On Wed, 4 May 2005, paul womack wrote:
> David Dawes wrote:
> > On Tue, May 03, 2005 at 12:53:43PM -0700, Mark Vojkovich wrote:
> >
> >> This stuff is HW specific so it needs to be done by the driver.
> >>Looking through the i810 driver source code, it appears the i810
> >>driver supports gamma but the i830 driver does not. I don't know
> >>the reason behind that. Perhaps David Dawes knows. I see he's
> >>worked on the i830 driver.
> >
> >
> > I no longer have access to the relevant documentation, and don't recall
> > if was omitted because of hardware limitations or other reasons. Someone
> > with access to the hardware specs should be able to provide a better answer
> > to this.
>
> OK. Assuming that some cards don't have HW support for gamma
> correction, that leaves owners of those cards with uncontrollable
> displays.
I would be very surprised if any modern graphics card did not
support gamma correction.
>
> I suppose I can split my question into 2; my real request
> is (of course) for wonderful accurate screen display.
>
> 1) Can gamma correction be added/incorporated into the driver?
If somebody has appropriate documentation for that chip, yes.
It's probably just a matter of passing the CMAP_PALETTED_TRUECOLOR
flag to xf86HandleColormaps and setting some magic bit in the
hardware somewhere.
Mark.
> 2) If the answer to (1) is no (for whatever reason) is it possible
> (even if undesirable) to gamma compensate the data being sent
> to the driver; it is clear that this approach will suffer from
> range and quantisation issues, but it can't be (much) worse
> than what I have at the moment, which is (judging by screen cards)
> a non-negotiable gamma of 1.6, against a desired 2.2
>
> Perhaps some kind of driver "decorator" ?
>
> http://www.exciton.cs.rice.edu/JavaResources/DesignPatterns/DecoratorPattern.htm
>
> BugBear
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