[argyllcms] Re: Bug: different colors in same patch

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Mon, 07 Jan 2008 01:03:44 +1100

Frédéric Mantegazza wrote:

I also tried to convert the hsv test file to tif, then used icctif to convert the file from sRGB to our generated profile, and get the same results...

Same result as what ? Is that a good result or a result with problems ?

Back to the projector calibration, once we use the profile, we can see huge banding effetcs, and a global over-saturated colors, especially in red. As this last problem only occurs on the projector, and as we use the same app (gqview), I guess the problem comes from the profile, or the usage of the profile. So, here is a few questions to try to understand what we are doing wrong.

What happens if you use the sRGB profile instead ?

1) What is axactly the differences between all profile types (matrix, lut, shaper+matrix...)? Which one should we use, in which condition?

It's a rather long explanation. You'd probably be better off taking
a look at the introductory chapter of the ICC specifications, rather
than me trying to summarize it here.

2) You said in a previous message that a shaper+matrix profile can't do gamut mapping (as I can read in the doc, it can only make colorimetric mapping. Can you explain why?

Because it doesn't have the flexibility, and because the ICC profile
format doesn't allow for one shaper/matrix per intent.

3) When using the 'profile' tool, there are -c and -d params. Can you explain how they change the final profile? Why 2 params?

They set the viewing conditions for the source and destination colorspace.
When using a color appearance space for the color conversion and
gamut mapping, the color appearance space takes into account the
effects of the observer viewing conditions.

PS: I've just discovered that the black point of the generated profile of the projector is totally wrong! I'm totally lost. Why such error? What are params that leads to that wrong black point? I attached the profile...

Which profile is that ?  The "porable_s+m.icc", or something else ?
If not, where is this profile ?
How did you determine that it has a wrong black point ?

Graeme Gill.



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