Color space specification ABC
Color space specification ABC
- Subject: Color space specification ABC
- From: Henrik Holmegaard <email@hidden>
- Date: Tue, 30 Oct 2001 11:51:07 +0100
email@hidden wrote:
Incidentally, PDF has no support for PostScript color management.
PostScript color management only exists in PostScript. When converting
PostScript to PDF, any CSA's (PostScript source profiles) are converted
into ICC profiles. So PDF supports ICC profiles, not PostScript profiles.
Not quite -:)
PostScript and PDF distinguish between color space spefications and
color rendering procedures. The color rendering procedure is intended
to be set up at the RIP, and developers are advised against setting
it up at the application. As a Color Space Array technically
corresponds to the AtoB direction of an ICC profile, it is correct
that only CSAs are embedded. Overall, this is part of the Adobe
concept of device independent color according to which the final
transformation is left to the RIP out of the control of the user, a
principle which InDesign actually violates by optionally setting up
the CRD and hence the color rendering procedure at the host.
PostScript Level 1: deviceRGB, deviceCMYK, deviceGray (hence the old
quip that PostScript doesn't have any color management).
PostScript Level 2: deviceRGB, deviceCMYK, deviceGray, CIELab,
calibratedRGB, calibratedGray.
PostScript Level 2 version 17: deviceRGB, deviceCMYK, deviceGray,
CIELab, calibratedRGB, calibratedCMYK, calibratedGray.
PostScript 3: See PostScript Level 2 version 2017.
PDF 1.2: See PostScript Level 2, that is, no support for
calibratedCMYK (for in-RIP CMYK to CMYK conversion).
PDF 1.3 and higher: See PostScript Level 2, that is, no support for
calibratedCMYK, but in addition to deviceColors and calibratedColors
PDF 1.3 and up supports ICCBased, either on a per-object basis or as
document default. The way ICCBased works in InDesign and iQueue, for
instance, is per object (the iQueue manual says as much as users are
generally better off with a strategic birds eye view in the manual to
get them started right).
When converting PostScript and EPS into PDF, deviceColor objects stay
deviceColor and calibratedColor objects stay calibratedColor except
for calibratedCMYK.
The problem for both InDesign 1.5.2 and Distiller 4.0.5 is that
calibratedCMYK isn't supported in PDF at all, so the solution adopted
is to use the CIEBasedDEFG table to hard-convert the data into CIELab.
The solution in Distiller 5 is to leave the data alone and convert
the format of the color space specification, that is, convert the
CIEBasedDEFG into a barely legal ICC CMYK profile, and one which
should certainly not be extracted for use in production (!), but
which will serve as source for a Relative Colorimetric proof.
If you want to use a device independent workflow for serious
production work, especially when using multi-object and multi-color
space specification formats like PDF, you are going to have to tell
users how their applications really work, and what they must NOT do
when selecting color space specification formats in their application
UIs.
I am aware that this is easier said than done, granted that the color
space conversion architectures available in PostScript, EPS and PDF,
and the color space conversion architectures implemented in
Photoshop, Illustrator, Acrobat and other desktop tools is not
clearly evangelized so that users can make informed choices.
Hope this helps clear the murky waters a bit