[argyllcms] Re: Lost shadow detail in PS CS2 with Lab profile

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Tue, 29 Dec 2009 12:34:46 +1100

Vallo Kallaste wrote:
Can anybody please tell me why using the Lab cLUT display profile cause
lost dark shadow detail? The data set for profile generation is same and
shaper+matrix profile (colprof -as) has no such effect in Photoshop CS2.

The usual reason is the lack of appropriate gamut mapping.
If you connect a source profile with a zero black (ie. such
an idealized sRGB or AdobeRGB type profile) to a profile
that has a non-zero black point (ie. like a real world
diplay profile) without gamut mapping, the blacks get clipped.

[For colorimetric they always get clipped, because that's what
you've asked for in selecting Colorimeric.]

In theory Adobe BPC should fix this, but (for some unknown
reason) it's not available for all intents, and BPC isn't available
for all applications. There is another way using Argyll:

colprof -v -qh -D"3008WFP-2.2-Lab" 3008WFP-2.2

Figure out what your source colorspace is, and feed it
into colprof as the source colorspace, so that it
can be used for creating the gamut mapping in the Perceptual
and Saturation B2A tables. For instance, say your source
image is in sRGB space:

        colprof -v -qh -S sRGB.icm -D"3008WFP-2.2-Lab" 3008WFP-2.2

[Use the sRGB profile in the Argyll distribution if you want to
 avoid problems caused by "sRGB" profiles that don't follow the sRGB spec.]

Make sure your image is in sRGB space (ie. that's what's embedded in it,
or selected as the RGB colorspace), and that you're selecting perceptual
intent when you use the display profile, so that the gamut mapping gets used.

know what to expect. Should also note that using the same Lab cLUT profile
in Picture Window Pro I'm currently trying out gives better details in the
deep shadows. PWP is set to using lcms. It's really frustrating because no

Maybe BPC is turned on for lcms.

Graeme Gill.

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