Verifying the 'Consistency' of
Shading Patterns and 3-D Structures
Pawan Sinha and Edward Adelson
Published in Proceedings of the IEEE Workshop on Qualitative
Vision (pp. 71-81)
New York; June 14 (1993)
The problem of interpreting images in terms of their shading and reflectance
components has traditionally been addressed as an early vision task in a simple
2D Mondrian domain. Recently it has been appreciated that in a 3D world, such
conventional approaches are inadequate; more sophisticated strategies are
required. One such strategy has been proposed by Sinha [22, 25], who has
addressed the problem as a mid-level vision task rather than as a purely
low-level one. Sinha suggested that a key computation that needs to be performed
for interpreting images acquired in a 3D domain is the verification of the
consistency of image shading patterns and the likely 3D structure of the scene.
This is the problem we have addressed in the present paper. Considerations of
robustness and generality have prompted us to discard available quantitative
techniques in favor of a qualitative one. The two prime attributes of our
technique are its use of qualitative comparisons of gray-levels instead of their
precise absolute measurements and also its doing away with the need of an exact
pre-specification of the surface reflectance function. We show that this idea
lends itself naturally to a linear-programming solution technique and that
results obtained with some sample images are in conformity with human perception.