1. An image processing method comprising steps of: dividing an image into a plurality of blocks, each block comprises a plurality of picture elements; sorting the picture elements in each block into a first group consisting of picture elements of densities not lower than a reference density and a second group consisting of picture elements of densities lower than said reference density; obtaining a representative density of picture elements of said first group in each block; obtaining a representative density of picture elements of said second group in each block; effecting an image discrimination in accordance with said representative densities; effecting a determination of threshold value in accordance with said representative densities and result of said image discrimination; said image discrimination and determination of threshold values are conducted by using histograms made out from said representative density of picture elements of said first group in each block and said representative density of picture elements of said second group in each block; and converting image information into binary signals according to said threshold value.