A method of license plate extraction using a fast pyramid hierarchical hough transformation
Takeshi Agui, Hyung Jin Choi, Masayuki Nakajima · Systems and Computers in Japan · 1988
Abstract Previously, the authors proposed a method of extracting the region of a vehicle number‐plate using the Hough transformation with a restricted parameter plane. The method offers a significant reduction of the amounts of memories and their processing time which are required for storing the parameter plane in a conventional Hough transformation. This paper describes a further improvement of the method in its processing speed. In the processing, first, a pyramid hierarchy is applied to the original image; second, some preliminarily selected straight lines are extracted from the image with a pyramid hierarchy; finally, the region of the original image corresponding to each straight line is obtained. This method restricts the computation of the plane‐region‐distracted Hough transformation into the region of the straight lines already obtained so that calculation points and the processing time are reduced. As an example of application of the method, extraction of license plates is described.