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Setting contrast with Spears and Munsil disc

48K views 483 replies 31 participants last post by  Mr.D 
#1 ·
Is there another pattern on this disc to set/verify contrast, other than the one labeled "contrast"? I'm having trouble getting the "contrast" test pattern to work correctly. Thanks.
 
#102 ·
It would be interesting to kind of turn things on its ear and map the YCbCr codes that result in "illegal" RGB codes... where are they in the color space, or are they?
 
#104 ·
If possible I will set contrast to make sure there is no clipping with receiver, etc. then I will set it off of ft/L. Every other way for me just does not seem to be consistant. I try to use 16-235 and stay away from component if possible. I set up every customers oppo player using 16-235.
 
#105 ·

Quote:
Originally Posted by Mr.D /forum/post/18480961


I can normally tell when I'm watching something (DVD/BD) on a display that is clipping at 235. Like I said try it and see rather than continually discussing it.

Outside of the AVS calibration disc, I have yet to see any difference between super-white on and off when playing a DVD or BD movie. I'm using the YCC color space, since super-white doesn't work in RGB color space on the PS3. I might not be looking at the right scenes, but then again perhaps the difference too subtle for the average viewer to notice.
 
#106 ·

Quote:
Originally Posted by Jim McC /forum/post/18478659


I still don't know how to find the proper contrast setting.

The easiest way to set contrast is probably to begin by setting contrast to a very low setting so that you can see all the detail in the contrast pattern. Start turning up contrast. Keep turning up contrast until the detail in the pattern begins to disappear. Now turn contrast down until most all the detail still appears and you can't go any higher without losing detail in the contrast pattern. Without any measurement equipment this sort of a method will probably result in a reasonably high contrast setting that is still likely to deliver all the detail in the original image.
 
#107 ·

Quote:
Originally Posted by PlasmaPZ80U /forum/post/18481915


Outside of the AVS calibration disc, I have yet to see any difference between super-white on and off when playing a DVD or BD movie. I'm using the YCC color space, since super-white doesn't work in RGB color space on the PS3. I might not be looking at the right scenes, but then again perhaps the difference too subtle for the average viewer to notice.

There is theory and reality.


Reality is you can still get a very good image with equipment that clips, much of the content is likely to look identical. What we are talking about is a fringe case. People who want their displays calibrated are typically looking for that last 5% of performance. Quantifing the value of WTW and the trade off with dynamic range is the scope of reality.


In theory where we have perfect 0 light blacks yeilding an infinite contrast ratio, WTW is no brainer.
 
#108 ·

Quote:
Originally Posted by alluringreality /forum/post/18481977


The easiest way to set contrast is probably to begin by setting contrast to a very low setting so that you can see all the detail in the contrast pattern. Start turning up contrast. Keep turning up contrast until the detail in the pattern begins to disappear (or you see a color shift from pure white). Now turn contrast down until most all the detail still appears and you can't go any higher without losing detail in the contrast pattern. Without any measurement equipment this sort of a method will probably result in a reasonably high contrast setting that is still likely to deliver all the detail in the original image.

alluringreality, I hope you don't mind me adding about the color shift.

-John
 
#109 ·

Quote:
Originally Posted by PlasmaPZ80U /forum/post/18481915


Outside of the AVS calibration disc, I have yet to see any difference between super-white on and off when playing a DVD or BD movie. I'm using the YCC color space, since super-white doesn't work in RGB color space on the PS3. I might not be looking at the right scenes, but then again perhaps the difference too subtle for the average viewer to notice.

I'm not familiar with the setup on a PS3 : as I'm a real gamer and own a 360


You should be able to have it setup to pass full range video from discussion on the net I've seen. Verify that first.


The difference between setting peak white at 235 or 254 is pretty massive visually to me.
 
#110 ·

Quote:
Originally Posted by Mr.D /forum/post/18482259


I'm not familiar with the setup on a PS3 : as I'm a real gamer and own a 360


You should be able to have it setup to pass full range video from discussion on the net I've seen. Verify that first.


The difference between setting peak white at 235 or 254 is pretty massive visually to me.

That's what he tested. The PS3 has a switch that is esentially clip or no clip.


With clipping the greyscale clips at 235, w/o it goes all the way up.


But what was interesting is that when he had it set on clipping, he could still see colors above 235 in the individual color ramps.
 
#111 ·
I have only looked at ChromaPure HCFR which don't seem to work in this way but it seems to me that instead of 10 zones for grayscale, there should be 11. I know HCFR allows you to free measure. I assume ChromPure does as well.


The highest zone woud be to 109%. If RGB was in balance across the zones through 11 with gamma right for zone 10 would you not almost by definition have a correct contrast setting. You would then choose the highest luminance that you were comfortable with that conitnued to allow the grayscale to have RGB balanced and gamma right.


I don't really know, but I suspect with my set is there is a gamma spike at high saturation. Is there a simple way to calculate what the luminance of 109% saturation should be given a target gamma and the known luminance at 100% and the calibration software's indicated gamma at 90%?
 
#112 ·

Quote:
Originally Posted by gtgray /forum/post/18482429


I have only looked at ChromaPure HCFR which don't seem to work in this way but it seems to me that instead of 10 zones for grayscale, there should be 11. I know HCFR allows you to free measure. I assume ChromPure does as well.


The highest zone woud be to 109%. If RGB was in balance across the zones through 11 with gamma right for zone 10 would you not almost by definition have a correct contrast setting. You would then choose the highest luminance that you were comfortable with that conitnued to allow the grayscale to have RGB balanced and gamma right.


I don't really know, but I suspect with my set is there is a gamma spike at high saturation. Is there a simple way to calculate what the luminance of 109% saturation should be given a target gamma and the known luminance at 100% and the calibration software's indicated gamma at 90%?

Depends on exactly what your target gamma is, but assuming it's 2.2 the...

maxY = 100% Y


Y = (1.09)^2.2 * maxY



So for 2.2 gamma it's about 20% more light than 100%.
 
#113 ·

Quote:
Originally Posted by dsskid /forum/post/18482104


alluringreality, I hope you don't mind me adding about the color shift.

-John

I agree if you're just using a grayscale pattern to watch for a loss of detail there will likely be some color shift, but it probably won't creep down to white if you're using a pattern that has above white detail like the thread title. A step further would be things like watching for color shift and seeing what happens with colors, but I was just trying to keep things as absolutely simple as possible. Really it's just the Digital Video Essentials description for setting contrast. The images from http://www.avsforum.com/avs-vb/showt...2#post16929442 show what happens as contrast is turned up and detail is lost near white on their bars and ramp pattern.
 
#114 ·

Quote:
Originally Posted by Mr.D /forum/post/18482259


I'm not familiar with the setup on a PS3 : as I'm a real gamer and own a 360


You should be able to have it setup to pass full range video from discussion on the net I've seen. Verify that first.


The difference between setting peak white at 235 or 254 is pretty massive visually to me.

It does show all bars above white with super-white enabled on the white clipping pattern and APL clipping pattern. Turning super-white off clips WTW and BTB. RGB output doesn't allow super-white, so YCC must be used. Like I said, maybe I'm not looking at the right scenes in the right movies, but it is odd that I've never seen a difference even though I have toggled that setting on and off during movie playback countless times to see what it did with real program material. Perhaps there are other factors in my setup that make the difference unnoticeable to the eye.


BTW, I have both a PS3 and a X360. The X360 may have many good games but it's not the best DVD player as it's noisy and has fewer controls/info for the DVD interface. It also can't do Blu-ray.


UPDATE: I just saw a 3 hour Blu-ray movie (XIII: The Conspiracy) that had plenty of bright scenes and scenes with bright areas. Some of these scenes were extremely bright or had extremely bright areas. I checked super-white on/off for as many as I could sometimes zeroing in on a single frame to capture the brightest image on-screen. I found zero difference time and time again. No difference whatsoever.
 
#115 ·

Quote:
Originally Posted by sotti /forum/post/18482533


Depends on exactly what your target gamma is, but assuming it's 2.2 the...

maxY = 100% Y


Y = (1.09)^2.2 * maxY



So for 2.2 gamma it's about 20% more light than 100%.

Thanks Scotti,


I am assuming that if my target gamma is 2.35, I would just use 2.35 as the exponent in the above formula?


The DUO is going to give me no way to control 109% but at least I can determine if I my gamma is spiking at above white as I suspect.
 
#117 ·

Quote:
Originally Posted by gtgray /forum/post/18483422


Thanks Scotti,


I am assuming that if my target gamma is 2.35, I would just use 2.35 as the exponent in the above formula?


The DUO is going to give me no way to control 109% but at least I can determine if I my gamma is spiking at above white as I suspect.

if you've got a duo, you're best bet is to calibrate 109% in the display, then use the duo to correct the rest of the grayscale.
 
#118 ·

Quote:
Originally Posted by alluringreality /forum/post/18481977


The easiest way to set contrast is probably to begin by setting contrast to a very low setting so that you can see all the detail in the contrast pattern. Start turning up contrast. Keep turning up contrast until the detail in the pattern begins to disappear. Now turn contrast down until most all the detail still appears and you can't go any higher without losing detail in the contrast pattern. Without any measurement equipment this sort of a method will probably result in a reasonably high contrast setting that is still likely to deliver all the detail in the original image.

When you say "detail in the contrast pattern", do you mean the bars on the bottom?
 
#119 ·

Quote:
Originally Posted by Jim McC /forum/post/18485562


When you say "detail in the contrast pattern", do you mean the bars on the bottom?

If you've ever tried the Monster ISF HDTV Calibration disc, the contrast adjustment is made by using a person in slight motion wearing a white shirt, with white buttons.


As you adjust contrast, the buttons, as well as the areas of shadows on the shirt caused by the fabric, will disappear as the contrast is raised too high. This is where the detail in the contrast gets lost.


People get caught up in the black levels losing detail, though they may not realize the same happens at the opposite end of the scale.
 
#120 ·

Quote:
Originally Posted by PlasmaPZ80U /forum/post/18483210



UPDATE: I just saw a 3 hour Blu-ray movie (XIII: The Conspiracy) that had plenty of bright scenes and scenes with bright areas. Some of these scenes were extremely bright or had extremely bright areas. I checked super-white on/off for as many as I could sometimes zeroing in on a single frame to capture the brightest image on-screen. I found zero difference time and time again. No difference whatsoever.

brrrrr! Terrible film that and 3 hours long...nasty.


here's what wikipedia has to say about rec.709.


Interface codes 0 and 255 are used for synchronization, and are prohibited from video data. Eight-bit codes between 1 and 15 provide footroom, and can be used to accommodate transient signal content such as filter undershoots. Eight-bit interface codes 236 through 254 provide headroom, and can be used to accommodate transient signal content such as filter overshoots and specular highlights.


As far as I'm concerned you want to be able to see the difference between specular highlights and level lower than that. By that logic...you want to set your display to show everything up to 254. 254 being mapped to the whitest point the display will reliably depict without incurring clipping in any of the color channels.


I'll have a look at some material over the weekend but like I said you can find evidence from S&M posted on here that demonstrates consistent level above 235. I have to say again I usually notice if range above 235 is clipped off on most material including broadcast TV over here in the UK.
 
#121 ·
And Final Cut Pro manual.


In fact, 8-bit Y′CBCR video does not use all 256 codes to represent picture information. Black is stored as code 16 and white is code 235. Codes 1-15 and 236-254 are retained for footroom and headroom, respectively. These areas allow for quick spikes in the signal caused by filtering in analog-to-digital conversions and, in the case of white levels, can prevent clipping for highlights that may exceed 235 (white). Levels above 235 are sometimes referred to as super-white levels.
 
#122 ·
 http://www.mastersofcinema.org/reviews/onibaba.html


Here's an interesting comparison of two masterings of "Onibaba" with pictorial examples. The comments on "superwhite" are interesting. Their assertion that the master that doesn't range out of 235 is doing a good thing is slightly misguided in my view even though they actually view it as a positive attribute of the master that does range above 235.


In trawling about I find lots of blunt assertion from pro/semi pro practitioners that video is 16-235 and everything outside that is "illegal". However if you read the standards for rec.709 and bt.601 what they continually state is that 236-254 is defined as headroom/superwhite/excursion.


(rather than just latching on to the obvious numbers 16-235 which is where I think a lot of this confusion stems from...people like absolute numbers)


Even if you ignore the fact that YCrCb maps higher into RGB and look just at the numbers in the spec sheet the chroma planes range from 16-240.


So that leaves us with 3 possible conclusions: ( this is referring to where the values end up on your display visually)


16 is black 235 is peak white and anything else is a bad thing.


16 is black and 254 is peak white and you should show the lot.


16 is black and peak white is 240 because the chroma planes range above 235 ( ignoring the mechanics of how YCrCb maps into RGB..someone else can do the maths I tend to fall asleep...I can't help it).


Last but not least what does this mean in the real world?


Watch some material with your display setup for peak white at 235 and then watch it at 254 and see what you think and post your observations.


I'm sure we can manage to do this without having a massive punchup if we remain a little open minded.


Things we think we know about video:


black ...16


ideal display gamma in a dim environment 2.35

(assuming a range between 2.2-2.5 depending on viewing situation and display performance)


Grayscale ...D.65

(B/W notionally justifiable as D.54 from a preferential/historical perspective)


Gamut... (according to standard and display capability and metering/adjustment capability)


white... see above (personally I'm sticking with 254 until I'm persuaded differently)
 
#123 ·

Quote:
Originally Posted by Mr.D /forum/post/18486472

http://www.mastersofcinema.org/reviews/onibaba.html


In trawling about I find lots of blunt assertion from pro/semi pro practitioners that video is 16-235 and everything outside that is "illegal". However if you read the standards for rec.709 and bt.601 what they continually state is that 236-254 is defined as headroom/superwhite/excursion.


(rather than just latching on to the obvious numbers 16-235 which is where I think a lot of this confusion stems from...people like absolute numbers)


Even if you ignore the fact that YCrCb maps higher into RGB and look just at the numbers in the spec sheet the chroma planes range from 16-240.


So that leaves us with 3 possible conclusions: ( this is referring to where the values end up on your display visually)


16 is black 235 is peak white and anything else is a bad thing.


16 is black and 254 is peak white and you should show the lot.


16 is black and peak white is 240 because the chroma planes range above 235 ( ignoring the mechanics of how YCrCb maps into RGB..someone else can do the maths I tend to fall asleep...I can't help it).


Last but not least what does this mean in the real world?


Watch some material with your display setup for peak white at 235 and then watch it at 254 and see what you think and post your observations.


I'm sure we can manage to do this without having a massive punchup if we remain a little open minded.


Things we think we know about video:


black ...16


ideal display gamma in a dim environment 2.35

(assuming a range between 2.2-2.5 depending on viewing situation and display performance)


Grayscale ...D.65

(B/W notionally justifiable as D.54 from a preferential/historical perspective)


Gamut... (according to standard and display capability and metering/adjustment capability)


white... see above (personally I'm sticking with 254 until I'm persuaded differently)

I agree with you. I like to use 16-235 is possible but I still want to see upwards of 250ish on the contrast scale. I have a denon 4310 that if set to 0 contrast it will clip down to about 237-238. I have to set the contrast at -2 for every input to see 250-254.
 
#125 ·

Quote:
Originally Posted by Mr.D /forum/post/18486472


...

16 is black 235 is peak white and anything else is a bad thing.

16 is black and 254 is peak white and you should show the lot.

...

Last but not least what does this mean in the real world?


Watch some material with your display setup for peak white at 235 and then watch it at 254 and see what you think and post your observations.

As I quoted earlier CEA is pretty clear on this and things that clip at 235 are almost certainly wrong but I believe it's not a completely unreasonable reading of 861-D. By that standard data above reference white is not bad but may be optional.


I thought that when S&M looked at discs they found lots of pixels both below 16 and above 235. But I also think the percentage of such pixels is low (the max. intensity histograms in the MoC article don't help here). It may also be worth noting that "bad" pixels are found in hard matted borders which certainly points to defective transfers.


I don't know if anyone has done a similar analysis of BD. I'd find that much more interesting than the DVD numbers.
 
#126 ·

Quote:
Originally Posted by bodosom /forum/post/18487711



I thought that when S&M looked at discs they found lots of pixels both below 16 and above 235. But I also think the percentage of such pixels is low

The question there is whether the percentage is low because its an error or whether its down to the fact that not every shot ( not even the majority) will have picture content that has areas that warrant by their nature excursion above 235.


This use of the word "occasional" in lots of the standards descriptions seems to infer unimportant which I don't necessarily agree with nor even suspect that was the original writers intent: ie that because its occasional the inference is you shouldn't worry about hanging on to it.


Its "occasional" because its not there in every single shot which is perfectly normal given the image content usually depicted.


Certainly the S&M examples seem to show the majority of the 235 "excursion" in areas of the image that you would reasonably expect to find it rather than lurking around as individual pixels.


What might be more useful to know is how high it tends to go. Given that if you don't want to calibrate for 235 but you don't want to hit 254 either what is a reasonable point to hit to maximise display contrast.
 
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