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Re: [Openexr-devel] color space conversion
From: |
Kai-Uwe Behrmann |
Subject: |
Re: [Openexr-devel] color space conversion |
Date: |
Sun, 25 Dec 2005 09:50:30 +0100 (CET) |
One option would be using lcms. The CMM has a small utility to do the
calculations in 16bit integer precission. <http://www.littlecms.com>
It should build pretty well.
A small example:
sirius:~/& icctrans -w -o '*Lab'
little cms ColorSpace conversion calculator - v2.0
Enter values, 'q' to quit
R (0..255)? 50
G (0..255)? 50
B (0..255)? 50
L*=20.7858 a*=-0.0312 b*=0.0000
Enter values, 'q' to quit
R (0..255)?
...
Of course feeding in a CGATS is more convenient.
regards
Kai-Uwe Behrmann
+ development for color management
+ imaging / panoramas
+ email: address@hidden
+ http://www.behrmann.name
Am 23.12.05, 17:42 -0800 schrieb Florian Kainz:
> I need help verifying the correctness of a few color
> space conversion functions...
>
> For the Color Transformation Language interpreter, I have
> implemented a set of functions that convert between RGB,
> CIE 1931 XYZ, CIE 1976 L*u*v* and CIE 1976 L*a*b*, but
> I don't have a test data set that would allow me to check
> if my conversions are correct. Does anyone have such a
> data set that they would be willing to share?
>
> Alternatively, if anyone has a program that does color space
> conversions, I would really appreciate help verifying that
> the table below is correct:
>
> R G B X Y Z L* u* v* a*
> b*
> 1.0 0.0 0.0 41.239 21.264 1.933 53.237 175.010 37.765 80.090
> 67.203
> 0.0 1.0 0.0 35.758 71.518 11.920 87.736 -83.067 107.418 -86.182
> 83.187
> 0.0 0.0 1.0 18.048 7.219 95.053 32.301 -9.402 -130.351 79.195
> -107.855
> 1.0 1.0 1.0 95.046 100.000 108.906 100.000 0.000 0.000 0.000
> 0.000
> 0.005 0.005 0.005 0.475 0.500 0.545 4.516 0.000 0.000 0.000
> 0.000
> 0.0 0.0 0.0 0.000 0.000 0.000 0.000 undefined undefined 0.000
> 0.000
>
> The table was constructed assuming that the CIE xy coordinates
> for the red, green and blue primaries and the white point are
> as specified in Recommendation ITU-R BT.709-3:
>
> x y
> red 0.6400 0.3300
> green 0.3000 0.6000
> blue 0.1500 0.0600
> white 0.3127 0.3290
>
> I assumed that the RGB triple (1, 1, 1) has a luminance of
> 100 candelas per square meter.
>
> The values of Xn, Yn, and Zn used in calculating L*u*v* and
> L*a*b* are 95.0456, 100.000 and 108.906 respectively.
>
> Florian
>
>