RE: U.S. Sheetfed vs. U.S. SWOP
RE: U.S. Sheetfed vs. U.S. SWOP
- Subject: RE: U.S. Sheetfed vs. U.S. SWOP
- From: email@hidden
- Date: Thu, 3 May 2007 15:44:02 -0400
Just a couple random comments on this thread.
> Steve Upton wrote:
> The graphs of 1-3 are of limited use (if any) to the average
> user as they describe the 'proofing' behavior of a specific
> part of the profile. They do NOT describe the gamut of the
> device OR the behavior of the profile when used to OUTPUT an
> image. It is interesting to see how rel col raises the black
> level vs perceptual and saturation though.
The ICC spec says that all A2Bx/B2Ax pairs should be inverses of one
another. If this is in fact adhered to rigorously, then viewing the A2Bx
gamut would be equivalent to viewing the B2Ax gamut. For Relative
Colorimetric transforms intended for proofing applications this perfect
inverse relationship is rarely adhered to. Rather vendors are more
interested in ensuring that the colorimetric A2Bx (x=1,3) transform can
replicate the characterization data which served as the basis for building
the profile. Consequently it is sometimes the case that the B2A1 (Lab ->
ink) side of the transform will have a gamut somewhat smaller than that
swept out by its A2B1 neighbor. This may be due to ink constraints (TAC,
max-K, GCR) as well as for image quality considerations. A gamut viewer
that built the B2Ax gamut and the ability to compare it with its A2Bx
counterpart would indeed be useful (Building a B2Ax gamut is a tougher
problem though than A2Bx gamuts).
It also strikes me that viewing the Perceptual Gamut is useful - sometimes
these secret sauces due weird things and a gamut is a useful construct for
discerning such things.
> Graeme Gill wrote:
> ... and on ICC V4 profiles it is meant to be a transformation
> from the device gamut to the Reference Medium Color Gamut,
> and hence should look pretty the same as the Reference Medium
> Color Gamut.
The Perceptual Reference Medium Gamut is an optional target for V4 profiles
- it is not required. All V4 profiles, however, must reflect the defined
white & black pt of the V4 PCS.
Harold
TOSHIBA AMERICA BUSINESS SOLUTIONS 2 Musick, Irvine, CA 92618
Harold Boll | 1.781.856.5174 | email@hidden
" The sunlights differ, but there is only one darkness. "
Ursula K. Leguin
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