Aspect Ratio and compression...still don't understand

[Superturtle]

I'm trying to backup matrix reloaded and yes I know I have another thread but that was just for people to look at image samples I took and comment on them. Out of that thread has come the issue of aspect ratio which I've read about on other threads in Doom forums but am still unsure of.

The matrix has an aspect ratio of 2.35:1 and so where I'm confused is do I somehow want to keep this aspect ratio the same AFTER cropping to maintain the best image quality after encode? And if so where in Gknot do I put this AR? Currently the AR under "Crop (before resize)" is 1.833, would I change that to 2.35 instead and then run the encode?

Or is it impossible to maintain the same AR when encoding to Divx because otherwise the compression wouldn't be possible? This is quite confusing...sorry for the noob questions here.


This all started out from my original thread because I was wanting to remove edge noise in my final encodes and a few people started talking about Aspect Ratio, and that is set in Gknot isn't it...so I'm pretty sure that when I loaded up the d2v file I had ntsc 16:9 anamorphic checked. As I'm looking at the Gknot screen my resolution is showing up as 704x384, is this incorrect for this movie?

Thanks for any help on this.

[DigitAl56K]

The aspect ratio is just the proportion of width to height (after cropping). 2.35:1 means that there are 2.35 pixels across for every 1 pixel down.

So 704 / 384 = 1.833 : 1

AR calculation is pretty simple. You say your movie quotes an AR of 2.35:1. If you want to reduce the height to fit the aspect ratio you would do:

704 / (2.35/1) = 299.574, rounding to the nearest multiple of 16 gives us 704x304 for ~2.35:1 aspect.

Obviously, this has reduced the height of the movie. Its possible to go the other way also: Instead of reducing the height expand the width to match the aspect.

384 * (2.35 / 1) = 902.4, rounding to the nearest multiple of 16 gives us 896x384 for ~2.35:1 aspect.

Hope that helps!

[Justinus]

But if you crop first and then resize later, the AR won't be perfectly 100% as it's intended to be.