1. An apparatus correcting the brightness of an image by using a correction curve, the apparatus comprising: an image input unit, receiving an image; a correction gradient selection unit, selecting a gradient of the correction curve corresponding to an object pixel, having the brightness desired to be corrected, of pixels of the image; a correction performance unit, converting original brightness of the object pixel into correction brightness according to the correction curve having the selected gradient; and an image output unit outputting the image allowing the object pixel to have the correction brightness by the correction performance unit; whereas the correction curve increases the contrast of the corresponding correction brightness if the original brightness is the same as or smaller than a predetermined brightness, and the correction curve decreases the contrast of the corresponding correction brightness if the original brightness is larger than a predetermined brightness.