1. A method of determining an optimum threshold for converting a video signal of an object into a binary signal, suitable for use in a process for recognizing a pattern on said object, comprising the steps of: storing a pattern expected to exist at one or more positions on a surface of an object as a reference pattern; converting a video signal of an object into a binary image signal on the basis of each of different values of threshold; cutting a plurality of partial patterns out of a predetermined region of said binary image signal corresponding to each value of threshold; detecting the degrees of coincidence each between each of said partial patterns and said reference pattern; and selecting from said different values of threshold a value of threshold for making highest the overall degree of coincidence between said plurality of partial patterns and said reference pattern, on the basis of aid degrees of coincidence detected at each value of threshold, wherein an image of said object is divided into a plurality of sections, the highest value of the degrees of coincidence is selected among the degrees of coincidence between a partial pattern and said reference pattern which are obtained for a plurality of partial patterns included in one section, at all of said sections, and the total sum of the highest values of the degrees of coincidence at all of said sections is used as said overall degree of coincidence.