I'm looking to create the effect of sliding a window across my scene and to have everything in that window rendered black & white. (Everything outside the window will still render via color channels).
I've considered multiple layers, multiple cameras and using a glassy material, and have tried the last of these directly. (It didn't have the desired effect).
I imagine the solution could be one of a few things: maybe rendering a black and white camera at the same time as rendering a color channel camera and later splicing the scenes together in editor?; or maybe slowly switching from one scene to another (as if a panel effect)?
My thanks in advance for any tips!