Abstract: An image processing apparatus divides a first image into a plurality of areas based on obtained image data of the first image and sets relationship information between input brightness values with output brightness values for each of the plurality of areas, and converts, based on the relationship information, a brightness value of pixels included in the first image into a brightness value of pixels of a second image whose brightness range is narrower than that of the first image. In the conversion, the apparatus sets, for at least some pixels of the first image, a size of a window for specifying pixels within a predetermined area including the pixels based on environment information in which the second image is observed, and calculates a brightness value in the second image for each of the at least some pixels based on the window.