can be represented by the following equation equ2 in the first binary digitizing the errors are not stored in the error buffer memory and are therefore not added to the input data fig6 2 shows an example of the weighting coefficients wherein 57 indicates the pixel position undergoing processing and the values in the matrix are larger as they are closer to said pixel position under processing the weighting generator 52 executes respective multiplications of the data a b c l of the error buffer memory 53 with 1 48 3 48 5 48 7 48 shown in fig6 2 and sends the sum of these multiplications to the adder 51 so that the data of the error buffer memory positioned close to the pixel position 57 undergoing processing are given heavier weighting the errors u03b5 ij stored in the error buffer memory 53 represent differences between the correction data x 39 ij obtained in the adder 51 prior to the currently processed data and the binarized output data y ij the corrected data x 39 ij obtained by addition in the adder 51 are then compared with a threshold value t in the binarizing circuit to generate data y ij which are in a binarized state for example y max or y min such as 34 255 34 or 34 0 34 on the other hand a calculator 55 determines the difference between the corrected data x 39 ij and the output data y ij and said difference is stored in a memory position in the.