[mythtv] [PATCH] Picture Adjust
bjm at lvcm.com
Wed Oct 8 18:17:09 EDT 2003
bobnvic at everestkc.net wrote:
> On Wednesday, October 8, 2003 0:12 am Ben Levitt wrote:
>>This patch lets you adjust the global playback
>>settings for brightness, contrast, saturation
>>("colour") :) , and hue.
> I would certainly love to have this feature, thanks. I think it
> would help me a great deal. I've used xvattr, but it's a little
> cumbersome switching back and forth.
> Do you just adjust it as you watch various shows or do you
> display a color bar test pattern? I've wished I had a test
> pattern to help in setting the color, but I have no idea how I
> would accomplish that. Does anyone do this?
I just plug a DVD player into the s-video of the bttv card and
use the test patterns from "Video Essentials". I've used this
to set the v4l settings so that recordings will look as good as
This brings up a key point. The v4l settings and the Xv settings
are very different things. The v4l setting affect the signal
before the recording and the Xv settings are after the fact.
If, say, the v4l contrast is too high (and btw the default is
way too high) there will be blooming in the signal as it is
recorded. Once the recording has blurred edges, there is nothing
that can be done with the TV or Xv controls to fix it. You can
get the brightness and contrast to about the right range but
the recording is still distorted.
A problem with using a DVD player is that its signal is not
necessarily typical of broadcast stations but does offer some
guidance as to where the blacker than black cutoff should be
and where blooming occurs. Next, no two stations are identical.
For my cable service, I know that I need to raise the black
level a lot for ESPN, ABC and smaller amounts for some others
and raise it for NBC and PBS. Saturation is too high on CBS
and ESPN and too low on several basic cable stations, etc.
MythTV is the only thing I know that allows making adjustments
per station which is one thing that makes it better than the
commercial DVRs I've used.
I do use xvattr and generally need to cut the contrast quite a
bit and lower the brightness a bit to get the best output from
nVidia TV-out. However, once I had these set I've never needed
to muck with them again. I simply set then in a script that
starts mythfrontend. When I do want to tweak the output, I use
the TV controls for minor, temporary adjustments.
Still, it would probably be a good thing to have the Xv settings
in myth. One concern might be that users may not understand
the difference between the v4l settings and the Xv setting and
what they need to do to get the best possible picture.
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