Is the ycbcr output using a rgb conversion?

[pbjr]

Hello,

Is the ycbcr output native or is there a RGB -> ycbcr conversion taking place?

My Pioneer Kuro can handle all video signals and I would like to cut down on the video conversions and keep it as pure as possible.

From what I have read ycbcr 4:2:2 would be the recommended option to watch blurays.

Thank you

[Fairchild7102]

I'm curious about this as well. For Nvidia cards which have a straight HDMI output, does the YCBCR 4:4:4 do pure YCBCR or is it converting from or to RGB at some point.

I know with ATI cards, they do some conversion so it's usually best to just choose RGB.

[AaronP]

I believe all displayed surfaces are RGB, including VDPAU surfaces, so configuring the display for YCbCr will involve another conversion step. Stephen will have to comment on the feasibility of displaying YCbCr surfaces directly without conversion.

[pbjr]

Originally Posted by AaronP

I believe all displayed surfaces are RGB, including VDPAU surfaces, so configuring the display for YCbCr will involve another conversion step. Stephen will have to comment on the feasibility of displaying YCbCr surfaces directly without conversion.

Aaron, thank you for the comments. In that case I will have to stick to RGB for now.

But which one?

Would you happen to know if the VDPAU surfaces are being initially displayed in the RGB 0-255 or the 16-235 colorspace?

I use MythTV and XBMC and they both have options for 16-235 space, but I don't know if that is just another conversion. Can they pull the video directly from VDPAU in 16-235 or are they doing another conversion to achieve the 16-235 from 0-255?

Again, just trying to cut down on all the conversions.

If possible, I am also looking forward to Stephen's comments on displaying YCbCr without conversion. From what I have read it improves video picture quality and would be a big hit with the HTPC crowd. I was reading this article written by madshi and he talks about it here on page 4 http://madshi.net/htpc/page4.html

Thanks again.

[Stephen Warren]

The desktop itself is always RGB 0..255 range. I doubt a native YCbCr desktop is possible under X.

I believe the default VDPAU color-space conversion matrices expand video to PC range (0..255). However, you can use a custom matrix to convert to CE (16..235) range instead if you want. That's probably what the MythTV/XBMC options are doing, so it's all rolled into 1 conversion during YCbCr->RGB post-processing rather than 2 conversions.

[pbjr]

Stephen & Aaron,

It sounds like RGB 16-235 is the way to go for now.

Thank you again,
- Mike

[mojito]

Originally Posted by pbjr

It sounds like RGB 16-235 is the way to go for now.

That would actually result in two conversions.
XBMC defaults to converting YCbCr to full range RGB. If you select limited range RGB in the nvidia driver, it will squeeze the full range RGB from XBMC into limited range RGB.

If you select "VDPAU studio level color conversion" in XBMC, it will use a different conversion matrix when it converts YCbCr to RGB (in that case: limited range RGB). If you would configure the nvidia driver to output at full range RGB you would end up with a single conversion.

At least that was the behaviour before colorspace settings were introduced in the nvidia driver. My TV assumes limited range RGB when it receives an RGB signal. When I configure the nvidia driver to output at full range RGB (and let XBMC do the conversion to limited range RGB) the picture ends up being too bright and I have no idea why (it should be the other way around - the picture should be darker than the picture that is displayed when I select limited range RGB in the nvidia driver)

[pbjr]

Originally Posted by mojito

That would actually result in two conversions.

My TV can handle 0-255. Should I just go with that and not enable any 16-235 options?