RE: linearization - luminance, chroma or density?
RE: linearization - luminance, chroma or density?
- Subject: RE: linearization - luminance, chroma or density?
- From: "Clark Omholt" <email@hidden>
- Date: Thu, 25 Jan 2007 06:09:34 -0800
- Thread-topic: linearization - luminance, chroma or density?
Ciao Marco:
Certainly the yellow contamination in the highlights would be consistent
with a profile built without a UV filter on a media with lots of optical
brighteners. The spectro sees the paper as "blue", so the profile adds
yellow to neutralize the gray axis.
WRT the evolution of the Colorburst RIP (Queue Series), I've actually
been pretty impressed. They've added profiling software and print
certification in the last year without raising their lowball price. And
it generally works well out of the box and sets up quickly. I've had
issues with the relinearization process, and some of the limitations of
the RIP (lack of production capabilities like cropping and resizing,
will only drive one printer) don't make it appropriate for larger
environments. We find that it's an ideal fit for smaller design
studios.
Per channel ink limiting can be a challenge given the limited tools now
available with Colorburst Queue. I've actually been working on
documenting the calibration methodology that we've used with some
success. It can be used with pretty much any RIP, but the write up is
not yet complete.
One general, though very valuable, piece of advice I can give you - talk
with Sarah in Colorburst technical support. She has tons of real world
experience and should be able to help sort out the shadow issues.
Regards,
--Clark
Clark Omholt
email@hidden
Spectraflow, LLC
Color Workflow Solutions
Phone: 415-472-0130
Mobile: 415-225-6644
122 Paul Dr., Suite B1
San Rafael, CA 94903
www.spectraflow.com
-----Original Message-----
From: Marco Ugolini [mailto:email@hidden]
Sent: Tuesday, January 23, 2007 10:31 PM
To: Clark Omholt
Cc: ColorSync Users Mailing List
Subject: Re: linearization - luminance, chroma or density?
In a message dated 1/23/07 7:31 AM, Clark Omholt wrote:
> This is an area where we've done a fair amount of investigation. The
> RIPs we've worked with most are EFI Colorproof XF/Best (Lab), Onyx
> (density), Colorburst (Lab), ImagePrint (no linearization currently).
> The ones that use Lab I believe use chroma for linearizing colorants
> and
> L* for linearizing K.
>
> Our experience has shown linearization to be pretty mechanistic,
> resulting in good results in combination with an ICC profile using
> either density or Lab. The area to pay the most attention is in
> per-channel ink limits. There's a number of reasons for per-channel
> ink limiting.
Hi Clark.
You mention ColorBurst: I assume you mean XProof.
I have felt disappointed with the Mac version of this RIP lately,
specially since ColorBurst decided to take away from the user the direct
controls that it used to offer via the Printer Settings command over
parameters such as print resolution, paper type, dot size, and ink type.
Now the user of the Mac version is forced to start from one of the
standard environments, which is trusted to include the correct choices
of resolution, dot size, etc, hopefully the correct ones for the paper
being used, then relinearize and profile starting from that (with the
added burden of having to use a UV-cut spectro -- but that's another
subject yet...).
I just went through a tough time linearizing and profiling Epson's
Single Weight Matte Paper on a client's 4800. Two problems proved to be
big
head-scratchers:
1) After linearizing and profiling, the print had a distinct yellow tone
in the highlight areas where there was any value at all above pure
white. (This was not the kind of even yellowish tone that may appear
when using an AbsCol intent, but instead localized areas of yellowish
tone that followed the shapes and locations of the highlights in the
image that carried something close to a minimum value this side of pure
white.) I was able to fix that through a hack that I made up on my own
(I became sure that my non-UV linearization was creating the problem,
and I was proven right: when I used the canned linearization and
profiled on top of that, the output finally appeared normal in the
highlights).
2) The shadow areas were heavy and plugged up, far more than would be
reasonable to expect in a matte paper. There was considerably more ink
in those areas than was to be expected in the circumstances.
(Incidentally, even using the OEM environment, the shadows appear
similarly heavy.) I used the per-channel ink limits that came with the
environment, but I wonder what procedure I could use to determine them
with more precision. I am at a loss for the time being, and I also don't
have the time and the consumables to try different possible solutions.
Do you have a tested-and-true procedure to determine the per-channel ink
limits in ColorBurst XProof? And on top of that there is another ink
limit setting to grapple with (320% in the OEM environment). The mystery
does thicken considerably...
Any advice would be welcome.
Be well.
Marco Ugolini
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