Re: gamut warning failure
Re: gamut warning failure
- Subject: Re: gamut warning failure
- From: Marco Ugolini <email@hidden>
- Date: Tue, 17 Oct 2006 21:11:17 -0700
In a message dated 10/17/06 4:28 PM, eugene appert wrote:
> Marco Ugolini wrote:
>
>> I don't think it's strange. Fortunately for all of us, Photoshop honors and
>> implements color profiles correctly, from what I can tell, so that the soft
>> proofing and printing procedures are accurate to the extent possible with
>> ICC technologies at their present state of development
>
> So it would appear that the only tool students possess to navigate effectively
> from data to ink is the visual examination of the image on the screen using
> soft proofing.
No, that does not exhaust the range of possibilities. If you have
ColorThink, you can view your image as a graph (something that I will refer
to as a "cloud of points", for lack of a better term). Save the image in
Photoshop as a TIFF RGB, for example, and embed the working space profile
(e.g, AdobeRGB). Drag and drop the file from the Finder into ColorThink's
Grapher window, and you will soon see the "cloud of points", each of which
represents the file's colors in Lab space.
Now, open the profile for your CMYK output in ColorThink's Grapher, then
make the profile's 3D volume semi-transparent (50% will do) so that you will
be able to see which of the colors in the "cloud of points" are inside and
which outside the output gamut.
Unfortunately, in ColorThink there is not yet a way (one that I know, at
least) to view the image itself and tag the out-of-gamut colors so that one
can see where they are exactly in the picture itself.
But at least, using this technique, you will see an exact 3D view of the
colors in the image and how many of them are in- or out-of-gamut.
> Soft proofing seems to bear up to close scrutiny even in situations where
> colour changes are unexplainable ( at least for a laymen like myself).
>
> One such situation, which you might be able to help me understand is, using
> soft proofing to examine a file after it has been converted to its output
> profile and then returned to the RGB workspace. I have heard of photographers
> using this technique to verify that they have successfully complied with
> requests from publishers that RGB files be sent in Adobe 1998 but with no
> colours out of gamut in US swap coated.
That sounds a bit silly to me...kind of a kludge just to please a client who
is being overly careful. The CMYK file should be enough, in that case.
> Soft proofing these converted files with the same output profile (using
> relative without BPC, no paper white and no black ink) still shows a change
> in brightness and colour (which displaces transitions in lightness along a
> gradation and could conceiveable produce banding). I cant figure out how out
> of gamut colours could survive this procedure.
They do not. One has to be very careful not to have colors that are so far
out of gamut that they cause visible clipping. In areas that appear clipped,
view the individual channels and see if they show detail in those areas. If
they do, it's possible that the detail is there, but that your monitor is
not able to produce the composite color. Remember that most displays
experience difficulties showing even some of the colors that are printable
within the gamut of US Web Coated (SWOP) v2 (often those in the range
between saturated greens and cyans).
The change in brightness that you mention here is probably due to the fact
that the conversion between AdobeRGB and output and back was done using
Relative Colorimetric plus BPC in both directions, which remaps the blacks
along with a good portion of other colors. Hence the visible difference in
lightness and in some of the colors in the image.
On the other hand, if you start with, say, an AdobeRGB image, convert it to
US WebCoated (SWOP) v2 using Relative Colorimetric with no BPC and no
dither, and then convert back to AdobeRGB, still with Rel Col and no BPC nor
dither, the image remains very much the same, because there is no remapping
taking place.
Regards.
--------------
Marco Ugolini
Mill Valley, CA
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