[mythtv-users] VDPAU picture degradation, possibly since 0.24 to 0.25 switch

Paul Gardiner lists at glidos.net
Sun Aug 19 19:40:36 UTC 2012


For some time now I've felt I was getting worse picture
quality than I used to. It's very subtle so I wasn't sure
if I was imagining it or not, but now I have definite
evidence that my myth frontend is the cause. It seems
to be producing too high a contrast even though all
picture settings are at 50%. It isn't because of confusion
over studio and PC settings. My TV can be set to expect
either, and I see the same problem with TV and Myth set
to studio or with TV and Myth set to PC.

Tonight while watching the news I noticed a strongly
lit skin area that looked wrong in colour. The pink
went to yellow and then to white as the intensity
increased. If you think about it, that's exactly
what you'd expect if the RGB values were being
clipped: for pink, R is strongest then G then B.
First R would become clipped, making the colour
yellow, and then both R and G, making the colour
white.

When I'd noticed that sort of discolouration before,
I'd put it down to the source, but I realised tonight,
that if it was the source, it should be impossible to
adjust it out. That's where I got the evidence that
the problem with the frontend: I found that I could
adjust it out, but only by adjusting Myth's settings,
not by adjusting my TV; it seems the RGB values are
being clipped before getting to my TV, hence it must
be Myth that's doing the clipping.

Has anything changed in the YUV => RGB conversion
for vdpau recently? Or has anybody noticed a problem
with recent nvidia drivers?

Cheers,
	Paul.


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