1. An image processing device comprising: a scaling unit configured to enlarge an input image represented by an input image signal to generate an enlarged image represented by an enlarged image signal; a gain calculating unit configured to calculate a gain for enhancing the enlarged image for each target pixel of the enlarged image, respectively, based on the input image signal; and an adding unit configured to add, for each target pixel of the enlarged image, the gain for the target pixel with a pixel value of the target pixel, respectively.