An apparatus and a method that decrease a banding phenomenon in a subsampled image and achieve high image quality are provided. A subsampled image obtained by copying an adjacent pixel value to a pixel value thinning position is accepted as an input image; a correction target signal global gain is calculated as a ratio between a slope of a correction target signal and a slope of a luminance signal of a global region made up of a plurality of consecutive pixels including a pixel position of the correction target pixel of the input image; a luminance local slope is calculated as a slope of the luminance signal of a local region which is a region within the global region, including the pixel position of the correction target pixel of the input image and smaller than the global region; and a corrected pixel value of the correction target pixel is calculated.