In parallel environment, can VTK remove the background of rendering?

I am trying to using VTK for parallel rendering. The problem is that the background will cause errors during image composition.

For example, I use two processes to render two images (A and B), respectively. When these two images are composited, I found that they have their own backgrounds. These two backgrounds lead to a wrong composited image.So,I wonder if VTK can remove the background of rendering in parallel environment?

I am looking forward to your reply!

we have the same problem.

I look forward to your help to solve this problem

This problem still exists. Does anyone encounter this problem?