[argyllcms] Re: Perceptual intent

  • From: <robert@xxxxxxxxxxxxxxxxxx>
  • To: <argyllcms@xxxxxxxxxxxxx>
  • Date: Thu, 18 Dec 2014 20:23:15 -0000

Florian said:

>Unlike the colorimetric B2A table which usually clips if BPC is not used
>(note that xicclu has no notion of BPC), the perceptual B2A table maps the
>lightness axis, i.e. an input L* of 5 will not result in an output
>L* of 5, and so the two xicclu results are not really comparable. If you
>want to compare the xicclu colorimetric to perceptual results, you'd need
>to at least offset & scale the input L* values by the black point for
>(only!) the colorimetric xicclu lookup.

Hi Florian,

Thanks for the info.  I can't say I understand what you're saying here.  It
would seem to me that how the perceptual mapping is done depends on the
author (Graeme in other words).

What I observe is that when I soft-proof an image with relative mapping and
then toggle to perceptual that the whole image becomes much lighter, as
though a Levels or Curves adjustment, boosting the mid-tones and whites, had
been applied.  If I do the same thing with a profile made by i1Profiler,
this doesn't happen.

Here is an example (but unfortunately it's extremely difficult to show this
in a static way ... it's much easier if you pick an image and then toggle
the soft-proof between relative and perceptual yourself. You can have
simulate black ink on or off, the same effect will be seen (at least if your
profile has been made with a larger source gamut like Beta RGB)).


As it's not possible to use BPC with xicclu it makes the test with xicclu a
bit meaningless as I would certainly always have BPC on.


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