[argyllcms] Re: "Development in progress" update

  • From: Gerhard Fuernkranz <nospam456@xxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Wed, 12 Jul 2006 22:06:26 +0200

Graeme Gill wrote:


icclink: Error - Write file: 1, icmColorantTableVal_write: write of PCS
coord failed 
but icclink causes errors:

OK, it turns out that the green in your LStar-RGB.icc isn't representable
in L*a*b* PCS, and a device link colorant table is mandated to be

The same problem seems to happen with Adobe RGB as source color space too. And Adobe RGB is IMO not an unusual profile.

in Lab. All I can do is clip such colors to the Lab PCS range.
Unfortunate, but it would need an ICC spec. change to fix it
any other way.

For a device -> A2Bx -> PCS -> B2Ax -> device conversion between two profiles, the ICC spec requires clipping in the PCS if necessary (and it may be indeed necessary if the src profile has a XYZ PCS and the destination profile has a Lab PCS, because only a limited L*a*b* range can be fed into the B2Ax table of the destination profile). However this applies to a "dumb" transformation, where che CMM just applies the A2B and B2A tables. But is there necessarily a need to enforce a +/-128 range when creating a gamut mapping devce link with "icclink -G ..."? (As the mapping is established in CIECAM02 space, I guess, CIELAB is not even involved, is it? And colors which are still out of gamut after the gamut compression are clipped to the destination gamut anyway.)

Regards,
Gerhard



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