Re: Colorsync-users Digest, Vol 6, Issue 236
Re: Colorsync-users Digest, Vol 6, Issue 236
- Subject: Re: Colorsync-users Digest, Vol 6, Issue 236
- From: Mike Strickler <email@hidden>
- Date: Fri, 25 Sep 2009 12:50:05 -0700
Hi Brian,
That Lab test image is a pretty tough test, especially if the target
CMYK profile has an especially small gamut, such as uncoated/
newsprint. Before chucking it altogether, try conversions from Adobe
RGB, and also try perceptual rendering. That being said, it may be a
crappy profile for any of the reasons stated by Terry and others. I
like to take a standard press test form image such as those you can
download from IDEAlliance and assign the press profile to it. This
gives you a visual window into the L*a*b* measurements the profile is
built on. Compare the result with that of assigning a good standard
profile for the same type of press and substrate. They should look
similar, though "real" profiles (not massaged after the fact) will
usually show less-than-perfect CMY grays and nonideal dot gain--
overall too light or too dark. Look for weird tonal progressions or
"jumps." These may indicate bad measurements, which are a common
cause of posterization and strange colors. Do this test before
anything more expensive or time-consuming.
Mike
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Message: 9
Date: Fri, 25 Sep 2009 10:26:19 -0400
From: "Pylant, Brian" <email@hidden>
Subject: Posterization in a Press Profile?
To: "email@hidden"
<email@hidden>
Message-ID:
<email@hidden>
Content-Type: text/plain; charset="us-ascii"
Hello all-
I'm trying to troubleshoot what I think is odd behavior on the part
of a profile I measured from a press. I've been hearing from some
of our designers that they are seeing some posterization in their
images when they use this new profile. I've posted some of my test
examples here:
http://brainpilot.com/press_profile/profile_testing.html
As you can see from the four images, when I take Bill Atkinson's
LAB test image and a Granger rainbow and convert them to this press
profile, there is a significant amount of posterization in the
result. The same image converted to Web SWOP v2 or Gracol 2006 does
not.
I am unsure if this indicates a problem with the profile (either
the file itself, how the target was read or the profile created), a
problem with the press that the pressmen need to sort out, or
simply the reality of what this press is capable of and the profile
should be used as-is. This is my first attempt to profile the
press, so I'm not sure if I've done something wrong.
The press profile was created using the ECI2002 target. 15 sheets
from across the press run were measured with an EyeOne Pro,
averaged using ProfileMaker 5 and then a profile generated using
GCR2 and a TIL of 300%.
Thanks in advance for any advice or insight!
Brian
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