subjective impressions on the next few projectors I review. I'm not sure how intuitive deltaC*, deltaH* plots would be for magazine reviews, but that's a different issue. Didn't you email me an example of those plots several months ago? I seem to remember that, but I can't find them now.

Greg Rogers
AccuPel
Widescreen Review

Kevin - I definitely like the revised MATLAB charts. They are really looking good now! (I'm not sure how I missed this thread...).

Bob - Definitely check your measurement technique. However, the rest of it is looking pretty good if you can validate the rest of the measurements. As a note, when I was putting my H77 through its paces using both the EyeOne and Spyder2, I definitely noticed a drop off at lower light levels with the EyeOne (Jeff recommended >5 Lux or so if I remember correctly!). Check out Kevin's technique to make sure that you are getting enough light into the meter.

One quick question, though: how important is focus here? I would imagine that some projectors may be dim enough and have a long enough throw that focusing at 2' - 3' may be more than the optics can handle.

Later,
Bill

gregr

Yeah - go ahead and use the one I linked to as it is the latest version. I just finished grad school course work and looking at these again - thought it time to put them out for public comment. Anyone is free to use - even ghbliss/umr/Ursa - though Excel is not very chart friendly! I fully intend to make sure ColorFacts gets it into a version update ASAP since it is what I use. No benefit to keeping it to myself if nobody else uses it and I have to explain it every time.

I have the specific equation references from the texts if anyone needs them - all I did was invent the visualization to focus on what I think is objectively/perceptually important. This is something I have lots of practice from using Matlab in my Acoustic Engineering assessments- my last assessment was 10Mb of .pdf charts/text and several 80Mb movies!

On delC*, delH* - while Green is much lighter than Red it is balanced out by the Green area being much smaller than Red on the u'v' chart. On the SP7210 it makes it clear that the Red (which is oversaturated) is worse error than the Green (which is desaturated towards yellow) - but it is hard to see either of those things looking at the CIE charts. On CIE31 Red looks perfect while Green looks bad, and CIE76 they look to be about equal error. But watching the SP7210 projector - the Reds are the first thing you notice - and you are hard pressed to see the Greens compared to the SP4805 (which is better color all around - just slightly desaturated)

The u*, v* should be obvious - it is not much different from an existing ColorFacts x,y chart - still need to double check my math on the angles for the different colors. Note I use u*, v* and not u', v' - this is intentional since black has no color by definition it should not show any error even though your sensor always shows more color error - and color at 10% is very hard to see so it's error range is limited - and so on out to white. The key was adding the radial circles at consistent target points - I hate how ColorFacts does an arbitrary zoom. You can easily see how white peaking and yellow/white segments or auto-iris causes color shifts using this chart.

Notice I do not do RGB bars and 6500K lines - as they are meaningless! Customers only expect them because we keep telling them to! I hate the RGB bars almost as much as the useless 6500K chart - as we have already pointed out in this thread - was it calculated with the primaries measured or not - and is it relative to an arbitrary gamut? How is the customer supposed to know that +Blue+Green means it is pushing Cyan?

delC* and delH* I think came from the Color Science using MatLab book - not the simple h angle that poynton uses - but a normalized version so that you can use it in delE units (the radius is delE). I have thought of surrounding color bubbles to help visualize this chart better - as it is the one I have to most explain. It assumes the L* between the color reference and target is the same - Colorfacts does not report this - and that would require a 3D target chart. I just took AV/Pro training from SethS - and the Runco VX2 has the ability to do not just blue only like the SP7210 - but RGBCMY only modes so that you can measure the video color decoder levels! I need to experiment with lens and filters to see if there is some way to more easily measure this on other projectors.

I toyed with gamma math for a while - I finally get the same numbers as ColorFacts. I did the average of each "IRE" step for a while like WSR/gregr and umr- but I think these is more meaningful using lightness variation - turns out we cannot see these slight slope differences. I want charts that represent what we see - not what we can't see. This is why the gamma chart is flat - if gamma is flat it will look tonally smooth. Infocus does exceptionally well on gamma - I have reviewed others that really kink this chart. I decided not to grade the gamma value itself - as that is purely subjective to your environment.

I may still assign letter or percentile grades just for those people that have to have a number and cannot figure this out from the target lines/circles. And I need to add brightness/contrast comparisons - I am toying with some novel ideas of presentation there as well - like validating marketing claims. The idea is to present these charts for the best calibrated preset, best contrast, brightest, and ISF calibrated so that people can really see what the marketed numbers are costing them. I think that is what is lacking in reviews currently (I know - more magazine space is required for ads not charts!)


Ursa

I have no problems focusing such a small image - but I don't think it matters when you are measuring color and brightness. I don't quite have room in the office setup to measure long/short throw differences with the lens - but something I want to look into.

Kevin - That's about what I thought. As for this:

It was my understanding that was why Colorfacts has you measure primaries before greyscale - so that RGB% can be computed to the actual projector rather than the standard that is never met. If so the 'constrain to gamut' option is still rather unclear why it exists.
If they do RGB% the way I do it, then it is merely the average color balance throughout the grayscale (10% stimulus and up for me). Others I have seen normalize the primary components, but that leads you to having no deviation at 100% Stim, which is not correct. I'll let Jeff comment on how he does it, but I do not know how ColorFacts does it.

Later,
Bill

I use the reference primaries for the RGB deviation although this is user configurable if someone wants to modify the spreadsheet to use display primaries instead. It seems to me to be a toss-up as to which you choose to use.

Using reference primaries:

Pro - no pre sampling required, gives a consistent reference for color error between displays
Con - less accurate for guiding a user on setting gray scale

I also did some testing on one of my displays that allows manual selection of color space for each input type to test the color space hypothesis for Bob's results. I tested a 480p and 720p component input from my AccuPel generator using 75% color windows with SD and HD color space processing on each. I could not see any shift in the primaries at all while the secondaries moved along the line between the primaries. With my display and signals I could not verify that Bob's results are the result of improper color decoding.

Not only is accuracy decreasing at lower light levels, but the influence of light that is contaminating the measurement also increases. Low light levels require dramatic efforts to exclude extraneous light.

gregr
Yeah - go ahead and use the one I linked to as it is the latest version.

Sorry, but I can't find the link you are talking about. I would really like to look at your delC*, delH* charts, but I can't find them.


On delC*, delH* - while Green is much lighter than Red it is balanced out by the Green area being much smaller than Red on the u'v' chart.

If you look at the MacAdam Ellipses on a u'v' chart they are similar in size near green and red. Of course the same is true for a u*v* chart for a constant L*. So the big difference between the luminance (Y) of green and red still concerns me (L* being related to the cube root of Y). The problem with using delC*, delH* alone to express the color difference is that doesn't fully incorporate delL*, i.e. the total color difference is delE* = SQRT [ (delL*)^2 + delC*^2 + delH*^2]. This is more easily expressed as the L*u*v* color-difference equation, delE* = SQRT [ (delL*)^2 + delu*^2 + delv*^2], which I use to express grayscale differences in my reviews (given that the measured grayscale luminance is equal to the target luminance, delL* = 0). But delL*=0 doesn't hold when comparing the relative perception of color differences around two colors that have widely different luminance values.

I'm sure this is getting too technical for this thread so perhaps we should take the color science discussion off line.


I toyed with gamma math for a while - I finally get the same numbers as ColorFacts. I did the average of each "IRE" step for a while like WSR/gregr and umr- but I think these is more meaningful using lightness variation - turns out we cannot see these slight slope differences. I want charts that represent what we see - not what we can't see.

I plot (or sometimes just describe in words) the "equivalent gamma" at 10 IRE steps over the grayscale, not an average of anything. It makes a huge visual difference if the gamma at 10 IRE changes to say 2.2 from 2.4 between 20 to 90 IRE. But many projectors have a much less constant gamma than that, and the differences are very visible.

I think that is what is lacking in reviews currently (I know - more magazine space is required for ads not charts!)

It's really not ad space that limits the number of charts in my projector reviews, which are usually 7-8 pages of pretty small print (that's probably 3x the length - in words - of the reviews in most magazines). Complex charts, that many readers won't understand, reduces readership and magazines must have readers (to get ads) to survive. Widescreen Review is certainly the most technical home theater magazine available in the US. WSR could increase its circulation by becoming less technical, but fortunately the publisher prefers to maintain the technical level of the magazine. I think my reviews include much more technical information than any other magazines, and as much as I might like to just write an engineering lab report for every review, we have to serve a slightly wider customer base. That said, I'm always open to finding a better way to show information, if I can make it understandable to our readers. Which takes me back to the beginning of this posting. Where are your charts posted? :)

Greg Rogers
AccuPel
Widescreen Review

Greg,

Off topic post...

I really appreciate your reviews they are always very well done. I would be very careful about changing how you present the information. Deviating greatly from other sources both current and historical would make it more difficult to compare displays on an equal basis.

Stupid AVSes new bulletin board does not underline links anymore.

It was in this post

http://www.avsforum.com/avs-vb/showthread.php?p=6143279&&#post6143279

click on the 'Infocus by krasmuzik' words

I was thinking of HomeTheaterMag when I said 2" charts - I think you get 3" charts and more of them! Anyways I reupped WSR because of your reviews - sorry about being flippant on that! In fact I was just at WSR headquarters for SethS AV/Pro training - amazing theater!

My goal here is indeed to reinvent the way that calibrations are charted. My experience with customers is they are unable to translate the existing charts no matter how scientifically simple I get on them into what they see - and they are not useful enough to me for doing detailed comparisons of displays.


My comment about gamma was the chart itself - we don't see gamma "transitions" - we see lightness variations from an ideal. I am striving to use perceptual measures in all my charts now in a way that are meaningful to both the calibrator and customer without having to teach color science to my customer.


delE* = SQRT [ (delL*)^2 + delu*^2 + delv*^2],

Rather than report delE directly in a confusing 3D chart (delE is simply the distance from origin (D65) to the cartesian L*u*v* points) -I would rather report the delL* from an ideal gamma curve (my last chart), and the delu*, delv* from D65 (my first chart) in the colorspace. The reason is the major problem in greyscale are those two things - gamma tracking and color shifts. delE is a single number that says it is off - but does not say why it is off - which is what I end up having to explain. Using these charts I can point to them and say something like "your bright whites shifted Cyan, and your dark blacks are a bit Red, and your middle greys are too light" - rather than - "You are within 10 dE".


delE* = SQRT [ (delL*)^2 + delC*^2 + delH*^2].

This I do use for the color target - ColorFacts does not dump out delL (I have to write an automation script then I can get it). I suppose if the color decoder is off (red push) you could have some delL* not showing up on the delC* delH* chart - but I would again prefer to avoid a confusing 3D chart and think of a good way of showing that in 2-2D charts.

On all my charts I use the L* of the ideal target color or greyscale point rather than 100%. Color L* I get from the HD/SD standard (convert Y), and greyscale L% I get from the ideal gamma fit.


umr/Ursa/ghbliss/Milori etc. are all welcome to participate if they want - I don't think discussing known color science should be tool/review proprietary - but maybe they think otherwise. Others have said they glean something amongst the scientific ramblings - so I help someone learns something! My goal is objective perceptual measures that can be used to compare pre/post calibration or A vs. B displays that Joe Blow can understand - so if they chime in and say hey I am confused - then I know there is more chart work to do.

And if my posts seem to be not very lucid - I have a good excuse besides fumble fingers - I had dental surgery last week and still on dental narcotics!

umr

I very much disagree with that- already you cannot compare CIE charts across magazines and even across reviewers. The may use a different mode than the other guy, a different screen, a different measurement setup. I searched the archives of HTMag and WSR - and found only one review that even correlated on projector mode setup (Sony HS51) - and the results did not even agree!

So I don't think that arguing that this is the way it always has been so don't change or I cannot compare is valid. It is still going to be true that you cannot compare even if you change charts for the same reasons.

The reality is most people reading these reviews do not even understand the colorscience behind the charts they are looking at - and have no idea how to compare a CIE chart or 6500K chart. I know because I have hung out in the <$3500 forum which most calibrators don't do - explaining the color science is way to difficult. That is why I do want to change the way I chart to objective/perceptual measures - because it helps my customers understand better what I did for them. I am not at all concerned that they cannot compare my work to a magazine review they read! What I am comparing against are the standards - and these charts do present that.

"Mark says the "constrain color gamut" option should be used to optimize grayscale calibration. I would trust that he knows how his product works."

Go it, good timing also as I'm doing 50 grayscale tunings in the next five weeks. :)
Got colorfacts! Don't use contrain to gamut for CIE readings just grayscale tunings.

Thx Greg.

guitarman

so the mail-in thing really works - I was afraid they would all be buying the SpyderTV instead! Guess I better get on the ball before you service the entire AVS market! :D

I would still not use the option - after discussion it sounds like Mark was really saying it makes the RGB % be relative to the standard you are tuning to - yet your displays primaries are likely not that standard. So you should first measure your RGB primaries - then your RGB% should be relative to those and be better for greyscale tuning.

krasmuzik,

I did not say the comparisons were perfect, but switching to a completely different coordinate system makes them even more difficult.

I am not arguing. I was stating my opinion.

I see no reason to contribute to your posts since you seem to have all the answers.

The large number amount is linked up to the upgrade firmware deal. Now you're saying leave it unchecked all the time? Did we get that wrong or misunderstood with Mark saying check it for grayscale tuning?

Actually 1976 has both the L*u*v* and L*a*b* standards - they are more suited to different applications. L*a*b* was because textile/paint etc are more suited to surface colors under various illumuniations. Lu'v' was more suited to self-luminous sources. Poynton does not discuss this - but it is covered in detail in the MatLab color science reference I have. Many of the more advanced error measures from the last decade are based on the CIELAB for the surface color industry.

And of course if I am talking to customers I don't talk in coordinate systems polar, cartesian, CIE or whatever.

I show them the greyscale target and say - see the colorwheel overlaying the target - that is the color that your greyscale was pushing.

I show them the color target and say - see the colored dots - this represents the colorfulness (B&W to laser intensity) and hue (rainbow) errors w.r.t. to the HD (or SD) standard.

Then I show them the gamma plot - and see how the lightness does not track?

This explanation of the color charts has no color science in it whatsover - you really do not have to explain the math behind the charts. It is a target - Joe Blow can understand a target. Most importantly being perceptual math - it is a target that represents what he sees.

Unlike if you show a 6500K chart - you have to explain the concepts of black body curve, and CCT and get into the science simply to explain that if that graph is on target - it may still not be calibrated as it might be Magenta or green. Then you show them the RGB histogram and they go - so where is the Magenta you talked about? OK Red+Blue = Magenta - then you argue about Magenta is not Purple as that is surface color mixing not light mixing......



This is much better than showing the RGB histogram (and I know guitarman is fond of that one) - unless you know your color science that Green+Blue is Cyan you cannot interpret it - and if the are various method for computing RGB% it really does not say anything.

I would still not use the option - after discussion it sounds like Mark was really saying it makes the RGB % be relative to the standard you are tuning to - yet your displays primaries are likely not that standard. So you should first measure your RGB primaries - then your RGB% should be relative to those and be better for greyscale tuning.

Yeah, I agree that RGB% measurements don't have much useful meaning unless they are made relative to the display's actual primary colors, as I said way back earlier in this thread.

Anyway, I would hope that the constrain option doesn't really affect the grayscale measurements at all, just the RGB% numbers. If I had time (which I don't) I would dig out ColorFacts and see if it affects the actual x,y,Y grayscale measurements.

Greg Rogers
AccuPel
Widescreen Review

umr

I am not trying to be argumentative here about your software! I am going off my experience getting customers to understand decade old conventions of the ISF way of presenting things - which currently does not even recognize or teach that the perceptual measures exist - even though Video Experts like Poynton do discuss them. I don't have all the answers which is why I hope to have a discussion about better ways of doing things - not reject them out of hand because they are "different".

It used to be 6500K charts were what all the magazines presented - before someone had the nerve to drop it and present the CIE chart with RGBW plots - and Greg has expanded that out alternating between the different CIE versions to highlite RGBCMY differences (which the other magazine does not even measure - but happily say it was only 500K off - and as a calibrator that tells me nothing!). The other magazine has no concept of gamma or even dE - and gregr discusses it - should he not because it is a new chart?

If we sticked to the old way of doing things we would show up with our composite LD and our blue filters - and look at a few testpatterns and say yep you are good - that will be $450 please.

Greg,

I think you would find the differences between using the displays primaries and the reference primaries on the RGB calculations are small enough to not render the values useless. These errors will diminish to zero at D65 with the method I used to formulate the solution.

Here is an example:

RGB percentages using reference primaries.

78% 88% 124%
81% 99% 111%
84% 105% 104%
86% 105% 103%
86% 102% 105%
88% 102% 105%
90% 101% 105%
90% 99% 107%
91% 98% 107%
92% 97% 108%

RGB percentages with display primaries.

73% 89% 118%
78% 99% 109%
84% 104% 103%
86% 104% 102%
85% 102% 104%
87% 101% 104%
89% 101% 104%
89% 99% 105%
90% 98% 105%
90% 97% 106%

Display primaries used in example...

Red Green Blue
x 0.7000 0.29 0.18
y 0.3392 0.7 0.05

Kevin,

I am not saying a new metric may not be warrented at times, but it needs to be tempered with what is lost. Obviously adding something is no problem at all unless it confuses people.

The large number amount is linked up to the upgrade firmware deal. Now you're saying leave it unchecked all the time? Did we get that wrong or misunderstood with Mark saying check it for grayscale tuning?

You realize that quote was from Mark was years ago in the archives? What numbers and firmware are you talking about here?

umr

Yes the RGB% accuracy makes me wonder what the whole point of the CF gamut option was to begin with - all RGB% is for is to say "you are off so fix it"!. Where is Mark anyways - he surely can ask Heath what the history on this was. I cannot say I noticed any greyscale changes when I switched it off - but it sure opened my eyes about oversaturated primaries (as guitarman would concur - I think we both were saying Optoma/Infocus had perfect reds). But it would be nice to know for sure that leaving it off is no harm.


I at least want to do away with the 6500K chart - it is misleading to the point of detrimental. I cringe everytime a calibrator review presents the 6500K chart as if it were the summary of the performance.

If you think of the color/greyscales targets as zooms onto the CIE chart RGBCMY points - it really is not different - just a closer view. The CIE shows you the gamut triangle - this gets you zoomed into to see what the color errors really are (I have even tried overlaying the little magazine charts against a light source to try to compare and it is a useless effort....). Now if they publish the x,y values - I enter it into the graphs and compare.

I do wish everyone would publish the xy values they measure.

I at least want to do away with the 6500K chart - it is misleading to the point of detrimental. I cringe everytime a calibrator review presents the 6500K chart as if it were the summary of the performance.

Are you talking about this chart?
http://members.cox.net/snidely/postcalcolortemp.jpg


And earlier this chart?
http://members.cox.net/snidely/postcalrgbtarget.jpg
These charts seem to be useful in that I have an idea where I need to go with my RGB gains/biases, or are you saying that these charts are useless?

I would not say that RGB chart is useless. I use it all the time and get great results with it.

The color temperature chart is next to useless, but many people want to see it.

This whole metric discussion is a major side issue. Without good measurement technique and quality instrumentation all the metrics are useless. Metrics can bring value once you have good measurements, but until you do they are worthless.

It was in this post ...
Thanks, I got it. You've done a lot of good work and thinking here, but I probably come to different conclusions on the grayscale/gamma graphs.


My comment about gamma was the chart itself - we don't see gamma "transitions" - we see lightness variations from an ideal.

That's a reasonable point, but plotting the L* error from a constant gamma (your gamma graphs) could really confuse the reader. In most situations it will be more important to have the right gamma with slightly bigger L* deviations, than the wrong gamma with slightly smaller L* deviations. In other words, a perfectly constant gamma of 1.8 is not going to be better than a gamma of 2.4 that varies slightly above and below 2.4. So the chart with the "best shape" doesn't necessarily convey the best performance, and the reader must somehow decide how to trade off different L* errors between charts with different average gammas. There is no way they are going to be able to do that. There are other practical issues such as a projector that has 15 different gamma curves, as some do, you would need 15 different charts to be readable with decent resolution.

delE is a single number that says it is off - but does not say why it is off - which is what I end up having to explain.

With respect to grayscale, which is where I use delE, when the calibrated grayscale is within a delE of about 2-3, it is so close to correct it doesn't really matter much whether it is off because it is slightly red or slightly blue, i.e. most users can't see a difference. But when it off by more than about delE=3, then the user can see the color shift and so that is something that is useful to describe. (I generally do this with words in the review to describe what happens at the dark end of the grayscale for instance.) I have thought about adding the h (hue) angle to the delE table so the hue color is known to anyone that wants the information, and then plotting a polar graph of delE and hue angle, which is essentially the same thing as your u*v* plot. The problem with the plot is that lots of points typically overlap each other and it is difficult to impossible to tell what point corresponds to what IRE value. Therefore, it is usually easier and clearer to simply say something like the delE value was 6 (significant) and the grayscale become blue at 10 IRE.

BTW, I should just note that the nearly worthless color temperature graphs that you see in WSR were there before I arrived (I added the delE measurements), and they have remained there because other magazines publish them. If we took them out, then less knowledeable readers would assume that we don't provide all of the information they can get from other magazines. So in almost every review I have to say that the delE values are what is most important for grayscale accuracy.

Anyway, I will play around with your delH*,delC* graphs for the color primaries and secondaries and see if they are an improvement (IMO) for describing the perceptual and subjective dislike of color errors.

Greg Rogers
AccuPel
Widescreen Review

This whole metric discussion is a major side issue. Without good measurement technique and quality instrumentation all the metrics are useless. Metrics can bring value once you have good measurements, but until you do they are worthless.

I'm just bringing in these charts for discussion purposes. I have to wait until the new tripod gets here before I am able to take better measurements using ambient mode.

Not only is accuracy decreasing at lower light levels, but the influence of light that is contaminating the measurement also increases. Low light levels require dramatic efforts to exclude extraneous light.

Actually my room conditions are quite good. The room is 100% light controlled, with very dark carpeted walls and floor, and a black velvet ceiling. I went to the extent of covering my equipment rack with a blanket in order to avoid any contamination from the LEDs. I also threw a black velvet cloth over my laptop to contain any other light and even faced my Pronto into a black cloth. The only source of any ambient light that I could imagine would come off of the screen itself. I wonder if having the EyeOne facing the screen is a good idea at all, as it might "gather" light from other areas of the screen. Thoughts?

The beamer at just 2' away from the screen produces a focused spot about the size of a quarter.

Kras I was talking about the H77 DMD upgrade firmware. 50 people want it and also want a grayscale tuning while I have their machines.

gregr

It was my understanding that was why Colorfacts has you measure primaries before greyscale - so that RGB% can be computed to the actual projector rather than the standard that is never met. If so the 'constrain to gamut' option is still rather unclear why it exists.

So, if I wanted to do a greyscale on a pj, I should take a primaries measurement first (and make sure the constrain option is unticked which it was when I last looked), then do the greyscale. Does CF remember the primaries data afterwards then and use it to calculate for greyscale better?

Also, and not wanting to appear to be too much of a dummy, but why is the colour temp graph so useless? Isn't it useful to see how far the greyscale was out before being calibrated so a potential purchaser knows how innacurate (or accurate) for greyscale the pj is likely to be?

Gary.

Gary Lightfoot,

Correlated color temperature is not very useful because a color temperature is a line on the xy coordinate system and not a point. The goal is to target D65 as the white point which is at x=0.3127 and y=0.3290. CCT does not describe this point to enough precision to be very useful.

For example, 6500K could be D65 and it might not be. A measurement at 6600K could possibly be closer than one at 6500K to D65. That is why a color tolerancing function like delta E of some form is much more useful.

Here is a link to a diagram that illustrates the problem.

http://www.ecse.rpi.edu/~schubert/Light-Emitting-Diodes-dot-org/chap18/F18-05%20CCT%20in%20xy%20diagram.jpg

guitarman

Great angle with Optoma firmware there - really am suprised they 'authorized' an 'unauthorized 'service! And you get the calibration bucks to boot while it is there! I have often wanted to clean customers colorwheels (NEC HT1100, SP4805 has a problem) - but no way I would touch it unauthorized - I would have to buy the projector if I had too much caffeine and broke a wheel! If I was guaranteed a dealer or calibrator authorized warranty colorwheel replacement - I would be doing it like crazy - as it makes a huge difference on projectors for which it is a problem! (and I see someone on cheaper projector forum posted same thing about LCD polarizers needing cleaning)

Bob

Ok back to the calibration charts for dummies. I'll let my charts soak in - they make sense to me anyways.

Why is 6500K useless? To explain it you need a CIE chart that has the black body curve on it - I have several copyrighted versions I cannot scan - but if anyone has a handy link. Think of the black body curve as the color of flame (technically incorrect analogy - but close enough) - red flame is warm, white flame is warmer, blue flame is hottest. What nobody realizes is that if you have a different element inflamed - you can actually get a different color than that curve - a green flame or a magenta flame. Think of your pressed christmas log with the wierd chemicals in it that makes the purty colors. To accomdate that - the invented the 6500K CCT (correlated color temperature). to capture those other colors normal (perpincular) to that curve that are the same 'temperature' but a different color.

So if the calibrator or customer or manfacturer focuses on the 6500K chart- you can actually have a major Green or Magenta push to White - yet still be absolutely perfect per the curve. Now it is now small accident that more green means more brighter displays - don't you think manufacturers would love it if we still used this 6500K measures? They can do green whites and nobody would be the wiser. Just like whiter than white Tide is actually a bluing agent....

It should have been dropped a long time ago to give the x,y coordinates in the CIE space - which is how all the video color standards define their greyscale and color points.

Why is RGB barchart useless? As we discussed the % maybe meaningless - already it looks like Ursa, ColorFacts, and umr are using different methods to figure the %. So a % chart across softwares may be meaningless. What if one guy zooms the chart - and the other does not - (this one really annoys me - as the default in ColorFacts is non-zoomed in which everything looks perfect - the first bar is 20% off!) So you label the chart (but the labels are not ever going to be intelligible on a jpeg or 2" magazine offset print).

OK disregrad all that and assume calculates the % and presents it the same way. What does it mean to you as a calibrator? Are your projector control labels for RGB gain/offset correlated with those % labels - NOPE!. Do you really think your customer knows what color a +10%R, -7%G, +16%B is - I have no idea myself!. And if another display is +5%R, +8%G, -12%B - can you tell which display is better by looking at this chart?

So this RBGB chart is really only usefully for getting the bars even. I bet as a novice calibrator - you did not know that when it says more Red, maybe you want to cut the other colors - how do you know which to do based on this chart (you don't) When I calibrate at local meets they are always confounded that I do not move in the directions the RGB bars are telling me - and that is a newbie assumption that I must be doing it 'wrong' I do however use the RGB histogram - solely for telling me when I have reached my RGB clipping points - because the lines will clip.

Greg

I did have an idea to stack all the gamma modes available onto one chart - so you can see 1.8 vs. 2.5 vs. 3.0 and how each of them varies individually. Just not sure how best to present it and still be understandable.

The greyscale chart I found most of my customers have groked it without any explanation - indeed the intent of the chart was to put into a picture what is said with a thousand words about the greyscale (what colors it is pushing to) and do what is difficult to say in words - how much it is pushing. The radius is indeed dC*.

Look at the older charts I just sent you that have bad greyscale - the dots are not cluttered all over the place (I hate the colorfacts report for that very reason!) - because I use L* from the ideal gamma fit to scale each dot. Black dot is always at the center - because black cannot have color. White dot is usually furthest away because White is brightest and can thus have the most color error (it would be more correct to say Chroma or Colorfulness error per Poynton - read his rants about video control names).

Colorfacts prints charts with or without the table of numbers as the calibrator always wants to record the real numbers - but the customer usually just wants the executive one-page summary with just the charts. I have done enough executive presentations in my former engineering career to know - the chart better say what you want it to say - don't make the executive thumb thru tables of data or worse yet - actually read a sentence!

Gary

Yes - do the Primaries & Secondaries measures first. Why Secondaries? If secondaries are off it is color decoder error or grey scale error. It is a lot easier to see your White is Blue by noticing that Cyan & Magenta are blue. Now do your greyscale.

Now retake the Primaries & Secondaries. The Primaries will not change - if they do your sensor or environment is drifiting - but the Secondaries should change!. Secondaries should be on the triangle edges - as well as be on a line thru White to the opposing primary. If not you have basic adjustment error - or service menu decoder error to fix (if the manufactuerer allows it!)

Greg,

I think you would find the differences between using the displays primaries and the reference primaries on the RGB calculations are small enough to not render the values useless.

I realize the differences aren't huge, but if the purpose of the RGB percentages is to adjust the RGB gain and bias controls to calibrate the grayscale, it makes those RGB percentages less accurate to calculate them relative to an idealized set of RGB primaries (even if the errors are small). The errors will even be different if you use the Rec 709 primaries, or the Rec 601 (SMPTE C) primaries. So why would/should a user pick Rec 601 vs Rec 709 to constrain to when they give different answers (both wrong)? The only advantage for using some arbitrary set of primaries is that the user doesn't have to take time to let the measuring instrument "learn" the actual primaries. That's reasonable because the errors are usually pretty small, and I would hope the user will ultimately finish the grayscale adjustment by looking at the x,y & dE(dC) values, not the RGB percentages. But the RGB percentages are still more accurate when the instrument "learns" the actual primaries.

So I still don't know why Mark said it was more accurate to use the "constrain" option when calibrating grayscale, but I do believe Mark understands his own product. I suspect we don't know the full context of what he meant, or what he was thinking. Perhaps he meant that if the instrument had previously "learned" very different primaries on another display, and you weren't going to take time for the instrument to learn the new primaries, that you would typically get smaller errors with the constain option.


Display primaries used in example...

Red Green Blue
x 0.7000 0.29 0.18
y 0.3392 0.7 0.05
I presume you just made up these x,y values because the red primary is impossible. The sum of x+y+z must always equal 1. In this example x+y=1.0392, which is impossible because z can not be negative.

Greg Rogers
AccuPel
Widescreen Review

I did just make up some very large errors in the primaries to illustrate the errors are small even in an extreme case. With reasonable primaries the differences are so small that they do not show up on most readings.

My goal in doing the calculations this way is to simplify the process and eliminate the potential error a person could enter into the equation if they measured the wrong color at the wrong time (i.e. red as green). That would provide completely wrong guidance and frustrate the process. I prefer eliminating those huge errors over eliminating some vanishingly small errors that are irrelevant to the process. I also recommend people check their calibration with a delta E function.

My goal in doing the calculations this way is to simplify the process and eliminate the potential error a person could enter into the equation if they measured the wrong color at the wrong time (i.e. red as green). That would provide completely wrong guidance and frustrate the process. I prefer eliminating those huge errors over eliminating some vanishingly small errors that are irrelevant to the process. I also recommend people check their calibration with a delta E function.


Good point, that would certainly frustrate the process without some primary error checking. And as krasmuzik suggested, I don't suppose anyone is looking at the actual numbers anyway. They are just trying to line up the RGB bars by increasing/decreasing the RGB gain and bias controls. When they get close they should revert back to the x,y, and dE measurements to finish the job.

Unfortunately, I need to bow out of this thread tonight. I have articles to write/edit. Publishing deadlines don't move.

Greg Rogers
AccuPel
Widescreen Review

umr - that is when you pop up the big screen saying plug in your AccuPel to get the color ordering right - if you don't have one then click here to order from gregr :D

Colorfacts wizard has the different order than AVIA PRO DVD- so I know what you mean though! PITA

Even so I still like to put up the primaries/secondaries first - it tells me where I am and what the display nature is before I begin mucking around with adjustments.

Kevin,

I never said you should not look at the color bars first. My measurement wizard puts up the color bars first for a visual check followed by pluge and contrast. This allows the user to confirm/adjust the levels are set correctly, confirms that the proper input type (RGB, YPbPr) has been selected when using a generator and it allows the display time to synchronize to a new resolution so the following tests do not need to wait for sync.

An AccuPel generator is a very useful tool in this process. When one is available and the connection supports color (not composite) the measurement process is highly automated.

Hi Guys,

Thanks for the info.

I do understand the difference between 6500k being a line in color space and D65 being a (white) point, but when you do a greyscale you can see if the RGB values at each IRE that were measured fell on the D65 point on the balck body curve within the CIE (I'm referring to Colorfacts btw). Often the values below 30IRE will fall outside due to the sensors low light sensitivity but generally they should all fall on the same place on the curve and appear as a single dot.

I assumed the color temp graph was just showing us those points as a line from left to right rather than as a set of dots on a curve in the CIE chart - the line is easier to see as the dots (should) all overlap on the BBC and if they're out by a small amount you can't really see it.

If the graph is D65 at each IRE value which is just different luminence of white IIRC, then isn't it a valid graph with respect to D65 acuracy?

I must be missing something but as this is for dummies I can only be helping. :)

Gary.

Gary

Nope the line graphs are 6500K. You could do a dE line graph for D65 (or another target) - ColorFacts does not do that - you have to pull up the raw data window or report to get it. gregr's reviews do publish that. Whenever ColorFacts forum comes back up - that would be a good chart request to put in though! The problem is that dE does not tell you the color push direction - you need dC and dH for that - or the greyscale polar diagram in my proposed charts. It is basically an improved version of the existing ColorFacts target instrument.

And the RGB line graphs kinda give this info if you could do RGB to xy to dE math in your head. But as we discussed already - the RGB% are probably meaningless.....

umr

I am sure nagware would increase sales - have the nag requestor say send me $$$ and gregr $$$$ to run the RGBCMYWB charts automagically - otherwise click here once you have found the chart on your DVD! Maybe not $$$ - but I know I have paid $$ to get rid of the nagwares!

What do you mean by nagware?

nagware is what sharewares do - pops up a reminder screen before you use it that you have not sent in your money - forcing you to click here to buy a license - or click over there to continue using it. Very effective for demos as long as it cannot be hacked - you can try out the software before you buy - but if you want to be productive - you have to pay.

You may have noticed my Matlab charts are nagware - the university has an educational license given to students - but it pops up these annoying for student use only screens and reports. Means if I want to charge someone for an acoustical report without looking like a rube - I have to payup! (Or figure out how to snapshot the graph only.....)

I see no reason to hastle people who have paid for the software. I am not distributing this on a shareware basis.

That is the point - you hassle those who have not paid! Shareware is a pretty effective distribution system - but obviously something like this that requires a sensor - probably makes little sense. The sensor is effectively the license to use anyways. But that is what ColorFacts Pro demo is - a simulated sensor in the real software. You don't pay for the software - you pay for an all instrument USB dongle key or a S/N licensed instrument file.

I also see no reason to make a demo version with the cost of the Eye-One required to use this. Anyone who wants the least expensive option for a colorimeter is not going to use an Eye-One Pro.

When people ask me how do I learn about calibration so I can decide if it is worth buying an instrument - I tell them to download ColorFacts Pro. Read the help files and play with the instruments and print the reports. Often they are afraid to make the investment because they are not sure they will grok the color science - a demo gets them over that fear.

I honestly don't know if Milori ever made any sales that way - but that is what I tell people when they ask. I certainly cannot spend the time to teach them calibration on the forum!

I do provide the documentation for download which includes calibration information, but I doubt I will develop a demo version.

Why is RGB barchart useless? As we discussed the % maybe meaningless - already it looks like Ursa, ColorFacts, and umr are using different methods to figure the %. So a % chart across softwares may be meaningless. What if one guy zooms the chart - and the other does not - (this one really annoys me - as the default in ColorFacts is non-zoomed in which everything looks perfect - the first bar is 20% off!) So you label the chart (but the labels are not ever going to be intelligible on a jpeg or 2" magazine offset print).
[..]
I do however use the RGB histogram - solely for telling me when I have reached my RGB clipping points - because the lines will clip.

Actually, for my $0.02, the RGB Bar chart should merely be a summary of the RGB histogram. At least, it is in my little corner of the universe. Since I could not reverse out several of the calculations that ColorFacts does, I gave up pretty quickly on mirroring those too closely. However, the RGB histogram can be calculated in several ways:

1) Calculate the light output contribution of each primary, then normalize each color (100% Stim == 1.0). Then, take an average of the primaries at each measurement point. The end result is that there is no error at 100% stim (Red = Green = Blue = 1.0), and there is a scaling error throughout the grayscale.

2) Calculate the light output of each primary, then create a set of three idealized white lights using one of the primaries from the measured set. Then relate each of these to a CCT graph. I believe that this is how ColorFacts does its histogram. I do not know how this then translates into the RGB% bar chart, but I doubt it is directly related to the CCT primary histogram chart.

3) Calculate the light output contribution of each primary at each measurement point. I then average the RGB blend, and use this for the histogram. Since the output of an XYZ->RGB transformation is normalized under ideal circumstances, deviations from an even "mix" are meaningful, as Kevin has noted. Of course, getting the right XYZ->RGB matrix is a bit of an issue (Poynton is too focused on Rec709, so Bruce Lindbloom's sight is a good second source)!

4 - n) There are several other ways to do this (xyY directly into RGB using a mixed matrix for both XYZ and RGB conversion, etc.), but others can post how they do this.

As a second line of defense, I also calculate an idealized output for each primary using D65 and the luminance measured at each point, giving an absolute deviation from ideal for each primary at each measurement point. It would be pretty easy to convert my crude percent measure into a dH/dC number if it was more useful.

Later,
Bill

Ursa

Yes I think that is the only point - the RGB only has dual states of information - balanced or not balanced. The many different ways of doing it means don't get concerned over RGB% for comparisons. The clipping point info though is very useful if you want to maximize contrast at D65 with or without color filters.

krasmusik,

Thank you for your correction on my previous posting regarding XYZ to xyY conversion which should have read XYZ to RGB conversion. All of the other statements were correct however. For additional information on this subject please check out this link: http://semmix.pl/color/extrans/etr80p3.htm

Here is an excerpt from this link,

"In the case of the transformation of colors from the model of area CIE XYZ to colors RGB it can be happened that result components will have values <0 or, more generally, exceeding interval 0..1. Such circumstances mean that a color from CIE XYZ has not an equivalent in RGB."

Good lord - what manglish translator did they use for that website - more color science links are always appreciated though.

krasmusik,

Thank you for your correction on my previous posting regarding XYZ to xyY conversion which should have read XYZ to RGB conversion. All of the other statements were correct however. For additional information on this subject please check out this link: http://semmix.pl/color/extrans/etr80p3.htm

Here is an excerpt from this link,

"In the case of the transformation of colors from the model of area CIE XYZ to colors RGB it can be happened that result components will have values <0 or, more generally, exceeding interval 0..1. Such circumstances mean that a color from CIE XYZ has not an equivalent in RGB."

I used those guys as a back-up validation to Bruce Lindbloom, but what's funny is that the XYZ->RGB matrices they show do not match Bruce's. They do agree at between 2 - 3 decimal places, but that's it. Very odd.

Later,
Bill

To get back to a dummy question: :)

When using the RGB% bars, how do you know when to increase one primary over the other? For example, if there is too much red relative to blue and green, how do you know when to decrease red or instead increase blue and green? I had the impression that the direction you go only affects brightness and may have a slight affect on gamma, but not the color. Should I only follow the x,y and dE coordinates instead?

That's the spiffy think about the CA-6X. I presume it's addressing just maxleung's question. It has a little bubble target where you can see RGB and work toward centering a moving ball which relates to the x,y coordinates. Nice feature for us dummies.

Balancing RGB takes experience and really is about learning the art of science.. It is not just about following the dancing bars and dots - which ColorFacts also has BTW. The pretty pictures tend to make the newbie think it is easy - and I don't doubt that the software vendors want you to think that!

The first thing I do is find the clipping points. Usually for DLP this is Red for gains and Green for offsets. Then I work my way back to the target using the other colors. Knowing that luminance Y is mostly Green - if you do the gamma math you can balance out your gamma curve at the same time as grey scale and doing the clipping check maximizes contrast at the same time. Also knowing that dE is a perceptual error - you can try different moves on the target and see which has less perceptual error if you cannot make things perfect. Other technologies (LCOS, DLP, CRT, plasma) will have different natures - and it requires experience on those technologies to see what works best! LCD tends to have S shaped gamma curves, LCOS tends to be blue limited, CRT usually never has a flat blue across greyscale - and I am sure plasma has something wierd about them too - but I have never done any. When you cannot make it perfect - like all engineering fields you have to learn how to make acceptable compromises.

Combine that with what Bob is learning now - you have to understand the nature of your instruments and the compromises made in making them affordable - and figuring out how to use them for best accuracy, speed, and reliability.

Hey guys,

I don't have long, but did want to clarify a few things:

Greg wrote:
Yeah, I agree that RGB% measurements don't have much useful meaning unless they are made relative to the display's actual primary colors, as I said way back earlier in this thread.

In ColorFacts, the RGB% levels *will* be relative to the display's actual primary colors, if those have been measured. If they have not been measured, the RGB% are relative to the color standard that is in use (HDTV, NTSC, etc).

However, the end result is *exactly* the same. When you get to 100%, 100%, 100%, you have reached the target (i.e. "D65"), no matter what set of primaries were used to calculate the RGB percentages.


Greg wrote:
I realize the differences aren't huge, but if the purpose of the RGB percentages is to adjust the RGB gain and bias controls to calibrate the grayscale, it makes those RGB percentages less accurate to calculate them relative to an idealized set of RGB primaries (even if the errors are small).

True.

The idealized primaries are only used if the "real" primaries are not known. It's a shortcut designed to get you into adjusting the gray scale immediately if you don't intend to (or can't) measure the primaries.

The only advantage for using some arbitrary set of primaries is that the user doesn't have to take time to let the measuring instrument "learn" the actual primaries. That's reasonable because the errors are usually pretty small...

Exactly.

Now, a completely different question is how the "Constrain Colors" option works.

The "Constrain colors to gamut" option in the Preferences creates an artificial "wall" at the edges of the color gamut (think WWF), and will not allow any colors to stray outside of this playground. If a color is measured and found to be outside of the gamut (theoretically impossible, but practically actually somewhat common), then that color is relocated to the closest point which is within the gamut (actually, on the very 'edge' of the gamut).

This feature was mainly for a customer in the Aerospace industry who wished to prioritize mathematical accuracy and purity over empirical data integrity.

Leaving this option OFF will make the software always show the raw readings that the hardware is providing, even if that means that a measurement plots outside of the gamut (and causes the RGB calculations, etc. to break down).

This option has *nothing* to do with calibrating gray scale, unless your gray scale is SO far off that it's outside of your RGB color gamut!

I hope that helps!

Mark

Thanks for the explanation - that was the answer we were looking for. Sounds like it does make more sense for the option to default to OFF - we got thrown for a loop because it defaulted to ON!

Same here - thanks Mark!

Jeff (aka umr :) ), does your software do the same thing? That is, if everything is at 100% then I hit the target?

Thanks for the explanation - that was the answer we were looking for. Sounds like it does make more sense for the option to default to OFF - we got thrown for a loop because it defaulted to ON!

So Mark is saying grayscale wise it doesn't matter whether it's off or on. But for true CIE readings it needs to be off.

I didn't see that link on the internet that Mark said would pop up during Cedia, the link for the free CF upgrade? I have the Accupel coming next week am I'm going to run into any hookup snags as is or with the upgrade with my laptop? Right now I have both sensors (1eye/trichromat) accessible in the directory.

Same here - thanks Mark!

Jeff (aka umr :) ), does your software do the same thing? That is, if everything is at 100% then I hit the target?

Yes.

This has been a very informative thread and it got me thinking about how calibration must keep up with new technologies.

Genoa ColorPeak and TI's BrilliantColor are expanding the color gamut that the displays that are using this technology can produce.

How does a calibrator accurately handle these new display technologies?

Here is Genoa Color's explanation of their technology. (http://www.genoacolor.com/techwall.pdf)

Pardon me Bob if I'm too off topic with this question, but I think it is relevent enough to benefit all of us.

hex gamuts rather than trigamuts are certainly interesting from a research point of view.

But wide trigamut has not even been accomplished for HDTV - which is barely an improvement over SDTV - so you can forget about hex gamuts for a long time.

A display composed of a hex gamut - only adds complexity and unused capability to the display - as long as there is no software to drive it.

All media currently is either RGB or YCbCr - which is a trigamut. The source media and interconnects would have to entirely change throughout the industry if hex gamuts are to be adopted for more than making pretty pictures.

What they will do is add more calibrator challenge if there are no controls to put the colors back where the HD/SD standards say they should be. The calibrator will leave and you will still be left with an unnatural looking picture.

So until the display manufacturers get it together with the broadcasters and filmmakers - they are doing nothing more than colorizing the picture. Which is nothing new - their marketing departments have always operated on the mistaken idea that "different" means "better".

Thanks Kevin,

I see, the improvements of video will have to be industry wide, from source to display for best results, and with that will be standards for calibrators to reference to.

It looks like companies like Genoa Color are getting the ball rolling by bringing to market a method of taking existing input RGB or YCbCr data and transferring this information through a multiple primary converter (post processed), resulting in a widened gamut.

Based on the Genoa Color White Paper (http://www.genoacolor.com/pdf/Genoa_White_Paper.pdf), I assume there would be no difference in the way a calibrator would calibrate this type of display.

I guess it reminds me of Dolby creating 5 channels out of only 2 channel sources. Not the ideal compared to 5 discrete channels, but does create a relatively believable soundstage.

Not the same thing as Dolby ProLogic. Dolby Prologic encoded the extra channels using 'inaudible" phase differences into stereo - which then extracts extra channels. This is actually rather similar the way that color was added to B&W TV signal.

Adding more colors is not the same thing as adding more audio channels! Rather adding more colors is more like a manufacturer enforced audio equalizer setting - does not sound so attractive anymore does it?

It will take more than a startups white paper to change the entire video industry. YCbCr is only a media compression format - it is not a camera and display format. That is a major problem to change considering that someone would have to invent cameras/displays that are not native RGB.

Just look how long HDTV is taking - ten years from release and ten years in development. And that includes a wide gamut HDTV standard that expands the trigamut to more saturated colors all the way around - that was never adopted.


The only issue for calibrators is having the controls to calibrate back to the standard tri-gamut - which means the expense of the "enhancement" is wasted - just like when you buy an audio equalizer only to set it to neutral. The problem is getting color point controls for calibrators often does not happen even now - with oversaturated primaries or yellow segments.

The genoa paper does not post the 5P primary values - but let me guess from the charts. I will post my zoomed color target so you can see how far they are off from the standard.

Here are the perceptual charts based on Genoas white paper. I posted here as it gives me a chance to add some review words to my charts - maybe making them more understandeable.

krasmuzik GENOA (http://krasmuzik.home.comcast.net/Genoa.pdf)

They first propose a Wide Gamut - the advantage here is that gamma is not changed because Cyan is a deeper towards Blue and thus you do not get brighter Whites - but Cyan gets an F---

The natural greyscale point defined by the RGBCY primaries is thus grossly blue - give it an F---

But that means Magenta is deeper towards Blue as well - give it a D-

Green is deeper and more Cyan - give it a D+

Blue and Yellow are just a bit overdone - give them a B. Red is overdone - give it a C (note many display like Sim2, Infocus SP7210, Optoma H79 are similar reds)

So if you were watching an HD source on this gamut - the picture would look very strange. Especially skies and grass - it would look like these SciFi shows that colorize things to make it look like another planet.

But Genoa realizes that and have a High Bright gamut - which is closer to HD spec.

The Red is a less pale Orange - causing Magenta to be pale as well - combined with a paler Blue. Give them all a B - but you can see they made the dark colors pale because it improves brightness.

The lighter colors Cyan, Yellow, and Green - they have oversaturated a bit - because Cyan and Yellow are used to create white they can afford to do this with the brighter colors. The hues are pretty good - also give them a B.

As a result the greyscale is not bad - give it a B+ for being just a bit Cyan.

I have seen worse color/greyscale points on other projectors - as a calibrator though I strive for an A - as I can see the difference to the point of annoyance. I would consider a B projector OK if you don't care about videophile stuff and are budget limited, but only an A projector would be highly recommended.

You can see the compromise in the gamma. The gamma curve is higher value and the blacks are crushed (or whites are popped depending on your viewpoint). I would give gamma a B as well.


So bottom line - the real point of these CMY colorwheels is to improve brightness - at the expense of a videophile calibration on greyscale/colors/gamma. In other words the usual game - market the big numbers - not the videophile numbers. Using them for wider gamuts makes little sense - no brightness improvement - but wierdly pushed colors for HD sources.

But something is clearly wrong on the chart at the start of this thread. The yellow measurement is outside the line between the green and red measurements, and that is physically impossible unless the projector has special processing to adjust the primaries separately from the complementary colors, and the 7210 doesn't have that type of processing.
Greg,

The ScreenPlay 7210 does use color correction processing to independently correct for primaries, secondaries, and white point. The corrected yellow indeed does not lie directly between the green and red primaries when viewed on a CIE 1931 chart like the one at the beginning of this thread. This non-triangular gamut is intentional.

Some people say we are "cheating" because we choose a yellower green than some others do, however the reason behind this choice is to preserve contrast. Adding yellow to the green moves the white point to a warmer temperature. If you turned off all processing, the natural white point in the ScreenPlay 7210 would be very close to D65. Because of this, you lose no contrast when you properly setup your projector for 6500K. Based on all of the feedback I have been able to gather (as well as my own personal preferences), this boost to contrast is more important to relative picture quality than the absolute saturation of green.

Greg,

The ScreenPlay 7210 does use color correction processing to independently correct for primaries, secondaries, and white point. The corrected yellow indeed does not lie directly between the green and red primaries when viewed on a CIE 1931 chart like the one at the beginning of this thread. This non-triangular gamut is intentional.


Thanks for the info Bob. I didn't see anything about user adjustable primaries and complementaries in the data sheet so I figured it had no capability for this kind of independent color correction. If it does have user control over the primary and complementary colors please confirm that.

I've never measured a 7210 but this will keep me from tearing my hair out puzzling over what happened to the yellow measurement if I ever do. :)

Greg Rogers
AccuPel
Widescreen Review

Bob,

"Based on all of the feedback I have been able to gather (as well as my own personal preferences), this boost to contrast is more important to relative picture quality than the absolute saturation of green."

Not to be a curmudgeon, but why then hasn't Infocus used an adjustable or dynamic iris to get more of that desirable contrast?

gregr

If you get BobWilliams to divulge any supersecret service codes - I want in on them :D. The accessible service menu only has the typical ADC YPbPr controls and only for HD - not 480i.

Even if it was NEC HT1100 style primary/secondary control of sliding along the triangle over to the next secondary/primary is something - though not as good as insanely more expensive projectors.

All of the ScreenPlay's I have measured have always had perfect hues on secondaries - I just want to try some tricks....

Bob,

"Based on all of the feedback I have been able to gather (as well as my own personal preferences), this boost to contrast is more important to relative picture quality than the absolute saturation of green."

Not to be a curmudgeon, but why then hasn't Infocus used an adjustable or dynamic iris to get more of that desirable contrast?
The optical design in the ScreenPlay 7210 is at its maximum contrast already, so no additional iris will make it any higher.

Welcome back to the high dollar forum Bob!! I haven't seen that smiling face for a while. I thought you quit the forum from being brain fried from all the questions. I see you frequent the "other" forum.

Scott

good one for calibration forum

As long as a few dummies post - then the subject is still valid :p
At this point I am too dumb to read further into this thread. While the math is not beyond me, some of the discussion is not being followed do to the condition that as a dummie I do not always 'get it' and the lack of layman discussion only serves to white-out my comprehension. :eek:

At this point I am too dumb to read further into this thread. While the math is not beyond me, some of the discussion is not being followed do to the condition that as a dummie I do not always 'get it' and the lack of layman discussion only serves to white-out my comprehension. :eek:
A fair point. Where did you get lost?

A fair point. Where did you get lost?

I must be dumber than Ferret, because I got lost off of the initial question posed in this thread....

Are the Primary (squares) on Bob's chart measured from his equipment or are they just a predetermined ideal?

What would a theoretically perfect chart look like? An equilateral triangle with white directly in the middle and the secondaries bisecting each line between primaries?

These are the type of dummy questions I need answered so I can even gain a limited understanding of these charts.

I must be dumber than Ferret, because I got lost off of the initial question posed in this thread....

Are the Primary (squares) on Bob's chart measured from his equipment or are they just a predetermined ideal?

What would a theoretically perfect chart look like? An equilateral triangle with white directly in the middle and the secondaries bisecting each line between primaries?

These are the type of dummy questions I need answered so I can even gain a limited understanding of these charts.

The squares are the target values (not measured) for each color and the triangles are the measurements except for white which is a black box with an asterisk in it. The measured primaries, secondaries and white would ideally be on their target values.

The squares are the target values (not measured) for each color and the triangles are the measurements except for white which is a black box with an asterisk in it. The measured primaries, secondaries and white would ideally be on their target values.

So here is a follow up dummy question...How are the targets determined? Are the targets based upon what chart you are looking at, ie CIE1931?

So here is a follow up dummy question...How are the targets determined? Are the targets based upon what chart you are looking at, ie CIE1931?

The color of each primary, secondary and white is set by the appropriate standard. Note the reference to the HDTV standard on the plot. They each assign an xy coordinate that is plotted on the CIE1931 chart. The type of coordinate system (CIE1976...) will change the plot, but the target color will remain the same.

Thanks Jeff, I think I am starting to get the jist of it, sorry to dumb down the thread.

You might want to go to my website and download the documentation for my software. It provides significant information on how to measure and calibrate a display and along with links to other resources on the web.

www.accucal.org (look under i1 Pro DCS software documentation)

Good Luck! This can be pretty fun once you figure out what is going on, but the climb can be a little steep.

You might want to go to my website and download the documentation for my software. It provides significant information on how to measure and calibrate a display and along with links to other resources on the web.

www.accucal.org (look under i1 Pro DCS software documentation)

Good Luck! This can be pretty fun once you figure out what is going on, but the climb can be a little steep.


Will do, thanks again. ps. Your site is timing out for me right now...provider issue? I'll try again later.

Will do, thanks again. ps. Your site is timing out for me right now...provider issue? I'll try again later.

You are probably seeing Cogent Communications/Level 3 problems. My web hosting service uses Cogent which is causing some problems at the moment if you are on Level 3. Many Time Warner users are on Level 3. Read the following news report for more information on this.

http://www.theregister.co.uk/2005/10/06/level3_cogent/

Yep, brighthouse user here, so that explains it.

Hi,
can anybody explain a dummy in what way can help DeltaE, also dC and dH to make a calibration. I have read the Posts to this issue in this thread but i can´t get the point.

Thanks a lot, rgds Damdy

Damdy - Delta E is a measure of color error that includes in its definition the amount of grayscale error. That is, if you have the "color" correct (think of the xy plane on the gamut), but you have too much or too little light, then that is the grayscale error component. This is also referred to as "Delta L*".

Think of Delta C* as the color error independent of the amount of light. However, using the 1976 formula, there is still a heavy influence from L* in calculating dC*. With me so far?

Delta H comes into play with the newer versions of Delta E*. Now, you have a much more complex set of calculations with more discrete components. This is essentially the error in hue, or angle from the HSL color space (HSL contains three components: an angle on a plane (hue), the "purity" of the color on that angle (Saturation, or the distance from white), and the amount of light (Lightness). If I understand the issue correctly, humans are very sensitive to changes in Hue, though Poynton dismisses this entire color space in a fairly offhand fashion.

I'll leave it to Kevin to give a more advanced iteration of this last point.

Later,
Bill

Ursa,

Would you be so kind to briefly run through the math for these various variables with a few examples with the output from i1 and CF (have both).

NiToNi - Here's the math conceptually for the 1976 dE calculation (highly simplified):

dE (1976)
- You can use either CIE Luv or Lab color spaces - I'm assuming Luv here
Step 1: Convert xy to u' and v' - this ends up being neutral with respect to light
Step 2: Convert u' and v' into u* and v*
- Converting to u' and u* starts by taking the difference between the measured u' and the white point u' (thus, you need to convert D65 xy into u' v')
- Then you scale this value by L* multiplied by 13.
- Converting v' into v* is similar.
Step 3: Since you are finding the difference between the measured grayscale point and the ideal grayscale point (expressed in CIE Luv values), the dE calculation is essentially the square root of the squares of dL*plus u* plus v* when calculating a difference in grayscale.

So, Delta C* ends up being dE, but without dL*, but even then, there is still influence from L* itself. To truly isolate dC* from the influence of grayscale issues, you need to use the ideal L* value, rather than the measured L*. Why? Here's a specific example:

Say your display has a gamma "hitch" (inflection point) such that it puts out less light at a particular percent stimulus than it is supposed to, but everything else is where it should be when normalized. For a given absolute deviation (e.g., your x and y are off 0.1 each), when your display puts out less light than it otherwise should be, your dC* is lower than if it is tracking gamma correctly. This is an odd result, but the idea is that color errors are more noticeable as relative light levels increase. The corollary is also true. That is, if your display is putting out more light than it should, then the dC* is larger than it would be if it were tracking a smooth gamma curve.

With me so far? Let's now look at setting L* to 100 for purposes of calculating u* and v* (again, using the 1976 formula). For blue, you are essentially forcing an artificial non-linearity into your equation, and overstate the error by roughly 4 times (blue should only be about 7% of total light output). Red is less dramatically overstated, but is still significant. Green is closest, but still overstated (by potentially a bit more than 20%, depending upon which color standard you are using).

If you pull the equations from Poynton's site/book, you will see what I am talking about. Other methods of calculating dE introduce additional complications (e.g., dH), so we would probably need a dedicated thread to discuss those issues.

HTH.

Later,
Bill

WOW,
what a monster of a thread.
Got some more ideas of the deal.
With the Metavision 576 projector, you can dial in primary and secondary. Once you've done both, you have to tweak the primary again. Playing with them is almost like maxing out the dynamic with brightness and contrast, where you also have to redo the settings.

Best
Armin

WOW,
what a monster of a thread.
Got some more ideas of the deal.
With the Metavision 576 projector, you can dial in primary and secondary. Once you've done both, you have to tweak the primary again. Playing with them is almost like maxing out the dynamic with brightness and contrast, where you also have to redo the settings.

Best
Armin



Yeah, really! IF dummies are supposed to understand this I'm in deep trouble! :eek:

I am a dummy, when you are going to calibrate using the Avia Disc with a Z2 do you turn down the IRIS and do you turn the enhanced black feature off on the DVD Player.

wow, my head is reeling.

Getting back to the titled subject:

1. How do you turn on the display device?
2. Where should you sit when playing with calibration settings?
3. How light or dark should the room be?
4. How long should you use the set before trying to calibrate it?
5. If you set has calibration charts available through it service menu should you try to use them or should you stick to a DVD, broadcast or calibration generator?
6. Which calibration chart should you start with, black, max white, color saturation, sharpness?
7. When setting basic calibration on a less than perfect display (100% on the current market) what are the best compromise settings?

You get my drift?

Richard.

alright need the experts to chime in and answer this one. to which standard do you calibrate to for a plasma tv in the united states do you choose NTSC or go with HD 709? i watch OTA some in HD c band satellite some in HD and DVD NOT HD. any help trying to set up my plasma using spydertv and would like to know which is my best choice. Thanks

Perhaps this question is answered somewhere here, and if so, I apologize. When using DVE, which is fed via component inputs, will the calibration also serve for HDMI. If not, how can the HDMI input be calibrated with this disc?

Getting back to the titled subject:

1. How do you turn on the display device?
The power switch? ;)
2. Where should you sit when playing with calibration settings?
In your normal seating position, or wherever your gear requires you to sit. Only focus really matters, unless you are blocking the light.
3. How light or dark should the room be?
As much or as little light as would be present when you are optimally watching your set. Measurements, though, work best in as completely dark of an environment as you can make it.
4. How long should you use the set before trying to calibrate it?
If you have your own gear, it doesn't matter. If you are using a professional, then a rule of thumb is to wait a few hundred hours, plus or minusm, depending upon your display type.
5. If you set has calibration charts available through it service menu should you try to use them or should you stick to a DVD, broadcast or calibration generator?
Some Samsung RPTVs need to use the interal patterns. However, you should generally use known references.
6. Which calibration chart should you start with, black, max white, color saturation, sharpness?
These would be "patterns" in the calibration lingo. The charts to which this thread refers are generated by a calibration software package, so they would be histograms, tracking charts, etc.
7. When setting basic calibration on a less than perfect display (100% on the current market) what are the best compromise settings?
Depends entirely upon the individual set.


Bill

Perhaps this question is answered somewhere here, and if so, I apologize. When using DVE, which is fed via component inputs, will the calibration also serve for HDMI. If not, how can the HDMI input be calibrated with this disc?
For the average person, a PC's DVI port and a converter cable is their best option to calibrate and HDMI port to the HD standard. For SD, all that you need is a DVD player with a DVI or HDMI output. These can be had for <<$200 these days.

Bill

Some basic "guidance" regarding Calibration Charts and Data seems to have gotten very deep :confused:

So , as a Dummy , I'll ask...is there any negative reason to not place the sensor closer to the PJ than leaving it at the screen facing the PJ ? I think that there is a benefit from excluding ambient light and increasing the values measured at low IRE or % Stim levels . What are the other positives ?

Also , if I read correctly , the Gray Scale adjustment can or does affect the Secondaries?This is new to me . I understand that the Primaries are what they are for any given PJ excluding the ones that allow adjustments but I thought the Secondaries were a result of the Primaries and not easily affected by the Gray Scale?

Scott................... :)

The secondaries (if tint and color decoder are corrected) lie on the gamut triangle enclosed by the primaries. Their location is the intersection of the gamut triangle and the line thru the white point to the opposing primary.

The reason is that white is a specific balance of RGB. The secondary is nothing but White without one of the opposing primaries mixed in. In color math the vector equations are

W = R+G+B
Y = W-B = R+G
C = W-R = G+B
M = W-G = R+B

So grayscale correction is also correcting all of the colors enclosed within that secondary gamut. It is just called grayscale because it is done with grayscale patterns - per the math get that right and the secondaries will be right (assuming the video is first decoded properly)

So if you have a typical bluish-cyanish greyscale - cyan/magenta will be bluish and yellow will be greenish. This is why you want to do grayscale - even though the eye/brain is white adaptive without a D65 reference - it will not adjust to the secondary colors being off. If a banana is not banana yellow but the slightest bit green - our brain has the reference and says that ain't right!

Very easy to see this for yourself - most displays have advanced menus with RGB grayscale controls - just throw up a standard colorbars pattern and watch what happens when you adjust.

Legend is that standard calibration source material came about because someone was using a fruitbowl as a calibration image - and since there is no blue fruit - someone painted a banana blue. So the person on the image display side reversed tint so it was yellow!

So , as a Dummy , I'll ask...is there any negative reason to not place the sensor closer to the PJ than leaving it at the screen facing the PJ ? I think that there is a benefit from excluding ambient light and increasing the values measured at low IRE or % Stim levels . What are the other positives ?

Scott................... :)

The negative reason is that PJ screens may not be neutral. But since you get better results with a lens reading by getting the light closer to the design target of the sensor - what you want to do is take a bright white reading of the screen and apply it as an offset to the lens reading.

The secondaries (if tint and color decoder are corrected) lie on the gamut triangle enclosed by the primaries. Their location is the intersection of the gamut triangle and the line thru the white point to the opposing primary.

The reason is that white is a specific balance of RGB. The secondary is nothing but White without one of the opposing primaries mixed in. In color math the vector equations are



Thanks Kraz ,

I was able to see this today after spending some quality time on my PJ . After getting the D65 point almost smack on , I remeasured the Secondaries and they had improved dramatically . My Primaries are just outside of the Gamut co-ordinates and are not adjustable from within the User Menu and thus will always affect the ultimate location for the Secondaries , yes ?

Is it not also true that you can have a 6500K calibration but not be on or near the D65 co-ordinate ? I think that this was my original problem and misconception . I'm learning :rolleyes:

Scott...................

Thanks Kraz ,

I was able to see this today after spending some quality time on my PJ . After getting the D65 point almost smack on , I remeasured the Secondaries and they had improved dramatically . My Primaries are just outside of the Gamut co-ordinates and are not adjustable from within the User Menu and thus will always affect the ultimate location for the Secondaries , yes ?
You've got it. Your color error will increase as you move out from the white point towards the perimeter of your display's gamut due to the primary locations being incorrect. Whether this is objectionable or not is a different question.

Is it not also true that you can have a 6500K calibration but not be on or near the D65 co-ordinate ? I think that this was my original problem and misconception . I'm learning :rolleyes:

Scott...................
You are two for two. :) 6500K is essentially a line segment on the gamut. D65 is merely one point on that line segment. You can actually be fairly green and still technically be at 6500K. :)

Bill

Yes check out the last WSR of a Sharp LCD - nailed 6500K - but the flourescent backlight made it 30dE off D65! Surely made earthlings look like martians!

The strange thing is this is something every newbie calibrator must learn - because the professional reviewers still report 6500K differences not D65dE. Despite it being the only failing question if they were to submit their ISF test. Their excuse is that is what the reader expects - and I disagree - customers only know what calibrators tell them - and getting a physics degree in blackbody curves is something they do not need to know - especially when it turns out it is not even a relevant measure - and certainly not a comparable metric!

Take a stand - abolish Kelvin charts from chartset!


As far as primary colors affecting secondaries - it depends. Certainly it will affect color depth if primaries are too deep. If just one is off rather than the other - then they should at least get the hue right by aligning with the white point in the color decoder - rather than just blinding mixing two primaries. I know Infocus has six axis color correction - even if primaries are a bit off - they nail the secondaries on hue relative to D65 (even if grayscale preset is different - they use D65 secondaries)

But there have been displays that cannot get secondaries right even when primaries are close and D65 is right. Red pushed color decoders are common - for a reddish magenta/yellow - as are color decoders that assume 9300K and align secondaries with that despite grayscale correction - giving blueish cyan/magenta.

Thanks Kraz and Bill ,

I've just seen posted in the Oppo Thread that someone had success bringing the Primaries in line by reducing "Color Saturation" in the DVD Player Menu . I haven't had time to explore this but will try this weekend . I'm also not clear on which Gamut is correct . The HDTV triangle better matches the location of the Primaries and the NTSC is definitely "smaller" . The Oppo outputs 720p RGB over HDMI/DVI into my Infocus SP5000 . I can select "native" and pass through the signal without further processing.

The other item I will go back and address is the effect each of the three Gammas and Color Temps have on the shape of the final Gamma curve . I'm now only getting a 2.92 Gamma with my current settings but these were set when I was using my eyes and I'm learning that they can be deceived ;)

With the new tool (thanks Bill) everything is so much faster than the Smart-III that I can afford to experiment a little now .

Scott.................. :)

Any advice on calibrating the PE7700 pj with the Spyder2pro. How to set it up, and be able to calibrate DVD's and also HI-Def tv from over the air antenna. I'm totaly new at this and all I want to achieve is a better picture over all. It doesn't have to be perfect, just better. I can't afford to pay an expert to achieve an optimal picture. I have to try to do this myself. Thanks!!

Any advice on calibrating the PE7700 pj with the Spyder2pro. How to set it up, and be able to calibrate DVD's and also HI-Def tv from over the air antenna. I'm totaly new at this and all I want to achieve is a better picture over all. It doesn't have to be perfect, just better. I can't afford to pay an expert to achieve an optimal picture. I have to try to do this myself. Thanks!!
These questions are probably better handled in this thread:
http://www.avsforum.com/avs-vb/showthread.php?t=697072

Bill

Scott

Don't reduce color saturation to bring in primaries...

http://www.avsforum.com/avs-vb/showthread.php?t=767155

Scott

Don't reduce color saturation to bring in primaries...

http://www.avsforum.com/avs-vb/showthread.php?t=767155

Hmmmm OK ? I read through the Thread and I gather that reducing the overall Saturation , with non-PJ controls , risks changing the ratio of the Primaries which is a bad thing ? Is this correct ?

Both the Primaries and Secondaries have specific xy locations for either REC601 or REC709 Gamuts . Would it be possible to calculate a dE for each of the six positions from theoretical to measured and determine whether a Display is likely to be getting or showing either of the two Gamuts ?

I know that you use the Green in the Pluge pattern to tell which Space is being processed , but you have an experienced , trained eye . I'm looking for a non-experienced user "tool" :D

Thanks for sticking with me on this ,

Scott............................ :)

It changes the brightness ratio of the primaries w.r.t. White - and since video is colorized B&W it is necessary to preserve this ratio. To eyeball color brightness is correct all you need is AVIA and the RGB filters and RGB colorbars.

Yes it is possible to measure the dE of color error - instead of using D65 white as your target - you just use REC709 RGBCMY as targets. I prefer to use CIELCH to break down dE into lightness (dL), colorfulness (dC) and hue (dH) errors - as that is much more informative and matches perceived errors. I discuss this earlier in this thread how I chart that.

You need a visual reference to truly identify color of color errors just as you do with grayscale errors - it is best done with colorimeter calibration gear and software that can measure the dE of colors. The point of the earlier thread on the Sony Pearl - is that sometimes you may need to make a choice of dC vs. dL when it comes to minimal dE. Which is worse - undersaturated video or candy primary colors?

Also just today I did a post on charting color which merits repeating again in this thread...

"
Referenced are charts from my Infocus SP7210 review. Based on the 1939 CIE chart which uses the spectral sensitivity of the eyes - you would think the Greens are bad, Reds are OK, Blues are great.

http://krasmuzik.biz/reviews/SP7210_demo_CIE39.jpg

But look at the CIE1976 chart which is based on psychovisual perception in the brain - and you see that RGB are perceived to be about the same amount of error - despite spectrally measuring different error.

http://krasmuzik.biz/reviews/SP7210_demo_CIE76.jpg

But we need to get a closer look so we zoom into the target - as well as consider color brightness biases perception...(in my newer charts I further break out color brightness)

http://krasmuzik.biz/reviews/SP7210.pdf

And now we can see that perceptually the stronger deep Reds are worse perceived error than the paler yellower Green! Since we also account for color brightness - Blues are not as bright - so on this chart there is less perceived error than on the previous chart.

And indeed anyone who has seen the Infocus SP7210 would probably agree with the last chart - your critical perception based on informed comparison is deeper crimson Reds, OK but paler yellow Greens, and great Blues. An uniformed comparison would simply say "Wow! Bright! Colorful!" But I think you would find few that would say the greens wanted to make you vomit for comparison....that only happens when reviewers look at charts to form subjective comments that are not based on objective perceptual measures.
"

Ok , Saturation is going back to default on the OPPO ;)

Somebodies Server is very slow tonight so I can't see the jpg's . The PDF came through but I have no idea on how that data is to be interpreted . It's very new to me . Looks very intriguing !

"But I think you would find few that would say the greens wanted to make you vomit for comparison....that only happens when reviewers look at charts to form subjective comments that are not based on objective perceptual measures."

Very funny :D I'm glad your sense of humour is still with us .

My CC30R filter arrived today so I'll spend some time with it and see if I can curb the excessive Blue/Green this unit has . Someone mentioned that some manufacturers will drive the UHP lamps a little harder to increase brightness . I wonder if there is anything as simple as a "jumper" on the power supply that would put the lamp back into a more normal operating range . This would surely prolong lamp life too .

Merry Christmas ,

Scott................. :)

Scott the review format section of my website discusses the chart interpretation - but the data in the charts are standard CIE1976 colorspaces (CIELCH and CIELUV) which is covered in many color science textbooks.

http://krasmuzik.biz/reviews/reviewformat.htm

My mail server is out as well so try again I guess - I do not have a dedicated server as those cost big moolah!

Thanks Kras ,

The Server was passing the jpg's later and I went to your site for all the explanations . Very interesting . I like the approach .

Back to more "interpreting" of graphs , how might you explain the differences in the RGB Tracking graphs where say the Blue and Green track fairly linearly but the Red has a very visible "hump" in the middle of the graph ? I know that this is hard without a graph to look at , but I've been unable with the controls I have to "flatten" out the hump for the Red .

If we use Figure 7 from the "Guide to Basic display Calibration for New Users" , page 16, my graph looks very similar except the Red tracking is the inverse of the example . I see that Bill changed Gamma options to remove the "hitch" , but of all the Gamma Options I have , three , I can't seem to change this response .

I do have individual Gamma controls for the RGB channels but even using them doesn't seem to affect this problem . I don't know what to try next .

Scott....................

Thanks Kras ,

The Server was passing the jpg's later and I went to your site for all the explanations . Very interesting . I like the approach .

Back to more "interpreting" of graphs , how might you explain the differences in the RGB Tracking graphs where say the Blue and Green track fairly linearly but the Red has a very visible "hump" in the middle of the graph ? I know that this is hard without a graph to look at , but I've been unable with the controls I have to "flatten" out the hump for the Red .

If we use Figure 7 from the "Guide to Basic display Calibration for New Users" , page 16, my graph looks very similar except the Red tracking is the inverse of the example . I see that Bill changed Gamma options to remove the "hitch" , but of all the Gamma Options I have , three , I can't seem to change this response .

I do have individual Gamma controls for the RGB channels but even using them doesn't seem to affect this problem . I don't know what to try next .

Scott....................
Scott - In many cases, you have to go with what the display provides. Where you have a large dip/hump, then this is a candidate for a parametric control like what Lumagen provides in the HDP/HDQ processors. This is also about the only time I endorse using these vs. continuing to work with the display's native controls. I'm much more inclined to use controls like these to change the incoming source information, rather than correcting the display. If you don't have a video processor, then once you have exhausted all of your possibilities, well, you are out of possibilities. :)

In other words, if you've tried various image modes, various gamma options and tried tweaking your gamma controls, then chances are you are out of options for correcting this. The only other thing to consider is to dive deep into the undocumented wild of the service menu and start playing there (e.g., some DLPs will expose the DLP panel controls in the service menu). The red hump at 20% is a bit of a signature for Optomas, by the way.

Bill

These humps are intentionally designed into the gamma tables. I see no perceptual reason for it. A hump at 80-90% they also use - that has the perceptual reason of detouring through magenta before you get to the bluish whites. Blue/Green pops at white are easy to get rid of - just lower the contrast (or better the Blue/Green gains) If you have a hump in the middle you can usually dial it out - that is just the gain/bias interacting badly.

You have to weigh the tradeoffs of using an external processor limited to 8b of adjustment on a limited number of steps (causing banding for sure) vs. living with it.

Calibration is the art of compromise applied to color science & video engineering - and some manufacturers have to be compromised more than others!

I have a simple question for anyone that might have an answer for me, thanks!!
If I want to calibrate my Projector with Syder2pro, do I need to have the Projector as the primary monitor comimg from the Computer, or can I just use my regular monitor for viewing the software details while I am reading the projector with the Spyder2?

Scott - In many cases, you have to go with what the display provides. Where you have a large dip/hump, then this is a candidate for a parametric control like what Lumagen provides in the HDP/HDQ processors. This is also about the only time I endorse using these vs. continuing to work with the display's native controls. I'm much more inclined to use controls like these to change the incoming source information, rather than correcting the display. If you don't have a video processor, then once you have exhausted all of your possibilities, well, you are out of possibilities. :)

In other words, if you've tried various image modes, various gamma options and tried tweaking your gamma controls, then chances are you are out of options for correcting this. The only other thing to consider is to dive deep into the undocumented wild of the service menu and start playing there (e.g., some DLPs will expose the DLP panel controls in the service menu). The red hump at 20% is a bit of a signature for Optomas, by the way.

Bill

Thanks Bill . The only good news is that I saw the same "hump" when I was using Smart-III and was convinced that it was that particular package . Now with CalMAN , I know it's the PJ . Did I say that was good news :rolleyes: I may try fiddling with the Oppo Gamma settings with the PJ at neutral . Nothing left to try except a new PJ and we all know that ain't gonna happen :o I have been making eyes at the DVDO product and I'll have to re-check and see what kind of video parameters are available for adjustment .

Quote"These humps are intentionally designed into the gamma tables. I see no perceptual reason for it. A hump at 80-90% they also use - that has the perceptual reason of detouring through magenta before you get to the bluish whites. Blue/Green pops at white are easy to get rid of - just lower the contrast (or better the Blue/Green gains) If you have a hump in the middle you can usually dial it out - that is just the gain/bias interacting badly.

You have to weigh the tradeoffs of using an external processor limited to 8b of adjustment on a limited number of steps (causing banding for sure) vs. living with it.

Calibration is the art of compromise applied to color science & video engineering - and some manufacturers have to be compromised more than others!"Kras

Thanks Kras . You say that the Gain/Bias interacting badly may be causing the "hump" and that it can be dialed out . That's encouraging as well . Any guidance here ? I'll be back at it tomorrow and Friday and see what I can learn .

Scott......................... :D

I have seen some gain/bias controls that instead of functioning like you would think as a gain multiplier with an additive offset - instead the gain controls the slope of the RGB histogram above 50% the offset controls the slope of the RGB histogram below 50%. So you have to range your controls and observe how they interact - and guess at what the designers intents are with the controls. There is no standard implementation for grayscale controls.

Sorry about the noob question :D .

what does it mean for an HD set to have high frequency rolloff? Is this something that can be seen with test patterns?

This thread is for calibration result charts you see in calibration software and reviews - not for test patterns.

I presume a HD version of DVE or AVIA will have something similar to the existing resolution and sharpness patterns. Ask in the main forum maybe someone knows the latest.

Sorry, didn't know where to ask.

i own a 4x3 thoshiba theaterview that can convert into a 16x9 screen. if i watch a 1.85 1 movie on the 4:3 screen i get the picture with the black bars at the top and bottom if i put my tv on the 16x9 mode i can get the same exact picture but the black spaces are are much darker therefore making my picture much more outstanding. if the both show the exact same thing only the 16x9 makes the picture more outstanding, is the 16x9 mode really just masking, is it no different than the masking you have for projection screens?

This is "reading and interpreting calibration charts and data for dummies". Unless you have charts and data from calibration software that you need to know how to read and interpret - nobody is going to help you here. Try the main calibration forum or TV forums.

Good stuff

Perhaps the experts that populate this forum can help another 'dummy'
I have calibrated a Vizio GV47L 1080p TV using HCFR, DPT-94 colorimeter and a Panny S97 running the getgray disc.
S97 HDMI to TV HDMI up converted to 1080i

Posted my results here:
http://www.avsforum.com/avs-vb/showthread.php?t=786966&page=10&pp=30
but not getting much feedback. The thread is not very active.

Is there another thread where LCD TV calibration is the main subject ?
While I have learned much here, this thread does not appear to be all that appropriate for the questions I have.

But just in case I have attached the HCFR .hcf file.

BTW the Vizio has RGB sliders in the custom color menu which were adjusted to get the best D65 gray scale. Other than that just the usual contrast, brightness, color, tint.
Used the last 2 for color decoder adjustment to get the CIE chart looking the best I could. No service menu access published, but would not use that in absence of a service manual.

catmother -- Have you tried the "Official Vizio GV47L 1080p" thread: http://www.avsforum.com/avs-vb/showthread.php?t=777914?

Just a suggestion.

Absolutely,
Have been posting there for some time.
Not much help there on calibration issues.
Mostly complaints about set problems issues.

My Vizio has none of those and works very well,

BTW after my HCFR calibration the PQ is excellent

Hello Catmother,

I took a quick look at your results. Overall not too shabby. It may be close to the best you can do given the controls you have available to you. To slice it much finer and get that last 5% or so, one often needs to get more precise control via LUT manipulation and ICC/ICM profiles but that doesn’t seem an option for you.

The biggest thing I see is that your blue starts to get excessive (relative to R/G) at 20IRE and lower and causes your color temp to start to rise there. This perhaps could be some meter error as most all of them start to go color blind or bonkers when the light levels get low. Sometimes you have to balance what your meter tells you with what your eyeballs tell you. If you put up a grayscale ramp, do you lower IREs appear to be taking on a bluish cast relative to the whites? If not you may not sweat it too much or verify with different instrumentation.

After that, I’d suggest trying to get out of black a little quicker and get a closer fit to the 2.2 curve where you are low from 20IRE on down but that can be subjective. Again, not too shabby overall though.

Dave

For those trying to better understand CIELUV and CIELCH (color lightness, chroma strength and color hue) perceptual colorspaces may I present this simple spreadsheet for educational non-commercial purposes only - feel free to use it as long as you can keep the reference links in place.

http://krasmuzik.biz/reviews/CIE%20calcs.xls

Again a reminder that this is not a "how do I calibrate my display or use my software" thread....use the calibration forum for such posts.

Kras,
Thank you for the info.
I notice that in the 1st colum, under REC 709, the values for Y are expressed normalized to white in decimals whereas the values of Y under pre and post are expressed in absolute value. Right?
If we look at R under pre and post and compare the values, there is almost no difference on x,y but a big difference on the values of Y and dE. Since the x to y distance is very small I assume that the difference in dE is mostly due to adjustment of the Y value; yes?
I have also noticed that the value of Y for RGB do not add up to the Y value of white; when adjusting for Y, what would you rather aim to: minimize dE or try to get the Ys add up right??
Thanks for your comments.
Fermin

The data is later normalized in the Xn, Yn, Zn columns - but you always want to keep unnormalized date for doing lumens and ftL calculations later. Did not matter what normalization REC709 was listed as - since I also renormalized it. Note that in Luv space normalization is to the Y component of white - which is different than Lab space that normalizes each component.

dE is the 3d magnitude of the vector formed with the LCH dimensions. So in the pre R is primarily Chroma error, but in the post LCH all contribute to the overall error but mostly Chroma is weakened because L was weaker - the actual xy did not change much. Chroma is not saturation it is color strength - we don't see saturation - we instead see color strength which is saturation and lightness mixed. L*u*v* is a perceptual space - so small errors in xy in Red are more important than larger xy errors in Green, yet this is somewhat counterbalanced - because in video Green is >3x brighter than Red - this is why a CIE xy chart is not the proper one to be used in reviews that discuss what you see.

Since it is equally weighted perceptual components - you should minimize dE - but you need dL, dC, dH details because adjusting for those errors require different controls and they likely interact. For example - it may be that reducing dL to weaken a strong dC may be the best overall dE. Or in this case Green/Cyan are the worst colors - maybe improving them at the expense of the other colors is the best overall dE. I personally prefer RMS of all dE rather than average or worst error- this is not in the spreadsheet since grading is subjective - but I discuss that in my review format on my website.

Ignore inconsistent data - this was a sensor used improperly and not tracking properly. I did not take it - but later runs the person read the lens and not the screen and got consistent data.

Thanks for this

if anyone knows why there is green in this test please post.http://i197.photobucket.com/albums/aa200/roost22/IMGP0610.jpg

This is not a help me calibrate my TV or is my sensor accurate or do I know what I am doing thread...

It is a reference thread so that people can understand calibration charts - so they can go learn how to calibrate.

Please delete your post and repost it either in the main calibration forum or in your TV's forum.

For those trying to better understand CIELUV and CIELCH (color lightness, chroma strength and color hue) perceptual colorspaces may I present this simple spreadsheet for educational non-commercial purposes only - feel free to use it as long as you can keep the reference links in place.

http://krasmuzik.biz/reviews/CIE%20calcs.xls

Again a reminder that this is not a "how do I calibrate my display or use my software" thread....use the calibration forum for such posts.
Hello KRAZ,

Great spreadsheet! I have been reading your review format on your website and I am trying to figure out where my PJ ranks. My main source is SD (progressive) dvd (until they get this stupid format war finished). If I replace the Rec709 values with the SMPTE-C values, will the accuracy of the calculations still be valid?

The spreadsheet is agnostic on the target - type in whatever numbers you want. I did fix where I had hardcoded the white value. dE is purely an error measure between a source and target. If you wanted to compare your sources Red against a target White - you could - actually it is interesting to do that and see the dE distance between the colors themselves vs. whites - it helps you better understand the dE magnitude.

Of course my review rankings are my subjective interpretation of dE - with me trying to be generous in public - I would be more harsh in private when deserved :D Which is likely why I have not publicly posted a lot of reviews :p

Our 46" Sony Bravia XBR4 will be delivered tomorrow. The room it will be in is only moderate light during the day and we keep the lights dimmed at night. I'm afraid the factory settings, which are set to show off its picture quality in bright showrooms, will be too "bright" for our room. I'm looking for information on the settings which I can use to "tone down" the picture to make it less "bright". I am not a techie and have no idea how to do this. Can anyone please assist me? Thank-you.

moca4

How about you read the thread especially the last few pages - which clearly state this is not a help me do my TV settings thread.

READING & INTERPRETING CALIBRATION CHARTS & DATA!!!!!!

Just scroll down the display calibration topic list until you see the "NORMAL THREADS" section. Ask as many questions regarding how to setup your new tv's there - PLEASE!!!

These threads are getting flooded with too many off-topic discussions!!!!

Carmine.

Perhaps one of you kind folks can explain what I am seeing on these charts in a manner commensurate with my level of understanding.

I have an InFocus 7210 that I have "calibrated" (term used very loosely) in the past with Avia and adjustments suggested by Bob Williams a couple of years back.

As I recently obtained a new "toy" I decided to check my Avia adjustments with the CA-6X and PL's software. I have attached the CIE graphs that I did both before and after showing both the 1931 graphs and the 1976 graphs.

Two things bother me here:

1. My grayscale adjustments did actually bring down the IRE that previously was close to 6800 down to ~6650, but it appears to me that the colors on the 1931 chart after calibration are farther from their targets than they were before I worked on the gray scale...... wah!

2. When I look at the pre and post CIE charts in the 1976 chart the pre looks okay, but the post is WAY out of the park... what the heck is going on here??? They are the same reading that produce the post_1931 chart so why would they be so very screwed up on the 1976 chart?

I will also post the IRE readings in case you guys need those to give me some ideas of what is happening. Obviously I still have work to do as so far I have only been playing with the gray scale adjustments with the RGB gains and offsets. I have not yet opened up the ISF menu (need to call InFocus and get the code) so I am not familiar with the adjustments available there.

Thank you for your assistance,

Only allow 5 files to be uploaded so here is the pre_adjustment IRE chart.

You will notice that for the foreseeable future I will use the term "adjustment" instead of calibration... :-)

Whatever I am doing wrong... is at least consistent :D

I went back and took a look at the charts from my "adjustments" to my Mitsubishi HD1000U.

For it to be that outta wack it has to be a software specific bug or usage error - the CIE76 gives more room to see red/blue error - but not that much!

Kevin....

that is what has my mystified... look at the 1931 graph... it is created from exactly the same data that the 1976 graph is... there is no way they should be this far apart.... (I think)..

Perhaps I should send them to Cliff and see if he can tell me what is going on........

For it to be that outta wack it has to be a software specific bug or usage error - the CIE76 gives more room to see red/blue error - but not that much!

Kevin........

This is the response I got from Cliff.
.................
You will see after installing the new software and using the measured primaries function in the CIE graph that your secondaries are significantly out of adjustment as you used the reference colorspace coordinates to adjust the chroma decoder, which is incorrect to use. The Primaries being so far out of alignment for Green and Red move the secondaries to entirely different points when making the calibration. By using the “Measured” primaries function we calculate the correct locations for the secondaries for you to calibrate to. You will not need the Blue filter to perform this calibration! Simply place either a Magenta/Cyan pattern on the display to measure with the probe and make the corrections with the chroma decoder using the R-Y and B-Y controls.
........................

Could you possibly translate this into English for me...? Especiially as it relates to the 7210 that I know you know very well.

Are the ISF and THX standards a secret, I can't find them doing searches, and it seems to me they would be necessary for interpreting calibration reports. You know, like gamma range, Peak White range, Delta E under x from a to b IRE, 6500K +- xK from a to b IRE?

I've been told the following:

+- 300K from 30 to 70 IRE (ISF) or +- 200K from 20 to 80 IRE (THX) from 6500K standard. Delta E under 10 from 20 to 80 IRE is both ISF and THX compliant. THX spec is 2.0 to 2.4 Gamma AVERAGE...30-37.5 ftL Peak White...Delta E under 10 from 20 to 80 IRE...6500K +- 200K from 20 to 80 IRE.

Thanks!

does control cal feature post calibration charts like the ones listed in this thread? thanks in advance.