A filter processing unit performs a bandpass filter process for a difference between an output pixel value and an input pixel value of an adjacent pixel to a target pixel. An error diffusion unit performs an error diffusion process of a quantization error for output of the filter processing unit. A quantizer performs quantization for a value obtained by the error diffusion process and thereby determines the output pixel value of the target pixel. The bandpass filter process is performed with characteristics different from each other (a) in respective ones of a primary scanning direction and a secondary scanning direction and (b) for respective ones of the component colors of the image. Furthermore, a filter coefficient of the bandpass filter process independently for each component color of an image is corrected for banding reduction with a correction coefficient corresponding to an angle from the primary scanning direction.