Randomized circle detection with isophotes curvature analysis

• An iterative randomized circle detection algorithm is proposed.
• Curvature of isophotes is used to reduce the number of necessary iterations.
• Edges on circumference(s) are selected by a Kernel density estimation strategy.
• Sub-pixel accuracy was maintained on real images even in presence of high noise levels.
• Isophotes analysis reduces the influence of the used edge map on the results.

Circle detection is a critical issue in image analysis and object detection. Although Hough transform based solvers are largely used, randomized approaches, based on the iterative sampling of the edge pixels, are object of research in order to provide solutions less computationally expensive. This work presents a randomized iterative work-flow, which exploits geometrical properties of isophotes in the image to select the most meaningful edge pixels and to classify them in subsets of equal isophote curvature. The analysis of candidate circles is then performed with a kernel density estimation based voting strategy, followed by a refinement algorithm based on linear error compensation. The method has been applied to a set of real images on which it has also been compared with two leading state of the art approaches and Hough transform based solutions. The achieved results show how, discarding up to 57% of unnecessary edge pixels, it is able to accurately detect circles within a limited number of iterations, maintaining a sub-pixel accuracy even in the presence of high level of noise.