[Openexr-devel] color space conversion

[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