Gene Heskett (gene.heskett@xxxxxxxxxxx): > On Wednesday 16 July 2003 23:04, Billy Biggs wrote: > >Vidiot (brown@xxxxxxxxxxxxxxxxxx): > >> > One annoyance with DV for NTSC is that it's 4:1:1 and converting > >> > from 4:1:1 to the 4:2:0 you need for MPEG-1/2 is a pain to do > >> > well. Still, that sort of annoyance is best left to those > >> > seeking ultra-correctness. > >> > >> Not had a problem so far. Unfortunately at this point it has all > >> been done under Windbloze. But, a friend has been playing with > >> Linux tools and as far as I know, hasn't had a problem either. > > > > At some point, someone has to convert from 4:1:1 to 4:2:0. Linux > >tools currently seem to simply duplicate chroma samples horizontally > > and drop vertically, resulting in poorer colour than could be > > achieved with a better filter. Test images to show problems would > > likely have jagged blue or red edges. > > > >> >> BTW, before going to VCD and/or DVD, the NTSC setup level needs > >> >> to be removed. So whatever tool you use, make sure that it can > >> >> remove NTSC setup, as the MPEG-1/2 standard does not use it and > >> >> leaving it in will cause problems. > >> > > >> > What are you talking about here? The Y'CbCr specs for MPEG-1/2 > >> > are the same as for DV. Please clarify. > >> > >> Please read what I wrote. I said that the "NTSC setup" needs to > >> be removed. Most consumer, and even pro-sumer, devices will not > >> remove NTSC setup when fed an analog signal for conversion to DV. > >> The setup is left intact in the DV data. My DVCAM decks are like > >> that. No switch to tell it to remove, or add, setup. It records > >> what you feed it. > > > > Ok I see what you mean. We discussed this before about how to > >properly cut it off. So, let's say I'm trying to get rid of the > > setup. Should I record at like 768x480 and then estimate where the > > setup ends, and then resample the active area with 720 samples ? I > > can't see how to do this though without messing up the aspect ratio > > of the content. > > > You are missing the point Billy. 'Setup' in the NTSC vernacular, > doesn't have a thing to do with the operating resolution, none, nada, > zip. > > Setup is a small step upwards in the black level during active picture > time, and on a scale where peak white=100, should be set to maintain > the videos black level at 7.5% of this 100 IRE peak white when > looking at the waveform monitoring scope. Effectively it makes the > blackest area of the picture into a medium grey since the eye is a > bit logarithmic. > > We've been trying to get the FCC to remove it for about 3 decades now. I keep trying to bring this back to what Vidiot asserted: that when you take a DVCAM recording you should remove setup for MPEG1/2. In both DV and in MPEG2, we deal with quantized Y'CbCr representations of the analog signal. It was always my understanding that a pure luminance signal at 7.5 IRE would map to a quantized luminance value of 16, and any superblack signals would be in the 0-16 range. Regardless, this data semantic of what the levels 'mean' is well defined in these digital specs. Any 'removal of setup' should be strictly in the hardware that takes this digital form and outputs it, or that captures it and provides me with a digital signal, and any MPEG2 file should use 16 as its black level and 235 as its white level and know nothing about the letters I, R or E. :) So, how does this make any sense: > >> >> BTW, before going to VCD and/or DVD, the NTSC setup level needs > >> >> to be removed. So whatever tool you use, make sure that it can > >> >> remove NTSC setup, as the MPEG-1/2 standard does not use it and > >> >> leaving it in will cause problems. -Billy
