On Tue, 10 Jun 2003, Steven M. Schultz wrote: > Hi - > > > From: Selva Nair <[EMAIL PROTECTED]> > > > > Forgot to mention that if this is meant to be 4:3 aspect, you should > > scale to 704x480 and then pad to 720x480. You can avoid vertical scaling > > using 640x480 ---(scale)--> 704x480 ---pad--> 720x480. > > Hmmm, I was told (at one time) to avoid horizontal scaling up and that > it was better to start out bigger and scale down. But perhaps that's > just another bit of advice that wasn't exactly right (wouldn't be > the first time ;))
The general advice is to avoid vertical scaling mainly because vertical scalers should be interlacing-aware -- also for interlaced frames the vertical samples per field is only half as much. For progressive frames it may not matter much, though. In any case, you will get proper aspect ratio only if you scale by the correct SAR value: 10:11 in case of NTSC. So 640x480 --> 704x480 or 720x540 --> 704x480, if you prefer 540. This need to scale in both directions is another reason to keep away from 720x540. For more reasons see Jukka Aho's page at http://www.uwasa.fi/~f76998/video/conversion/ > > Actually since some of the files being created are for DVD menus > a number of tools have presets for dealing with the 'action safe' > and 'title safe' zones of a 720x540 frame. Actually a couple > places say to use 720x534 and scale to 720x480 for creating menus 720x534 makes no sense to me. Apparently, the popularity of 720x540 is because it appears related to both PAL and NTSC by a vertical scaling factor -- scale to 720x480 in one case and 720x576 in the other. But that is a myth. If the idea is to avoid horizontal scaling, one should start with a an odd sized 720x527 frame -- guess what would happen to interlacing and chroma subsmapling with such frames... > and overlays (something about "D1 NTSC" vs "DVD/DV NTSC"). It's > all very confusing ;) Very confusing indeed;) Take a look at Aho's page (the link above), you may find some logic behind all those convoluted and confusing standards. Selva ------------------------------------------------------- This SF.NET email is sponsored by: eBay Great deals on office technology -- on eBay now! Click here: http://adfarm.mediaplex.com/ad/ck/711-11697-6916-5 _______________________________________________ Mjpeg-users mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/mjpeg-users
