--- Andrew C Aitchison <[EMAIL PROTECTED]> wrote: > 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)) >
What about gammas less than 1.0? or are those not worth advertising/using? Unfortunately I'm not an expert when it comes to gamma. > > 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. the radeon driver already has red, green and blue intensity attributes. They aren't really r, g, and b gamma per se, but the gamma value is used in the calculation of the those components. See RADEONSetTransform() in radeon_video.c. For now I guess we can just have XV_GAMMA. If I can get some consensus, I'll put together a new patch that will hopefully be a good basis for device independant xv gamma. Alex __________________________________ Do you Yahoo!? New Yahoo! Photos - easier uploading and sharing. http://photos.yahoo.com/ _______________________________________________ Devel mailing list [EMAIL PROTECTED] http://XFree86.Org/mailman/listinfo/devel
