[argyllcms] Re: Newbie targen and colprof questions.

  • From: Symphony Photography <symphonyphoto@xxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Fri, 21 May 2010 09:58:01 -0400

On Fri, May 21, 2010 at 1:32 AM, Graeme Gill <graeme@xxxxxxxxxxxxx> wrote:

> Symphony Photography wrote:
> It's hard to comment without the details. For instance, is the source
> image Lab space, or something else ?

The source is the Bill Atkinson test image which is in L*a*b*. I took screen
shots of all three instances in Photoshop and then converted them to sRGB.
The shots posted are an accurate representation of what I am seeing with
regards to the specular highlights and the shadows.

> How did you create a profile
> using gamut mapping ? (to be sure that there isn't a mistake,
> and to see what choices you made). etc.

All of the profiles I've created exhibit the same behavior as the posted
images. Here's a few of the tests I ran:

targen -v -d2 InvaFPUS_default
printtarg -v -ii1 -pLetter -T InvaFPUS_default
chartread InvaFPUS_default
colprof -v -qu InvaFPUS_default

targen -v -d2 -G -f924 -e8 InvaFPUS_default_e8
printtarg -v -ii1 -pLetter -T InvaFPUS_default_e8
chartread InvaFPUS_default_e8
colprof -v -qu InvaFPUS_default_e8

targen -v -d2 -G -f1848 -e32 -g256 -cInvaFPUS_default_e8.icc
printtarg -v -ii1 -pLetter -T InvaFPUS_Cond_f1848_e32_g256
chartread InvaFPUS_Cond_f1848_e32_g256
colprof -v -qu InvaFPUS_Cond_f1848_e32_g256

targen -v -d2 -G -f1848 -e32 -g256 -cInvaFPUS_default_e8.icc
printtarg -v -ii1 -pLetter -T InvaFPUS_GamutMap
chartread -H InvaFPUS_GamutMap
colprof -v -qu -S AdobeRGB1998.icm InvaFPUS_GamutMap

> Is that your RGB original, or is that the Lab original converted into
> some RGB space ?

That was the L*a*b* image.... screenshot and converted to sRGB for posting
on the web. The sRGB images are an accurate depiction of what I'm seeing
when I'm softproofing in Photoshop. This happens not just with one profile,
but all profiles I've created with Argyll so far.

>  Soft proofing with the Argyll profile (rendering intent is perceptual,
>> black point comp
>> on, simulate paper off (I just wanted to see the changes to the color
>> itself)) http://www.symphonyphoto.com/argyllcms/Atkinson_Argyll.jpg
> Argyll doesn't have BPC, it has gamut mapping instead, so it's hard
> to guess exactly what you've done here.

It's just a checkbox in the Photoshop softproofing options. If it's not
present then it has no effect on the image (and indeed I see no change when
toggling it off and on).

> Without a definition of the source and destination colorspaces, it's
> hard to comment. This could be exactly what's needed to compensate for
> the destination colorspace for instance. (The image you refer to hints
> that a colorimetric intent is being applied though, whereas the Logo
> image obviously has a high degree of compression applied.)

Everything is in L*a*b*. The examples posted were to demonstrate the
differences I'm seeing in soft proofing when the printer profile is applied
and they do that accurately. Rendering intent is always perceptual in terms
of soft proofing and in the driver when printing. From what I've read I'm
assuming the default intent for Argyll is perceptual (if I'm not mistaken it
also builds maps in the profiles to support colorimetric and saturation
intents as well but I'm not using those).

Cheers, Joe

Symphony Photography

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