high-end inkjet proofing ABC
high-end inkjet proofing ABC
- Subject: high-end inkjet proofing ABC
- From: Henrik Holmegaard <email@hidden>
- Date: Wed, 15 Aug 2001 09:36:31 +0200
Sam Martin wrote:
Let me give you our situation. In the next year we hope to go CTP, and we
were planning on Epson 10000 for a color proofer with maybe a 3000 or 5000
for the Art design department.
I don't know the Epson 10000, but after a minor mountain of research
into inkjets and inkjet proofing, here are my two cents on
implementation:
1. Make sure the inkjet is self-calibrating. Back a while I used a
Kodak 8650 with the ColorFlow Calibrator for the DCP9000. This
software supported the Digital Swatchbook in densitometry mode. You
printed some twenty steps of CMY and K patches, measured them, and
the software then fed the RIP the correction table. Dye subs are
thermal devices and not awfully stable. These days I play with an
HP5000PS with on-board densitometer. The densitometric calibration
happens automatically.
To check how stable your reference printing system is, print a PMPro
CMYK test chart multiple times, measure the charts, and check the
average dE for the best 90% patches and the worst outliers for the
remaining 10% using the MeasureTool (the user friendly version of the
old ColorLab colorimetric tolerancing method).
The figures for the HP5KPS are around de 0.5 for average and dE 1 for
outliers. This is using the same spectrophotometer, because the
repeatability among spectrophotometers is as high or higher (or
should I say lower ...). Meaning that in laboratory situations if you
measure the same patches with a set of high-end manual spectros of
different make and model, you get a dE tolerance of less than 1 (see
the TR001 report, for instance). Outside the laboratory and at this
level of precision you need to know what make and model of
spectrophotometer made the reference measurements you are comparing
to. Most industry reference measurements are de facto made by the
Spectrolino.
You can linearize the profile ex post facto using ProfileMaker Pro,
but as Steve Upton pointed out a while back, you really need the
device itself to map input values to output values with no clamping
(ten input steps map to the same output step, for instance).
2. Keep in mind that for best screening results, inkjets need light
cyan and light magenta as well as CMYK. The midtones and highlights
are largely built with the light inks which are laid down in higher
quantity to get the same optical density as you would have got with C
and M. This means that ink limiting and ink balancing is no trifling
matter on an inkjet. (It is no trifling matter on a press either, of
course.)
The art of separation is to limit the inks only just enough that you
don't get flooding / coalescence / cockle and other proximity
problems, and still keep the colorimetric values high. If you limit
ink beyond that floating border down there somewhere, you cut back
gamut. And with a proofer that is just about the last thing you want
to do (if the gamut is too low, you have to shop for another proofer
as the proof is a facsimile conversion, the production colors which
are out of gamut for the proofer simply won't appear!).
I have printed IT8.7-3 charts to inkjet RIPs and seen nearly zero
differentiation in the dark patches (of which the IT8.7-3 has a
superabundance). The test chart is by definition printed raw at 400%
which on an inkjet means that much higher ink densitities are
actually laid down (as explained in a January inkjet ABC post), so
the ink limiting is in my experience best done in the RIP prior to
and independently of the profile. And again I have printed the
IT8.7-3 raw at 400% to the HP5KPS RIP with third party papers loaded,
there is good differentiation, and you are ready to profile that
paper right off the bat.
3. The gamut of an inkjet is highly dependent on the paper. Inkjet
inks are soluble and soak into the paper, offset inks are fatty and
sit on top of the paper. Therefore, the art deparatment and the
production department should use the same paper. Your life will be
easier, if your inkjet proofs look the same. This again means that
Macs and PCs need to be able to connect easily to the inkjet, for
instance, the HP5KPS lets Macs and PCs across a LAN or Intranet
follow print jobs (a driver-level feature), and the RIP has on-board
queuing and nesting of jobs.
Self-calibration, self-linearization, ink limiting and connectivity
are the items on your shopping list.
Hope this helps