Using an image from a projector as a studio background

[NigelD]

I'm thinking of using an image from a projector to create a back/floor drop for a scene I want to create. How would you do this for best effect. Not having experience of using such a technique I have no idea of the pitfalls and problems. Any help appreciated please!

[oleleclos]

The problem you'll encounter is mainly with the lights for your foreground washing out your background, which after all has to be highly reflective in order to reflect your projected image.

There are various techniques to avoid or minimise this, and broadly speaking they consist of 1) optimising the reflection of the background and 2) shielding it from the the foreground lighting.

In commercial photography (at least back in the stone age when I did it) the first objective is often achieved by using a front projector and a highly directionally reflective screen. The front projector will line up with the camera axis, with the picture being projected by a semi-reflective mirror through which the camera sees the scene. The result is that nearly all the light from the background comes back to the camera and other light doesn't because it's reflected in other directions.

Front projection with a simpler setup is not going to be easy, especially if you also want to project on the floor which will be difficult to screen from the foreground light. So maybe blue (or green) screening and adding your background in post production would work better for you?

[NigelD]

Thanks Ole, I had thought of green screen - the subject will be difficult to isolate from the projected light. I had also thought about the possibility of projecting the background I want through a white curtain or something similar but that in itself will contribute to the background being washed out I think.

[oleleclos]

Yes, rear projection requires complete shielding of foreground lights from the background screen and also takes up a huge amount of space because the projector has to be quite a way behind the screen for even illumination. There were some systems using a translucent screen that was not white when seen from the front, a bit like the rear projection TVs of yore. That helped a little, but they weren't really worth the trouble if you ask me. And of course the technique can't be used for the floor.