
A Mathematical Theory of Primal Sketch and Sketchability
Speaker: Ying Nian Wu
UCLA Department of Statistics
Time: Friday 28 March 10:1511:00 am
Place: N014 DIKU
Abstract
Walking in Copenhagen in the early Spring and looking at the trees, we can
easily notice a scaling phenomenon. For the trees far from us, the twigs,
branches only give us a texture impression, and they are nonsketchable.
But for the trees close to us, we can notice the individual branches and
twigs, and they become sketchable. While the change of the retina image
with distance can be accounted by continuous scalespace theory, our
perception in V1 experiences a quantum jump between sketchable and
nonsketchable. This sketchability phenomenon is ubiquitous in natural
scenes.
In this talk, I will present a mathematical theory for Marr's primal
sketch. The central piece of the theory is a primal sketch model, where
the sketchable part of the image is represented by the constructive scheme
of sparse coding, whereas the nonsketchable part of the image is
represented by the restrictive scheme of Markov random field. The theory
reveals the two complexity regimes for the two classes of patterns and
modeling schemes, and suggests the role of V1 cells as both linear filters
without lateral inhibition and linear bases with lateral inhibition. A
large number of natural images can be modeled by our theory.
Based on joint work with C. Guo and S. C. Zhu.

Peter Johansen, Professor
DIKU, Universitetsparken 1,
2100 Copenhagen, Denmark
http://www.diku.dk/users/peterjo/
