Higher resize resolutions = higher video quality?

[iKlEiTlH]

I've been capturing/encoding videos (mostly cartoons off of VHS source)for a while now and usually follow the format:

capture avi @ 640x480
deinterlace
resize -> 352x240
encode -> divx

I've also done other tests by resizing some vids to be 480x352 instead of the usual 352x240 or 320x240
I was under the impression that the resulting divx files would be of higher quality if I were to resize at a higher resolution...
I've noticed however that 2 videos (same content/source etc) resized to different resolutions (say one is 480x352 other is 352x240) produce end files that are the same file size (bytes).
Also, when I load up both files and watch them both in full-screen, they look pretty much the same...
Does that mean that they produce two files of equal quality (just different resolution)?
If this is the case, I'm just going to forget about resizing to the higher res and go back to making my vids 352x240.
Anyone know enough about video resolution to answer my question?

[mats.hogberg]

Well, what actually counts is bitrate/pixel when it comes to compression, and higher compression results in blockier output. So (in theory) 480x352=168960 px each frame, 352*240=84480 px each frame=exactly 1/2. To acheive the same compression rate (and blockiness), the higher resolution would require the double bitrate. This is "made up for" by the higher resolution, as each pixel will be smaller compared to the full screen when viewed. What looks best is mostly a matter of what's in the movie: If it's a lot of action (much change between each frame=doesn't compress well), it'd be better to lower the res, but if it's not too much action, the higher res may look better.

/Mats

[iKlEiTlH]

Well, the strange thing is that BOTH resulting files (the high and low res ones) seem to have the exact same filesize, as well as overall quality (when I fullscreen them, they SEEM to look pretty much identical).
Am I wrong to believe that both files CAN be of identical quality even though one has a resolution 2x greater than the other?

[Thorn]

Unless you change the target bitrate in the codec, it tries to encode to the same filesize even when the resolution changes.

While you may see a difference if you give higher bitrate to the higher resolution one, I think you may simply be seeing this because it's a cartoon. Cartoons don't have a lot of extremely complex detail, so the differences in quality between the methods may not be large enough to matter. In real-life video you'll see more of a difference between resolutions, because the crispness is higher with higher resolution. Higher resolution with the same bitrate can actually have poorer quality because each pixel has less space to store the information in.

Lastly, don't forget that the source data affects the quality as well. I think you get slightly better quality by capturing at 720x480 regardles of the final size, but that's hard to prove. Having better source such as digital cable rather than analog will make the biggest difference. So even if you improve your encoding techniques and resolution, there may be an upper limit to what you can do without improving the source.

[iKlEiTlH]

Hm...
Thanks for the great input/help. I always wondered why bitrate calculators calculated filesize without taking into account the file's final resolution.
Now I know...
I was also never aware that resizing to a higher resolution while encoding to the same BR as I would with a lower resolution might actually produce a file that's of lower quality than lower res one. It makes sense though through your explanation.
Yeah, I also understand the limits of having a mediocre source for my videos (such as analog cable recorded onto a VHS tape), but that isn't really something I can help for now unless I upgrade to digital cable and get TiVO or something.

Thanks a LOT!!!
I'll be sure to update my processing settings accordingly.