Re: Photoshop Gamut warning vs ColorThink
Re: Photoshop Gamut warning vs ColorThink
- Subject: Re: Photoshop Gamut warning vs ColorThink
- From: "dpascale" <email@hidden>
- Date: Sat, 23 Feb 2008 13:40:53 -0500
I appreciate the distinctions you make on the usage of the A2B and B2A LUTs.
Different needs require different tools. I also realize that many would like
a simple GO/NO-GO flag.
I compared at one time or another the various tools available to check
in/out of gamut status (Photoshop, Argyll "xicclu" (this one yesterday,
using the latest beta, thanks to Graeme and Klauss), ColorThink,
GamutVision). They generally (roughly) agree but often differ close to the
gamut limits (this is not as bad a statement as it looks!). Apart from
different computing methods, as pointed by many in this post, another reason
is that even if a color is well within a gamut, there is always a small
residual DeltaE error when going back and forth between the input and output
spaces. In addition, our own "tolerance" for errors will vary with projects,
personal (or corporate) preferences, and deadline closeness.
With GO/NO-GO approaches, such as Photoshop, or Argyll (for color lists),
an "overlay" or "clip" status is given. Since we do not know the criteria
for this flag (it cannot be a non-zero error, so it is a programmer's
decision; ColorThink and GamutVision have more flexibility for setting this
limit but require expertise), there is room for interpretation. In any case,
the info is valid enough to prompt the user that he/she should be careful
with these colors. I, for one, do appreciate such a simple flag (sorry
Andrew ;-) ); however, I would like it even more if I could set the
individual L*, C*, h* thresholds (yes it is geeky, sorry again Andrew, but
you know where I come from!). I realize that, in practice, this is too much
to ask to Photoshop, except maybe a single Delta-E setting, with a selection
of the Delta formula....).
My final appreciation is by measuring the print and comparing to the
predictions. This is labour intensive, not applicable to images with
non-uniform color mixes, and a very good method to find arguments to dump
color management altogether, since any "mistake" or "problem" in the
printing chain will result in non-conclusive conclusions (is that unclear
enough!), with the onus to explain these conclusions to your boss, customer,
or oneself. When it does work, you still have to explain why you did it or
justify the time and expense to your boss or customer (Example: "Explain to
me why, if Photoshop says this color will print, it may not..., or the
reverse...")
Danny
email@hidden
----- Original Message -----
From: <email@hidden>
To: <email@hidden>
Sent: Saturday, February 23, 2008 12:20 PM
Subject: Re: Photoshop Gamut warning vs ColorThink
Lars Borg writes on Fri, 22 Feb 2008 22:51:46 -0800
In my view, the A2B tag is useless as a gamut indicator.
There are 2 gamut types deriveable from a Profile and which one to use
depends upon the question being asked.
The A2B gamut reflects the maximum extent of the colorant set; can be
defined with high precision; does not reflect print constraints.
The B2A gamut reflects print constraints; due to nature of B2A xform its
boundary positions possess a far higher degree of uncertainty in
comparison to its A2B counterpart.
The person who started this thread (Mike Eddington, Date: Thu, 21 Feb 2008
10:39:31 -0500), asked the following question:
... if I want to determine a group of Pantone colors that are within a
particular gamut ...
I would submit that the A2B gamut is more appropriate to provide his
answer
than the B2A gamut. He's intersted in the intrinsic properties of a
particular colorant set free of any constraints.
People who want to know if a given color is in-gamut for a particular RI
of
a particular Profile when printed on a particular Printer are better
served
by the B2A gamut.
I would also argue that a Perceptual and Saturation gamut alarm should be
no more ambiguous to interpret than a gamut alarm applied to the
Relative/Absolute RI. In principle, the B2Ax table of each RI will sweep
out a unique gamut. The question a gamut alarm should be answering is
whether an initial color is in or out of that B2A gamut. It should not be
answering the question whether that initial color is inked
colorimetrically
in any of the Rendering Intents. The Perceptual/Satn RI move colors
around. In general, this latter question is not answerable by a gamut
alarm.
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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