[cairo] Color, Cairo and Cups

Larry Ewing lewing at gnome.org
Wed Mar 8 15:11:08 PST 2006

I want to follow up on the discussion some of us had concerning printing
at the gnome summit and how things have progressed since then.
Unfortunately I've been busy and and haven't had time to look into
everyone's plans as closely as I'd like so let me apologize ahead of
time if I've missed something.

Looking over what I've seen of the current plans there will be no way
for Cairo to specify image sources of anything but 8bit sRGB data
anywhere from Cairo to the printer.  So if a desktop publishing or image
manipulation application wanted to use Cairo to print an image the idea
would be to convert everything to 8bit sRGB and trust that cups maps the
sRGB to the printer output profile with reasonable quality. Is this the
basic plan?  

It seems to me that with no ability to pre-adjust output to the printer
profile and being strictly limited to 8bit sRGB all but the most basic
forms of color management fall in the realm of custom printing code.
While printing at all is a definite step forward are there any plans to
extend the available options in the future?  

At the summit Owen had suggested the possibility of using colors less
than 0.0 and greater than 1.0 still using the sRGB chromaticities, and
there was some talk of 16 bit surfaces, are either of these still being
Additionally if you ignore gamma (which Cairo does anyway right?) the
working space doesn't matter too much for many operations. If there was
some way to tag the output with the intended space an application could
avoid being forced into sRGB for all output.  Both Postscript (with CRD
and CSA) and PDF (with ICC profiles) have mechanisms for embedding some
color space information in the file, is there any possibility that
applications will be able to add this metadata to the printer surfaces?

I'm sorry if this mail is a bit scattered, but I wanted to see if any
more thought had been given to these issues before 1.2 comes out.


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