Figure 1: A vertical edge is present at z if |I(z) − I(y)| > |I(z) − I(zi)| and
|I(z)−I(y)| > |I(y)−I(yi)| for all i = 1, 2, 3. The polarity depends on the sign of
I(z) − I(y). Horizontal edges are defined by rotating this scheme by 90 degrees.
are simple binary filters computed on the edge maps. We emphasize that the computational
approach and associated architecture can be implemented with other
families of local features exhibiting similar statistical properties.