Parallel Local Operations for a New Distance Transformation of a Line Pattern and Their Applications

The distance transformation of a line pattern (DTLP) is proposed and its properties are studied in detail. DTLP is the transformation of a binary line pattern by which the value at each 1-pixel in an input pattern is changed into the distance measured along a line pattern from that pixel to the furthest edge point (type I DTLP) or to the nearest edge point (type II DTLP). Both types of DTLP are performed by iterative local parallel operations. DTLP is effectively used in the processing of line patterns, such as the elimination or extraction of branches having prespecified features, and the description of the structure of a line pattern. The transformation can also be applied to the texture analysis of line patterns. Several parallel operations for feature extraction related to line patterns based upon the DTLP are given. Experimental results are shown concerning the application of the DTLP to the processing of blood vessel images in chest radiograms and to the texture analysis of photomicrographs of metal pieces. Line pattern analysis based on the DTLP is distinguished from other line pattern processing methods, such as graphical network analysis techniques, in that a two-dimensional line pattern can be processed directly by parallel local operations; and properties based on length as well as topology are effectively used.