Re: Pigment Ink - "blues turing purple and reds turning orange"
Re: Pigment Ink - "blues turing purple and reds turning orange"
- Subject: Re: Pigment Ink - "blues turing purple and reds turning orange"
- From: Johan Lammens <email@hidden>
- Date: Tue, 30 Jul 2002 16:01:34 +0200
- Organization: Hewlett-Packard ICD
email@hidden wrote:
Subject: Re: Pigment Ink - "blues turing purple and reds turning
orange"
Date: Mon, 29 Jul 2002 20:16:46 -0400
From: "Dave King" <email@hidden>
> First of all, I have to say this problem is not limited to pigment
inks.
> Bruce Lindbloom's explanation is very insightful, and I have to
give it
> credence since I'm for below his level of expertise. But having
battled
> this in a crude sort of way for a couple of years, it's my opinion
that
> there is more to it.
I agree that Bruce's explanation is right on the mark. As his diagram
illustrates nicely, the problem will get worse the more chromatic (and
possibly out of gamut) the original color is. It also illustrates that a
linear gradient in CIELAB from such a far-out color down to gray will
pass through various intermediate and different hues. Considering that
ICC printer profiles need to map a verly large CIELAB subspace into the
printer's device gamut, these issues do show up unless specific
countermeasures are taken.
I still think some profiling software is not
> letting us get to the gamut of our devices. If I print out a ramp
of RGB
> 255-255-255 to 0-0-255 with no color adjustment same as source, I
can
> see with my own tired eyes a wonderful, non hue shifting, rich,
white to
> blue ramp on paper.
These problems do not occur (as much) when working directly in device
color since there the proportions of inks are being kept constant, which
typically results in more or less constant hue. In other words, the
problem stems from the transformation to and from CIELAB which is
inherent in ICC printer profiles. These issues are well known in the
color science community, btw.
> I have profiles from different sources made with different
software,
> only one lets me get to these blues. In every other way it sucks.
The
> other profiles print this ramp terribly, the entire ramp is
> undersaturated, it hue shifts dramatically as it gradates, and
0-0-255
> is some lame undersaturated purple.
Gamut mapping is part of the problem, and certainly an area where
profiling software differs, but to a lesser extent you will see the same
phenomena even in colorimetric mode for entirely in-gamut gradients (i.e.
where gamut mapping is not normally an issue). The problem is certainly
known to profiling software vendors, and some have found more effective
ways to deal with it than others.
In environments where conversions to and from CIELAB are not mandatory,
for instance in GDI/QD RGB-only printer drivers, it is in some respects
easier to deal with this issue. If you define your blue to white (or
black) gradient strictly in RGB and print through an RGB driver without
applying any host or application based color management, you will
typically get better results. An example would be any old DeskJet driver
printing from MS Paintbrush, but surely there are others too.
JOhan
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