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Problems with RGB coordinate values for absolute error EOTFs

 
Author CQHandsome
ZRO
Male
#1 | Posted: 29 Oct 2024 13:53 
Hi steve
Regarding the RGB coordinate values of the absolute error EOTF, I don't know if it's my calculations or if there is indeed an error in the colourspace zro, as shown in attachment 1, the measured XYZ coordinates are converted according to the target colourspace (rec709 and the white point of 126.2247 132.804 144.6316) to obtain linear RGB values ( 1.00686296355603, 0.998835775138023 , 0.99131864499517), are significantly different from the chart's coordinates, and don't look like rounding differences. (I noticed that the G-value of the chart is just equal to 1. Was G-value normalization performed? But there's no need to change the original data, right?), but even when I scaled the G-value normalization (1.008036545, 1, 0.992474108), it's still not the same as the chart value, especially the R-value, but it's still not the same as the chart value.
Also after a linear RGB calculation (0.966575364, 0.955392653, 0.947386334) for the 250/255 grayscale points, and a normalized scaling for maximum brightness (0.967701987
, 0.956506242, 0.94849059), which is even further from the Annex 2 chart coordinate values.

Is this a problem with the ZRO calculation? Or is there something wrong with my algorithm?
If there is a problem, there will be problems with other charts that reference linear RGB.

This linear RGB conversion algorithm is validated in calman and there are no errors, so I don't think it's a problem with the conversion calculation!
Of course, if colourspace has other optimized algorithms, I'd appreciate any help in solving the problem.

Thank you!






Author Steve

INF
Male
#2 | Posted: 29 Oct 2024 15:54 
The graphs plot the XYZ error.
If you look at the XYZ values for the Target and Actual for the point you have selected:
X: 126.3372/126.2247=1.0009
You can tell that as the Y plot is 1.0

Steve
Steve Shaw
Mob Boss at Light Illusion

Author CQHandsome
ZRO
Male
#3 | Posted: 30 Oct 2024 02:54 
Steve
oh,extremely grateful!

BTW, how is the gamma value of the eotf (without selecting ABSOLUTE ERROR) calculated?
As shown in the attachment, I think: total gamma=log(measured Y/maximum Y)/log(input signal)=log(127.119/132.804)/log(250/255)=2.209338226, but that's not the same as the eotf point 2.2102 on the bottom right corner (the other points are different as well).

① So how is the TOTAL gamma value calculated?
② How do you calculate the Y-axis value of 0.9575 for the R/G/B lines?
(I noticed that the RGB lines don't change when switching color spaces, it doesn't seem to be a linear RGB that XYZ calculates inversely based on the target color space)

Thanks




Author Steve

INF
Male
#4 | Posted: 30 Oct 2024 08:07 
We don't provide such information.
Things like that we leave to users to research for themselves, as that is the best way to learn.

Steve
Steve Shaw
Mob Boss at Light Illusion

Author CQHandsome
ZRO
Male
#5 | Posted: 30 Oct 2024 08:33 
Steve
I've been studying it for a long time now, but I can never find the right algorithm, so much so that I suspect that colourspace is wrong
But I know that colourspace can't be wrong, and I must be the one who is wrong, so I can only count on you to point me in the right direction!

Author Steve

INF
Male
#6 | Posted: 30 Oct 2024 09:32 
I can only redirect you to my above comment.
We do not provide free training on colour mathematics/understanding.
That would come under the realm of consultancy services.

Steve
Steve Shaw
Mob Boss at Light Illusion

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 Problems with RGB coordinate values for absolute error EOTFs

 

 
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