[argyllcms] Re: colormouse vs. digital camera

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Thu, 20 Oct 2005 08:06:51 +1000

Gerhard Fuernkranz wrote:

 # multiply RGB numbers by 255
 # (convert to 0..255 range)
 $ bc -l
 0.326174*255
 83.174370
 0.428683*255
 109.314165
 0.439484*255
 112.068420

Note that in the *next* version of xicclu, there is a -s option, that you can use to do the scaling to 255, ie:

 # find printer RGB for a middle gray patch, L*=50
 $ xicclu -s255 -ir -fif -pl myprinter.icc
 50 0 0
 50.000000 0.000000 0.000000 [Lab] -> Lut
   -> 83.174370 109.314165 112.068420 [RGB]

 # Compute absolute L*a*b* for these RGB values.
 # That's what your colorimeter should read, if
 # you would print this patch and measure it.
 $ xicclu -s255 -ia -ff -pl myprinter.icc
 83.174370 109.314165 112.068420
 83.174370 109.314165 112.068420 [RGB] -> Lut
   -> 44.778623 0.026997 -3.770875 [Lab]

IMHO it would be nice, if "targen -d3 -c <profile> -g <steps> ..." would not generate patches with R=G=B, but if it would instead create a ramp of true neutral patches (i.e. a ramp of patches with a* = b* = 0 in the PCS, according to the relcol intent of the given preliminary profile).

Yes, that thought has crossed my mind (or a way to increase the density of sample points along the neutral axis even more than is done by default.) It's not perfectly straightforward though, because the preliminary profile has to be inverted within targen to do this, and what sample points should be generated for CMYK, where there there can be a variable amount of black used ? (ie. the black has to be sampled, just like the rest of the distribution).

You could try bumping up #define NEF in targen.c to see if that
gives you something like the effect you are after.

Graeme Gill.

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