Blur 'stepping' issue, any ideas?
 

I have a few shots that have an 'ok' color/light range. I'm doing a 'post production selective focus' by bluring one actor. The issue I'm getting is I'm getting fairly bad stepping in some areas instead of nice smooth 'gradients between colors'. I've tried using Motion and Combustion and having the same issues.

To help clarify, I'm getting chunks of color (look below, generic example) instead of smooth transitions. The original footage is not stellar but does not have any stepping (shot HDV, editing in ProResHQ), and i'm only getting it where there are larger areas of a single color. Any idea what specifically is the culprit or how to fix this?

Thanks

One time I did a smooth gradient over an animation in after effects. It looked pretty bad as you were just describing, and even caused more artifacting or compression blocks than usual. I was exporting with the animation codec, so the quality should have been near perfect. Because of this I decided that there is absolutely no way to get a smooth gradient. I think you can still use gradients it just depends on how, and you have to be more careful.

You might want to try rendering in 32bit to see if that helps, but I don't know how in Motion.