[Openicc] Is CUPS the right place for printer color management...

[Jan-Peter Homann]

... and if not, where is the place ?

hello list,
I try to understand, the ICC-related options in in CUPS, but I still 
feel lost. May somebody can help or correct me:

cupsICCProfile
***************
http://www.cups.org/documentation.php/doc-1.4/spec-ppd.html#cupsICCProfile

Comment Jan-Peter Homann:
This PPD attribute delivers a possibility in the printing GUI to specify 
an ICC profile for the driver setup by keywords like e.g. 
ColorModel.MediaType.Resolution/Description

As CUPS is not able to perform ICC based transformations itself, this 
functionality is helpful for an external filter to identify the correct 
printer ICC-profile for the choosen driver setting

cupsRenderingIntent
*********************
http://www.cups.org/documentation.php/doc-1.4/spec-raster.html#TABLE2

Comment by Jan-Peter Homann:
Extremly poorly documented feature. It may allow to specify a 
RenderingIntent for an ICC based color conversion from the document 
colorspace to cupsICCProfile. (Or it is may means something complete 
different...)

Implementing Color Management
*********************************
http://www.cups.org/documentation.php/doc-1.4/raster-driver.html#COLOR

Comment by Jan-Peter Homann:
This text describes NOT how to implement Color management with CUPS. It 
only describes the part of specifying a selector to printer profiles 
with cupsICCProfile.


Conclusion
***********
So far as I understand, the main idea of color management in CUPS is 
framework for PPD-options to select printer profiles in the directory 
/usr/share/cups/profiles.
If the CUPS profile selector should be linked with settings of the 
printer driver (e.g. Gutenprint) it is the responsibilty of the driver 
vendor to create the link.
cupsICC also allows to define individual Keywords through 
cupsICCQualifier2 and cupsICCQualifier3
to be defined in the PPD.
This could e.g.
"mediatype"
"NameOfDriverSetting"
If the special settings are specified in the driver, this allows to 
organize the driver settings according mediatypes.

CUPS delivers only a mapping of Printing-Device/Setting to ICC-profiles.
If such mappings are managed outside CUPS e.g. via Oyranos or Gnome 
Color Manager, it is not a must for ICC aware print workflow usind CUPS 
as transport mechanism.
For the enduser, the presentation of different printer driver settings 
from e.g. Gutenprint in the Printing UI could be realized without  CUPS 
through the LINUX OpenPrinting Dialogue as an individual option.

Workflow with cupsICC:
- Driver-Vendor, Media-Vendor or User creating driver settings with 
attached ICC-Profiles
- The generic Driver PPD is updated with entries for cupsICC according 
the settings
- Oyranos or g-c-m parse cupsICC in updated PPD and know, which profile 
belongs to which driver-setting
- The enduser sees the different driver settings according the updated 
PPD in the print dialogue
- Choosing a driver setting signals Oyranos or g-c-m the current valid 
printer profile, which configures the ICC transformation from document 
colorspace to the printer profile in the preferred toolkit

Workflow without cupsICC
- Driver-Vendor, Media-Vendor or User creating driver settings with 
attached ICC-Profiles
- The driver has a direct link to Oyranos or g-c-m
- Oyranos or g-c-m create an Option in the OpenPrinting Dialogue
- Choosing the Option in the print dialogue signals Oyranos or g-c-m the 
current valid printer profile, which configures the ICC transformation 
from document colorspace to the printer profile in the preferred toolkit


Any comments ?

Best regards
Jan-Peter


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