Re: Posterization in a Press Profile?
Re: Posterization in a Press Profile?
- Subject: Re: Posterization in a Press Profile?
- From: Terence Wyse <email@hidden>
- Date: Fri, 25 Sep 2009 11:19:53 -0400
Where's the profile itself? It would be more telling to have a look at
the profile and be able to analyze it directly.
A few things....
* Averaging is a good thing!
* Since you were using an EyeOne Pro target, I'm assuming that the
target took up quite a bit of press sheet real estate......this could
cause of a couple of issues: 1) not enough room to place two charts on
the press rotated 180 degrees from each other and 2) The chart was
likely wide enough across the ink keys to cause issues with ink
balance/uniformity which will cause irregularities in the profile, a
possible source of posterization. Best to use a very narrow chart that
spans the fewest ink keys and then work like hell to keep the ink
balance even both across that area and from front-to-back. Problem is,
the spectro you're using handcuffs you in that regard due to the large
patch size requirement. If you do press profiling on a regular basis,
I'd invest in an iSisXL or at least an iO table (patch sizes can be
smaller with the EyeOne iO compared to the EyeOne by itself but
nothing like as small as patches for an iSis....patch size for an iSis
can be 6x6mm whereas for the iO I think they still have to be in the
8-10mm range minimum). Personally, I don't use an EyeOne Pro for
anything but proof verification and general measurement purposes....as
a profiling chart measurement device I think it pretty much sucks. I
had a "bout" a couple of months ago with my EyeOne (RevD, no filter)
where I was measuring very large targets and also multiple
targets....I couldn't believe how often I needed to recalibrate that
thing to keep from getting bad measurements (paper L* was usually the
give away when it would exceed L*100 for paper white). In any case, I
wouldn't trust *my* EyeOne for anything as important or critical as a
press profile. Your mileage may vary.
* Profile settings....I would question the use of GCR2 in
ProfileMaker....I never go less than GCR3 and mostly use GCR4...I find
the K curve too steep past the midtone with GCR2 which can also cause
some lack of smoothness in the CMY in the gray balance curves. Also,
I'd try the different gamut mappings...this can have a profound effect
on the smoothness of color transitions evident in the color gradients
you're using....or you could just use MonacoPROFILER and get smoother
profiles to begin with! :-) I ditched PMPro5 a long time ago for this
very reason. Only thing that I've seen PMPro do better than Monaco is
a slight bit better accuracy in the A2B transform....but Monaco makes
up for it with much better B2A accuracy....since B2A performance is
what counts for most transforms, I've stuck with Monaco.
Regards,
Terry Wyse
On Sep 25, 2009, at 10:26 AM, Pylant, Brian wrote:
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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