The Hough transform is a feature extraction technique used in image analysis, computer vision, pattern recognition, and digital image processing. The purpose of the technique is to find imperfect instances of objects within a certain class of shapes by a voting procedure. This voting procedure is carried out in a parameter space, from which object candidates are obtained as local maxima in a so-called accumulator space that is explicitly constructed by the algorithm for computing the Hough transform. Mathematically it is simply the Radon transform in the plane, known since at least 1917, but the Hough transform refers to its use in image analysis.