Intel: XV Gamma correction (GAMC[5:0])

Thomas Fritzsche tf at
Mon May 12 08:21:31 PDT 2008

Hello Keith,

I hope you have a nice day!
I had a look at XV (Overlay) parameter GAMC[5:0] (Register
specification section:
Sorry to ask you directly, but I found the following patch from you in
the source:

I have 3 questions:
1) You are checking the gamma correction bounds (somehow difference in
gamma values should not be lager the 0x7E). Sorry asking so easy
question, but how come this bounds? Maybe a very natural issue, but
it's not mentioned in the specification so I thought I ask you better.
2)  The specification of GAMC registers has just values in the lower
24 bits, but you are checking values in the highest bit too? Is there
any particular reason?
3)  General question about the sense or nonsense of this XV attribute.
With this parameter basically with this interface you are mapping the
internal gamma interface 1:1 on the XV attributes.
If this doesn't get set very particular it's almost unusable. I first
found this trying to make these parameters with with program
"gxvattr", and as you can imagine this just produce a colorful effect
on the screen.
E.g. a parameter that can set all color channels at once would be much
easier. (or additional for every color channel separately).

Sorry again for bothering you.

Thomas Fritzsche

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