Hi,
I am trying to build a profile that I can use in photoshop to imitate a
LUT that I use in Shake. I use the forward sampler to go from RGB to
LAB, converting each RGB sample by calling a function to apply the lut
to that value then converting to LAB. The code looks something like this:
int forward(unsigned short *in, unsigned short *out, void *lut) {
transformValue(lut, in);
float rgb[3] = {float(in[0])/65535, float(in[1])/65535,
float(in[2])/65535};
float lab[3];
rgb2lab(rgb, lab);
cmsCIELab cmsLab;
cmsLab.L = lab[0];
cmsLab.a = lab[1];
cmsLab.b = lab[2];
cmsFloat2LabEncoded(out, &cmsLab);
return 0;
}
The calculation I use to convert from RGB to LAB comes from
http://www.easyrgb.com/math.php . When I 'burn in' the input profile to
an image using tifficc most colours get very close to what the Shake LUT
does but some are still not quite there. I'm wondering if there is a
correct calculation to use, or a better way of using lcms to get closer.
One other issue is that when I convert from LAB to RGB in the reverse
sampler, the majority of RGB values are out of gamut. This is
unsurprising since LAB has a much larger gamut than RGB but it means
that only a small number of samples are actually contributing which
further reduces the accuracy. Is there a better way to do this that will
allow more, or all, samples to contribute?
Any hints or tips appreciated!
Thanks,
Ian
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