Hallo > > Agreed, if its sampling at 14.75Mhz no scaling is needed, only a 1 > > pixel padding. > > Oops - slight misunderstanding there. For PAL if it was sampling at > 13.5MHz there would be no need for scaling because the card would be > giving 704 samples/line. At 14.5MHz it is giving 768. In analog to > digital conversion fractional and odd sample counts get rounded up to an > easier to implement (in hardware) multiple of 8 - thus the 702.xxx > gets bumped up to 704. > > Perhaps a little arithmetic will clear things up (and besides, I > feel like improving my typing skills ;)). > > PAL > --- > Square pixel sampling freq: 14.75 MHz > Rectangular (Rec.601) sampling freq: 13.5 MHz > > NTSC > ---- > Square pixel sampling freq: 12 + 3/11 MHz > Rectangular (Rec.601) sampling freq: 13.5 MHz > > Notice anything interesting? The rectangular rates are the same. You are mixing up some things, only a little. You refer to PAL and NTSC. Correct would be PAL/NTSC Colorsystem with the CCIR B/G for the Pal Colorsystem, and CCIR M with the NTSC Colorsystem. I'm soure your NTSC example isn't working for NTSC colorsystem in Argentinia, where they use the CCIR N (which has 25 Frames/s).
> You can look those numbers up in any broadcast TV reference. > > From those numbers the ratio of the rectangular/square pixels is > derived. I'll omit the reduction of common factors - I assume we've > all have basic math skills :-) Now I have a interresting observation. In for CCIR B/G (Which ar mainly used with the PAL Colorsystem) it is defined that every 64us (15625Hz) the ray has to be at the beginning of the next line. And the ray needs 12 (+-0,3) us to get back to the beginning. So we have 64us - 12us = 52us to "draw" the 720 Pixles, which is about 72ns for one pixle. So we need to samplerate of 13,846....MHz to get each pixle. To sample 768 Pixles in 52us, we need a samplerate of 14,76923MHz, or we need to sample every 68ns. So the information from your other link: http://www.uwasa.fi/~f76998/video/conversion/ The row "sampling matrix width in µs" means the time the card needs to sample the amount of pixles. Which is basiacly a TV line and that line should be always 52us, and the row shows us what time the card needs to sample that amount of pixles, anth The line, with a "sampling matrix width" of 53,3us, which is 720x576, the card should sample every 72ns (=13,846MHz) and not every 74ns (or 13,5MHz), to get really every pixle exact. After all I would gess that we have some other timeoffset and errors by the timing circuits and frequency generation. So we have to be happy that we get anything ;) auf hoffentlich bald, Berni the Chaos of Woodquarter Email: [EMAIL PROTECTED] www: http://www.lysator.liu.se/~gz/bernhard ------------------------------------------------------- SF.Net email is sponsored by Shop4tech.com-Lowest price on Blank Media 100pk Sonic DVD-R 4x for only $29 -100pk Sonic DVD+R for only $33 Save 50% off Retail on Ink & Toner - Free Shipping and Free Gift. http://www.shop4tech.com/z/Inkjet_Cartridges/9_108_r285 _______________________________________________ Mjpeg-users mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/mjpeg-users
