[Xr] API questions

David Forster dforste at arbornet.org
Tue Jun 10 15:12:23 PDT 2003

On Mon, Jun 09, 2003 at 06:41:12PM -0700, Bill Spitzak wrote:
> On Monday 09 June 2003 11:04 am, Keith Packard wrote:
> > > To allow devices to support any color space Xr does have to offer an
> > > interface that allows sRGB to be specified with values outside the 0-1
> > > range. Not all interfaces need to, just for instance a floating-point
> > > one.
> >
> > Hmm.  That's just crazy enough that it might work.  I'll have to think how
> > this would affect the compositing algebra.
> The alpha should always be clamped to the 0-1 range, but I believe all color 
> values will go through the compositing algebra ok. I think implementations 
> should be allowed to clamp incoming data to their gamut before compositing, 
> this means that that the exact result of partially-transparent pixels that 
> are out of gamut is undefined.

FWIW, this whole idea sounds very much like e-sRGB or scRGB (used in
GDI+ I believe), of which each allow upto 16bits per channel.  i.e.,
e-sRGB allows values in the range of (-0.53, 1.68).  More info at

-David Forster

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