A generalized distance transformation of a line pattern with gray values and its applications

The distance transformation of a line pattern (DTLP) is discussed. The DTLP is a transformation of a binary pattern developed for extracting useful features to analyze and recognize a given pictorial data. The basic type (BDTLP) has already been reported; a modification and a generalization of the BDTLP is presented. The modified DTLP (MDTLP) is derived by defining an inhibited edge point among the edge points of an input line pattern. By applying the MDTLP, information on the length of a line pattern is concentrated on the inhibited edge point instead of the center point as in the case of the BDTLP. The generalized DTLP (GDTLP) is a parallel iterative local operation applied to a line pattern with gray values, whose execution is controlled by the BDTLP or the MDTLP performed on another picture plane containing a binarized version of an input line pattern. It enables one to process a line pattern with arbitrary gray values on it as well as a binary pattern. Experimental results are shown concerning the application of the GDTLP to the processing of ridge and ravine lines extracted from a digitized map data. An application of the type II MDTLP to the extraction of information on the loop structure of a line pattern is also presented with illustrative examples.