[mythtv-users] Nvidia 260 yuv gives better image quality

James Courtier-Dutton james.dutton at gmail.com
Wed Nov 10 12:26:59 UTC 2010


On 8 November 2010 15:35, Andre <mythtv-list at dinkum.org.uk> wrote:
> I recently upgraded my frontend to mythbuntu 10.10 to get GT220 HDMi audio working (upgraded alsa on 10.04 was giving grief) and as a consequence got Nvidia 260.19.06.
>
> Big improvement for me, Nvidia settings now has an RGB/YUV setting and this is resolved a nagging problem I had with vdpau. Previously in shadows and dark scenes there is a colour cast which varies from recording to recording in it's colour and severity, the display (a DLP projector) is calibrated to reduce this but it varies so still shows up some of the time. Set display mode to YUV and immediately shadows are as they should be, detail in shadows is clear and the correct colour :-))
>
> I've flipped this back and forth a few times, calibrated the projector in each mode and consistently in RGB there's a cast, in YUV it's gone. I've been running this for a couple of weeks and it seems to be always good.
>

Hi,

Are you able to post a link to a picture demonstrating the difference.
I am not familiar with the term "colour cast".
The difference with the two settings is this.

YUV over HDMI
DVB in YUV format -> decoder in software (YUV) -> graphics card (YUV)
-> HDMI (YUV) -> Display device(RGB)
So the conversion from YUV to RGB happens in the display device.

RGB over HDMI
DVB in YUV format -> decoder in software (YUV) -> graphics card (YUV)
-> HDMI (RGB) -> Display device(RGB)
So the conversion from YUV to RGB happens in the graphics card.

There is a third option, but unlikely to be used because it is slow.
RGB over HDMI
DVB in YUV format -> decoder in software (YUV->RGB) -> graphics card
(RGB) -> HDMI (RGB) -> Display device(RGB)
Conversion from YUV to RGB happens in software running on the central
CPU so is slow.

Comparison
YUV over HDMI is good for video reproduction, but less good for use as
a PC display for Desktop use or Games  due to the lower resolution in
the UV components.

RGB over HDMI is good for video reproduction (if the conversion from
YUV to RGB is done well) and also good for use as a PC display for
Desktop use and Games due to the resolution being the same for all Y,
U, V components.

When displaying MPEG video on a display device, a conversion between
YUV and RGB is required as some point.
The conversion is CPU intensive so many implementations take short
cuts and the result is artifacts.

Note: YUV and RGB might not be the exact correct terms to use, but I
used them to be consistent with the original poster.


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