An error diffusion process section performs an error diffusion process on a pixel value of each of processing object pixels and outputs the processed pixel value to an output selection section. A blue noise mask process performs a blue noise mask process on a pixel value of each of processing object pixels and outputs the processed pixel value to the output selection section. The output selection section selects and outputs the pixel value outputted from the error diffusion process section when a segmentation class signal indicates a character (text) area or a halftone dot area, namely an edge area, and selects and outputs the pixel value outputted from the blue noise mask process section when a segmentation class signal indicates an area other than the character area or the halftone dot area, namely non-edge area.