Re: Illustrator conversion
Re: Illustrator conversion
- Subject: Re: Illustrator conversion
- From: Graeme Gill <email@hidden>
- Date: Wed, 30 Apr 2003 11:39:10 +1000
Henrik Holmegaard wrote:
>
2. The acronyms CSA and CRD are used in Adobe documentation as well as
>
in the industry generally.
I can find no reference in the Adobe PostScript documentation to the
acronyms CSA or CSD. (Searched the PDF of the PLRM3). CRD is used widely.
The Phrases "Color Space Array" and "Color Space Dictionary"
are both used in the Adobe PostSCript documentation.
The setcolorspace operator takes an array as an argument
but it is meaningless in distinguishing anything, since
the setcolorspace operator is used to set any PostScript colorspace
using the array, including DeviceGray, DeviceRGB, DeviceCMYK, etc.
CSD (Color Space Dictionary), does mean something, since
only CIE based (non-special) colorspaces use dictionaries,
so CSD implies a non-device dependent color selection.
"CIE colorspace" is probably the best identification.
>
The List has used the terms for years. Does
>
this make the term correct? No, it doesn't. Does it make the term
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incorrect? No, it is a convention. For toCIE we use CSA and for fromCIE
>
we use CRD. Do we need to know how expressions are constructed and the
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processing stack built in PostScript 3, for instance, where exactly
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arrays and dictionaries come into the picture? To be honest, I don't
>
think so (and to be honest, I'm surprised at finding myself saying
>
this, but there is a balance to be struck between technology level and
>
interface level language(*)).
Lack of precision in nomenclature is often the source of
confusion. A novice looking into what all this "CSA" stuff
is about, would be right to feel confused.
>
3. An object that references a CSA introduces a choice, either to
>
ignore the CIE reference or to apply the CIE reference.
This is not correct. Some colorspace families offer an alternative
(fallback) colorspace (For instance, Separation, deviceN),
but CIE colorspaces do not. A RIP can't simply ignore them,
as it has no other source of information as to the current
colorspace.
>
There are
>
implementations which ignore the CSA and apply the user's choice of
>
assumed source ICC profile and there are implementations which apply
>
the CSA.
>
Nobody designates the object as non-rendering (or to be on the
>
safe side, nobody I have knowledge of). Similarly, there are
>
implementations which allow a device color object to be assigned a
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default CSA. Which is right and which is wrong? The only thing that
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matters is documenting the implementation so the user knows how the
>
switches in fact work.
I can't interpret your comments, as I'm not clear what you
mean by "CSA". If you actually mean CSA (the argument to
the setcolorspace operator), then what you say may be correct
if the array is a device colorspace.
If by CSA you actually mean a CIE colorspace dictionary, then
your comments are simply not correct. A RIP might substitute an
ICC profile for a device dependent color setting, or for a CRD,
but cannot do so for a CIE colorspace, since the color is
already in CIE space, and there is nothing for the ICC device
profile to do.
>
((*) Standards should have been written for users to read, but
>
traditionally they are not. Partly because standards refer to technical
>
constructs which age much slower than software functions and
>
interfaces, partly because software functions and interfaces differ in
>
how they dub the technical constructs they are in fact based upon. But
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that is a broader discussion which I am certain we will return to
>
frequently in coming years.)
One of good things that goes on in a forum like this is the debunking
widely held myths. That "CSA" == "CIE colorspace specification" is (IMHO)
such a myth.
Graeme Gill.
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