METHOD AND DEVICE FOR FORMING IMAGE AND RECORDING MEDIUM

PROBLEM TO BE SOLVED: To reduce the capacity for storing a threshold conventionally required for expressing an input image signal with a lot of gradations through a dither method. SOLUTION: A threshold matrix 91 is composed of four sub matrixes of respective two longitudinal and lateral sub matrixes, each sub threshold matrix is composed of 16 cells of respective four longitudinal and lateral cells and a minimum threshold 95, maximum threshold 97 and threshold correction value 99 are set. When an image signal is inputted, concerning the cell having the minimum threshold 95 lower than the density shown by the input signal and the maximum threshold 97 higher than the density shown by the input signal, corresponding to the density shown by the input signal and the threshold correction value 99, any suitable gradation is calculated from the number of gradation ('4' in this case) expressible with such a cell. Thus, since the number of gradation for each cell can be changed without increasing the number of thresholds or the like to be stored for each cell, the capacity for storing the threshold or the like is not pressured.