To enable high-speed error diffusion processing wherein a change of an image is small before and after the processing.

A linearization part 100 removes a characteristic added to input image data to generate linear input image data. An error diffusion processing part 12 performs the error diffusion processing by use of a color value inside a linear color space inputted from a representative color determination part 14. A color space conversion part 102 converts the linear input image data into nonlinear image data. The representative color determination part 14 determines a representative color of a pixel included in the nonlinear image data, and outputs the color value inside the linear color space corresponding to the representative color to the error diffusion processing part 12.