Re: Color space specification ABC
Re: Color space specification ABC
- Subject: Re: Color space specification ABC
- From: Henrik Holmegaard <email@hidden>
- Date: Tue, 30 Oct 2001 12:43:35 +0100
Acrobat is not PDF. PDF is a file format. The
PDF specification does not have an allowance for PostScript color
management in it. Starting with PDF spec 1.3, we could have ICC profiles
in PDF, but still no PostScript profiles.
PostScript Color Management is a term visible in Adobe and Apple UIs
where it is loosely used for the functionality provided in PostScript
Level 2 and up, and in PDF 1.2, 1.3 and 1.4. This functionality
differs in format as well as in many other ways from ICC color
management.
The ICC and the PostScript color technologies are designed to be
compatible, but only from ICC to PS and not from PS to ICC. It is in
my opinion not helpful to speak of profiles with respect to
PostScript, because in the context of PostScript Level 2, PostScript
Level 2 version 2017, PostScript 3 and PDF versions 1.2, 1.3 and 1.4
what we are actually talking about are Color Space Arrays.
ICC color space specification format files (aka ICC profiles) can be
converted into PostScript color space specification files (aka what
Adobe calls profiles as in the above passage). The conventional way
of doing this is for the application to call the Apple ICC API
(ColorSync) asking for an ICC profile to be converted into a
PostScript CSA (and recently also a CRD).
The Apple ICC API offers the option in the LaserWriter driver to use
a PostScript 3 command called 'findcolorrendering'. This command
selects from among the CRDs in the RIP the one that matches by NAME
from a group of CRDs. The group will have been implicitly
pre-selected by the user when she picks a substate and colorant in
the UI of the RIP or by the RIP auto-detecting the substrate and
colorant from a bar code or some other mechanism.
The Apple driver is built to support applications that do not write
their own PostScript. Therefore, the mechanism for selecting the CSA
is simple too: One CSA for all objects in the document. With the
QuickTime PictureViewer an embedded RGB profile will be used rather
than the designated Display profile.
Hope this helps