[argyllcms] Re: Characterizing a scanner using Argyll

  • From: Klaus Karcher <lists@xxxxxxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Tue, 03 Feb 2009 02:03:01 +0100

Gerhard Fuernkranz wrote:
The model of a "lut16Type" for the A2B tables is RGB -> matrix -> shaper
-> CLUT -> shaper -> PCS. So I'm not sure, whether using this matrix
makes sense for non-linear RGB. If we assume linear (gamma 1.0) RGB
(e.g. raw data from the sensors), and if we populate this matrix with an
approximate RGB -> XYZ transformation, then it would likely shrink the
coverage of the CLUT, resulting in the need for a CLUT with an even
higher grid resolution in order to achieve the same accuracy. More
appropriate would be IMO rather a matrix, which maximizes the CLUT
utilization for the set of all valid RGB triples which can be returned
by the scanner, while still producing non-negative numbers after
applying the matrix for all valid RGB triples which can be returned by
the scanner.

BTW: The ICC spec also sais that the matrix shall be the identity matrix
unless the input color space is XYZ.

oh ... I've overlooked that the /input/ space has to be XYZ, sorry.

What I had in mind was ultimately something like refining the results of a matrix profile with an (abstract) Lab CLUT profile, but I didn't think through the details.

Maybe "refine" can do the trick? -- I'll see.

Klaus

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