Billy Biggsposted: > Ok, how about that there tends to be a transition from black to >picture at the beginning and end of every scanline. But ok, I'd like >someone's opinion on this. Should I provide an option to discount them? >Like, is the active picture area 4:3 or should i just let the whole >scanline area be 4:3? You're definitely on the way to convincing me to >rip out my little bias feature. :) OK, here is the spec. The horizontal blanking area is 10.9 microseconds long, counted from the 20 IRE level at the end of the active video line to the 20 IRE level at the start of the active video line. The front porch, or the end of the active video line at 4 IRE, to the leading edge of the horizontal sync pulse, at -20 IRE, is 1.5 usec (+/- 0.1 usec). The horizontal sync pulse is 4.7 usec (+/- 0.1 usec) and the start of the active line, measured from start of the sync pulse to setup (7.5 IRE) is 9.4 usec (+/- 0.1 usec). Of course, a horizontal line is 63.5 usec, give or take a little. Don't look at a local TV station. If you can, find someone who has a C-Band sat system, like me, and work with the color bars they use before feeds, both analog and digital (MPEG-2), to get the best NTSC standard signal possible. If you can capture line 19 and your local station uses the VIR signal, then you can use your local station and capture that line. The spec is referenced from the beginning of the horizontal sync pulse: 12 usec - pulse to chroma reference 24 usec - chroma reference width 12 usec - luminance reference level 12 usec - black level reference level Chroma reference at 70 IRE, burst size 40 IRE Luminance reference at 50 IRE Black level reference at 7.5 IRE Hope this helps. > Poynton in his new book indicates that signals should build to full >amplitude over a few samples, and that does seem to correspond to many >of the stations that I receive. Unfortunately, the book that I have doesn't give the spec for rise and fall times for the start and end of an active line. That is largely determined by the NTSC broadcast bandwidth, or about 4 MHz, because the audio carrier is at 4.5 MHz. MB -- e-mail: vidiot@xxxxxxxxxx /~\ The ASCII [I'm just the one who beat him off... Repelled him] \ / Ribbon Campaign [would perhaps be the better phrase. Spike 2/18/03] X Against Visit - URL: http://vidiot.com/ / \ HTML Email
