Aspect Ratio and mod16 rule question

Tiiscool · Post by **Tiiscool** » Fri Jul 06, 2007 4:33 am

Hello,

It seems that Aspect Ratio is one of the most difficult topics

I am a little confused about the numbers I read in EADFAG:

Background:
Footage (DVD) -> add Pictures -> Editing -> Resizing for Encoding

Footage: has TV PAR, looks squetched, "not square pixel"
Pictures: has to get the same squetching like the footage, so it gets first PAR 1 and then it is resized to TV PAR
Resizing for Encoding: Sometimes we want PAR 1, so the video is resized to PAR 1, but because of mod16 we have to "adjust" it a little
mod16: this means that mpeg2 saves the data in 16 x 16 blocks, and so horizontally and vertically it has to be a multiple of 16.

Footage (TV PAR) -> Picture make (PAR 1) resize to (TV PAR) -> editing -> resizing whole video to (PAR 1) with mod16

Here are the numbers in EADFAG:
Resizing the picture: PAR 1 to TV PAR:
PAL (16:9): 1024x576 (PAR 1) to 720x576 (TV PAR)
NTSC (16:9): 848x480 (PAR 1?) to 720x480 (TV PAR)

Explanation PAL:
720 x 576,
576 * 16/9 = 1024
Because 1024 is 16 * 64, we do not need to adjust it.

So for NTSC, this is my opinion:
Pictures:
720 x480, 480 *16/9 = 853,33
The Pictures get the same squitchiness like the footage.
I think that here the mod16 rule is not necessary??

Footage Resizing:
But 853,33 is not a multiple of 16, we have to adjust it.
So we get: 848 x 480

When this is right, (I am still a noob) it would be nice to have two resizing explanation: one for pictures and one for the video.

Best regards,
Ti

Keeper of Hellfire · Post by **Keeper of Hellfire** » Fri Jul 06, 2007 12:38 pm

Simply said - if you draw your picture, make it the correct AR for square pixels, so 640x480 for 4:3. For 16:9, it doesn't matter much if you make it 853x480 or 848x480, since it's less than 1% difference. No one will note it. Make it how you like it. Before exporting the picture, resize it to 720 x 480.

Keeper of Hellfire · Post by **Keeper of Hellfire** » Fri Jul 06, 2007 12:42 pm

Damn missing edit button: If you wanna store the picture unresized too, check the possible restrictions of the file format. Maybe it needs multiples of a certain number too.

Tiiscool · Post by **Tiiscool** » Fri Jul 06, 2007 1:16 pm

Hello,

@Keeper of Hellfire, thanks for your answer.

Keeper of Hellfire wrote:Simply said - if you draw your picture, make it the correct AR for square pixels, so 640x480 for 4:3. For 16:9, it doesn't matter much if you make it 853x480 or 848x480, since it's less than 1% difference. No one will note it. Make it how you like it. Before exporting the picture, resize it to 720 x 480.

Of course you are right. It is only a little different.

I still have the view of a noob, and becaue the topic aspect ratio is really difficult, I think it should not be confusing.

First I thought I did understand it, then I was wondering about this number 848. EADFAG is really great, special for people who do not now anything about video. (I love it) So when we have parts which are confusing, we should try to get them easy.

Best regards,
Ti