Preserve Color Numbers - on a proof
Preserve Color Numbers - on a proof
- Subject: Preserve Color Numbers - on a proof
- From: Thomas Holm / Pixl <email@hidden>
- Date: Thu, 06 May 2004 17:42:58 +0200
This is one of those things I've been wondering about, which starts looking
like uncharted rabbit-holes once you start digging.
In Photoshop > View > Proof setup > Custom, you can select the Preserve
Color Numbers, which will show you how your CMYK document (whether or not a
profile is assigned) will print on a certain other device that has been
characterised by a profile. It may not be prefect but it's pretty close.
It does this, I assume, by assuming the reference profile and convert RelCol
to the monitor.
Fine, but suppose you want to do the same on an ICC based proofer, then what
(or HOW) do you do?
Will it work just selecting your offset profile as the simulation/reference
profile in the RIP and then print away?
Logic says "Sure, your document is a set of CMYK numbers, these values are
converted via Lab to your proofer profile and you will get a representation
on your printer of how the images will print on the reference device".
So if you print an untagged SWOP file (TAC300) and use a Euroscale reference
profile (TAC350) the file should be washed out and light as the inklimit is
a bit on the low side, and the image will be a bit too light as SWOP use
negative plates and thus have higher dotgain. This is what will happen if
you print it on a press set up to Euroscale/ISO.
However in practical terms it doesn't work quite that easy:
One of my clients are proofing magazines. They use the IsoWebcoated profile
for separation, and use this as the reference profile in the RIP. The offset
printers in Spain can print according to ISO specifications, and the proofs
my client makes for correctly separated files (anything done inhouse) are
extremely accurate matches.
However when they get files from elsewhere, usually PDF without profiles
(think advertising) it is anything BUT accurate.
On these untagged files the proofs are all over the place (ok mild
exaggeration). They are not consistently too light or dark, but rather
different in various directions and amounts.
The reason, of course, is that the files are separated using many different
flavours of CMYK. Some of which are appropriate, some that aren't even
close.
Now to produce stuff that will print well some of these files need to be
converted to IsoWebcoated, but which ones and converted from what?
The easy workflow would be to print the files and the ones that aren't
looking good (remember we are simulation the press) should be fixed (assume
an appropriate profile and convert to IsoWebcoated). However there isn't any
consistency between the proofs and the print, so the printer can't be used
for this evaluation...
So we're back to rasterising all the PDF files in Photoshop, and choosing
Softproof > Preserve colour numbers and do a screen evaluation...
How, (or why can't) something similar be built into a RIP?
Could a DeviceLink be used to perform this "presslike" behaviour on an
inkjet, on untagged files?
If the image has a too high inklimit I'd like to see closed down shadows, if
it has a too low limit I'd like to see it washed out. Essentially I want
what I get on the press, nothing more, nothing less...
All ideas are welcome...
Best Regards,
Thomas Holm / Pixl Aps
- Photographer, Educator, Colour Management Consultant & Seminar speaker
- Remote Profiling Service (Output ICC profiles)
- www.pixl.dk 7 Email: th[AT]pixl.dk
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