A image adjustment method applicable to a display includes: defining multiple areas on a display region of the display; obtaining statistics of grayscale of a preliminary image; determining an image type of the preliminary image according to the statistics of grayscale of the preliminary image; generating a Cumulative Distribution Function (CDF) of luminance according to the statistics of grayscale of the preliminary image; individually adjusting a backlight level for each of the areas according to the CDF and the image type of the preliminary image; and generating an output image with each of the areas being individually adjusted.