Browse Prior Art Database

Digital Contour Following

IP.com Disclosure Number: IPCOM000083426D
Original Publication Date: 1975-May-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Crawford, JL: AUTHOR [+2]

Abstract

A contour follower records the position of successive points on the edges of a stored pattern. Given one such point, the following method provides an efficient search method for finding the next point.

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Digital Contour Following

A contour follower records the position of successive points on the edges of a stored pattern. Given one such point, the following method provides an efficient search method for finding the next point.

Fig. 1 shows the storage of a raster-scanned pattern. The pattern is scanned horizontally from left to right, and the scan lines 10 proceed from top to bottom. Every scan line has W picture elements stored at successively increasing addresses, successive scans being stored contiguously. Dashed line 11 represents an edge between a white area to the left and a black area to the right of edge 11.

The box marked C represents a current point on edge 11, arrived at from above. The boxed numbers 0-7 represent indices J of the eight neighbors of point C, labelled in clockwise sequence. For W elements per scan line, the displacement of each neighbor from the address of the current point C is as follows: Index 0 1 2 3 4 5 6 7 Displacement D(J) -1 - W-1 -W -W+1 +1 +W+1 +W +W-1.

Fig. 2 shows an efficient method 20 for finding successive edge points. Starting from line 21, block 22 initializes the beginning storage address A and neighbor index J to arbitrary values. Block 23 then determines whether the point at address A is an edge point of the pattern. If it is, block 24 records the address as the address A(c) of the current point C, and block 25 determines whether that point is the last point, i.e., whether the contour has been closed. If so, the method terminates on line 26.

For all nonterminal points in the con...