ATI 9100 IGP TV Out - brightness control?

Mark Knecht markknecht at
Mon Sep 7 10:17:24 PDT 2009

On Thu, Aug 13, 2009 at 9:18 AM, Mark Knecht<markknecht at> wrote:
> On Tue, Aug 11, 2009 at 6:54 PM, Alex Deucher<alexdeucher at> wrote:
>> On Mon, Aug 10, 2009 at 7:38 PM, Mark Knecht<markknecht at> wrote:
>>> Hello,
>>>   I'm successfully using the newer Open source Radeon driver with my
>>> 3 Asus Pundit-R 9100 IGP machines. All 3 PCs drive different older TVs
>>> using their S-video inputs. This was something that for years I had to
>>> do with the ATI driver and am now very happy that it works so well
>>> with the Open Source driver.
>>>   One thing we are finding with this new driver is that the overall
>>> color level of the picture using S-video only is MUCH darker than the
>>> older fglrx driver. Even with the brightness turned all the way up on
>>> the TVs it's still doesn't get to the level that the older ATI driver
>>> did with brightness at a midrange setting. I'm wondering if there is
>>> possibly some settings in the xorg.conf file that might be able to
>>> improve this?
>>>   Note that this is NOT a problem for the same driver driving a
>>> normal monitor - it's only dark using the TVout.
>> You can mess with the RGB_ATTEN_VAL field of TV_RGB_CNTL.  See
>> radeon_tv.c.  I had thought about exposing it as a brightness option
>> for tv-out but never got around to it.  Note that setting it too low
>> (or high, I don't remember which) causes noise in white areas of the
>> screen.
>> Alex
> Alex,
>   Thanks. I'll look into it but on Gentoo I think this is sort of
> difficult to do as the system builds all the code. I'm not a
> programmer so it seems likely I'll just create more problems than I'll
> solve.
>   If you do happen to expose these as variables I can set in
> xorg.conf in a version I could get through portage then I'd be happy
> to do some testing and report back.
> Thanks,
> Mark

Just reporting back that I've looked at the S-video output from two
identical machines on multiple TVs. The output from the Open Source
radeon driver does tend to be quiet a bit darker than the closed
source driver on the same material. In some cases, such as night
scenes, so much darker that the scenes are almost indistinguishable.

CPU usage continues to be MUCH better. I've never heard the CPU fan on
these machines speed up using the radeon driver. It takes only seconds
with the closed source before it is running full speed and making lots
of noise so my vote is clearly for Open Source, but it would be great
to get some control over this in the xorg.conf file someday.


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