Bug#540723: Subject: vlc: video brightness/contrast/gamma is really off

Gary Dale garydale at rogers.com
Mon Aug 10 20:10:23 UTC 2009

Reinhard Tartler wrote:
> Gary Dale <garydale at rogers.com> writes:
>> Reinhard Tartler wrote:
>>> This really sounds like video driver issues here. I'm reassigning this
>>> bug to both packages for now. However, since fglrx is developed by
>>> AMD/ATI, I persume they would be in the best position to actually do
>>> something about that.
>> I might agree except that:
>> 1) my desktop display is fine. I didn't have to do anything with gimp,
>> gwenview or any of my other desktop applications. It was just the video
>> applications that were messed up.
> gimp and other 'normal' applications do not require hardware assistance
> in the same way as a media player needs it. Xv is useful to lower CPU
> consumption in media players. X11 backends makes media players to behave
> like other 'normal' applications, at the expense of wasting CPU time.
Reasonable enough explanation for what is going on, except that x11 
doesn't work with vlc while xv does (just not very well). Using x11 with 
vlc, the video is squashed into the left quarter of the window and it 
appears to be greyscale.  I've just switched Kaffeine to xv from auto 
and it works. mPlayer also gave the high-contrast output when using xv 
until I found the video control under "equalizer" to set the contrast to 
a sane value (the same problem I was having with Kaffeine - the contrast 
control was set to its maximum).
>> 2) the Kafeine fix was a simple setting that was off while mPlayer
>> needed a different output to be selected. It appears that the fglrx GL
>> implementation is faulty, since I can't get good output from
>> it. However both Kaffeine and mPlayer have no problem with normal x11
>> video. Kaffeine picks x11 automatically while mPlayer needed to be
>> told to use it.
> Video drivers sometimes offer only limited xv ports, which limits the
> number of applications that can simultaneously use the xv extension.

See my previous reply. The problem seems to be that the contrast on xv 
is way too high.

>> Unfortunately vlc's x11 video output, which works fine for the other two
>> players, produces bad output. And there doesn't appear to be a way to
>> reduce the extreme contrast like there was in Kaffeine.
> The application could indeed influence this. However, I see little point
> in working around bugs in proprietary display drivers like this in open
> source applications.
OK, but the fix turned out to just be finding out where in the program 
to tone down the contrast - to its default value (i.e. hitting the reset 
t default values button) in Kaffeine and to its centre value (0) in 
mPlayer. The apparent lack of brightness and contrast controls in vlc is 
strange. Interestingly, once I located and adjusted the contrast in 
mPlayer using xv, vlc's contrast seemed to be fixed as well.

I'm guessing that they're both using the same back-end and that 
mPlayer's controls adjust the contrast. Kaffeine must be using something 

Mark this one closed. Thanks!

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