[mythtv-users] Need help trying to nail down some picture quality issues

Bruce Markey bjm at lvcm.com
Wed Aug 25 18:35:46 EDT 2004

DTR wrote:
> I'm having some picture quality issues.  Watching the olympics, when I 
> see a shot of the track with the white lane lines running diagonally 
> across the screen, the lines seem to shimmer and squirm around.
> I've looked thru the archives and closest I've found is mention of 
> jaggies... it's not so much the jagged edge that bothers me as how they 
> kind of dance around.  I'm not sure if this is the sort of artifact 
> people are referring to when they say "jaggies".
> I've tried running kerneldeint and denoise3d with default parameters 
> which didn't seem to make a difference.
> Here is my info:
> PVR250
> MX-440 TV out
> recording at 720x480
> kerneldeint, denoise3d
> xvmc disabled

Try this. If you are using the nvidia 4363 driver, set

        Driver          "nvidia"
        Option          "TVOverScan" "0.979"

in your XF86Config-4 file and set the display size to 640x480
then restart X. If you are using 6111, still set the size to
640x489 and run nvidia-settings and set TVOverScan to "250".
This will probably be too big for your TV screen and push stuff
off the edge but these settings will do a better job if lining
up the scanlines in the recording with the scanlines on the TV
This should correct most of the jagged edges of the diagonal
white lines. It should also significantly reduce (but not
eliminate) interlace artifacts.

As for the shimmering, if you press Pause then right arrow
you will step through frames one at a time, you will see that
the white line has a rainbow of colors around the edges. Each
frame has a different combination of colors. Played at normal
speed, it looks white but shimmering. The kerneldeint filter
actually seems to exaggerate this effect. Even though I'm the
fool ;-) who wrote in the docs that kerneldeint and denoise3d
are a good choice for good deinterlace and noise reduction,
I now use the alignment trick above and longer use kerneldeint.
This reduces the shimmer a lot. I also use "quickdnr=0:20" in
place of denoise3d. This uses a little less CPU and the args
are geared to dampen small variations in color.

With these settings I've almost forgotten that I'd had this
annoying shimmer in the past ;-).

--  bjm

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