DesignJet profiling ABC (2)
DesignJet profiling ABC (2)
- Subject: DesignJet profiling ABC (2)
- From: Henrik Holmegaard <email@hidden>
- Date: Wed, 28 Nov 2001 18:31:35 +0100
How is the hp different from the Epson in terms of profiling?
That would depend on the RIP and the printer, but in general the
interplay between calibration and characterization, like so:
The prepress-oriented DesignJets have built in densitometric
functionality (and not colorimeters as if for profiling which was a
question earlier). That is, the tonal range is evenly distributed (:
linearization) and over time there is consistency (: calibration).
This also entails ink limiting in the RIP, so if you wish to build
your own profile then in the profiling application just set total
CMYK to 400% and a black replacement that keeps K dots out of
highlights. This is all a simple separation presetting in Eye-One and
ProfileMaker software, for instance. The RIP is the place to limit
ink as part of the wider calibration procedure, the measured profile
is the place to match color. To profile a DesignJet, switch off
in-RIP CMYK to CMYK conversion (see below) and switch off Automatic
Black Replacement (ABR) which changes K only dots into CMY composed
dots in highlights. Then your ICC profile has control of the black
replacement and the color which is what you want.
If a printer is not stable from print to print and from proof to
proof, you are not going to be able to use it for prepress work. For
instance, without calibration you won't get two printers with the
same consumables to print the same proof, whether locally or
remotely. This is why calibration is also a feature of say the Iris
ColorZone software. Or again if you include a 50 patch FOGRA control
strip for ISO 12647 proof verification, then the lower patch number
(compared to the minimum size test chart with +300 patches) would
raise the average deltaE for the proof to press target tolerance,
viz. the tighter the repeatability tolerance the less waste in the
proof printing cycle.
I still have my old Kodak 8650PS dye sub (not the QuickDraw version
-:)). To linearize and calibrate it, you used a Kodak software
utility on the Mac (or PC) which first printed a CMY and a K stepped
wedge, then let you measure the 60 patches with a spectrophotometer
in densitometry mode or a dedicated densitometer, and finally
recalculated the calibration table which it downloaded into firmware
memory in the printer. Printing the calibration sheet, measuring it
and recalculating the table took about fifteen minutes of
concentrated work.
Can you send
pre-converted files through the RIP without any further "correction"
in the RIP.
Yes, just switch of CMYK Emulation :
The DesignJet interface offers simple color server functionality, cf
the Inkjet profiling ABC posted earlier. Look at it this way: A CIE
proof is a CMYK to CMYK conversion which BOTH converts the colors AND
the separation. Your offset press requires other ink limits and other
black replacement settings than your inkjet. Notably an inkjet
requires lower black start and lower ink limits than offset.
Most applications in actual use can't convert from OutputCMYK to
ProoferCMYK and most users don't realize they want to cross-render.
Therefore, if you simply print OutputCMYK directly to the inkjet
because you don't know that your application doesn't support color
matching / reseparation, or you don't know this is a boon rather than
a bane (: the typical print shop would assume that if the same CMYK
values are not laid down, then it's not a proof, a legacy concept
inherited from first generation film laminate proofing systems), your
screening will not be optimal.
PostScript Level 2 version 2017 and PostScript 3 allow the RIP to
assign a CMYK Color Space Array (CSA) to incoming CMYK objects so
that they can be reseparated using a Color Rendering Dictionary in
the RIP. This way you still get OK output when printing from
QuarkXPress, for instance.
When printing a CMYK test chart to a PostScript DesignJet RIP, you
switch off this in-RIP reseparation by switching off what the DJ UI
calls 'CMYK Emulation'. Then when you apply the profile you keep the
emulation mode set to off. Always configure workflows for compatible
assumptions. If you manage color including the last conversion from
OutputCMYK to ProoferCMYK in Linocolor / Photoshop / InDesign /
iQueue, then don't re-color manage in the RIP.
Host-based versus RIP-based color management is a long discussion,
but the short of it you have here -:).
(End part 2)