Stereo Projections: Background, Mathematics, and Use

5. Shading and Shadowing

Objects farther from a light source are not illuminated as brightly as those near it. Similarly, objects that cast shadows provide depth cues to our eyes according to known or inferred relationships between the objects and the light source. Finally, the way the shading along the surface of an object changes tells us something about depth relationships.

Compare the two images to the left – the one on the top without lighting and shading cues; the one on the bottom with them – and notice the effectiveness of these cues. There are two light sources, both near the right edge of the scene. One is at the same height as the spheres, the other is considerably higher up.

The green sphere is brighter which tells us it is closer to the light source than is the red sphere. Note also how the position of the yellow plane with respect to the two spheres (and even its oriention) is much clearer with the shading and shadowing cues.