“If you want improved quality from DV (especially with PAL, which is 4:2:0), you can capture via SDI from a DVCAM deck that has SDI outputs to uncompressed 4:2:2 with a Decklink card. This will help you with compositing and chroma key. ”
But, to clarify, you would have to do that while shooting. Once the signal is on DV tape, it’s 4:1:1 (or 4:2:0), and that’s all you have. You don’t get to magically re-create those missing bits.
-jeff