RE: Qualifying a CMYK Press Profile
RE: Qualifying a CMYK Press Profile
- Subject: RE: Qualifying a CMYK Press Profile
- From: "Darrian Young" <email@hidden>
- Date: Fri, 22 Nov 2002 08:39:10 +0100
Graeme Gill wrote:
>
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
>
> guarantee no repeatability and any problem with your printing device
would
>
> 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.
Ok. I believe we are talking about the same thing which wasn't clear in your
last post. I do not use the term RIP interchangeably with proofing system.
In fact a proofing system many times does not need a RIP component - for
proofing raster data, whether TIFF 1Bit, Tiff-IT, etc. the only thing that
is needed are the linearizazion tools (which once again are always to be
separated from the simulation, or profile to profile conversion, or whatever
one prefers to call it) the printing module or program which handles the
jobs, and a spot color database. The RIP element of course is needed for
PS, PDF and EPS. If you make the distinction between "simulated device
space to proofing device colorspace conversion" and "calibration", then no
complaints here.
.....
>
> Also, what got my attention was your use of density to keep the printer
in
>
> the desired state instead of using colorimetric calibration.
>
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.
Rock solid??? With an HP5000 or an Epson 7/9600 print a full calibratio
wedge and measure density. You will find that the density starts to go down
in cyan and magenta in the 80% up region (with the 5000 it is just in cyan).
Then, when yo look at the wedge, you will see that the density is not in
fact less in this range but really higher. What has happened is that there
is a color shift with this amount of density so the density meter does not
read the values correctly. Aside from this interesting problem there is
also the matter of simple experience. Having two printers with the same
densities has not given me the same colors. If you think about it
logically, this is not surprising. That is why when you profile a printer
(which is a different process) you do not do so with 31 patches but rather
with a few hundred on up.
>
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.]
GMG Colorproof and the new ORIS Colortuner about to be released use
colorimetric calibration to name a couple. The issue of more expensive
instruments is a non-issue for two reasons. The first is that you need them
anyway to creat your profiles, and the second is that if you are talking
about having to have numerous devices at remote sites, etc. the i1 is not
expensive. I also don't think linearizazion is a misleading term.
>
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.
I did not say characterizazion - if you use colorimetric data to change the
curves or tables to bring your printer to a certain state, this is not
characterization - it is linearization or calibration.
>
[ The printer characterization is combined ("linked") with the
>
target press characterization ("colorspace to be simulated") to
>
create the proofing RIP colorspace conversion.]
No problems here.
Regards.
Darrian Young
MGV
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