Re: Scanning in CMYK vs. RGB
Re: Scanning in CMYK vs. RGB
- Subject: Re: Scanning in CMYK vs. RGB
- From: Stephen Marsh <email@hidden>
- Date: Wed, 14 Nov 2001 02:07:30 +1100
William Barrett wrote:
>
I need an argument settled.
Words are cheap.
The only real way to solve the 'argument' is to do controlled tests side
by side comparing the CMYK vs RGB workflow and associated issues for the
specific setting in question.
I do not think that a list is the place for that - although it can give
you some points for discussion.
You need amunition for your debate - its between yourself and your
friend on whether the issue gets settled. <g>
Also with full respect to this list and its memebrs - this may not be
the most objective forum for this debate.
>
A friend of mine is using a drum scanner and
>
is letting the scanner convert the file to CMYK.
A long honoured practice - with pros and cons (just as an RGB workflow
has pros and cons).
>
My recommendation was
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to scan in RGB and let Photoshop CMYK setup handle the conversion
>
process to CMYK.
It would depend on the workflow.
If there are many uses for one scan - with all uses as critical as each
other, then a RGB workflow makes sense. Obviously for archival and for
users 'further upstream' this is obvious.
For pre press whose only or critical concern is print - and usually a
few 'standardised' forms of CMYK, then the RGB workflow may not benefit
the majority of images.
Quite often the proprietary scanner separation method produces a better
separation than Photoshop or ICC methods. At the end of the day, the
concern of press is the halftone screen values which make up this CMYK
mixture - not about RGB, LAB or XYZ in the original file.
Depending on the scanner and operator - results may be better than
Photoshop or other ICC aware software, or worse.
How the file gets to CMYK may not be an issue - as long as the grey
balance was correct for the intended output. A lot is possible with post
correction edits, even in CMYK.
>
My argument was for *better* control over the
>
conversion process-- adjusting ink limits and control for dot gain
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depending on your final destination device. I told my friend they only
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thing that needed to be adjusted on the pre-scan was white/black point
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setting, but save it as RGB. He replied that most of his settings were
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done directly via the drum scanner including the CMYK conversion.
>
Take a step back in time ten years, and this was no shock. Today, if
your drum scanner is capable - one can scan RGB, or even ICC RGB or ICC
CMYK .
Without ICC RGB scanning is not fun.
Without ICC CMYK - who cares?
The scanner is presumed to set the scan for a known print or contract
proofing condition.
The CMYK 'profile' is simply assumed. One can make a presumption about
colour - whether using ICC methods or not.
>
Ok. Anyone want to tell me the advantages of doing this conversion
>
process at the scanner?
Presuming a prepress/print biased input/output delivering 8 bpc
'corrected' files ready for the intended output:
Some scanners non ICC proprietary tables are better than other methods
that may be available to the user in question.
The raw high bit colour data in the scanner can be mapped to output
space, while taking full advantage of colour and tonal correction in the
scanner software on the internal high bit data - All during pre
scan/scan time.
Productivity.
Simplified workflow for press.
>
I told him once you're locked into CMYK, there's
>
really no way to go back.
True, for out of gamut colours, particulary blues - this is the case.
Visually, many images commonly survive the trip to CMYK and back. Small
luminosity differences can be managed, and there may not be too much
colour degradation to the human visual system (an artificial measuring
instrument may say othewise however).
A quick trip into LAB mode in Photoshop - and some linear curve edits to
the AB channels can quickly increase the gamut of a file which has been
to CMYK, even a newsprint separation. Keep the 50% point unchanged so
you dont toast neutrality - and keep an eye on gamut warning coupled
with your intended output workspace and info readings.
So technically, the original colour and gamut may be lost for good. But
this does not mean that if a CMYK was the _only_ original available for
repurposing that you would be at a loss. Both luminosity and
hue/saturation can be increased to insane sized gamuts.
>
RGB provides more flexibility in the long run,
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since you still have control of your conversion process at a later point
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in time.
True.
But if a users primary purpose is CMYK - and a few limited forms at
that, then these arguments mean less.
Perhaps one should ask - what are the associated benefits and problems
of a RGB workflow, and are they worth the switch for your friend.
I personally see less issues for the user learning RGB from a CMYK
backgound - as opposed to the RGB user entering the prit world.
As you have not mentioned the workflow - I can only presume that your
friend is an old school 'by the numbers' CMYK drum scanner operator who
lives and breathes print.
Have fun with your debate.
Sincerely,
Stephen Marsh.