crop/resize

[grrrinnnt]

Hi, I got an anamorphic Pal 16:9 DVD. The Movie's aspect ratio is 2.35:1. I want to frameserve it to VirtualDubMod using Avisynth. Now for the question: Crop before or after resize? (which is faster?)

If the Crop filter is applied before resize: what resolution do i resize to after cropping away all bars? 720x306(minimum ar-error)? 720x304(mod16)?

If the Crop filter is applied after resize: What resolution do i resize to to get the right ar? (720x576 --> 720x??? or ???x576 ?)

[killingspree]

hi,
what you are asking is a rather controversial topic :) i personally always crop before resizing, but i know a couple of people who again do it the other way around.
honestly i do not know exactly which one is faster, but i would not expect a large difference. in gordianknot it is done the same way, so i would say it is a safe bet to crop before resizing.

most important is the resulting ar though! it is definitely desirable (if not required) to end up with a mod 16 ar (even better would be a mod 32 ar)! why? because mpeg codecs (mpeg1,2 and 4) all encode in macroblocks of 16x16 (8x8 pixel blocks). everything below mod 16 would therefore require the codec to use up more bits than actually required.

hth
steVe

[hakko504]

Originally posted by grrrinnnt
Hi, I got an anamorphic Pal 16:9 DVD. The Movie's aspect ratio is 2.35:1. I want to frameserve it to VirtualDubMod using Avisynth. Now for the question: Crop before or after resize? (which is faster?)
Crop before is much faster!
If the Crop filter is applied before resize: what resolution do i resize to after cropping away all bars? 720x306(minimum ar-error)? 720x304(mod16)?
I'd go with mod-16 res. AR errors less than say 1% is not noticeable in my eyes at least. You can always crop a little more than necessary to ensure correct AR
If the Crop filter is applied after resize: What resolution do i resize to to get the right ar? (720x576 --> 720x??? or ???x576 ?) 1024x576 or 720x405 (or better 704x400)

[grrrinnnt]

Thank you, I'll try cropping before resizing to a mod16 resolution then.