Abstract: A contrast ratio promotion method for a display device is provided. The display device contains a back light module having a brightness and has a maximum luminance. The contrast ratio promotion method comprises the steps of continuously receiving a picture signal during each unit time, continuously calculating a ratio of a luminance of a picture corresponding to the picture signal to the maximum luminance, where the ratio is defined as an instant relative luminance, setting a first ratio, a first buffer time and a first adjusting time, and gradually reducing the brightness of the back light module to a minimum brightness during the first adjusting time when a first cumulated time for the respective consecutive plural instant relative luminances being smaller than the first ratio is longer than the first buffer time.

Abstract: An adjustment method for a display device is provided. The display device includes a screen, a button and plural display modes including at least a first display mode and a second display mode. The adjustment method comprises steps of pressing the button once to display the first display mode on the screen when the display device is on, waiting for a waiting time when the first mode is desired to be selected, pressing the button again during the waiting time to display the second display mode on the screen when the first mode is not desired to be selected, and waiting for a waiting time when the second mode is desired to be selected.

Abstract: A contrast ratio promotion method for a display device is provided. The display device contains a back light module having a brightness and has a maximum luminance. The contrast ratio promotion method comprises the steps of continuously receiving a picture signal during each unit time, continuously calculating a ratio of a luminance of a picture corresponding to the picture signal to the maximum luminance, where the ratio is defined as an instant relative luminance, setting a first ratio, a first buffer time and a first adjusting time, and gradually reducing the brightness of the back light module to a minimum brightness during the first adjusting time when a first cumulated time for the respective consecutive plural instant relative luminances being smaller than the first ratio is longer than the first buffer time.