Re: some thoughts on CIELAB was Dry Time for UltraChromeinks/Calibration
Re: some thoughts on CIELAB was Dry Time for UltraChromeinks/Calibration
- Subject: Re: some thoughts on CIELAB was Dry Time for UltraChromeinks/Calibration
- From: Graeme Gill <email@hidden>
- Date: Thu, 06 Feb 2003 17:15:12 +1100
tlianza wrote:
>
6. Finally, when plotted in Lab space, most hardcopy devices, "hooked" which
>
implied that numerical mappings would not be single valued....very "uncool"
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mathematically. If the devices included a pre linearization and limiting
>
step, then the hooking was minimized.
Are you sure about this ? In all the messing about I've done
with forward and reverse mappings between device and L*a*b* values,
I don't seem to have stumbled across any instances of non-monotonicity
that could be attributed to using L*a*b* space. XYZ space is generally
a worse choice from many points of view unless you have a device model
that particularly suits it (such as a CRT additive model or Neugenbauer
printing model), and other appearance model spaces are generally more complicated
and controversial. As a rough perceptual space, and the one that is used
for as the basis for many color difference measures (including CIE94,
CMC etc.), it doesn't seem that bad a choice, particularly when values
are going to be quantized in some fashion.
"The book" on color appearance models is Mark Fairchild's, and he
certainly treats L*a*b* as a primitive predecessor of the many
more advanced appearance models, and even something like CIECAM97,
or Hunts appearance models have a lot in common with L*a*b* in their
general approach.
>
The densitometer is very useful because it makes a measurement that better
>
relates to the machine dependencies than a spectro. It costs less so they
>
can be deployed in greater numbers than spectros.It was suggested that one
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might want to include linearization information in the profile so that the
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profile could be checked with a minimum number of measurements. Had the
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historical elements been stored in the profile, we could easily see if the
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process has drifted. . The politics of the time dictated that everyone would
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soon own a spectro so why bother putting the quality control features in the
>
system?
There are some tags to do this in the spec., but I'm not sure
how widely this is used in practice because it is patented by
someone or other, thereby defeating the whole idea of using a standard.
Graeme Gill.
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