Re: No Color Adjustment
Re: No Color Adjustment
- Subject: Re: No Color Adjustment
- From: email@hidden
- Date: Fri, 26 Apr 2002 14:18:20 EDT
In a message dated 4/26/02 7:29:11 AM, email@hidden writes:
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As a driver developer the recent threads on selection of colour paths through
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non-Postscript drivers for profiling has been interesting.
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Obviously your requirements for such a path include:
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1. The colour behaviour must be repeatable.
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2. Colour gamut should be maximised.
Agreed, those are the basics... which we have already.
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What else would you add? I can see that a linear response and an appropriate
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ink
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limit when printing the testchart would be candidates if your
characterisation
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tool does not have pre-profile linearisation and testchart ink limit
controls.
How does one ink limit and preliniarize with a characterizition tool, for RGB
printer profiles? Rolling curves in before the LUTs is problematic, and
usually doesn't help all that much.
To use an example (sorry if its a bit close to home), as the Epson 12xx
printer series progressed, the quantity of ink that an uncalibrated target
showed increased to an undesirable point, especially at the highest rez
settings for glossy papers, so that getting a valid 2880 glossy target print
became impractical. At the same time the move from the 1270 to the 1280
introduced a far more nonliniar gradiant to the uncalibrated prints, so that
I can recognize an ordered patch target from the 1280/90 at a glance, due to
the breaks at the edges of the color ranges.
On the other hand I am looking at a similar target printed on a 5500, and not
only is it amazingly linear in all directions, but the gray patches on it are
actually gray!
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Would you prefer the driver perform those functions even if they are in
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the
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characterisation tool? If so, why?
A Characterization tool correction (unless you are using a RIP, which is not
what we are discussing) means printing a liniarization target in advance, and
if the lin target bleeds all over, or has eight black patches before it hits
a gray one, then that is still not very helpful, as these things all need to
get crammed into the profile, instead of being adjusted in advance in the
driver.
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The driver obviously has to do the RGB to CMYK conversion for you due to
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that
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pesky operating system limitation. Would you prefer it do a simple conversion
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which makes no assumption about the nature of the ink and substrate, such
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as the
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"classic" one-minus RGB to CMY conversion with K=min(C,M,Y), or would you
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prefer
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a "fixed" accurate colour conversion, from say Adobe 98 to a canned output
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profile?
Clearly this is not up for negotiation, as in current generation printers,
with so many factors at the bleeding edge, black generation choices are
balanced with ink metamerism issues, split ink channels (even a split black
channel!), and other factors. It is refreshing to hear someone mention that
an RGB assumption is needed at the front end, however... that tends to get
ignored in most discussion.
I would like to see a wider range of media settings in the drivers, as they
are the only controls for an RGB driver that can effectively change the ink
limits, liniarization, and color balance before a profiling target is
printed. This could incorporate all of the above, and instead of only
offering a short list of settings named for Epson media, it could include
other settings that would offer higher and lower ink limits, allowing
effective profiling of assorted media. Media settings entitled
AdobeRGB/uncoated, or AdobeRGB/Glossy that offered that source assumption
coupled with increased or decreased ink limits, and appropriate linearization
for the dot gain of the media types that the ink limits were appropriate for,
would be a huge help. If that is not viable, then advanced setting in the
driver that allow ink limits and gamma to be adjusted (and which remain in
force when a profile, or no color management is specified) would do the
trick. But building a few extra media settings would seem easier than wiring
numerical choices into the driver.
C. David Tobie
Design Cooperative
email@hidden
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