A first signal of a pixel of interest in second image data is generated by adding a plurality of signals that correspond to the same color component in first image data consisting of signals corresponding to a plurality of color components. A second signal of the pixel of interest in the second image data is generated by adding a plurality of signals in the first image data that correspond to different color components. The first signal and the second signal are mixed based on color information of the pixel of interest. Jaggies are effectively ameliorated by replacing the value of the pixel of interest with the mixing result.