On Sat, 20 Dec 2003, Alex Deucher wrote:
> yeah, I had thought about that too. I guess we need to decide what's a
> good way to advertise gamma. I just did it that way since I had 8
> presets, but like you said there could be more down the road. The
> hardware is capable of independently adjusting 18 points (6 on r100 hw)
> along the gamma curve. I just worked out some common gamma values
> since I don't know of a good way to expose the curve. We can't use
> float values for attributes (perhaps we could add float support to the
> device independant Xv code), but we can use ints like 85 for 0.85 or
> 110 for 1.1. the question is, what should the limit be? 300? 400?
> should we multiply by 1000 instead of 100?
The EDID (Extended Display indentification Data) standard used by Monitor
DDC, encodes gamma values in the range [1.0,3.56) usual one byte with:
encodedValue = (gamma*100)-100
Since we have a CARD32 we could use
gamma = 1.0 + (encodedValue*(100.0/0x1000000))
> having a basic XV_GAMMA
> attribute is probably easier for users than having XV_GAMMA_RED, etc.
> especially since not all hardware does gamma the same way.
DDC and xgamma both allow either a single gamma, or one for each channel.
If we don't allow separate channels now, we will only need to add the
option later.
Andrew C Aitchison
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