[argyllcms] Re: Colorport CGATS to Argyll CTI3 conversion utility

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Fri, 10 Feb 2006 23:20:58 +1100

Gerhard Fuernkranz wrote:

I've noticed, that V0.53 seems to choose a too light "black" for perceptual
intent (noticeably lighter than the darkest reproducible neutral L*, at the
relcol. [a*,b*]==[0,0] locus), which also results eventuelly in a "washed
out" or low-contrast appearance. This seems not to happen in previous
versions - their perceptual intent renders black darker. I haven't yet
attempted to analyze the root cause. Might it be related to the skewed
perceptual gray axis issue, I had discussed with you? Did you probably
already include some changes regarding this issue in 0.53, which might lead
to the behaviour we see now?

I don't think I made any changes in that area, except for the attempt to clip the black point from profiles that don't have a black point tag, to their gamut. Maybe it was that that caused a problem ? (I've discovered that change wasn't effective. V0.54 will fix it properly.)

Another issue in the current code, is that there's no way to
specify an ink limit for the source profile of icclink or
profile. This may then give it an unrealistically low black point.
(I haven't noticed this much up to now, because I have mainly
been testing RGB->CMYK for perceptual intent.) I'm right at
this moment working on some new code to get the ink limit
defaults to be more sensible ....

I'm doing some more extensive testing of different profile
combinations, so I hope these problems will have disappeared
from V0.54.

Graeme Gill.

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