Image blur as a pictorial depth cue.

A range of cues are already known to mediate depth perception in pictures and have been exploited by artists in drawings and paintings. Modern images are commonly generated by photographic or video equipment, and these images contain a depth cue that cannot be found in artistic depictions of natural scenes: different image regions are often blurred by different amounts, because of depth of focus limitations. Demonstrations presented here show that this selective image blur also acts as a pictorial depth cue, even when other pictorial cues are removed. Experimental data indicate that the degree of blur at borders between blurred and sharp image regions is used by the visual system to establish the depth ordering of different regions. Selective image blur is thus a potentially useful addition to computer-generated and cartoon images to enhance the impression of depth they convey. It may well also contribute to depth perception in natural retinal images, because the depth of focus of the human eye is limited.