Re: Dry Time for UltraChrome inks/Calibration
Re: Dry Time for UltraChrome inks/Calibration
- Subject: Re: Dry Time for UltraChrome inks/Calibration
- From: Robin Myers <email@hidden>
- Date: Tue, 04 Feb 2003 08:47:47 -0800
Darrian Young wrote:
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I don't think lightness is the only problem here, at least from my
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experience. I also have seen problems with color shift. There is is
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something unclear here - if not limiting the ink correctly leads to
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"hooking", while the "hooking" goes away or is less apparent when limited,
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and the resulting profile works much better, what part does "the natural
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features of L*a*b*" play. In my case, I am interested in getting good and
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precise prints out of the printer. I also don't think that Mr. Maxwell was
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saying a L*a*b analysis is everthing either - at least not the way I read it
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<<I suggest that you look at a spider Lab plot and not just density when
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setting ink limits>> I see this as look at density AND L*a*b. Are you
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recommending then to only look at density? I don't think density was
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intended for color matching calculations either (especially given that
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density doesn't deal with color). Thank you for the refereneces to your
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site - I will take a look.
By limiting the amount of ink delivered to the substrate, you are using
the straighter (notice I did not say 'straight') portion of the
increasing saturation vector before it "hooks" around. It is one of the
"tricks" you must use if using L*a*b* color lookup tables since the
regularly spaced sampling grid cannot handle non-monotonically
increasing saturation.
As for density, I almost never use density measurements. They are
representations of the color as viewed through specific filters. These
filters were designed for CMY printing inks only (and photographic dyes
for transmissive density) and are not universally applicable to other colorants.
Analyzing printing colorants and determining how to create the best
color reproductions is a complex task that cannot be relegated to one or
two simple tests. It must always be analyzed specific to the color
technology involved in the printer (or any device, for that matter).
All that being written, I prefer to analyze inks with xyY chromaticity
diagrams and tonal reproduction curves (TRC). The xyY space is not
perceptually uniform (nor does anyone expect it to be so), but for well
behaved printers the color mixing occurs on straight lines in a xy
diagram (the rate of change along the line is non-linear but the line is
straight). This makes visualization easier, without the problems from
the color space encoding that you get in L*a*b* space. Once the problem
is understood using xyY diagrams and TRCs, I calculate color mixing in
XYZ tristimulus space.
By the way, I can't remember the last time I used any perceptual
rendering intent calculations. All my calculations are performed with
relative or absolute colorimetric algorithms.
Robin Myers
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