[Lcms-user] How to create a gray profile with L-star grey response?

[Marco F. <Mar...@en...>]

Hi!

I'm trying to create a gray profile that has an L* (L-star) response curve, but I'm a little confused about the "parametric tone curve" syntax.

Is there an example how to create the correct tone curve? I guess I need the inverted version of L* companding, right? Would that be a 4 parametric curve, with:
y(Gamma) = 3.0
a=1.0/1.16
b=0.16/1.16
c=100.0/903.3
d=0.008856*903.3/100.0

So in code something like that:
cmsFloat64Number lStarParams[5] = { 3.0, 1.0/1.16, 0.16/1.16, 100.0/903.3, 0.008856*903.3/100.0 };
cmsBuildParametricToneCurve( ctx, 4, lStarParams );
???

Or is it as easy as passing a NULL for the TransferFunction parameter in cmsCreateGrayProfileTHR() because the response matches the PCS response?

Thanks,
Marco