[argyllcms] Re: Beta RGB As a Color Workspace

  • From: Chris Lilley <chris@xxxxxx>
  • To: "Andreas F.X. Siegert" <lists@xxxxxxxxxxxxx>
  • Date: Thu, 17 Jul 2014 10:13:11 +0200

Hello Andreas,

Wednesday, July 16, 2014, 10:17:05 PM, you wrote:

> on 16.07.2014 21:26 robert@xxxxxxxxxxxxxxxxxx said the following:
>> I’m afraid that the Luminous Landscape discussion is my fault J.  Why don’t
>> you join in? I could do with some moral support (Graeme has thrown in a
>> couple of punches).

> Why should I support something that I consider obviously wrong and have
> empirical evidence to support my position?
> See http://www.afximages.com/articles.php?article=WorkingColorProfile

> There is a reason why all raw converters use ProPhoto variants internally....

That is a useful and interesting article, but two important aspects
are not addressed there.

Firstly, the rendering intent used for gamut mapping is not
discussed. When a wide gamut image is reduced down to a very small
one, relative colorimetric tends to keep the in-gamut colours the same
and piles up all the OOG colours at the boundary to give flat areas
where there used to be gradients. Perceptual, aka do something magic
and undefined, tends to map the entire source gamut to the destination
gamut in a content-unaware way which results in significant and
needless desaturation.

Its possible to do a per-image colourspace analysis and to map the
convex hull of the image data to the destination colourspace; and to
have a smooth progression from "keep colours the same" near the middle
through "move them a little" near the edges and "clip less than 2% of
pixels" at the edges. but not in an ICC defined gamut mapping, I

The second thing that is missing is an examination of whether 16 bits
per component is actually sufficient for ProPhoto. It isn't, really,
for Lab and it needs to be shown, rather than assumed, that 16 bit is
sufficient resolution for ProPhoto.

Some words on the gamut of your printer, and links to the various
profiles used, would also round out a nicely argued article.

Best regards,
 Chris                            mailto:chris@xxxxxx

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