Why need to apply 1D pre-shapers LUT at applyclut function?

I read the source code of applyclut.m file, and I don't understand that why need to apply 1D pre-shapers LUT to the ICC profile process flow. As the spec. of ICC profile v4.3.0.0, there are no 1D curves like that,or it means "M" curve of ICC profile model?

% Apply 1D pre-shapers, if present if ~isempty(luttag.PreShaper) out = cellinterp(out, luttag.PreShaper); end

Answer 1

[Pengfei Wang]

Certain type of ICC profile is structed as "Shaper + Matrix", the "shaper" works just like "TRC".

In CLUT case, this tag is normally empty, and the "prematrix" an identity matrix.