[argyllcms] Re: Of ink limiting and maximizing gamut
- From: Graeme Gill <graeme@xxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Thu, 29 Jan 2009 10:53:51 +1100
Alastair M. Robinson wrote:
I have to admit I've been looking more closely at L* than a/b for signs
of over-inking. How much of the a/b curvature here, I wonder, is down
to over-inking, or does the fact that a given hue doesn't necessarily
have totally constant hue angle in L*ab space have anything to do with
it? (As per the infamous blue-turns-purple problem)
There two "blue-turns-purple problem"s that I'm aware of:
Perceptual hue non-linearity of L*a*b* space.
"Wrong" Von Kries adaptation.
Maybe there is third for systems that assume that inks have
a constant hue ?
I suppose the crux of my question is really why
super-saturated-colorants-and-super-dense-black-but-low-ink-limit
performs so much worse in terms of overall gamut than
restricted-saturation-of-colorants-but-higher-ink-limits. I guess just
that's an unusual scenario, and thus the tools aren't really geared up
for it?
The best idea I have off the top of my head, is that when calibration curves
are being applied, the in-profile ink limiting is unaware of exactly what ink
is being put down, so you have to err on the cautious side when setting
the total ink limit, thereby unreasonably limiting the gamut. This is also
an issue when the profile channels are actually composites of combinations
of light and dark.
Since the very beginning I've had some hooks in place inside Argyll to
allow this to be taken into account, but without having settled on
a calibration table format, the hooks aren't currently able to be used.
Graeme Gill.
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