[argyllcms] Re: How handle Lab tiffs?

Alastair M. Robinson wrote:
The one scenario where you might want to do this is if you're using tiffgamut to compute a given image's gamut with a view to making a devicelink specifically for that image, and that image happens to be in CIELab space. 

That, I think, is the scenario Nikolay had in mind.


Ok, yes you're right. I thought it might just work, but there
are several problems currently. The problems hint at some conceptual
issues as well. Problems that I notice are:

 The image gamut has no white and black point. I can simply assume
 in tiffgamut that an Lab image has white and black points of 100,0,0 and 0,0,0,
 but there is a trap waiting if someone converts from a device
 space straight to Lab and doesn't ensure that the conversion
 also expands and maps the device space white and black to
 100,0,0 and 0,0,0

 There is a bug in tiffgamut that means that selecting CIECAM02
 output for compatibility with collink is being ignored. The resulting
 gamut will be in L*a*b* space.

 The gamut mapping code takes the number of guide points from
 the source gamut surface, and this depends on the surface complexity
 (number of facets) and shape. For the Lab space source, the surface is
 a cube with only 8 vertices so the number  of guide points, or for Jab
 it is stupidly large with facets in places that aren't relevant to the
 image gamut.

It should be possible to fix these various problems for the next release.

Graeme Gill.

Other related posts: