Tham khảo tài liệu 'robotics handbook of computer vision algorithms in image algebra part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | EARTHWEB HOME SUBSCRIBE FAQ SITEMAP _ SM Need IT. Find IT. Know IT. KEYWORD SEARCH Handbook of Computer Vision Algorithms in Image Algebra by Gerhard X. Ritter Joseph N. Wilson CRC Press CRC Press LLC ISBN 0849326362 Pub Date 05 01 96 Search Tips I Advanced Search PUBLICATION LOOKUP GOI Search this book I Previous Table of Contents Next Title . Generalized Hough Algorithm for Shape Detection JUMP TO TOPIC In this section we show how the Hough algorithm can be generalized to detect non-analytic shapes. A non-analytic shape is one that does not have a representation of the lbrm x. p 0 see Section . The lack of an analytic representation for the shape is compensated for by the use of a lookup table. This lookup table is often referred to as the shape s R-table. We begin our discussion by showing how to construct an R-table for an arbitrary shape. Next we show how the R-table is used in the generalized Hough algorithm. The origin of this technique can be found in Ballard 23 Let s be an arbitrary shape in the domain of the image see Figure . Choose any point C. E off the boundary of s to serve as a reference point for the shape. This reference point will serve to parameterize the shape .S C. E . For any point on the boundary of .S C. E let be the angle of the gradient at x y relative to the xy coordinate axis. The vector from x y to Ọ È can be expressed as a magnitude-direction pair r x y x y where r x y is the distance from x y to C. E and x y is the angle makes with the positive X axis. The R-table is indexed by values of gradient angles i for points on the boundary of .S C. È . For each gradient angle in the R-table there corresponds a set Wi of r magnitude-angle pairs. The pair r is an element of if anc oniy if there exists a point x y on the boundary of .S C. È whose gradient direction is tpi and whose vector rK y has magnitude r and direction . Thus which we will shorten for notational ease to where . Table illustrates the structure
