Abstract: In order to overcome the limitation of current image enhancement algorithms for non-uniform illumination images, a brightness equalization algorithm is proposed to preserve the detail information in low illumination region and normal illumination region at the same time. The algorithm uses the adjacent frequency and position of pixels to generate illumination filter, so it can effectively separate illumination information and reflection information with details. The illumination threshold is used to divide different illumination areas to compensate for low illumination brightness, so as to balance the image brightness. The experimental results show that compared with the classical naturalness preserved enhancement algorithm (NPEA), the average peak signal to noise ratio of the image increases by 15.4%, the average enhancement degree increases by 245.0%, and the average brightness step difference decreases by 25.4%. The results of the proposed algorithm can maintain the details of different illumination areas while balancing the brightness and obtain a better visual effect.