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

[Andre]

On 10 Nov 2010, at 12:26, James Courtier-Dutton wrote:

> 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'll find a way or find some examples from elsewhere.

For now:
http://en.wikipedia.org/wiki/Colour_cast

They show an orange cast (or tint) caused by incandescent light, the cast I'm talking about shows only in shadows, the well lit parts of the image are fine but shadows are not black or grey, they are slightly purple (magenta) or green instead. If you calibrate the display so that this magenta cast is now black it looks ok for some scenes but others shift to green.

> I am not familiar with the term "colour cast".
> The difference with the two settings is this.

Not all displays are inherently RGB and even when they are the YUV path can be the one that is optimised, always worth trying to see which gives best results.

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

Not really but they are close enough and most people associate YUV with colour difference, I didn't see any point in getting into Y′CbCr and ITU colour space definitions, the point is that the Nvidia conversion seems to have some minor issues and now that YUV out is available maybe it's worth trying both modes. 

Andre

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