Re: PRMG gamut
Re: PRMG gamut
- Subject: Re: PRMG gamut
- From: Klaus Karcher <email@hidden>
- Date: Fri, 29 Feb 2008 23:05:44 +0100
Roger Breton wrote:
Klaus,
I downloaded your PDF. Thank you. I see many figures showing "clipping". I
was under the impression (wrong, perhaps?) that PRMG stood for "perceptual"
and therefore "no clipping". Desaturation, maybe, but no clipping.
The PRMG stands for the effort to "harmonize" the perceptual gamut
mapping between different vendors and to avoid needless desaturation and
clipping.
In practice "perceptual" never was a synonym for "no clipping" (at the
most for "less clipping") and unfortunately the PRMG will not solve the
central problem: The optimal gamut mapping can only be computed at link
time, i.e. when *both* the source and destination gamut is known.
Also, isn't the PRMG much 'smaller' than +/-128 in a* and b*? I had the
impression that PRMG was a subset of the ICC Lab PCS.
that's true.
Here, in your diagrams, I have the impression that it is still very big.
that's also true (even though I don't know how you deduce this from my
diagrams: they are just schematic).
Is it as big as sRGB?
It's considerably bigger:
viewgam -i:
Intersecting volume = 756772.9 cubic units
'RefMediumGamut.gam' volume = 1261173.5 cubic units, intersect = 60.01%
'sRGB.gam' volume = 833600.9 cubic units, intersect = 90.78%
(the stated sRGB volume is somewhat too high: I used Adobes sRGB profile
relative colorimetric, therefore the gamut is "stretched" slightly (Lab
min = 0/0/0, Lab max= 100/0/0)
I'll send you argyll GAM, VRML and CGATS files off-list.
Which is one of the PRMG being developped with HP?
The ICC PRMG is a proposal by Jack Holm and Ingeborg Tastl (HP), Ann
McCarthy (Lexmark) & Max Derhak (Onyx Graphics). See
<http://color.org/ICCSpecRevision_22_02_05_PRMG.pdf>
Klaus
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