1. An image processing apparatus, comprising: a high-frequency component translating unit configured to extract and translate a plurality of first high-frequency components of an input image to generate a first image; a high-frequency component extracting unit configured to extract a plurality of second high-frequency components of the input image to generate a second image; a detail-gain generating unit configured to store a conversion table and generate a plurality of detail gains respectively associated with a plurality of input pixels in the input image according to the conversion table and pixel values of the input pixels; and an image output unit configured to calculate a weighted superposition of the first image and the second image and to generate a high-frequency component of an output image according to the detail gains and the weighted superposition.