[argyllcms] Re: Patching profiles with non-D50 illuminants for Absolute Colorimetric

Hi,

Graeme Gill wrote:

I'm not clear that what you're attempting to do, makes any sense. If 

It may not :)

you set the white point manually, then it's not really the real absolute,
it's some fake value that may or may not match the white you actually
have. You are really applying a manual "tweak".

Yep, I just thought, from reading the post I quoted, that under certain circumstances such patching was necessary to get around a profile format limitation. And I was curious as to how one would go about it, since it might have helped with Roger's question... The answer, it seems, is ProfileEditor, which I presume is costly?

If you measure under D65, then presumably you want to view
under D65, and "absolute" is doing what you want.

To be honest, I'm not sure how you'd describe my lighting conditions. Daylight, diffused through a roller blind, and fluorescent lighting. My goal in all this is pleasing photographic prints, and "general" viewing.

Anyway, my colorimeter can capture samples under D50 or D65 (possibly others too, haven't checked yet). Prints produce using Perceptual transform with the D65-generated profiles are noticeably more pleasing that the D50-generated ones.

I don't really understand why.

If I scan an IT8.7/2 target, profile the scanner, then do an absolute colorimetric transform to the printer profile, I get a pretty good match (within the limitations of the scanner) with the D50 profile and a very yellowy print with the D65 profile.

The reason for my orginal question was that I was wondering if patching the D65 profile with a D50 white/black point would result in a profile usable for both perceptual/rel.col and abs.col - if I can avoid having two versions of every profile lying around it would be nice :)

If anyone can explain to me why I'm seeing what I'm seeing, and what I'm misunderstanding, I'd be most grateful :)

All the best,
--
Alastair M. Robinson


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