Coring device, luminance processor using coring device, and methods thereof

A coring device provide with a signal receiving part which receives luminance signals, and a coring part which linearly outputs an output luminance signal by applying a coring slope corresponding to a preset critical luminance level to only an input luminance signal, which is the critical luminance level or more, among the luminance signals. The coring slope means the slope when input luminance signals from the critical luminance level to the maximum input luminance level match with all the range of output luminance level. Accordingly, a gain of a high gradation signal in a high frequency band can be compensated, and the sharpness of the image quality can be improved.