Abstract: An image is processed by using an error diffusion method of propagating density distribution errors in pixels around a pixel to be noted. A method includes the steps of calculating thresholds (Th.sub.1, Th.sub.2) of densities corresponding to the area ratio between the pixels; selecting a pixel to be noted (f) which are different in the area ratio from each other; calculating errors (E) produced in the peripheral pixels according to the distances from the peripheral pixels to the noted pixel and areas of the individual peripheral pixels; adding the propagated errors to a density of the noted pixel so as to make a rearrangement (f') on the density of the noted pixel; comparing the rearranged density of the noted pixel with the thresholds to obtain a corresponding level (G) represented in a binary form, and obtaining density distribution errors (e).