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: Graeme Gill <email@hidden>
- Date: Thu, 01 Aug 2002 18:08:06 +1000
Tyler Boley wrote:
>
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.
This is certainly the explanation in most cases. More advanced CMS
use a colorspace with fewer of these "hue bend" problems for gamut
mapping and clipping, such as CIECAM97.
>
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 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.
>
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
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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. I know the difference between the
>
public's blue and true photo blue, that's not the problem. These
>
profiles tend to be superior in other ways, is there a trade-off?
It depends greatly on the gamut mapping algorithm, and profile
linking approach. Many packages use simple but well behaved gamut
mapping algorithms that map towards a central point keeping
hue angle constant. This often leads to desaturation of saturated
colors, particularly if the "cusps" (primary colorant combination
values) are at dissimilar hue or lightness values between source
and destination gamuts. If you could discover it, there is a color
that will map to your "nice blue", but it is not the obvious color.
The ICC approach of fudging gamut mapping into the destination
profile somehow, even though the gamut mapping doesn't know what
the source gamut is at the point it is created, can also lead to
unnecessary loss of saturation.
An approach which created the gamut mapping at link time,
and uses a mapping influenced by the nearest color to
an out of gamut color (and allows the hue angle to change as
well as saturation and lightness), will generally preserve
saturation better, although it can lead to a loss of detail
in highly saturated areas of the color space, and under some
circumstances, may not be terribly well behaved.
>
I think a lot of this software is not letting us fully utilize the
>
capabilities of our devices, even though it's obviously light years
>
ahead of no profile at all.
I agree with you.
Graeme Gill.
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