A display device includes a display panel including first, second, and third color sub-pixels, a data driver, a scan driver, a power supply to provide a power supply voltage to the display panel, and a controller. The controller includes a pure color index calculator to calculate first through third pure color indexes of first through third sub-pixel data, a pure color index histogram generator to generate first through third high pure color index histograms, and first through third low pure color index histograms, a histogram analyzer to determine first through third effective maximum gray levels for the first through third color sub-pixels according to the first through third high pure color index histograms and the first through third low pure color index histograms, and a power supply voltage controller to determine a voltage level of the power supply voltage according to the first through third effective maximum gray levels.