Edge Halo when compositing

[cprettyman]

I'm sure there is an easy fix to this, but I can't seem to find the right terms when searching, and its making me feel dumb.

This is from a sample scene that is part of a series of tutorials we're developing in house - this one is about alpha, and compositing - and its basically an argument for using file formats that support an alpha channel - but I need to show some people how to do this with jpg. DSo, I rendered out the image, and an Alpha render element, both to jpg,a nd brought them into composite and composited in a new background.

My initial render looks fine - but some objects, most noticeably the tree branches and leaves have a nasty halo around them. It seems to me like an issue with AA, and playing with sampling settings, and which filter I use affects it, but nothing seems to eliminate it.

What am I missing?

(Note: the image I am attaching is zoomed way, way in)

[Steve_Curley]

No image - please read this post for help with attachments.

[cprettyman]

Thanks - it was that preview thing. That's annoying. I edited the initial post, so you should see it now.

[Steve_Curley]

Check your Alpha channel carefully - if it's Anti-Aliased then you'll get that "halo" effect. It needs to be sharp (no AA) and follow the image exactly. Also make sure it's full black and full white - nothing else or you'll get semi-transparency.