1. A display device comprising: an average picture level (APL) calculator configured to calculate an APL of an input image and output the APL of the input image and an APL curve data; a luminance adjuster including at least two luminance adjusting units, which are enabled in response to a user input through a user interface, the luminance adjuster adjusting the APL curve data; a data modulator configured to modulate data of the input image using a luminance defined in the APL curve data adjusted by the luminance adjuster; and a display panel driving circuit configured to write data from the data modulator on a display panel and reproduce the input image on the display panel.