In reply to:
Inevitably there will be compression artifacts that will show up, and in my view these may be exacerbated by further processing in the line-doublers in HD sets. On my Time-Warner box, I can choose what it will output and there are discernible differences.
Just to add to what Alan mentioned - the compression used for almost all NTSC video signals is a reduction of the resolution of the chroma (colour) side. Betacam is 4:2:2, meaning for every 2x2 block (a 4 pixel square) of discrete luminance (brightness) values (timed against the video subcarrier), there is only 1 discrete value of chroma. That brings the bandwidth required down from ~31MB/s to ~15.5MB/s. And for a normal NTSC tube, this is a darned good tradeoff.
1 1 2 2 3 3 4 4
1 1 2 2 3 3 4 4
Imagine this as part of your TV line - it has 16 distinct luma values (one on each of the pixels shown by numerals) but every group of 4 only has one colour value (all "same" numbers will have the same chroma value) - so if, say, one of the groups has two pixels from a maroon Texas A&M jersey and two pixels from the green grass, the colour behind all four pixels will be halfway between the two colours.
Problem is, once it hits a line doubler/up-res-er in a HD TV, resolution in the luminance channel is half the subcarrier, and chroma becomes a quarter of the subcarrier... still with me?
Now you have the following:
11 11 22 22
11 11 22 22
11 11 22 22
11 11 22 22
33 33 44 44
33 33 44 44
33 33 44 44
33 33 44 44
Each group of 4 pixels has a single luminance value and the group of 16 with the same number has the same chroma value.
Ouch.
Hope this made sense. I took a few liberties about the line doubling scale so I didn't have to worry about sub-pixel values, and pixels are realy phosphors in the analog domain, but you get the idea.
For those who care - DVCAM is 4:1:1, meaning it's 16 luma values for each chroma which is why, despite what product lit says, it is NOT broadcast quality.
Bren R.
