What Type of Color Errors are the Most Noticeable? - AVS Forum
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post #1 of 19 Old 12-03-2011, 09:58 PM - Thread Starter
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This is a question I often get. Are errors in hue, saturation, or luminance most detrimental to an image? Fortunately, this question can be answered in a relatively straightforward way.
First, we have a very good metric for grading perceived color errorDelta E. There are several dE formulas, but for color I think that CIE94 is the best.

Second, we have clearly defined gamuts that we can use as a reference. For the purpose of this test, I'll use Rec. 709, the high-definition standard.

Third, measuring the amount of error is fairly straightforward as well. Color is a three-dimensional property, including hue, saturation, and lightness. We can assign numerical values to any color using u'v' or ab chromaticity coordinates for saturation and hue and the CIE L value for lightness.

Terms and Methodology
  • Selecting an arbitrary amount of error, let's say 10%, then it is a simple matter to determine how much dE results from a uniform 10% error in each of the primary colors. All you need to know is how to identify quantities of error in HSL.
  • Saturation is defined as the chromatic element of color minus lightness. Chroma is the square root of the sum of color coordinates (either u'v' or ab) each squared. You can also think of saturation within a defined gamut as distance from the white point. However, since the available chromaticity charts on which we would plot such distance are not perceptually uniform, this is an approximation only.
  • Hue is defined as the degrees around a 360 degree circle with the white point at the center. Within a defined gamut, hue is the angle of a color from the white point. It is also arguably the most important characteristic, because it is hue that distinguishes one color from another.
  • Lightness is a perceptually-weighted measurement of luminance. It is defined as 116 times the root cube of relative luminance minus 16. Relative luminance is just the measured luminance of a color as a percentage of white at the same level of stimulus.
  • Although the calculations for HSL and dE require using the 1976 color spaces (Luv or Lab), values will be presented here in xyY simply because this is more familiar.
Since this is all done through mathematical calculation, we don't have to worry about the accuracy of a measuring device or the general applicability of a specific display.

Here's the data.

10% HSL errors and CIE94

Red
x y Y CIE94
H 0.603 0.292 0.2126 11.8
S 0.669 0.330 0.2126 6.3
L 0.640 0.330 0.2658 5.5
Green
H 0.272 0.580 0.7152 5.8
S 0.298 0.644 0.7152 3.7
L 0.300 0.600 0.9120 8.9
Blue
H 0.175 0.059 0.0722 4.7
S 0.142 0.046 0.0722 4.3
L 0.150 0.060 0.0879 3.5

Conclusions
  • From this it seems clear that hue errors are the most perceptually noticeable. A 10% error in hue results in the highest average dE of 7.4 and is the most noticeable for blue and red and the second most noticeable for green.
  • Determining the second most noticeable type of color error is less clear. Although lightness errors result in a higher average dE than saturation errors (6.0 vs. 4.8), saturation errors are more noticeable for red and blue where lightness errors are the least offensive. Only with green is a lightness error more noticeable (by a relatively large margin) than an equivalent saturation error.

Tom Huffman
ChromaPure Software/AccuPel Video Signal Generators
ISF/THX Calibrations
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post #2 of 19 Old 12-04-2011, 06:02 AM
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thanks for another educational post tom...

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post #3 of 19 Old 12-04-2011, 09:11 AM
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Love it! Clarity and precision are virtues. Thanks.

Best regards and beautiful pictures,
G. Alan Brown, President
CinemaQuest, Inc.
A Lion AV Consultants affiliate

"Advancing the art and science of electronic imaging"
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post #4 of 19 Old 12-17-2011, 02:09 PM
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Interesting stuff.

Correct me if I'm wrong, but the info above also appears to confirm that the most obvious errors are red color decoding errors (ie flesh tones), and green grayscale errors, which has been the conventional wisdom here for a long time.

ADU

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post #5 of 19 Old 12-18-2011, 01:39 AM - Thread Starter
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Errors in red are biggest when they are in hue or saturation. Color decoding errors for red are in luminance.

This is just about gamut error, so it has no direct relationship to the grayscale. However, it is easy enough to perform a similar analysis on white. Let's say we analyze a 10% error in R, G, and B and see which one yields the highest dE.

Red: x0.321, y0.329 (CIE94 4.7)
Green: x0.3127, y0.340 (CIE94 6.9)
Blue: 0.306, y0.318 (CIE94 5.9)

It seems that green is the worst offender.

Red color decoding errors and red errors in video grayscale seem larger than they are probably because we are very sensitive to their effects on skin color.


Quote:
Originally Posted by ADU View Post

Correct me if I'm wrong, but the info above also appears to confirm that the most obvious errors are red color decoding errors (ie flesh tones), and green grayscale errors, which has been the conventional wisdom here for a long time.


Tom Huffman
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post #6 of 19 Old 05-01-2012, 10:43 AM
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TomHuffman!
Сan result in the same table for the secondary colors?
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post #7 of 19 Old 05-01-2012, 12:16 PM
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10% HSL errors and CIE94
Yellow
x y Y CIE94
H-3 0.4305 0.4964 0.9278 2.8
S-2 0.4336 0.5288 0.9278 4.2
L-1 0.4193 0.5053 0.708 9.9
Cyan
H-2 0.2362 0.3386 0.7874 2.7
S-3 0.2336 0.3287 0.7874 1.7
L-1 0.2246 0.3287 0.603 9.2
Magenta
H-2 0.34 0.1619 0.2848 2.3(10.1)
S-3 0.3204 0.1663 0.2848 2.0
L-1 0.3209 0.1542 0.358 6.2
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post #8 of 19 Old 05-01-2012, 12:17 PM
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I did (chroma calculator).
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post #9 of 19 Old 05-01-2012, 12:38 PM
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Quote:
Originally Posted by TomHuffman View Post

This is a question I often get. Are errors in hue, saturation, or luminance most detrimental to an image? Fortunately, this question can be answered in a relatively straightforward way.
First, we have a very good metric for grading perceived color errorDelta E. There are several dE formulas, but for color I think that CIE94 is the best.

Second, we have clearly defined gamuts that we can use as a reference. For the purpose of this test, I'll use Rec. 709, the high-definition standard.

Third, measuring the amount of error is fairly straightforward as well. Color is a three-dimensional property, including hue, saturation, and lightness. We can assign numerical values to any color using u'v' or ab chromaticity coordinates for saturation and hue and the CIE L value for lightness.

Terms and Methodology
  • Selecting an arbitrary amount of error, let's say 10%, then it is a simple matter to determine how much dE results from a uniform 10% error in each of the primary colors. All you need to know is how to identify quantities of error in HSL.
  • Saturation is defined as the chromatic element of color minus lightness. Chroma is the square root of the sum of color coordinates (either u'v' or ab) each squared. You can also think of saturation within a defined gamut as distance from the white point. However, since the available chromaticity charts on which we would plot such distance are not perceptually uniform, this is an approximation only.
  • Hue is defined as the degrees around a 360 degree circle with the white point at the center. Within a defined gamut, hue is the angle of a color from the white point. It is also arguably the most important characteristic, because it is hue that distinguishes one color from another.
  • Lightness is a perceptually-weighted measurement of luminance. It is defined as 116 times the root cube of relative luminance minus 16. Relative luminance is just the measured luminance of a color as a percentage of white at the same level of stimulus.
  • Although the calculations for HSL and dE require using the 1976 color spaces (Luv or Lab), values will be presented here in xyY simply because this is more familiar.
Since this is all done through mathematical calculation, we don't have to worry about the accuracy of a measuring device or the general applicability of a specific display.

Here's the data.

10% HSL errors and CIE94

Red
x y Y CIE94
H 0.603 0.292 0.2126 11.8
S 0.669 0.330 0.2126 6.3
L 0.640 0.330 0.2658 5.5
Green
H 0.272 0.580 0.7152 5.8
S 0.298 0.644 0.7152 3.7
L 0.300 0.600 0.9120 8.9
Blue
H 0.175 0.059 0.0722 4.7
S 0.142 0.046 0.0722 4.3
L 0.150 0.060 0.0879 3.5

Conclusions
  • From this it seems clear that hue errors are the most perceptually noticeable. A 10% error in hue results in the highest average dE of 7.4 and is the most noticeable for blue and red and the second most noticeable for green.
  • Determining the second most noticeable type of color error is less clear. Although lightness errors result in a higher average dE than saturation errors (6.0 vs. 4.8), saturation errors are more noticeable for red and blue where lightness errors are the least offensive. Only with green is a lightness error more noticeable (by a relatively large margin) than an equivalent saturation error.

great post!

a very objective answer to a question that many have asked or wanted to ask
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post #10 of 19 Old 05-01-2012, 02:29 PM
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On my cable -some channels( rough guess 10%) there is a quite noticeable green tinge in the dark areas.( not sure if it's in light scenes).

If I calibrate to 6500k I don't notice the green problem.6500k makes a lot of other channels look too red.

Another piece to the puzzle.
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post #11 of 19 Old 05-01-2012, 03:55 PM
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Quote:
Originally Posted by Vic12345 View Post

On my cable -some channels( rough guess 10%) there is a quite noticeable green tinge in the dark areas.( not sure if it's in light scenes).

If I calibrate to 6500k I don't notice the green problem.6500k makes a lot of other channels look too red.

Another piece to the puzzle.

Cable channels have little consistency, because many of them don't do good quality control. You can't optimize for them, because the target is unpredictable. If you notice you said channels, not programs. You should get program to program variation as you see the different directors intent. Instead you get channel to channel variation as someone just isn't putting the content on air with the right settings.

You need reference content to view to check your calibration.

Joel Barsotti
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post #12 of 19 Old 05-02-2012, 11:23 PM
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What is good reference content? Color bars on tv station,video essentials,black and white tv show?
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post #13 of 19 Old 05-03-2012, 08:41 AM
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Quote:
Originally Posted by Vic12345 View Post

What is good reference content? Color bars on tv station,video essentials,black and white tv show?

DVDs or Blu-Rays are typically mastered correctly.

Something like the Spears and Munsil Disc has a nice montage of extremely well mastered content (As well as patterns to help you setup the display correctly).

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post #14 of 19 Old 05-03-2012, 03:42 PM
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Have video essentials,but never carefully went through it all.i got an old tired CRT where I have to turn the blue and green drives down so much to achieve 6500 that there's hardly contrast.

What type of color error is most noticeable?
I would say magenta and red and fleshtones,then blue and (edit red) in whites.
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post #15 of 19 Old 06-03-2012, 04:36 AM
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NO!
DOUG
Our vision is most sensitive to Green so you want green to be as accurate as you can make it. Cyan and Yellow should be the next most accurate colors. Red and magenta should be next in line for accuracy, and blue errors would be the least-obvious errors. But large errors in any color will be visible so you have to keep things in balance (again, part of the "art" of calibration that you can't learn in descriptions of how to calibrate).
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post #16 of 19 Old 06-03-2012, 04:36 AM
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1) green
2) cyan and yellow
3) red and magenta
4) blue
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post #17 of 19 Old 06-03-2012, 05:23 AM
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Tom has already answered this question with his calculations above, hue/saturation errors in red are most important, followed by luminance of green.

Here is the same calculation with a different assumption - error levels for each type were set to generate the same average dE94 of 2.8.

Error 10% Luminance 2% Saturation 5% Hue
R 2.3 7.2 5.3
G 3.4 2.8 2.8
B 1.7 0.5 1
Y 3.7 3 3.3
C 3.5 2.5 2.2
M 2.5 1.2 2.1

So for a given error (10%) in luminance, Green Yellow and Cyan will be most noticeable. However, just a 2% error in saturation generates the highest dE (red).
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post #18 of 19 Old 06-03-2012, 05:36 AM
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Thank you very match!
But You got me wrong, I wrote about the importance of color with the same delta error.
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post #19 of 19 Old 06-03-2012, 06:00 AM
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Zoyd! Please Explain your table.
What is this average dE94?
Why do I have other values ​​are obtained?


Error 10% Luminance 10% Saturation 10% Hue
R 5.5 6.3 11.8
G 8.9 3.7 5.8
B 3.5 4.3 4.7
Y 9.9 4.2 2.8
C 9.2 1.7 2.7
M 6.2 2.0 2.3
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