Abstract: To improve the sharpness of the hazy image，utilizing the prior dark-channel method and the multiscale Retinex (MSR) algorithm，a defogging algorithm based on the prior dark-channel and the theory of Retinex is proposed in this paper.First of all，the prior dark-channel method is applied to dehaze the original image in physically，and the detail of image is thus enhanced.Then，the image obtained is treated as the originated input of the MSR algorithm.After that the contrast and average brightness of the final image are improved.Simulation shows that the contrast of hazy image is increased，the average brightness of image is moderate，and the overall effect is good.Furthermore，the clarity of hazy image can be improved in some extent.

Key words: Retinex algorithm, image enhancement and restoration, histogram, standard deviation, entropy