A display device, comprising: a display panel comprising a pixel connected to a gate line (G1-Gn) and a data line (D1-Dm); a data driver connected to the data line (D1-Dm) to apply a data voltage; a gate driver connected to the gate line (G1-Gn) to sequentially apply a gate-on voltage (Von); and a signal controller configured to determine image data as corresponding to one of a motion picture, a still image, and a text screen, wherein the signal controller is further configured to drive the display panel, the data driver, and the gate driver at a driving frequency being one of a motion picture frequency for displaying the motion picture, a still image frequency lower than the motion picture frequency for displaying the still image, and an ultra-low frequency of about 10 Hz or less for displaying the text screen, wherein the ultra-low frequency is lower than the still image frequency; wherein the signal controller is configured to receive an externally generated panel self-refresh signal to determine whether the image data corresponds to one of the motion picture and the still image; characterized in that the signal controller comprises a driving condition setting unit comprising: a histogram checking unit configured to determine whether the image data corresponds to the text screen or not by dividing pixels of one frame of the image data into one of a low gray region, a medium gray region, and a high gray region based on gray levels of the pixels, and determining whether a ratio of a number of pixels within the low gray region and the high gray region to a total number of pixels exceeds a predetermined ratio; a gray checking unit configured to determine whether the image data corresponds to the text screen or not by determining whether a number of pixels having dominant gray levels within the pixels of one frame exceeds a predetermined number, a dominant gray level being defined as a gray level occurring a specific number of times or more in the one frame; a combining unit configured to receive outputs of the histogram checking unit and the gray checking unit and to perform thereon one of an AND operation and an OR operation to generate a combined output; a frequency selection unit configured to select the ultra-low frequency as the driving frequency if the combined output of the combining unit indicates that the image data corresponds to the text screen, and to otherwise change the driving frequency based on a value of a main gray level received from the gray checking unit, the main gray level being the gray level occurring the most number of times in the one frame; and a register selection unit configured to select a register value according to the selected driving frequency. a display panel comprising a pixel connected to a gate line (G1-Gn) and a data line (D1-Dm); a data driver connected to the data line (D1-Dm) to apply a data voltage; a gate driver connected to the gate line (G1-Gn) to sequentially apply a gate-on voltage (Von); and a signal controller configured to determine image data as corresponding to one of a motion picture, a still image, and a text screen, wherein the signal controller is further configured to drive the display panel, the data driver, and the gate driver at a driving frequency being one of a motion picture frequency for displaying the motion picture, a still image frequency lower than the motion picture frequency for displaying the still image, and an ultra-low frequency of about 10 Hz or less for displaying the text screen, wherein the ultra-low frequency is lower than the still image frequency; wherein the signal controller is configured to receive an externally generated panel self-refresh signal to determine whether the image data corresponds to one of the motion picture and the still image; a histogram checking unit configured to determine whether the image data corresponds to the text screen or not by dividing pixels of one frame of the image data into one of a low gray region, a medium gray region, and a high gray region based on gray levels of the pixels, and determining whether a ratio of a number of pixels within the low gray region and the high gray region to a total number of pixels exceeds a predetermined ratio; a gray checking unit configured to determine whether the image data corresponds to the text screen or not by determining whether a number of pixels having dominant gray levels within the pixels of one frame exceeds a predetermined number, a dominant gray level being defined as a gray level occurring a specific number of times or more in the one frame; a combining unit configured to receive outputs of the histogram checking unit and the gray checking unit and to perform thereon one of an AND operation and an OR operation to generate a combined output; a frequency selection unit configured to select the ultra-low frequency as the driving frequency if the combined output of the combining unit indicates that the image data corresponds to the text screen, and to otherwise change the driving frequency based on a value of a main gray level received from the gray checking unit, the main gray level being the gray level occurring the most number of times in the one frame; and a register selection unit configured to select a register value according to the selected driving frequency.