[Openicc] [cairo] Creating CMYK and spot colors

[Jan-Peter Homann]

Hello list,
As an colormanagement consultant, monitoring the openICC list, I´m happy 
that colormanagement in cairo is now dicussed. I believe, that a working 
support for ICC-profiles in cairo would be a big step forward for 
professional handling of colors in LINUX environments.

I think a good way for implementing more sophisticated color into cairo 
would be first to concentrate on workflows, where all parts/objects of 
an document must have the same colorspace (described by an ICC-profile)

The job of cairo would be to translate this flat color document to 
several output formats (Bytemaps, PDF, PS) and tag the output file with 
the valid ICC-profile.

The colortransformation from the cairo-output to the output-device 
(monitor, printer, file processor) is handled outside cairo.

If eg. a CMYK document is rendered to a CMYK bytemap for viewing on the 
monitor it must be converted to RGB.
Lets assume, that CMYK bitmap provides by cairo has an embedded 
SWOP-profile.
The bitmap is than processed by littleCMS. If there is an valid monitor 
profile in the system, little CMS transforms the CMYK-bytetmap from SWOP 
to monitor-RGB. If there no valid monitor profile, little CMS uses sRGB 
as target profile.
For standard CMYK colorspaces, littleCMS could cache standard conversion 
to the monitor-profile or to sRGB for faster processing.

For PDF-output the CMYK-profile from the cairo document is embedded as 
outputintent and all objcets in PDF-file are DeviceCMYK.

For printing output, we should define a mechanism, that either littleCMS 
could be triggered, if cairo delivers a bytemap or cairo delivers the 
document only with embedded profile for processing in the printing 
application (CUPS, etc.)

For defining standard RGB and CMYK profiles for cairo, Oyranos would be 
a good place.

If it is possible to work in cairo with flatcolor documents defines by 
an ICC-profile with monitor-output, print-output and PDF-generation, we 
can look forward how to handle workflows, where every object can have 
his own profile and rendering intent.

But be prepared, that this is even by the big vendors like Adobe, Apple, 
Microsoft a field on ongoing research. E.g. Adobe introduced for 
CreativeSuite 2 the colormamagement policy "preserve CMYK numbers" which 
deactivates embbeded profiles in placed CMYK-objects in InDesign and 
Illustrator.

Regards
Jan-Peter



-- 
--

homann colormanagement ------ fon/fax +49 30 611 075 18
Jan-Peter Homann ------------- mobile +49 171 54 70 358
Kastanienallee 71 ------- http://www.colormanagement.de
10435 Berlin --------- mailto:homann at colormanagement.de