Re: Photoshop Gamut warning vs ColorThink
Re: Photoshop Gamut warning vs ColorThink
- Subject: Re: Photoshop Gamut warning vs ColorThink
- From: Mark McCormick-Goodhart <email@hidden>
- Date: Sun, 24 Feb 2008 16:52:26 -0500
Lars Borg writes on Fri, 22 Feb 2008 22:51:46 -0800
A "gamut warning" indicates whether a specified source color can be
"reproduced accurately ...
Harald Bolls' reply
After giving some more thought to the above statement I would
contend that
it is not a succinct definition of a gamut alarm.
Rather I think it would be a concise description for a new kind of
alarm,
say one called a "Color Alarm".
These comments cemented the final piece of the puzzle for me.
Photoshop's Gamut Warning is very useful, but its description is
simply a misnomer. As suggested by Harald Boll, et al, it should be
called a "Color Alarm" or "Color Error" warning rather than Gamut
Warning. When using AbScol and BPC unchecked in the Color Settings
conversion dialogue box, the PS gamut warning feature alerts the user
with its overlay to any colors that have been mapped from source to
destination with approximately 5dE or more error. The ambiguity of
the tool's meaning occurs when one turns on the BPC feature or
chooses RELcol or Perceptual rendering intents. This choice confounds
the meaning of the overlaid gamut warning, or rather, "color error"
warning because PS is first applying the rendering and BPC
corrections to image data before comparing the "before and after"
results with its gamut warning algorithm. The end user then sees
colors with no warning that are often well beyond 5dE if one truly
compares original source colors against output colors. For example,
if I set BPC on and move an RGB 0,0,0 = LAB 0,0,0 working space black
value to a matte inkjet paper Max black value of LAB 19,0,0, BPC
first transforms the source data to within 5dE (LAB =14,0,0) before
pushing the value through the gamut warning algorithm. So, no
warning occurs. The source color black is now considered within the
printer/ink/paper allowable tolerance, but I have no direct way of
really knowing via info tool behavior, what total shift in color
acutally occurred. To find out the actual color change values, I
have to resort to work-arounds involving conversion to profile and
then LAB mode, etc. That sort of defeats the dynamic warning
sensibility of the gamut warning feature, so I use PS gamut warning
in the more constrained role of checking ABScol color transformation
errors. Although not the total functionality I'd like to see, this
utility is still very instructive.
Thanks to everyone for much insight on this interesting PS feature.
Now back to lurk mode!
Mark McCormick-Goodhart
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