there is provided an image processing apparatus employing an error diffusion method capable of preventing a pseudo contour attributable to a delayed dot . the image processing apparatus receives an error diffused from a neighboring pixel and corrects a value of a pixel to be processed before it reduces a tone . then a subtracter calculates an error associated with the tone reduction , which is diffused to a neighboring pixel . herein , only for an input value of no less than 0 . 5 an inversion portion multiplies by − 1 an error from a neighboring pixel and an error to a neighboring pixel . thus a dot can be free of delay to prevent a pseudo contour .