This just started happening today.
I did notice that if I apply the same vignette to an existing shot the rings are not there. It only seems to be on BG's that I filled with a solid color. Does that make sense?
A gradation on a solid color will often show rings, particularly if the transition is high contrast. That's just the way the pixels work. The best way to solve that is to add noise (2 or 3% should do it).
It usually depends on the color you pick. Some have a lot more increments then others. I think it's usually the yellow/red/violet areas that have this problem. I think it has something to do with the human eye picking up these color differences better then the other hues.
I don't notice it much with this particular image, but when I do notice it I just add a very very light noise filter (1-2%) and the rings go away.
it is at 32bit. I don't have a 24 bit option only 16 and 32.
In windows 24bit and 32bit are effectively the same thing. Both are 8 bits per channel, but with 32bit they include an alpha channel. It doesn't make any sense why they label it that way.
Unless you have a high end workstation graphics card (such as a Quadro) and a very high end monitor, you can never see anything over 24bit. Even then only a few applications support pushing around images with that color range.
