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post #1 of 89 Old 10-18-2014, 06:47 PM - Thread Starter
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Modifying White Point / Color Space

My television's white-balance/color temp controls don't perform well enough to allow me to get my grayscale to reach D65 without significant (gamma and/or chromaticity) error. So, short of new hardware, I am forced to compromise. I believe there are four ways to compromise (i.e., a workflow approach) as follows:

1. Minimize gamma error at the expense of chromaticity.

2. Minimize chromaticity error at the expense of gamma.

3. Seek and accept some amount of error in both gamma and chromaticity that is neither minimal for either but represents some semblance of "error balance".

4. Perhaps controversially/illegitimately "calibrate" to a slightly higher white point. HCFR software currently allows this to be done rather easily.

So a couple of questions follow:

1. Which compromise above is best in your opinion and why?

2. I know the formula for finding out the x and y coordinates of a different white point on the daytime locus. So if, hypothetically and potentially against the advice of the community I nevertheless choose option 4, would the coordinates for the primary colors (RGB) need to also change from the sRGB/Rec709 coordinates? And, if so, where is the formula for backing in to the alternate RGB coordinates based on a manually chosen white point?
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post #2 of 89 Old 10-18-2014, 07:01 PM
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Brand name and model of the display would help.
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post #3 of 89 Old 10-18-2014, 08:49 PM - Thread Starter
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Sharp Aquos Quattron LC-70LE847U...although I can't imagine why that would affect the answers. Do the principles of calibration change from display to display? Wouldn't that be like the laws of physics changing from city to city?
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post #4 of 89 Old 10-18-2014, 11:57 PM
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I remember a Sharp owner telling me that he could only calibrate his TV with a higher white point. I think he was in Europe. Sharps in general are just messed up. Mine is awful
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post #5 of 89 Old 10-19-2014, 05:15 AM - Thread Starter
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Yes my Sharp has this problem. However, if anyone knows how to get into the service menu and how to make the appropriate changes in the service menu then I'm all ears.
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post #6 of 89 Old 10-19-2014, 10:12 AM
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I'm not an expert, but I have had 2 Quattrons in the last 3 years, which I have set up with
the AVS calibration disc and my own perception of white point. The blue LED that supplies
the primary light for these sets is the culprit for a lot of the problems that they exhibit.
You almost certainly have to use a higher temperature because of the predominance of blue
light source. Compound that with the deliberate use of yellow to complement the excess
blue and you have a chrominance nightmare -- until you get it tamed.
Sharp uses the industry standard blue LED to generate white light, with a phosphor that
radiates in yellow frequencies as well as green and red. They give no tools for directly affecting
the yellow pixels, other than the CMS, which only affects chromacity.
My best efforts are published for my new set and my old set. See what you think:

Sharp UQ17U Calibrations

Sharp LC-70LE845U Calibration, including 3D!

The second listing is for my old set, which is very similar to yours.
Lots of people tried the settings and found them pleasing.
I can say that my first set was much easier to calibrate than the new
one, which more aggressively uses the yellow pixel and is harder
to tame.

Last edited by johnfull; 10-19-2014 at 10:21 AM.
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post #7 of 89 Old 10-19-2014, 10:22 AM - Thread Starter
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Thanks but I'm a firm believer that using other people's settings is worse than useless.

I thought my original post would spark a general discussion above the idiosyncrasies of any particular TV. So I'm hoping the responses to the original post are still to come.
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post #8 of 89 Old 10-19-2014, 10:50 AM
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I understand, but there is general hostility to Quattron among calibrators because of the
hoops you have to jump through. Adding the yellow wavelength of light, in addition to
the yellow generated with R+G, causes hardware calibration equipment to misread too
much blue. This has been disputed, but everyone who uses hardware comes up with
a decidedly green/yellow cast to their white balance and without other explanation.
Anyway, the readings are NOT worse than out of the box and are there for you to use
or not. You can always re-set to factory specs and never mention it again...
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post #9 of 89 Old 10-19-2014, 12:43 PM
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Quote:
Originally Posted by johnfull View Post
I understand, but there is general hostility to Quattron among calibrators because of the
hoops you have to jump through. Adding the yellow wavelength of light, in addition to
the yellow generated with R+G, causes hardware calibration equipment to misread too
much blue.
How can adding extra yellow energy cause a meter (at least a spectro) to read "too much blue?"

Let's be clear here. The hostility (at least on my part) comes as a reaction to Sharp completely breaking the HDTV/REC709 color system and marketing the results as a "fix" to something that was not broken. Then subsequently offering the calibrator *no way* to undo the so-called "fix."

Sorry for the rant ... first day back on caffeine in a while ... bit twichy.
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post #10 of 89 Old 10-19-2014, 02:16 PM - Thread Starter
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Very well put.

So which compromise approach do you recommend and why?

And if, in this special circumstance, the use of a different white point has some merit then do the Rec 709 primary coordinates need tweaking?
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post #11 of 89 Old 10-19-2014, 02:44 PM
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Quote:
Originally Posted by robarivas View Post
Sharp Aquos Quattron LC-70LE847U...although I can't imagine why that would affect the answers. Do the principles of calibration change from display to display? Wouldn't that be like the laws of physics changing from city to city?
To answer the need to know the make and model; it is important. Each manufacturers and models have different idiosyncrasies. With Sharp, their displays push about 9000 K ~ 10000 K white point out of the box. Many professionals have had difficulty setting the D65. Most of the time the best that is achieved is around 7500 K but this is not without sacrificing something along the way. It is as if Sharp had not bothered to adjust their displays from the Asian 9300 K white point standard to the REC-BT709 D65 white point standard. Others have stated that on some models the CMS features do not work as they should.

If you read posting #6 of this thread by "johnfull", you will see he states, "I have had 2 Quattrons in the last 3 years, which I have set up with the AVS calibration disc and my own perception of white point". Why did he need to create his own white point? Is it that he could not achieve D65?

Your statement, "Sharp Aquos Quattron LC-70LE847U...although I can't imagine why that would affect the answers. Do the principles of calibration change from display to display? Wouldn't that be like the laws of physics changing from city to city"? Yes, it does effect the answer. The principles of calibration do not change, it is dealing with the quarks of the display to achieve the desired settings of a calibration this makes it more difficult. No the laws of physics still apply from city to city. Many better than you or I would opt out for option #4 from the option list from the first posting. If I were doing such a display, I too would probably settle for #4 .

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post #12 of 89 Old 10-19-2014, 02:53 PM
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Quote:
Originally Posted by HDTVChallenged View Post
How can adding extra yellow energy cause a meter (at least a spectro) to read "too much blue?"

Let's be clear here. The hostility (at least on my part) comes as a reaction to Sharp completely breaking the HDTV/REC709 color system and marketing the results as a "fix" to something that was not broken. Then subsequently offering the calibrator *no way* to undo the so-called "fix."

Sorry for the rant ... first day back on caffeine in a while ... bit twichy.
A colorimeter may or may not register a completely alien wavelength
accurately. The blue is counteracting both G+R and Y to make white. Do you know it the wavelength range of yellow is accurately
read by any RGB calibration meter, whether colorimeter or spectrometer? That seems to be the nub of the problem.
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post #13 of 89 Old 10-19-2014, 03:35 PM
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Quote:
Originally Posted by robarivas View Post
My television's white-balance/color temp controls don't perform well enough to allow me to get my grayscale to reach D65 without significant (gamma and/or chromaticity) error. So, short of new hardware, I am forced to compromise. I believe there are four ways to compromise (i.e., a workflow approach) as follows:

1. Minimize gamma error at the expense of chromaticity.

2. Minimize chromaticity error at the expense of gamma.

3. Seek and accept some amount of error in both gamma and chromaticity that is neither minimal for either but represents some semblance of "error balance".

4. Perhaps controversially/illegitimately "calibrate" to a slightly higher white point. HCFR software currently allows this to be done rather easily.

So a couple of questions follow:

1. Which compromise above is best in your opinion and why?

2. I know the formula for finding out the x and y coordinates of a different white point on the daytime locus. So if, hypothetically and potentially against the advice of the community I nevertheless choose option 4, would the coordinates for the primary colors (RGB) need to also change from the sRGB/Rec709 coordinates? And, if so, where is the formula for backing in to the alternate RGB coordinates based on a manually chosen white point?
Hi,
There is something called the Bradford Matrix that might provide a basis for you to work through your option 4. Go here for a brief discussion of the Bradford:

http://www.brucelindbloom.com/index....hromAdapt.html

It's been a while since I looked at this sort of thing, but I do have still on hand, a Mathematica notebook that performs the Matrix inversions, etc.
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post #14 of 89 Old 10-19-2014, 04:24 PM
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Quote:
Originally Posted by randal_r View Post
To answer the need to know the make and model; it is important. Each manufacturers and models have different idiosyncrasies. With Sharp, their displays push about 9000 K ~ 10000 K white point out of the box. Many professionals have had difficulty setting the D65. Most of the time the best that is achieved is around 7500 K but this is not without sacrificing something along the way. It is as if Sharp had not bothered to adjust their displays from the Asian 9300 K white point standard to the REC-BT709 D65 white point standard. Others have stated that on some models the CMS features do not work as they should.

If you read posting #6 of this thread by "johnfull", you will see he states, "I have had 2 Quattrons in the last 3 years, which I have set up with the AVS calibration disc and my own perception of white point". Why did he need to create his own white point? Is it that he could not achieve D65?

Your statement, "Sharp Aquos Quattron LC-70LE847U...although I can't imagine why that would affect the answers. Do the principles of calibration change from display to display? Wouldn't that be like the laws of physics changing from city to city"? Yes, it does effect the answer. The principles of calibration do not change, it is dealing with the quarks of the display to achieve the desired settings of a calibration this makes it more difficult. No the laws of physics still apply from city to city. Many better than you or I would opt out for option #4 from the option list from the first posting. If I were doing such a display, I too would probably settle for #4 .
Quattron utilizes a wavelength range that RGB equipment is not
able to properly read or incorporate into formulae.
Several people have tried to calibrate a white point with SpectraCal
and ended up with the same yellow/green white as each other.
There is something fundamentally wrong with calibrating a RGBY
screen using RGB tools -- the Y is ignored and the amount of blue
needed to counteract it is thought to be excess. Does this make
sense? I used the calibration disc to get a clean white and then'
fine-tuned it to properly bias the chroma signal for decent fleshtones.
The guys with the software and colorimeters have not been kind to
my efforts, but others who own these sets have been very appreciative. The quirks of the Quattron system can be tamed, but
not by traditional calibration methods, unfortunately.
Same can be said of Quantum Dots, which are proving to give false
readings on last year's Sony Triluminous models.
My hunch is that the royal blue LED that supplies the blue primary
and energizes the phosphors/dots of red and green (and yellow) is
not an ideal blue to begin with. Most problems have been coming
from the attempt to compensate for a very cold indigo/blue in making
blue/greens and cyans. Sony actually used a bluer shade of green!
Sharp was going to make a wide gamut with Quattron, but that
blue has scotched the idea of opening up the middle at all.
Instead, they have had to retreat to using the yellow merely as a
counteracting element to the miserable blue. It makes for brightness,
but the original promise of tropical blues is dead for now.
So is Quattron dead for now in their new 4K sets.
Maybe a better backlight will come along to make a truly wide gamut
possible and then Quattron yellow can allow a deeper green as well.
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post #15 of 89 Old 10-19-2014, 05:10 PM
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You bring up a point that is very interesting, do you have any documentation for us to read? I am interested in what Sharp is doing. I can not help but feel that Sharp is skirting the standards but this is only a hunch.

Here is something that I came across;

Analysis of Quattron

Color researchers at Queen Mary University of London investigated the Quattron technology and found that although Quattron does have 4 physical color sub-pixels it does not have a fourth primary in the backlight to drive it (yellow is approximately 575 nm). Quattron has a yellow sub-pixel but the manufacturer has not made any provision to produce the yellow light needed to pass through it. On that basis they conclude that it serves no useful function.[11]
The lack of a fourth primary is clearly shown by a spectrogram where the red primary is given separately from the green primary. Yellow may be seen to be simply the sum of red and green. A yellow push may also be observed when yellow is compared with the red and green primaries. The spectral power of yellow is approximately twice that of red and green. Yellow colors will therefore appear more prominently on a Quattron display than red or green colors, but this is because the manufacturer has 'pushed' yellow to a higher luminance rather than having improved the color to more closely approximate a natural yellow (such as the yellow of a sunflower), which has a flat spectral power distribution from lime-green to deep red wavelengths. Green dominates the Quattron yellow and this is confirmed perceptually by color matching.[11] The human visual system is particularly sensitive to yellow, and as a result of the lack of a yellow primary (or a yellow boost to either red or green) there will be difficulty in discriminating between green, red and yellow. The reproduction of a yellow image will as a result always be perceived as slightly green or slightly red (or orange) but never a pure natural yellow.


Criticism

According to an analysis published in MaximumPC Magazine by Raymond Soneira, president of DisplayMate Technologies, a video calibration equipment producer, Sharp's Quattron technology does not have the ability to show more colors than a standard RGB set. He argues that, due to industry-standard color spaces used by content providers, there is no existing source material that contains the fourth color channel. He further states that any "extra" colors displayed must simply be created in the television itself through video processing, resulting in exaggerated, less accurate color
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post #16 of 89 Old 10-19-2014, 05:55 PM
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Hi,
There is something called the Bradford Matrix that might provide a basis for you to work through your option 4. Go here for a brief discussion of the Bradford:

http://www.brucelindbloom.com/index....hromAdapt.html

It's been a while since I looked at this sort of thing, but I do have still on hand, a Mathematica notebook that performs the Matrix inversions, etc.
In fact, as I look more closely at Lindbloom's article, he actually has the matrix for a case similar to yours, already worked out for you to use! Look closely at his Matrix of coefficients for transforming from D65 to D75! There is your answer!
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post #17 of 89 Old 10-19-2014, 06:07 PM
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Quote:
Originally Posted by randal_r View Post
You bring up a point that is very interesting, do you have any documentation for us to read? I am interested in what Sharp is doing. I can not help but feel that Sharp is skirting the standards but this is only a hunch.

Here is something that I came across;

Analysis of Quattron

Color researchers at Queen Mary University of London investigated the Quattron technology and found that although Quattron does have 4 physical color sub-pixels it does not have a fourth primary in the backlight to drive it (yellow is approximately 575 nm). Quattron has a yellow sub-pixel but the manufacturer has not made any provision to produce the yellow light needed to pass through it. On that basis they conclude that it serves no useful function.[11]
The lack of a fourth primary is clearly shown by a spectrogram where the red primary is given separately from the green primary. Yellow may be seen to be simply the sum of red and green. A yellow push may also be observed when yellow is compared with the red and green primaries. The spectral power of yellow is approximately twice that of red and green. Yellow colors will therefore appear more prominently on a Quattron display than red or green colors, but this is because the manufacturer has 'pushed' yellow to a higher luminance rather than having improved the color to more closely approximate a natural yellow (such as the yellow of a sunflower), which has a flat spectral power distribution from lime-green to deep red wavelengths. Green dominates the Quattron yellow and this is confirmed perceptually by color matching.[11] The human visual system is particularly sensitive to yellow, and as a result of the lack of a yellow primary (or a yellow boost to either red or green) there will be difficulty in discriminating between green, red and yellow. The reproduction of a yellow image will as a result always be perceived as slightly green or slightly red (or orange) but never a pure natural yellow.


Criticism

According to an analysis published in MaximumPC Magazine by Raymond Soneira, president of DisplayMate Technologies, a video calibration equipment producer, Sharp's Quattron technology does not have the ability to show more colors than a standard RGB set. He argues that, due to industry-standard color spaces used by content providers, there is no existing source material that contains the fourth color channel. He further states that any "extra" colors displayed must simply be created in the television itself through video processing, resulting in exaggerated, less accurate color
The white LED backlight generates red, yellow, and green wavelengths from its yellow phosphor. A colorimeter set up to see only red and green will not accurately record the yellow spectrum.
Sharp was onto something with a tetrahedron-shaped color space,
similar to some of the better desktop printers that use multiple
primaries. A benefit was to be pure yellow from the far righthand
margin, and bluegreens from the interior of the colorspace that is'
untouched by conventional RGB devices. Sony used a blue-green
without the compensating yellow pixel and stopped after one year.
You can't have pure yellow and robust cyan on a triangular plot.
When backlighting improves, I hope Sharp will return to Quattron in
the 4K sets and produce a truly wide spectrum -- and one that is
controllable by calibrators! As it is, the yellow adds a great deal of
efficiency to the light output, in particular because of the overbearing
blue LED; B+Y=white, afterall, which boosts the R+G+B=white considerably...
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post #18 of 89 Old 10-19-2014, 06:19 PM
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The white LED backlight generates red, yellow, and green wavelengths from its yellow phosphor. A colorimeter set up to see only red and green will not accurately record the yellow spectrum.
What do you mean by this?
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Quote:
Originally Posted by johnfull View Post
A colorimeter may or may not register a completely alien wavelength
accurately.
That's why we have spectros and don't rely upon colorimeters alone.

Quote:
Do you know it the wavelength range of yellow is accurately
read by any RGB calibration meter, whether colorimeter or spectrometer?
Well for spectros it would only make a difference if the "yellow" was some how disturbing the Standard Observer function integrations. If so, then it would also "disturb" human vision ... IOW, I simply can't follow your logic here.
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Originally Posted by robarivas View Post
So which compromise approach do you recommend and why?
I can't answer that without looking at the set and the calibration results. But of your original choices, I would tend toward Option 2: Sacrificing the gamma. Of course, that would depend on the actual results: i.e. whether that would actually allow you to hit D65 and minimize r.709 gamut errors.
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post #21 of 89 Old 10-20-2014, 01:58 AM
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What do you mean by this?
Metamerism. R+G looks the same as the spectral yellow, but
is seen differently with equipment other than our eyes.
A prism will show red and green lines for the first and yellow
for the second. Calibrations that don't take into account actual
yellow will show an excess of blue in the white point.
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Originally Posted by HDTVChallenged View Post
That's why we have spectros and don't rely upon colorimeters alone.



Well for spectros it would only make a difference if the "yellow" was some how disturbing the Standard Observer function integrations. If so, then it would also "disturb" human vision ... IOW, I simply can't follow your logic here.
The disturbance comes from not adding the spectral yellow to
the calculation of white. The calculation will show excesss blue.
Other functions of the yellow are handled by the chroma circuit,
which substitutes the yellow pixel for some of the R+G LUT.
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post #23 of 89 Old 10-20-2014, 02:21 AM
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Quote:
Originally Posted by johnfull View Post
Metamerism. R+G looks the same as the spectral yellow, but
is seen differently with equipment other than our eyes.
A prism will show red and green lines for the first and yellow
for the second. Calibrations that don't take into account actual
yellow will show an excess of blue in the white point.
Maybe I'm misunderstanding your point here, but an accurate colorimeter will be able to accurately measure the chromaticity, regardless of metamerism. A colorimeter only cares about what our eyes would see. It doesn't care about whether the color is a spectral color or not. This holds for whites and primaries.

So I'm not sure what you mean when you say that a calibration "that doesn't take into account actual yellow will shown an excess of blue in the white point". Are you saying a colorimeter will show more blue than there actually is? Or are you saying that there will be more blue than desired, and the colorimeter won't be able to detect this?
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post #24 of 89 Old 10-20-2014, 02:32 AM
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Quote:
Originally Posted by spacediver View Post
Maybe I'm misunderstanding your point here, but an accurate colorimeter will be able to accurately measure the chromaticity, regardless of metamerism. A colorimeter only cares about what our eyes would see. It doesn't care about whether the color is a spectral color or not. This holds for whites and primaries.

So I'm not sure what you mean when you say that a calibration "that doesn't take into account actual yellow will shown an excess of blue in the white point". Are you saying a colorimeter will show more blue than there actually is? Or are you saying that there will be more blue than desired, and the colorimeter won't be able to detect this?
This is my question and it is reverse-engineered from observations
of calibrators using colorimeters. Their calculations of white point
are way off in the direction of yellow. I posit the theory that RGB
colorimeters see Red, Green, and Blue and either don't see the
part of the spectrum that is actually yellow or are not calibrated
properly for those frequencies. This would have downstream
effects in the calculation of the white point if the data on the yellow
is not accurate. What theory do you propose that makes SpectraCal
show a white point that the eye disagrees with?
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post #25 of 89 Old 10-20-2014, 02:38 AM
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I won't quibble over language here -- colorimeters don't actually 'care' about anything.
My question is about the range of each of the three receptors in the equipment.
Yellow lies outside of either red or green, but may or may not be perceived as one or the other or both.
It just depends on the equipment. Sharp is using the yellow part of the spectrum in the phosphor
that would ordinarily be thrown out by red and green filters on an RGB set. It uses this yellow to
alter the white point of the final image.
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post #26 of 89 Old 10-20-2014, 03:16 AM
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My question is about the range of each of the three receptors in the equipment.
Yellow lies outside of either red or green, but may or may not be perceived as one or the other or both.
It just depends on the equipment. Sharp is using the yellow part of the spectrum in the phosphor
that would ordinarily be thrown out by red and green filters on an RGB set. It uses this yellow to
alter the white point of the final image.
Colorimeters don't have a "range". They have filters which, in the ideal, match the standard observer functions, which in turn are a set of functions that describe how the average human integrates radiant energy across the spectrum.

Thus, a colorimeter, in the ideal, will provide an accurate measure of what "color" the average human sees.

There are typically two sources of uncertainty, however:

1: mismatch between any given colorimeter and the standard observer functions
2: the fact that there is variance within the visual systems of the human population, which means that even an ideal colorimeter will not accurately predict what color every single human will see.

Importantly, both of these sources of error tend to be exacerbated with narrow wavelength sources.

None of what you are saying makes any sense to me, in light of this. You seem to be operating with a few conceptual flaws.
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Colorimeters are set up around Red, Green, and Blue wavelengths for the sake of economy.
Sensitivity is not Panchromatic, but Orthochromatic in a colorimeter, correct?
If a wavelength of 580 nanometers strikes a colorimeter's pickup, the results will be something
that is iterpreted either as red or green or not seen at all. 570-590 nanometers is the range of
yellow light and there has been, heretofore, no reason to design a colorimeter that is sensitive
to this range or software to take it into account in calibrations. The white LEDs have a large
part of their spectral output in this range, but a RGB set will filter it out. Not so a Quattron.
If there is a mismatch between the sensitivity of the colorimeter and the output of the set, then
the calculations will be thrown off. Spectrometers are panchromatic, but not colorimeters, right?...
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If a wavelength of 580 nm strikes a colorimeter, it will produce three quantities, which correspond to X, Y (luminance), and Z. These in turn can be transformed into chromaticity coordinates (x,y) which represent the particular color that a human would see if a wavelength of 580 nm struck her eye.

I've never heard of the terms panchromatic or orthochromatic, but a quick google search suggests that they are concepts that relate to types of photographic film, and are not appropriate for discussing colorimeters.

A colorimeter will integrate light across the entire visible spectrum.

I've given you this link before, but I'm not sure if you read it. Give it a read and see if things start to make more sense. I've also given you links to craig blackwell's youtube series on color vision, which is an excellent introduction to the CIE system. Again, here is part 1 (watch the first four parts).

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Another thing that bolsters my theory is the trouble that some calibrators are having
with extremely narrow sources of spectrum -- like Quantum Dots. Colorimeters may miss
part of the output by having a peak sensitivity other than the specific wavelength emitted.
This lends credence to the idea that the yellow output of a Quattron is missed by colorimeters
that are sensitive in the red and the green, but not between.
You can find the discussion on Sony Quantum Dots and false readings
that result from the narrow spectra elsewhere.
You're a bit glib about the capabilities of colorimeters.

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post #30 of 89 Old 10-20-2014, 04:21 AM
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Quote:
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This lends credence to the idea that the yellow output of a Quattron is missed by colorimeters
that are sensitive in the red and the green, but not between.
Quattron's may have issues with narrow wavelengths and poor primary selection (I don't know and I don't care), but you clearly haven't a clue how colorimeters work, and presumably have no wish to learn.

I'm done trying to explain things to you. Enjoy your theories.
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