Aha, the dreaded HVX noise problem rears its head at last. Currently I've been hired to fix some truly awful greenscreen keys that came from HVX200 footage. I've shot greenscreen on the HVX myself, and it's been more than fine, so obviously there's something wrong with the footage to start. Anyway, after quite a bit of effort, I've been able to get decent keys. The problem is that Keylight (or some part of the process) is noticeably amplifying the image noise! The gray areas after keying are just dancing pixel nightmares. I can't explain this. My mattes are perfectly opaque in foreground elements, and I'm applying no compression to the renders. It appears in RAM previews as well. Any ideas?

use primatte, i pulled much better keys from an hvx200 with it

ALSO, YOU MUST MUST MUST USE GARBAGE MATTES!!!! ABSOLUTELY ESSENTIAL!

Yes, garbage mattes (via procedural keys or manual roto) are critical.

Also, you can use keylight to simply derive the matte, then apply the result as a mask to ensure that you bypass any color processing on the clip itself.

It's not so much the HVX footage. Keylight defaults to using the Softlight method for Screen Matte/Replace Method, and that's where the noise in dark areas comes from. I've had this happen with F900 footage, shows up on dark fabric and in shadows.

Reset this to Hard Light or Source and see if the noise goes away!

Ditto on the hard/soft light suggestion.

Also, the try changing the color-replacement color. It defaults to gray, I think: change that to a closer match to the new backgound color that you're comping over.

If nothing else works, switch to the "intermediate" View setting instead of "final result." That shuts off Keylight's color correction, and you then can use the basic spill supressor or other trick of your choice.

Also, if you've never seen this:

http://www.thefoundry.co.uk/FoundryFileServer/Keylight1.2v8_AECS3.pdf