[argyllcms] Re: Weighted averaged source gamuts

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Mon, 30 Jul 2007 20:54:16 +1000

H. Teeuwen wrote:

I have just started experimenting with Argyll cms and I'm know redoing some
profiles that I initially created with Profilemaker.
As Argyll cms allows to specify an icc profile to apply gamut mapping to
perceptual and saturation B2A table, I was wondering how to go about when
creating an weighted averaged matrix profile myself.

There's no particular facility in to do this currently. I'm not
quite sure off hand even how to go about it for a general gamut
as it is handled in Argyll since it uses a triangular gamut surface
representation. One approach would be to first deal with any
differences in white point, and then for each triangle vertex
locate the equivalent points on the other gamuts, average them,
and use the averaged surface points to construct a gamut
surface.

I suspect from the nature of the colorspaces mentioned, that
"averaging" has been done simply by averaging the colorant
locations to construct a single matrix style profile.


- Supposed that I'm able to create/tweak such profiles myself, could I just
average the white point and primaries of two working spaces (as specified in
profile which is always relative to D50) and include and sRGB or L* tone
response curve?
- How do I average white point and primaries?

There's only one logical answer - pick a colorspace and average
the coordinates. Of course you could apply other 3D geometry in
the colorspace if you liked as an alternative (ie. center of the smallest volume
enclosing the points etc.) - the trick is to come up with some rationale
for your choices.

- For the weight, could I use something like the relative occurrence of each
of the working spaces? For example, suppose that 75% of images that will be
used with a specific profile is in sRGB, and 25% is in aRGB, and then use
these percentages for the weight?

Sure. You just need a rationale for the weights.

Graeme Gill


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