Is it possible to render red / blue 3d from one image and a depth buffer? To render an image for use with red &amp; blue 3d glasses, the usual way to do it is to render from one point of view, convert it to a single intensity (greyscale) value per pixel, and then put that into the red color channel.  Render from a slightly different point of view, convert that to greyscale again and put that into the blue channel.

This can be prohibitive when rendering a single time is already very costly.

Are there any methods by which you could take a single render, and corresponding depth buffer, and come up with something suitable for both red and blue channels?
Yes, this is essentially the same problem that occours in paralax mapping. What you basically have is a colored height field. That needs to be rendered from a second view.

There are several ways in which you can approach this. You could cheat and just shift pixels by their depth and ignore occlusion. Or you could just render a textured height map as if every pixel would be opaque. Or you could use any of the available paralax mapping methods to eliminate occlusion. 

How well this works depends on the. A scene multiple transparent surfaces wouldnt work very well without some deep map.