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Discussion Starter · #1 ·
I measured an 11 point grayscale run on an LG LED with CalMAN, then ChromaPure. The differences between the x, y, Y readings are small, yet the differences in dE are enormous. I overlaid the two programs so we can compare the numbers.


I also tried changing CP to dE2000 and changing CalMAN to dEXXXX_LuminanceCompensated, without much change in difference.


Which result should be believed, and why such radical differences?
 

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Discussion Starter · #4 ·
Thanks Larry. It looks like HCFR and CP are in agreement.


When I was switching different options, if I remember right with dE2000 selected in CP the two programs matched at 100% and then diverged as it went down, with CM giving much lower readings at the low end.


Interestingly, here with dE1994, even at 100% there's a big difference.
 

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Discussion Starter · #5 ·

Quote:
Originally Posted by LarryInRI  /t/1520371/huge-de94-differences-between-chromapure-and-calman#post_24423945


If I change to CEI2000 and Absolute Y with gamma, I get this:




Larry
Very interesting. So the Absolute Y with gamma selection makes it agree with CalMAN...
 

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Chad,


Looking more carefully at the data and the settings in HCFR, it appears that the contributing factor which make the result about the same as CalMAN is more the selection of dE2000 instead of dE1994. The dE result with or without considering gamma (absolute or relative Y) makes little if any difference.


Larry
 

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I think this issue, or a version thereof, has come up before. In the case I recall, the discrepancy was explained by a difference in the way the programs weighted Y (or not.)


The original, pre-revival version of HCFR even had an option to 'Include Y (Luminance) in dE' calculations. IOW, you could base dE solely on x,y or on x,y,Y. I'm guessing something similar is going on here.
 

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Quote:
Originally Posted by Chad B  /t/1520371/huge-de94-differences-between-chromapure-and-calman/0_100#post_24423775


I measured an 11 point grayscale run on an LG LED with CalMAN, then ChromaPure. The differences between the x, y, Y readings are small, yet the differences in dE are enormous. I overlaid the two programs so we can compare the numbers.


I also tried changing CP to dE2000 and changing CalMAN to dEXXXX_LuminanceCompensated, without much change in difference.


Which result should be believed, and why such radical differences?
Whenever you see problems like this there is a relative simple way to resolve the issue.


1. Go to http://www.brucelindbloom.com/index.html?ColorCalculator.html

2. In a separate tab open http://www.brucelindbloom.com/index.html?ColorDifferenceCalc.html

3. In the Color Calculator select the following options, Ref white D65 and RGB model sRGB.

4. Type the x,y values in the provided spaces.

5. Type 1.0 for Y.

6. Click the xyY button. This populates all of the other color spaces with equivalent values.

7. Go to the Color Difference Calculator.

8. In the Lab Reference type 100, 0, 0

9. In the Lab Sample type the Lab equivalents to the xyY values shown in the Color Calculator.

10. Click Calculate.

Results will display in CIELAB, CIE94 (Graphic Arts and Textiles), CIEDE2000, and two versions of CMC

Example


The colorimetric values you provided at 30% are 0.275, 0.281, 1.0

The Lab equivalent is 100, 4.893, -26.4308

The CIE94 value for this color is 26.9


There was a time when CalMan's default method for calculating grayscale dE included luminance, which is generally accounted for by gamma. The result is that the exact same color would have substantially decreasing dE values as you went lower on the video scale. However, this appears to not be the case here because the large discrepancy exists even at 100% video.
 

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Quote:
Originally Posted by TomHuffman  /t/1520371/huge-de94-differences-between-chromapure-and-calman#post_24424382


There was a time when CalMan's default method for calculating grayscale dE included luminance, which is generally accounted for by gamma. The result is that the exact same color would have substantially decreasing dE values as you went lower on the video scale. However, this appears to not be the case here because the large discrepancy exists even at 100% video.

I just checked the dE charts in design mode for the Quick Analysis and HT Enthusiast workflows in Calman 5.3, and each has "Include Luminance Error" checked in its Properties.


This thread talks about it a little more, but I'm still unclear as to when and why you would want to include or exclude luminance from the calculation (same for profiling meters):

http://www.spectracal.com/forum/viewtopic.php?f=94&t=4150
 

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Quote:
Originally Posted by sawfish  /t/1520371/huge-de94-differences-between-chromapure-and-calman/0_100#post_24426532


I just checked the dE charts in design mode for the Quick Analysis and HT Enthusiast workflows in Calman 5.3, and each has "Include Luminance Error" checked in its Properties.


This thread talks about it a little more, but I'm still unclear as to when and why you would want to include or exclude luminance from the calculation (same for profiling meters):

http://www.spectracal.com/forum/viewtopic.php?f=94&t=4150
You'd have to ask SpectraCal about the grayscale. I'm really not sure. I think that they would argue that, all else being equal, a colorimetric error at a high level of luminance is more perceptually evident than an equal error at a low level of luminance. But I hate to speak for them and they can certainly explain their approach better than I can.


The thing is, all else is not equal. Film is a relatively dark medium and a white balance error at 20-30% will almost certainly have more visual impact on what you see than an error at 90% where there is almost no actual content. Also, this approach is at odds with what we normally do when adjusting white balance using RGB indicators. The target is R100%, G100%, B100%. However, these are valid targets only if you assume a fixed level of luminance at 100%.


Regarding meter profiling, you would only include luminance if you had some reason to believe that the colorimeter being profiled was returning inaccurate luminance readings. Typically, they don't. Luminance is really easy, even for inexpensive colorimeters.


Lastly, this is not really relevant to Chad's original question, because as I and others have pointed out, the discrepancy--at least with CIE94--exists even at 100% video.
 

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Quote:
Originally Posted by TomHuffman  /t/1520371/huge-de94-differences-between-chromapure-and-calman#post_24426860


You'd have to ask SpectraCal about the grayscale. I'm really not sure. I think that they would argue that, all else being equal, a colorimetric error at a high level of luminance is more perceptually evident than an equal error at a low level of luminance. But I hate to speak for them and they can certainly explain their approach better than I can.


The thing is, all else is not equal. Film is a relatively dark medium and a white balance error at 20-30% will almost certainly have more visual impact on what you see than an error at 90% where there is almost no actual content.

OK, so including luminance errors can muddy the waters WRT white balance, which you wouldn't want if you prefer dEs to describe only white balance. OTOH, if you can get luminance close to correct, it won't contribute much, and then dEs do a better job capturing the whole error.

Quote:
Also, this approach is at odds with what we normally do when adjusting white balance using RGB indicators. The target is R100%, G100%, B100%. However, these are valid targets only if you assume a fixed level of luminance at 100%.

When I look at white balance, I try to get RGB to balance out at each IRE level 10%, 20%, etc. I don't see how to relate that to what you're saying. That is, I don't get what the issue is that you're referring to.
 

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CalMAN 5 will show larger errors at the top end whether or not include luminance error is checked or not. Ted had mentioned more about the weighting of grayscale errors in cm5 vs cm4 a while back on this forum.
 

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Quote:
Originally Posted by sawfish  /t/1520371/huge-de94-differences-between-chromapure-and-calman/0_100#post_24427144


When I look at white balance, I try to get RGB to balance out at each IRE level 10%, 20%, etc. I don't see how to relate that to what you're saying. That is, I don't get what the issue is that you're referring to.
Every real-time RGB mechanism I have ever seen for adjusting white balance centers on 100%, the goal being to get RGB all equal to 100%. But xyY will have a perfectly balanced equivalent in 100% RGB only if Y = 100%. Otherwise, perfect balance might be R42%, G42%, B42% or whatever.
 

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Quote:
Originally Posted by sawfish  /t/1520371/huge-de94-differences-between-chromapure-and-calman#post_24427144


When I look at white balance, I try to get RGB to balance out at each IRE level 10%, 20%, etc. I don't see how to relate that to what you're saying. That is, I don't get what the issue is that you're referring to.

What he means is that typical adjustments of white balance don't include any indication of how far off you are from your Y luminance target. CalMAN includes this information in their RGB graph by showing the three colored lines to be above or below the target line even though they might be "balanced".
 

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Quote:
Originally Posted by zoyd  /t/1520371/huge-de94-differences-between-chromapure-and-calman#post_24427523


What he means is that typical adjustments of white balance don't include any indication of how far off you are from your Y luminance target. CalMAN includes this information in their RGB graph by showing the three colored lines to be above or below the target line even though they might be "balanced".

Thanks, I was just about to post the following. Does it sound right?


What do the percentages refer to? In Calman, each IRE level is the same. There is a target luminance level and an RGB graph with +/- integer scale centered on zero, corresponding to the target level, and I try to get the RGB bars as close to zero as possible. Actually, I try to get the red and blue bars equal to green, and then I adjust gamma to try and get them down to zero as a group. I typically have to go back and forth a couple of times. Do your percentages correspond to the zero point in this graph and the bar lengths?
 

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Quote:
Originally Posted by Chad B  /t/1520371/huge-de94-differences-between-chromapure-and-calman#post_24423948


Interestingly, here with dE1994, even at 100% there's a big difference.

It's possible that you've unearthed an actual bug in the CM dE94 calculation. Given that CM, CP and HCFR appear to be in agreement on dE2000, I would lean in that direction.


Lot's of lines of code ... stuff happens.
 

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Quote:
Originally Posted by HDTVChallenged  /t/1520371/huge-de94-differences-between-chromapure-and-calman#post_24427894


It's possible that you've unearthed an actual bug in the CM dE94 calculation. Given that CM, CP and HCFR appear to be in agreement on dE2000, I would lean in that direction.


Lot's of lines of code ... stuff happens.

This is exactly the case. It wasn't any sort of ideological choice. It was a bug and it's fixed.
 

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Quote:
Originally Posted by sotti  /t/1520371/huge-de94-differences-between-chromapure-and-calman#post_24429530


This is exactly the case. It wasn't any sort of ideological choice. It was a bug and it's fixed.

In what version is it fixed ?
 
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