[argyllcms] Re: Posterization caused by profiles

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Mon, 11 Dec 2006 11:52:55 +1100

william.wood@xxxxxxx wrote:
I'm having trouble with posterization when applying the profiles created by
"profile".  Would you mind taking a look at this example please?  Thanks,

Sorry, I'm not entirely clear on the specific issues you're
referring to, but then I'm not observing the same responses
you are (different monitor, calibration and profile). What
is least clear is what you were expecting. Every color
transform will trade one area against another, there is
only a finite gamut and range within which to work.
So what to one person can be a good trade-off ("I got
a really bright, colorful result and lost a little shadow
detail", can be terrible to someone else ("I lost all
my shadow detail").

The "with profile applied" image has a strong degree of
saturation and contrast enhancement, and this is often
indicative of linking a large gamut colorspace to a
small gamut destination without proper gamut mapping.
In this situation there could be gamut clipping, leading
to loss of detail in areas that are out of gamut. Saturated
light and dark colors are often those that fall out of gamut.

It's not possible to say more without knowing:

        How your profile was created.
        What intent tables were built.
        What source gamut the tables were created for.
        What source profile it was linked to.
        What intent was used in the linking.
        What type of linking was used (ie. active or passive linking).

[A device profile doesn't transform colors on its own -
 this only happens when it's linked with another device profile.]

Graeme Gill

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