[argyllcms] Re: Custom Illuminant

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Mon, 07 Jul 2014 20:54:48 +1000

robert@xxxxxxxxxxxxxxxxxx wrote:


> I take it that the relationship ONLY breaks down in large/unlimited gamut
> spaces IF the image gamut is larger than the destination gamut.

No, it breaks down if the colorspace gamut is noticeably larger than
the image gamut.

Gamut mapping is determined by the relationship between the source and
destination gamuts. If you are using the source colorspace as your
definition of the source gamut, but it does not actually represent
the gamut of the images you are gamut mapping, then it won't work very
well for those images.

> If I use
> ProPhoto, say, but I make sure that my image is within the gamut of my print
> profile, I should be OK for Colomimetric intents, surely?

For colorimetric, yes, but colorimetric doesn't use gamut mapping - it will
clip if source colors are outside the destination gamut.

> And also for
> Perceptual or Saturation also, since no mapping is required?

How does the gamut mapping know that no mapping is required ? If you
tell it the source gamut is ProPhoto, then it will think that lots
of gamut mapping is needed, since the ProPhoto gamut is so much larger
than a printer !

> The only issue
> then would be resolution, presumably, but that should be OK in 16 bit, I
> would have thought.

Yes, large gamut color spaces typically need a higher pixel depth.

> In relation to this I have another question.  Is there any reason why one
> should not convert the image to the print color space prior to doing some
> small final edits before printing?  The advantage is that these edits would
> then be constrained to the print gamut, and also the gamut warning can be
> set to the monitor profile to indicate which colors are not viewable

It's a reasonable approach, if you know what you are doing.

Graeme Gill.

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