[Openicc] Print and monitor Color Pipeline

[Jan-Peter Homann]

Hello Kai-Uwe and all,
I still think, that colormanagement from the document-colorspace to 
monitor and to a print setting should be done with the same technology. 
This should be done
- best through an systemwide graphics library or
- second best solution through an application depending graphics layer.

Technically different ways for rendering data to the monitor and to the 
print out does not make sense in my eyes.

If we concentrate on this road, a central depository for profiles and 
their connections to devices like Oyranos and / or Gnome Color Manager 
can help a lot provide transparency in the workflow.

If we are beginning in an uncoordinated way to implement ICC based color 
transformations in islands like e.g.
- Ghostscript
- CUPS
- Printerdriver Addons
- Application side
....
we will end in chaos like we already have under Windows and Mac OS X

I have also described, that assigning ICC profiles in the printer driver 
with a dynamic link to Oyranos and/or Gnome Color Manager makes a lot of 
sense.

Now we have to discuss, how to get the colordata from the application to 
the printer driver and  which step in this chain is ideal to apply the 
color transformation.

Here we have at least three different types of document

1) Images only:
****************
The document is already rasterized and can be matched to the monitor or 
the print out with small effort.
Colortransforming rasterized data could be implemented as an module 
directly into Oyranos and/or Gnome Color Manager, as here is the central 
depository for all valid profiles.

2) Complex Flat color document
*********************************
This are RGB or CMYK documents with text, images and vectorgraphics, 
where one document-profile describes all parts of the document.

2a) If the used graphic libray is able to raster to the monitor, it can 
also raster to the printout. Color Conversion after rasterization could 
still a be an module directly into Oyranos and/or Gnome Color Manager, 
as here is the central depository for all valid profiles.


2a) Old School way to print is creating PostScript and using a RIP like 
GhostScript to create a rasterfile. PostScript is not able to transport 
an ICC based document colorspace, but there are ways, to solve this 
issues /especially with Oyranos and/or Gnome Color Manager in the 
background,

2b) new school is directly to create PDF for the printout. All PDF 
content would be either DeviceRGB or DeviceCMYK with an Output Intent 
describing the document colorspace. Colormanagement will be applied 
after rasterization.

2c) If the PDF-printout is already colormanaged, the embedded output 
intent will be the same as for the printer driver setting. There will be 
no need for colormanagement during PDF rasterization or after.


3) Complex Mixed color document
************************************
This are RGB or CMYK documents with text, images and vectorgraphics can 
have individually embedded ICC profiles.
3a) PostScript must be avoided for the printdata of such documents, 
because handling of ICC-profiles in individual elements is a nightmare 
in PostScript.
3b) Direct creation of PDF for the printstream is a MUST. As a  user 
also expects a correct match to the monitor, the graphics libray in use 
should have the option to rasterize for print out on non PDF/PostScript 
print-worklflows.
If the printdata is not colormanaged direct by the graphics library, the 
created PDF for the print stream should contain both profiles for 
individual objects and also one profile describing the colorspace of the 
complete document (PDF output intent)
If the OutputIntent of the print stream PDF is not identical with the 
ICC-profile of the current printer setting. The PDF-rendering and 
rasterizing should be done firstly to the document colorspace and than 
to ICC of the printer driver setting.

Summary
**********
Colormanagement for the printing chain grows exponantially in complexity 
with differnt types of documents. I would recommend firstly to concentrate
1)image only documents with applying the colortransformation in an 
additional module  of Oyranos and/or Gnome Color Manager. CUPS should be 
neutral to color. The printer profile should be configured in the 
printer driver with dynamic link to Oyranos and/or Gnome Color Manager.

2) Add complex flat color documents to this workflow, if we have a 
graphics library able to render both to the monitor and to a rasterized 
printout. Rest of the workflow is identical to pure image workflows.

3) Add complex mixed color documents to this workflow, if we have a 
graphics library able to render both to the monitor and to a rasterized 
printout. If GhostScript should be used for rasterizing and 
colormanagement of the print file, it should also be used for 
rasterizing to the monitor.

Best regards
Jan-Peter

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