Max_Rebo said:
... as for the levels I'm no expert but I'd say you need to reduce the brightness and increase contrast on the capture card settings to try and use the full range of the capture card, this will give much better results than adjusting afterwards with Avisynth.
I've been thinking about this, and concluded that adjustment afterwards in Avisynth is the better option if you're doing a multiple cap average. Will post in the technical forum later when I've got some example screenshots showing what I mean.