Abstract: A non-linear gain algorithm for both global and local contrast enhancement of infrared images is proposed,and it is based mainly on the simulated annealing and discrete stationary wavelet transform.Firstly,a histogram-based criterion is introduced,and by which the type of the original image is determined, then followed by the selection of searching direction as well as the initial values of simulated annealing.Secondly,the global contrast enhancement is obtained by optimizing the non-linear gray transform parameters by the simulated annealing.Thirdly,the globally enhanced image is further transformed by the discrete stationary wavelet transform to enhance the local details by a non-linear operator in the high frequency subbands of each decomposition level.The experiments show that the proposed algorithm can both enhance the global contrast of the image and the details of the target within the image.It performs better than the traditional histogram equalization method and the un-sharp mask method in terms of visual quality.