Try making the room invisible.  Get Z-depth render of the contents. In photo app, select and delete the white background.  Get a Z-depth render of just the room prop.  Overlay first render extract atop the second (room) render.

Just throwing out ideas;  don't know if it will help.

The problem with that is that the room's invisible wall gives the gradation so I can't get any zdepth with it in the render. I'guess it's easier to just place simple planes where the wall would be. It's a pain but at least it gives me a complete map :)