[Lcms-user] How does a transformation work

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Hi list,

what I want: an 8 bit grey-scale output for my printer, where the input dot 
values (0 … 255) are scaled and limited to values of 40 … 240 (…just an 
example).

So I created a simple test input data (256 elements of unsigned char) with a 
linear ramp from 0 (at index 0) … 255 (at index 255).

And I created an array with 4096 short entries beginning with 40 (* 256 for 
unsigned short) and ramp up linear to 240 (* 256 for unsigned short) and feed 
it into cmsBuildTabulatedToneCurve16() and cmsCreateGrayProfile() with 
cmsD50_xyY() as its whitepoint (for the output profile).

For the input profile I used cmsBuildGamma() with a value of 1.0 and 
cmsCreateGrayProfile() with cmsD50_xyY().

After creating the transformation with cmsCreateTransform() with input/output 
types both TYPE_GRAY_8 and an intent of INTENT_PERCEPTUAL and applying this 
transformation with cmsDoTransformLineStride () to my simple input data, the 
output result is still almost linear from 0 to 255 and not limited to 40 … 
240.

So, I think I'm using the tone curves in a wrong way. But where is my mistake?

Cheers,
Jürgen