Originally Posted by amirm
. That was one of the point of my original post! You have never had any "source direct" ability for video no matter which device you used. All require at least upsampling to 4:2:2 before transmission on HDMI. So this type of conversion is par for the coarse and not a step down relative to stand-alone products.
Making things interesting, your display is likely upsampling 4:2:2 to 4:4:4 to display it. So you may be OK feeding it that just the same.
I was asked to comment on 4:2:2, 4:2:0 and HDMI.
4:2:2 is upsampled from the 4:2:0 for consumer grade MPEG (DVD, Bluray, cable, satellite). However, if the source device were to upsample in a known way it is possible to precisely extract the 4:2:0 out of a 4:2:2 HDMI connection.
The 4:2:0 Chroma samples are coincident with the vertically "even" Luma samples. So if the source either replicates the samples, or upsamples to generate the in-between samples, but leaves the coincident samples alone, we could precisely extract the 4:2:0 samples from the HDMI stream.
However, since we don't know what the source device is doing we treat the incoming 4:2:2 as 4:2:2 rather than trying to re-extract 4:2:0. If a media server was modiifed to do one of the two things I suggest above, we (Lumagen) could change our scaling to treat the source as true 4:2:0 even though it comes to us as 4:2:2.
I actually suspect that most upsampling from 4:2:0 to 4:2:2 is one of these two cases, but since this is only a guess we do not assume this is true and so do not try to optimize for it.
To have such an optimization, we would need to know this is true, and there would be a manual setting by the user for this, since HDMI has no concept of 4:2:0. And of course a media server company would need to choose to support a special 4:2:2 output mode that allows extracting 4:2:0.
Also note that all current displays upsample to 4:4:4 for display. Since display technology is RGB this must be the case.
Since the human eye is much less sensitive to Chroma than Luma, we do not preceive it as a bad thing that the vertical Chroma upsampling is done in the player and horizontal 4:2:2 to 4:4:4 Chroma upsampling in the TV/projector. We could do a better job upsampling the Chroma with our No-ring (TM) scaling than the player or TV, but it is much less critical than Luma upsampling, so we concentrate on the Luma. We also think upsampling to full (12-bit) 4:4:4 outside the display is not a good idea when one considers that it increases the HDMI clock rate by 50%, verses (12-bit) 4:2:2, which dramatically increases the likelyhood of cable issues for (probably) no visible increase in picture quality.