Re: Qualifying a CMYK Press Profile
Re: Qualifying a CMYK Press Profile
- Subject: Re: Qualifying a CMYK Press Profile
- From: Graeme Gill <email@hidden>
- Date: Fri, 22 Nov 2002 11:27:57 +1100
Darrian Young wrote:
>
After a great post regarding your newspaper configuration, which is normally
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how we set things up as well, this post seems less of a clarification than
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the question from Mr. Lindstrom.
I was trying to avoid getting too system specific.
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A good proofing system has at least two
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components aside from the hardware (which you call I believe the proofing
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printer (which I understand as the printing device): 1. which is responsible
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for maintaining the printer in a known and repeatable state, and 2. the
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color profiles, tables, etc, etc. which handle the conversions from your
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press conditions your printer conditions. Are you saying that you send a
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density chart and then compensate within the proofing tables (i.e.
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simulation tables) of the system instead of within the calibration tables of
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the printing device?
The sort of proofing printing devices I'm familiar with don't have anything
like calibration tables (ie. all inkjet printers). What the proofing
RIP sends the printer is what gets printed (the raster sent from the RIP
to the inkjet exactly controls whether a nozzle fires or not). All color
space conversion, device calibration and screening therefore has to be
done in the proofing RIP (that's its job).
>
This is a very flawed configuration as you can
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guarantee no repeatability and any problem with your printing device would
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results in the possible need to correct your proofing tables.
Nothing else is possible. The printer is an open loop device. The RIP is
the only thing that closes the loop. The RIP calibration tables guarantee
output quality. If by "proofing tables" you mean the simulated device
space to proofing device colorspace conversion, then no, of course
calibration isn't achieved there, it's a separate logical step
in processing the raster sent to the printer.
>
Also, what got my attention was your use of density to keep the printer in
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the desired state instead of using colorimetric calibration. In order to
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gurantee the same proof at the print site and another site, and to reproduce
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the same print time and time again, it is necessary to keep establish the
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printer's response with more than just 20+ patches of density values. While
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density is great for imagesetters, CTP's etc., it is not the the best
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solution for proofing linearization.
I disagree. We've been using linearisation as a method of keeping
a wide variety of devices in calibration for quite a while now,
and it has been a rock solid approach. Typically we've used 31
graduated patches to get sufficient detail in the highlights.
Off hand I can't think of anyone who uses colorimetric calibration,
since it demands more expensive instruments, and adds nothing to
what is a process control task.
[Actually, linearisation is slightly misleading term, the device is
made to conform to a chosen per channel target response curve.]
For colorimetric characterization of course, a very much larger number
of test patches is used (typically 3000) and colorimetric instruments
have to be used, but the whole point of separating calibration from
characterization is that the calibration keeps the characterization
valid, and allows the one characterization to be applied with success
to many different instances of a particular printer under a wide
variety of operating conditions.
[ The printer characterization is combined ("linked") with the
target press characterization ("colorspace to be simulated") to
create the proofing RIP colorspace conversion.]
Graeme Gill.
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