
According to this invention, in image data A and B which are respectively constituted by pixel groups .SIGMA.A.sub.ij and .SIGMA.B.sub.ij consisting of N pixels A.sub.ij and B.sub.ij (N is a positive integer; i and j respectively indicate a row position and a column position), and in which density data A.sub.dij and B.sub.dij of the pixels are expressed by n(2m)-bit data (n and m are positive integers), designated 2m-bit portion a.sub.ij of each density data A.sub.dij of image data A is divided ...











