Brightness adjusting device and method for dynamically adjusting backlight module brightness

The invention provides a brightness adjusting device, comprising a storage unit, a receiving/processing unit and an output unit. The receiving/processing unit is connected with the storage unit, and the output unit is connected with the receiving/processing unit. The storage unit stores a comparison table, and the comparison table is corresponding to a modulation curve, so as to show the correspondence of backlight opening time scale and reference value. The modulation curve is a Gamma curve, the Gamma curve has a stop-loss point and the slopes of the modulation curve at the two sides of the stop-loss point are not continuous. The receiving/processing unit compares the comparison table with the reference value in image data to obtain the backlight opening scale corresponding to the reference value, and the output unit generates a pulse width modulation signal according to the backlight opening time scale to dynamically adjust the brightness of backlight module. The invention also provides a method used for dy