Stereopsis is the brainâs creation of a world in three dimensions from two flat images.

But then they gave us two pictures of the same city, each taken by a different camera on the same plane.These had been positioned so that they emulated the angle of sight from two human eyes.

Now when we looked at each picture with each eye separately, the brain created its 3D illusion from the two flat photographs. Some patches seemed to rise up to become easily recognizable as skyscrapers, while others were at ground level like parking lots.
Note that it takes two functional and coordinated eyes to experience 3D. Also consider what happens when the stereopsis process is disturbed, by perhaps a blow to the head or two many beers. We see reality as the transducer portrays it--in double overlapping images; and our judgement of depth is diminished.