For this image instead of relaxing your eyes, cross them slowly. Eventually you will see a cone that is pointed towards you. Try one or the other or both. All of the other cues to depth are called monocular or one-eye. One such cue, the relative motion of objects at different distances, can be a powerful cue to depth but is unavailable to the painter.
Perception of motion requires only one eye and is thus monocular .
The the artist is even more limited than, say, television or movies which use moving pictures. So that you can get some idea how motion can give a powerful sense of depth, here is a computer generated movie of a flight through the Grand Canyon . Even though the picture is low resolution and small, most viewers will report that the depth of the canyon is vivid. It is these depth cues that will be discussed in this tutorial. Before continuing, I should correct the impression that some readers may have that the depth generated on paintings is inferiour.