When I run the RGB to Lab conversion below (it is the same as the one I showed you in my previous request, but this time on a 256x3 array), it works wonderfully. LAB=[] for rgb_val in RGB255: rgb_r, ...

Image of color chart should be 600x400 pixels debayered rgb linear(!) data, 3x8 bit, captured without saturation. Illumination must be as uniform as possible: no correction for this in the script.