An image brightness adjustment device, comprising an image data processing unit for extracting brightness values of subpixels arranged in a matrix manner in a frame image according to the received image data, wherein each two adjacent subpixels in a frame image form one group, a calculating unit for calculating a difference between brightness values of the two subpixels in at least part of groups and outputting a calculation result, and a comparing unit for comparing the calculation result with a predetermined value Q, a brightness adjusting unit for adjusting the brightness values of the two subpixels in the group if the calculation result is greater than the predetermined value Q, a display data generating unit for generating display data from the image data if the calculation result is smaller than or equal to the predetermined value Q, and generating display data from the adjusted image data if the calculation result is greater than the predetermined value Q.