gamma correction

[Billy Biggs]

Martijn Sipkema (msipkema@sipkema-digital.com):

> I've been thinking some more about gamma correction...
> 
> - (almost) no hardware can do per window gamma correction, i.e.  gamma
>   corrected and uncorrected visuals.
> - most systems don't do full gamma correction in the framebuffer LUT.
>   SGI has a default system gamma of 1.5, Mac uses 1.8. I suppose
>   Windows uses 2.2.

  Well, Mac's API uses 1.8 and I think it gets converted, at least that
was my understanding.  Like, that's just for their software drawing API.
I don't think they actually set up the LUTs for a 1.8 gamma.

> - With 8 bits per RGB channel on a fully gamma corrected display the
> resolution is somewhat low for dark colors (though I don't think
> unusable).
> 
> A reasonable solution might be to use the SGI system gamma of 1.5
> (gamma correction between 1.3 and 1.7 depending on the monitor). This
> seems like a reasonable compromise between speed and quality.

> An application shouldn't assume a certain system gamma IMHO. On
> graphics hardware with more than 8 bits per RGB channel one might want
> to run with a system gamma of 1 and one might want to run at 2.2 for
> backwards compatibility. Is there a standard way to get the system
> gamma under X11?

  I think we agree that there should be some way to query information
about the display.  My understand is that X provides this right now.
This does not need to live in the X server though, it could just as
easily live somewhere else.  Arguably, if we had a stronger colour
management system based on something like littlecms, this information
should live in the same place as your ICC profiles and all that.

  -Billy