[Openicc] Introduction / Gutenprint

[Gerhard Fuernkranz]

Bob Friesenhahn schrieb:

> Beyond telling the printer driver which profile describes the existing 
> image data, and which profile describes the printer, what additional 
> functions are required of an open color management system in order to 
> support printing?

IMO the general case (e.g. desktop publishing) is that a page contains 
not only a single image, but several objects (images, vector graphics, 
text, etc.), where each of the objects may be represented in a different 
(source) color space, and may need to be rendered with a different 
rendering intent.

Basically I imagine the following printing flow:

    Application -> page description (PS, PDF, PCL, or whatsoever) ->
      -> Spooler(optional) -> RIP -> printer

If the CM is done in the application, then the application will convert 
all object colors to the printer's native device color space and the 
page description will only refer to colors in the printer's color space. 
The resulting page descript is bound to a particular printer and cannot 
be used on a different printer.

If no color conversions are done in the application, and the CM is 
delegated to the printing subsystem, then the page description created 
by the application needs to contain all objects in their original color 
spaces, together with descriptions (profile) of all these color spaces, 
and rendering intents for the objects, in order that the RIP can 
eventually convert all objects to the printer color space. In this case 
the CM is eventually done in the RIP. Since the color conversion is 
delayed, the same page description may be even usable with different 
printers.

The use of different rendering intents for different objects may even 
require to use not only a single printer profile, but several ones (for 
instance, if a different black generation is desired for different 
objects, etc.).

In the first case (CM in the application), the "page description" could 
also be a simple page image in the printer's native device color space. 
In the second case this is no longer possible (severel objects in 
different color space need to be represented) and a more sophisticated 
page description is required.

That's a brief summary of my understanding of printing, but maybe others 
have a completely different understanding.

Regard,
Gerhard