An image processing method is performed by a processor. The image processing method includes following operations: generating an average brightness value of each of a plurality windows in image data; generating a pixel ratio value according to the image data; generating a weight value of the each of the windows according to the pixel ratio value, a first brightness weight, and a second brightness weight; generating an adjusted brightness value according to the average brightness values of the windows and the weight values of the windows; and performing an auto exposure process according to the adjusted brightness value to generate final image data. The final image data is for a display panel to display.