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: Sat, 23 Feb 2008 19:12:22 -0500
I've been a long time lurker, but I never felt the need to chime in
because there are so many highly qualified people answering all the
questions. This thread on gamut warning, however, is very timely
with some testing I've been doing lately. I, too, have been
intrigued and puzzled by the PS gamut warning feature for a long time
and now with the helpful comments I've read in this thread, I finally
think I get it. So, let me throw in my two cents and see if it agrees
with others' conclusion about this very interesting feature in PS.
Cris Cox wrote:
The gamut warning has to change with intent -- because the colors
that will
be in gamut after the conversion depend entirely on what intent was
used to
make the conversion.
Totally agreed. Gamut warning is comparing the source color value
with the predicted destination color value which is a function of the
chosen profile in the softproof menu and the chosen rendering intent
as well. It appears that if ABScol is chosen as rendering intent,
BPC is left off, and the final predicted output color is within
approximately 5 dE of the original source image color, then the gamut
warning does not get overlaid. As others have noted, there is an
apparent inconsistency in the fact that BPC "on" in the conversion
settings of color settings dialogue window affects is registered by
the gamut warning feature, but BPC set in the softproof dialogue box
is not, even though the softproof appearance changes on screen.
The closest the gamut warning feature can come to describing the
actual gamut limit of the output device is by choosing absolute
rendering intent, BPC off, and very important, choosing an image file
target that fully exceeds the color gamut of the output device.
Because PS users typically just want to know how their image colors
will look on output, aka softproofing, the softproof view often
satisfies that need and gamut warning seems pointless to some folks.
However, I think the gamut warning is very instructive and helps to
alert one where the larger color translations in the image are taking
place. I also find it very useful to differentiate color clipping
caused by the limits of the output device from color clipping
originating with one's display device when wide gamut working spaces
confound print output clipping with monitor clipping.
Because profile rendering intents and BPC can be considered just
another kind of "image editing", the fact that these translations of
the source data are reflected in the gamut warning along with
traditional image edits makes sense to me. Where things get
confusing to colorgeeks who actually like to use the info tool is
that although the end-user can see the rendering intents and BPC
reflected in the softproof view, the info tool does not reveal how
much translation of the source data occurred as a result of these
"behind the scenes" rendering and/or BPC corrections. Therefore, one
cannot determine what source data values the gamut warning feature is
using to compare against the predicted destination result... unless
one turns off BPC and sticks with ABScol.
Quick analogy: If I'm trying to get to Topeka, what matters is if
I land
in Topeka or Omaha - not that I started the trip in Tokyo.
Chris, I thought everything you said was on the mark except this
analogy, but you did say it was quick, so feel free to serve up
another analogy! Because gamut warning is comparing source color to
destination color, where you start out and where you end up are
indeed both important. The starting point and the ending point are
indeed the basis for the gamut warning comparison. As noted above,
the user often cannot tell what the source data being use by gamut
warning really is because rendering intents and BPC don't flow
through to the info tool as do normal image edits.
So, for those who don't find Photoshop's gamut warning useful:
what other
information could we provide to help you? What is missing?
Glad you asked. My wish would be for an improvement to the info tool
that allows one the option to measure directly the Actual LAB color
predicted by the profile for the output. At the current time we can
only pick "Actual color" that shows us the source values but not
destination values or the "Proof color" that expresses destination
values in RGB or CMYK but not LAB which are the numbers I want
really to see. Because I often want to evaluate the destination
values expresses as their LAB conversion equivalents, a work around
is currently needed where one has to convert to output and then set
Abscol in the Color Setting conversion options to get at the final
output LAB values. It would be much nicer to get at those predicted
final predicted LAB numbers without having to convert the file. If I
could compare the predicted LAB values dynamically with the source
LAB values in the info tool window, that would suffice very well for
me in lieu of trying to make a "graduated Gamut Warning color coding
feature or whatever.
I have an image file (PSD format) I found very useful in helping me
to figure out what the Gamut warning feature was doing. Perhaps it
might be of help to others as well, so I a have just posted in on my
website. You can find it here: Scroll down the page a little ways to
find the file called "AaI_HueSlice_image.psd" .
http://www.aardenburg-imaging.com/digitalprintresearch.html
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