[Mr. E. Trane] "It is my understanding that the 4:2:0 color sampling of HDV is a limitation of the MPEG2 encoding process.
MPEG2 is not the limitation -- it can encode 4:2:2. Consider Digital-S, DigiBeta, and DVCPRO50 which all use MPEG2 and are 4:2:2. The limitation is that recording twice the color information like this takes about twice the bandwidth, which takes us over DV's 25 Mbps data rate. As well it is a more intense compression process, so to implement 4:2:2 would require almost double the horsepower for the encoding chips. No small feat for battery-conscious consumer gear.
In the long run, HDV is really trying to address the consumer market, not the pros. As such, it samples color with the same frequency as did the DV format. DV did 4:2:0 for PAL and 4:1:1 for NTSC, and these both equate to the same ratio of one color sample for every four luma samples.
[Mr. E. Trane] "I fail to get to excited about a 3 chip HDV camera if the color sampling doesn’t improve to 4:2:2 along with it."
The thing we gain -- and the thing that makes HDV compelling in the near term to users of low-end pro gear -- is resolution. So it's 4:2:0. If that's your only metric of quality, you're missing the boat. Compare overall just how much more chroma detail we're actually getting in contrast to the 4:2:2 NTSC of today!
- NTSC @ 4:2:2 - Chroma is 360x480= 172800 samples per frame
- HDV 720p @ 4:2:0 - Chroma is 640x360 = 230400 samples per frame, and don't forget this format offers double the framerate to boot!
- HDV 1080p @ 4:2:0 - Chroma is 720x540 = 388800 samples per frame at the same framerate as NTSC. May take awhile for these cameras to appear in the prosumer price range, though.
For most, there is no real need to get bogged down worrying about 4:2:0 vs 4:2:2. We're still advancing by leaps and bounds both in resolution and color.
I'm sure as Steve said, future pro formats will address 4:2:2 recording. But for the moment, especially those of us on a budget or who are used to standard DV, HDV is pretty compelling indeed!
Consider also that if for some reason you're only interested in color quality, then if you divide the resolution on each axis exactly in half, a 720p HDV camera gives you 4:4:4 sampling, with 640x360 progressive video at 60fps. Amazing. And if 1080p cameras ever go mainstream, you'll have 720x540 at 30fps. You'd still have traces of what would then be 4x4 MPEG2 macroblock artifacts in high-motion sequences, but don't miss the fact that it's tons of color resolution for cheap.
-Lorin
