An adjustment amount of a brightness level is determined for each pixel of an image based on the value of each pixel of a luminance distribution image which represents the distribution of luminance of the image. A portion contributing to adjustment of brightness and a portion contributing to adjustment of saturation are determined for each pixel of the image so that the sum thereof is equal to the adjustment amount of the brightness level. Then, an adjustment value of saturation, which is obtained by weighting the value of each pixel in the image based on the portion contributing to saturation, and an adjustment value of brightness, which is obtained by weighting the value of each pixel in the luminance distribution image, which corresponds to each pixel of the image, based on the portion contributing to brightness are added to the value of each pixel of the image.