Abstract: The gap images taken under industrial environment usually have serious loss of visibility and contrast due to low light.To solve the problem,an enhancement algorithm of gap image is proposed based on improved dark channel prior.The algorithm worked by first filtering and inverting an input image and then applied an improved dark channel to estimate the atmospheric light and initial transmission.The guided filter and median filter were used to optimize the initial transmission for smoothing the image and maintaining the edge.The final enhanced image was obtained by the inversion of the enhanced inversion.The experimental results demonstrate that the proposed approach can effectively improve the perceptual quality of low light gap image.