F.a.q. comments

StealthTT · Messages: 15 Registration: 08.31.2001

Hello folks, I wanted to keep the F.A.Q. itself short and lean, but please feel free to comment and add here. I'll add anything to the F.A.Q. that's worth it. bb

monterey · Messages: 32 Registration: 03.01.2001

non-square pixels

stiff///M&02 · Messages: 111 Registration: 03.17.2003

@pyropir: Thank you for your post. I'll try to elaborate this stuff. Do you have an example ready? bb

JasonH · Messages: 533 Registration: 06.02.2003

Sorry for the late reply - it took me a while to find the files on my computer ... So, I wanted to capture an old VHS film ('Troublemaker' - a cult film where I come from) using my camcorder. I recorded the film with my Canon Mv4i's analogue in, then captured the DV file to my harddrive, frameserved it to Virtualdub via a one-line avisynth script to make an XviD encode. I didn't know anything much about aspect ratios, I couldn't be bothered because my DVD rips always seemed to look sort of OK. I just cropped the image a little (720x576->694x555), filtered a bit, and used GKnot to get a reasonable bit/(pixel*frame) value, so I decided to resize to 480x400. Well, the result looked very weird because everything was squashed - not surprisingly, since I had transformed a 4:3 film (with non-square pixels) into something with an aspect ratio of 3.6:3 (with square pixels). (screenshot: troublemaker_3.6;3.jpg) I took me quite a while to find out about the square/non-square pixels in PAL and NTSC (the table at is very useful), but as far as I understand it the proper way to do this is to (1) crop the image from 720x576 to 703x576 (because the DV captures an additional 17+5/59 pixels, making it slightly wider than a standard 4:3 image) - at this point we are still dealing with 59:54 non-square pixels (2) then to resize from 703x576 to 703x(576*54/59) = 703x527 [or (703*59/54)x576 = 768x576] which corresponds to 4:3, i.e. we are dealing with square pixels now (3) then to resize to a resolution with multiples of 16, such as 480x352 in my case. Of course (2) and (3) can be done in one step.(attachment: troublemaker_4;3.jpg) All this is with PAL and 4:3. If you have NTSC or 16:9, then the aspect ratios are different: PAL, DAR 4:3 ; pixel aspect ratio: 59:54 PAL, DAR 16:9 ; pixel aspect ratio: 118:81 NTSC, DAR 4:3 pixel aspect ratio: 10:11 NTSC, DAR 16:9 pixel aspect ratio: 40:33 I hope I got this right ? regards, pyropir

:Monty: · Messages: 184 Registration: 03.14.2003

The thread has been extended to contain comments to any of the sticky threads. bb