An image processing apparatus includes a high-frequency component translating unit, a high-frequency component extracting unit, a detail-gain generating unit and an image output unit. The high-frequency component translating unit extracts and translates first high-frequency components of an input image to generate a first image. The high-frequency component extracting unit extracts second high-frequency components to generate a second image. The detail-gain generating unit stores a conversion table and generates detail gains respectively associated with input pixels in the input image according to pixel values of the input pixels and the conversion table. The image output unit calculates a weighted superposition of the first image and the second image and generates a high frequency component of an output image according to the weighted superposition and the detail gains.