JPS6482181A - Automatic deciding method for binarizing threshold value - Google Patents

Abstract

PURPOSE:To automatically decide the binarizing threshold value with which the edge position of a work can be measured with high accuracy by selecting two mountains out of the larger one or two frequency distributions and defining the density at the midslope point of a descending part toward the bottom of a valley from the dark one of both peaks of said two mountains as the threshold value at the binarization processing. CONSTITUTION:A gradation picture of a work 2 is supplied via an ITV 1 and a processing area is set to obtain a frequency distribution, i.e., the frequency (picture element number) H of the density B in said processing area. Thus the big bright and dark mountains are usually shown when a hole 21 is measured by the reflected illumination. Thus the dark and bright mountains correspond to the hole 21 and the upper surface 23 of the work 2 respectively. Then the density of a point where a level higher than the dark peak is secured and at the same time the primary differential dH/dB is first minimized to the density B of the frequency H is prescribed as the threshold value Btau. As a result, the threshold value of density is obtained in response to an edge even though the chamfering is applied to the work 2. Thus the edge position can be measured with high accuracy by binalization.