In order to suitably perform image processing on each partial area of an input image, an image processing apparatus divides an input image into a plurality of rectangular images, and performs image processing for each rectangular image. The apparatus stores intermediate information corresponding to each pixel in a rectangular image; performs image processing on pixel data of a rectangular image of interest based on the intermediate information, and generates intermediate information to be used in image processing on pixel data subsequent to the rectangular image of interest; and updates the intermediate information with the generated intermediate information. The apparatus updates the intermediate information based on given update period information that indicates an intermediate information update period.