A display device includes a display panel including: a plurality of pixels; and a signal controller which generates, on a frame-by-frame basis, a display signal based on an input image signal and a control signal from an outside. The signal controller includes a memory which stores a preset image signal, a receiver which receives the control signal, a clock signal modulator which generates an internal clock signal having a first frequency during a blank period, which is determined based on the control signal in a frame period, and a data processor which reads the preset image signal from the memory in response to the internal clock signal for an image processing.