I'm using Motion 2.0.1 in 10.4.3 on a G5 Dual 2GHz (rev A) with a Radeon 9800 Pro (AGP4X version) and a Blackmagic Decklink Extreme, and getting very poor render quality manipulating still images.
I'm using a combination of the Basic 3D filter and the Throw behaviour to mimic a kind of rostrum photography look. I find that images with high-frequency detail create a lot of buzzing crawling lines (I'm aware of course of the obvious problems with parallel lines or dot patterns etc; but this is other than that, and the resulting noise is really A LOT) and there are even what look like "drop outs" in the rendered output -- i.e. suddenly a 'block' or 'blocky' spot will appear for one frame or one field. I don't know if what I'm seeing is standard fare for Motion's renderer (is it all handled by openGL?), a possible weak point of the program or of the Basic 3D filter (I never had this poor results with stills in AE) or perhaps due to some voodoo between my Radeon card, my Decklink Card, the G5 etc.
If anyone can suggest a way/place to upload a file I'll clip a small sample of it.
Mmm...no, the fixed resolution thing didn't come in to it; but I did some more tests and I found I got better results when I set anti-aliasing to Best -- infact, it wasn't just an incremental improvement but really a different look, to the way motion handled hi-frequency details and line-crawling. etc. I wonder, is it sort of switching over to a more software-based renderer when you use the "Best" setting? Because it was also accompanied by a huge slowdown in performance, so much that I think one can only really set it when you're ready to render out.