PL: Turning a flat image into one that pops out of the surface is all about depth perception. In order to appreciate depth, your brain needs to see two different angles of the same image just as we get with our binocular, two-eyed, vision. So, the main principle of 3D imaging is to send one angle of a picture to your left eye and a different angle of the same scene to the right, which your visual cortex will then put together as an object with depth. That's the theory. The last 169 years have been spent working out how the hell to actually do it.