Abstract: In order to achieve the maximum of human eye perceived image information, an image enhancement algorithm with objective function was proposed considering human visual system brightness threshold characteristic. Firstly, put forward a method to obtain perceived image under the global grayscale map constraints, and make the mutual information between perceived image and the original image as objective function; Secondly, achieve a global optimum grayscale merger strategy by using dynamic programming algorithm to merge the grayscales which human eye could not distinguish; Finally, adjust the combined grayscale to maximize the objective function. Experimental results demonstrate the proposed algorithm has a good treatment effect, and the proposed objective function is reasonable and effective.