Re: Preserving the black channel
Re: Preserving the black channel
- Subject: Re: Preserving the black channel
- From: Marc Levine <email@hidden>
- Date: Mon, 15 Apr 2002 17:06:01 -0400
About the black...
I have seen some debate about the black channel issue in the past few
digests and would like to cast my own perspective into the fire. First of
all, I think that ICC is a nice way of "starting over" when it comes to the
black. In professional quality applications such as Gretag PM4.0 and
MonacoPROFILER4.0, users can control the black construction precisely (max
ink, max black, black width, black shape, UCR, GCR, preserve gamut, etc...)
In such cases, the remanufacturing of black should be embraced as an
opportunity to create a black channel for a specific device/media
combination that allows for the optimum balance of printability and color
fidelity.
However, in many professional environments, CMYK is the foundation of the
workflow and preserving the black channel can be an important capability. In
such a case, link profiles can be used. When creating a link profile, a
table is built directly from the source CMYK space to the destination CMYK -
no Lab transform. There is 3 important attributes of link profiles
1) Less calculation required. Anytime software is require to perform
calculations, it is forced to make decisions that can potentially create
margin for error. The fewer calculations, the better.
2) (And this is the big one!) Black channel preservation. Because a link is
a more direct transform table, special functionality such as channel
preservation can be used. MonacoPROFILER has a "preserve black" option when
making link profiles that basically takes the black channel from the
original file and moves it to the destination. After that, it recomputes the
CMY to achieve proper color matching and tonality.
3) Fixed parameters. With links, the input, output, and rendering intents
are all fixed. From a support perspective, this can be attractive. However,
users wishing to evaluate the profile in Photoshop or ICC diagnostic
applications may be frustrated by incompatibility.
At the end of the day, if preserving the black channel is that important,
ICC link workflow can provide that in addition to the standard color
management benefits of input/output profiles. However, you will have to
adjust workflow accordingly and possible implment new tools. One thing you
gotta ask yourself...... do ya feel lucky.....?
-Marc
--
Marc Levine
Monaco Systems
Technical Manager
Sales Division
www.monacosys.com
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From: email@hidden
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Reply-To: email@hidden
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Date: Sat, 13 Apr 2002 22:05:07 -0700 (PDT)
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To: email@hidden
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Subject: colorsync-users digest, Vol 3 #163 - 5 msgs
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Subject: Re: Preserving the black channel
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From: Terry Wyse <email@hidden>
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To: ColorSync User List <email@hidden>
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>
on 4/13/02 9:20 AM, Lee Blevins wrote:
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> We are using inkjet (hp5000) for graphic arts proofing.
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> We rip our files in our rampage and output a large contone (cmyk) to
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> print.
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> Problem is,
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> Black only halftones come out in 4C.
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> Using Postershop, Monaco Proof.
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> We really need the black only things to remain black only.
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> Any suggestions?
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Using the RAMproof Contone option I presume. Where exactly are you applying
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ICC Profiles? Are you using the Rampage ICC Option or are you opening the
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CMYK Tiffs in Photoshop and doing the conversion there? Although I know that
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Rampage ICC has the option for maintaining 100%K, it obviously doesn't apply
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to screens of black. (Oops! I just read your post more carefully and realize
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you're doing the conversion in Postershop - duh!).
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With your current workflow using ICC profiles there's no way to do what
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you're asking. The ONLY way that I can think of would be to avoid profiles
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altogether and try to linearize/calibrate your HP5000 via Postershop using
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simply density/ink limiting adjustments and dot gain compensation curves (I
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have no idea if you can even do this in Postershop - with a BestRIP this
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could be done and still be able to bypass profiles). This would get you
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close except the ink hues on the HP are likely to be way different than your
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press simulation. This would however let you output "straight" CMYK data
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thru the HP.
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So...
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* Use ICC profiles and get the correct color APPEARANCE (%K->%CMYK) but get
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an incorrect MECHANICAL proof or...
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* Disable profiles in Postershop and get a correct mechanical proof (%K->%K)
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but accept the fact that the color appearance will not be correct.
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Yet another case of needing a "Smart CMM" or equivalent.
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>
Terry
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