
 Figure 1: Edge cooccurrences (A) An example image with the list of extracted edges overlaid. Each edge is represented by a red line segment which represents its position (center of segment), orientation, and scale (length of segment). We controlled the quality of the reconstruction from the edge information such that the residual energy was less than 5%. (B) The relationship between a reference edge "A" and another edge "B" can be quantified in terms of the difference between their orientations $\theta$, ratio of scale $\sigma$, distance $d$ between their centers, and difference of azimuth (angular location) $\phi$. Additionally, we define $\psi=\phi  \theta/2$, which is symmetric with respect to the choice of the reference edge; in particular, $\psi=0$ for cocircular edges. % (see text). As in~\citet{Geisler01}, edges outside a central circular mask are discarded in the computation of the statistics to avoid artifacts. (Image credit:Andrew Shiva, Creative Commons AttributionShare Alike 3.0 Unported license).
 