GH2 Upressing 1080 to 4k to key better... And other upressing advantages?

[zombified]

Yeah, uprezzing probably won't help with keying because the color space is still 4:2:0. You have less color samples to work with from the start, so enlarging them just means enlarging some muddy color borders. You'll end up with more pixels that suffer from a poorly defined border area because the interpolation will add some in-between guestimate colors that won't key (at least, any better than they would have originally).

 

[Thomas Smet]

interpolating a image to 4k for the most part is useless and in fact will soften the image. Every time pixels run through a formula the image gets degraded and softens up a tiny bit. By blowing up to 4k and then back down to 1080p one would likely end up with softer images without a single natural pixel left that you shot. Every pixel would be a mathematical guess.

What does help a lot however is chroma interpolation. 4:2:0 when chroma interpolated or chroma smoothed can get much closer to 4:4:4. It isn't perfect of course but typically better then not doing it at all. In fact CS6 in Premiere and After Effects converts all AVCHD footage to 32bit float 4:4:4 on the fly. 5DtoRGB also up-converts 4:2:0 to 4:4:4. The tradeoff of course slightly softer edges.