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

  • From: Vallo Kallaste <kalts@xxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Tue, 29 Dec 2009 21:53:56 +0200

On Tue, Dec 29, 2009 at 12:34:46PM +1100, Graeme Gill <graeme@xxxxxxxxxxxxx>

> 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.]

Yes I undestand that by not choosing the source color space the created
cLUT profile has only colorimetric intent.

> 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.

Now this is getting hairy. I've converted bunch of raw's and saved them as
16bpc TIFF's with embedded "Chrome 2000 D50.icm" profile. Are you saying
that I should create one monitor profile for every source profile I
possibly could come accross? In current case use "Chrome 2000 D50.icm"
profile as the source one, as argument for the -S switch? I don't actually
understand what the following constraint in colprof manual means:
Note that a input, output, display or device colororspace profile should
be specified, not a non-device colorspace, device link, abstract or named
color profile.
What kind of profile the "Chrome 2000 D50.icm" actually is? In the raw
converter sense it's output profile.

What about that bwtest.jpg image which has embedded "Gray Gamma 2.2"
profile? Should I extract the embedded profile (or convert the file to
TIFF leaving the profile intact) and use that profile (or TIFF) as
argument for -S switch while creating cLUT profile?

I think that I understand the need for PCS space, A2B/B2A tables and
different mapping intents, but seems I'm not able to map that
understanding back to real life. I'm not rocket scientist, only lone
UNIX systems admin trying to get hang of it :)

> >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.
Yes it was. Unfortunately my trial copy expired today so I cannot use it

thank you for wasting your time on me
Vallo Kallaste

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