HDMI YCbCr 4:4:4 or 4:2:2? - AVS Forum
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post #1 of 8 Old 09-09-2005, 12:41 PM - Thread Starter
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I'm a little confused on this topic. It seems from what I've read that YCbCr 4:4:4 has more samplings for the blue/red chroma differentials, but the depth is limited to 8-bit, whereas YCbCr 4:2:2 has fewer samplings, but in turn the depth can achieve 8/10/12-bit.

I'm also under the impression DVDs are encoded YCbCr 4:2:0 at 8-bit.

So for DVD playback, it seems YCbCr 4:4:4 is overkill in the sampling department based on the source material and YCbCr 4:2:2 is overkill in the bit depth department (assuming the connection was able to use 10-bit or 12-bit)

I'm using Panasonic S77 upscaling DVD player over HDMI connection. My display is Sharp LC-45GX6U which is capable of accepting YCbCr 4:4:4 and YCbCr 4:2:2.

I don't have any way of knowing whether the bit depth is 8, 10, or 12 when using YCbCr 4:2:2 (at least I don't see any way to have the information reported)

Any comments? Am I confused how this stuff works? I guess one could say if I can't tell the difference visually then it really doesn't matter whether I choose YCbCr 4:4:4 or YCbCr 4:2:2 (in part due to DVD source being YCbCr 4:2:0 8-bit), but it could be there are some peculiarities I'm not aware of and thus am not actively looking for.

I think my DVD player internally processes at 10-bit.
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post #2 of 8 Old 09-09-2005, 08:36 PM
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? I guess one could say if I can't tell the difference visually then it really doesn't matter whether I choose YCbCr 4:4:4 or YCbCr 4:2:2 (in part due to DVD source being YCbCr 4:2:0 8-bit), but it could be there are some peculiarities I'm not aware of and thus am not actively looking for.
Ding ding ding. We have a winner! If you were able to see a difference you would not see color "banding" or "contours" with 10bit YCbCr with a 10bit display vs 8bit. eg. transitions between the shades of blue in a sky would not be seen. However, this is sometimes hard to determine because the banding is in the source.

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post #3 of 8 Old 09-10-2005, 07:57 AM
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Current domestic digital TV sources such as DVDs, HD and SD digital TV receivers etc., are, AIUI, usually based on 4:2:0 MPEG2 with 8 bit sampling. (*)

Some broadcast production gear will run at both 8 and 10 bit depths, and usually operates at 4:2:2. SDI - the broadcast standard SD interconnect - allows for 10 bit video - and some VTRs (D5 for example) allows for 10 bit recording and replay.

There are various algorithms for dealing with the loss of the 2 LSBs when converting 10 bit to 8 bit. Quantel have a patented algorithm for such situations called Dynamic Rounding (it adds some pseudo random dither to minimise the quantisation banding caused by losing LSBs) which has been licensed to other manufacturers in the past.

I guess HDMI includes 10/12 bit 4:2:2 options to allow it to be used in monitoring applications in broadcast areas as well as in domestic applications, and also to allow for future proofing. (AIUI HDMI's bandwith isn't sufficient for 4:4:4 10 bit, but by subsampling the chroma in the same way broadcast video is usually subsampled, the reduction in samples allows for an increase in bit depth)

(*) US miniDV is based around 4:1:1 at 8 bit I believe, European miniDV is based around 4:2:0 at 8 bit AFAIK - and both use the DV25 codec rather than MPEG2.
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post #4 of 8 Old 09-10-2005, 11:11 AM - Thread Starter
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Thanks for the information. Is it possible the upsampling DVD players have algorithms to smooth out the picture going from 8-bit to 10-bit internal processing? I'm bouncing around in my head any advantage to using 4:2:2 (where there is at least potential to do 10-bit) when the source material is 4:2:0 8-bit. I guess the same question goes for 4:4:4, is it possibly advantageous when the DVD player is spitting out 720p to go with higher sampling of 4:4:4?

I'm trying to put together the "theoretical" advantages of 4:4:4 8-bit vs 4:2:2 8/10/12-bit (or vice versa). I'm also trying to find some visible differences related to these advantages so I can pay attention to them as I change my DVD player and display from 4:4:4 to 4:2:2.
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post #5 of 8 Old 09-10-2005, 12:14 PM
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DVD MPEG decoders upsample the chroma from 4:2:0 to 4:2:2 (8bit). (This is where the infamous Chroma Upsampling Error happened). The Faroudja deinterlacers upsample to 10bit and can output 10bit 4:2:2 (according to Kris). IIRC, the Silicon Image deinterlacers process in 9bit and output 8bit. For your testing you may want to use something like DVE video clips or something else that is known to be mastered as best as is possible. It would also be nice if you knew what the player was outputting too. :)

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post #6 of 8 Old 09-11-2005, 06:11 AM
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Originally Posted by sfhub
Thanks for the information. Is it possible the upsampling DVD players have algorithms to smooth out the picture going from 8-bit to 10-bit internal processing? I'm bouncing around in my head any advantage to using 4:2:2 (where there is at least potential to do 10-bit) when the source material is 4:2:0 8-bit. I guess the same question goes for 4:4:4, is it possibly advantageous when the DVD player is spitting out 720p to go with higher sampling of 4:4:4?

I'm trying to put together the "theoretical" advantages of 4:4:4 8-bit vs 4:2:2 8/10/12-bit (or vice versa). I'm also trying to find some visible differences related to these advantages so I can pay attention to them as I change my DVD player and display from 4:4:4 to 4:2:2.
I suspect it depends on the processing the player or scaler is undertaking.

4:2:0 will usually be converted to 4:2:2 as part of the MPEG2 decode process

Any maths performed inside a processor/scaler etc. to de-interlace, scale etc. is likely to be done at greater than 8 bit accuracy, and so there will be a potential benefit to retaining more LSBs than were present on the source. If you aren't processing the source video then there is no real benefit.

In broadcast video gear it isn't uncommon for 14, 20 or even 32 bit video representation to be used internally, to allow for quality processing without needles quantisation errors being introduced.

4:4:4 interconnection would be a requirement for RGB quality representation of a 4:2:2 YCrCb signal (as the subsampling of chroma-difference signals is more visually acceptable than subsampling of R and B channels as a whole) 4:4:4 YCrCb may be beneficial if the processing algorithm's attempt to upsample the Cr and Cb from 2:2 to 4:4 are any good I guess...
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post #7 of 8 Old 09-11-2005, 09:35 AM - Thread Starter
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Thanks for the info.

So in case it was lost, I'm using Panasonic S77 DVD player which uses Faroudja FLI-2310 processor. I've read it internally processes at 10-bit but I don't believe it upsamples to 4:4:4.

I'm connecting to Sharp LC-45GX6U LCD display. During HDMI negotiations it indicates it can accept YCbCr 4:4:4 and YCbCr 4:2:2.

I'm thinking I might want to change it to 4:2:2 instead of 4:4:4 since the way I'm reading things, with my equipment it shouldn't be worse and there is at least some remote potential (completely unconfirmed) for 10-bit to be transferred over HDMI (where with 4:4:4 there was zero potential)

I think I'll switch for 4:4:4 to 4:2:2 and leave it that way for a while to see if I notice any differences. If someone has objective picture artifacts or other things to pay special attention to, feel free to chime in. I haven't really noticed banding in blue sky area, but I'll look closer with my experimentation.
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post #8 of 8 Old 09-11-2005, 03:53 PM
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Upsampling to 4:4:4 doesn't make much sense, especially when the DVD is 4:2:0. Either sneals said it prior or somebody else did, you have a hard time seeing the difference in larger chroma values as opposed to luminance. If the S77 does output 10bit 4:2:2 and your display processes it, you might see a difference compared to 4:4:4 (if the S77 does it) and 8bit 4:2:2.
Me, I wouldn't waste any time on it, I'd rather spend it watching movies. :)

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