Upsample 4:2:0 HD to 4:4:4 SD video?
 

I have a basic understanding of chroma subsampling, and I was thinking that if you have the number of pixels in HD sampled at 4:2:0, you could upsample if you reduce the picture size. Granted, there aren't a huge number of situations in my mind where this would be applied, but if I film something in mediocre 4k it should come out as spectacular HD.

Does this work?

I read this 3 times, and still am not sure what you're asking here. :compress:

A 1920x1080 video with 4:2:0 subsampling uses 960x540 chroma planes. These can be downscaled to SD to create a 4:4:4 video with the same resolution across all planes. The same idea applies to 2160p 4:2:0 -> 1080p 4:4:4 (where the chroma is already at the correct size).

This topic is a lot more complex than it seems at first. My memory is hazy but I think the main issue is ensuring that centering is properly accounted for. There are threads on Doom9 that tackle all the intricate details. OP may have already read those as I've seen a few topics in the months since his post.

Thats what I'm talking about. If you have more color at HD, would you be able to take the availible color and make a correct 4:4:4 SD version. I haven't figured it out yet.