Illustration of working principle of the Hough Transform for circles.

(A) Hough accumulator space for a circle (a,b,r) when the radius r is unknown. The scanning circles in the parameter space are on the cone surface in the 3-d space. (B) 5 points on a circle (100, 100, 50). (C) Circles in the Hough accumulator space corresponding to each of the input points in (B). (D) 20 points on a circle (100, 100, 50). (E) Circles in the Hough accumulator space corresponding to each of the input points in (D). The intersecting peak represents the center of the circle we are searching.