A method for controlling a display device is disclosed. The method includes receiving an input video image having a plurality of active scan lines, controlling the display device to display a plurality of background scan lines on a first display area with a first scan line frequency, and controlling the display device to display an output image on a second display area with a second scan line frequency. A second aspect ratio of the output image is substantially equal to a first aspect ratio of the input video image. The second scan line frequency is substantially lower than the first scan line frequency.