|
|
Magic Mailing List |
|
From: Jeff Solomon (jsolomon AT vlsi DOT stanford.edu) Date: Mon Feb 18 2002 - 15:28:02 EST
Awhile ago, when I first tried Tim's OGL magic version on my Sun, the
window looked really washed out. I thought that either it was supposed
to look that way or that there was a bug in Tim's code or OGL itself.
After lots of investigation, it turns out that some Sun hardware
supports visuals that are either gamma-corrected or not. Turns out
that Tim's code was using one of these gamma-corrected visuals through
not fault of his own.
If you want to see how bad this looks. On linux, bring up a magic
design (either OGL or X11) and type:
xgamma -g 2.2
This will set the gamma to 2.2, which is the standard gamma for
gamma-corrected Sun visuals. To turn it back off, type:
xgamma -g 1.0
On a Sun, you can set the gamma value similarly with "fbconfig -g".
This brings up a few issues.
1) The magic color maps are designed for non-gamma corrected displays.
In some sense this is bad since it means we're not getting a linear
intensity response for our colors. Since magic is all about colors
(unlike a text editor), it might be better in the long run to
create a colormap that is gamma-corrected.
2) There are a few ways around the "washed out" problem. The first is
to have Sun specific code (see XSolarisGetVisualGamma(3)) to detect
that a visual is gamma-corrected and ask for one that isn't.
Another thing we could do is add a "gamma" command which would
raise each color to the 1/gamma power so that when it was drawn to
the screen (and raised to the gamma power) it would look the same
as if no gamma-correction had taken place.
We could also have both of these things.
Has anyone else ever seen this "washed out" phenomenon? Does anybody
have any thoughts on this?
Jeff
|
|
|
|