Patent US 4,959,869

A method for determining a binary coding threshold value for a target object comprises determining reference binarization characteristic values for each reference object, storing the reference values in a memory, selecting the reference value associated with a reference object corresponding to the target object, generating in a learning procedure a histogram corresponding to the selected reference value, extracting feature data, i.e., binarization characteristic values, in a threshold control step from the histogram, and setting the binary coding threshold value to a predetermined weight mean value calculated from the binarization characteristics. 7257