Abstract:A comprehensive algorithm that combines direct calculation method and variable step adjustment method, aiming at the disadvantage of traditional autoexposure algorithm that can not realize instantaneity and smoothness simultaneously, was proposed in this paper. The principles of the algorithm were studied and the design process was provided. The time for adjusting the image brightness to the target value can be set unconditionally by modifying the step size parameter, thus it is suitable for various applications. The algorithm is implemented on the CMOS image acquisition platform based on FPGA and the test results prove that the camera using the algorithm can obtain video images with an excellent quality.