Speaker/Affiliation: Martin Banks Ph.D. Professo

r Optometry & Psychology University of California Berkeley

When/L

ocation: 1/30/2006 12:00 SEA 4.244

Title of Talk: Why pictures loo

k right when viewed from the wrong place (and sometimes look wrong when vie

wed from the right place)

Abstract: Abstract: Perspective paintings
photographs computer-graphic images and motion pictures can yield a comp

elling sensation of the 3d layout of the depicted scene. If they are viewed
from the correct viewing position (the center of projection) the retinal

image created by the picture is the same as the image that would be created
by the scene itself. But we seldom view a picture from the center of proje

ction. For example the center of projection in a movie theater is in the m

iddle of the room above the audience. Nonetheless viewers sitting too low
and off to the side seem to perceive the depicted 3d layout correctly. We

asked how the visual system accomplishes the perceptual compensation that a

llows robustness to changes in viewing position. Three possible mechanisms

have been described in the literature. Our experiments show that two of the

m do not account for compensation in picture viewing. Rather the visual sys

tem uses a local estimate of surface slant to adjust the retinal image for

the expected foreshortening due to oblique viewing. This method is not geom

etrically correct particularly for wide-angle pictures. We develop a quant

itative model of the compensation process. We also discuss the consequences
of the visual system''s usage of this compensation method for picture comp

osition and the design of pictorial displays such as cinema screens comput

er screens and virtual-reality devices.

Reception with Refreshments
at 11:30 AM