Abstract: Due to the complexity of tunnel structure and environment,strong interference exists in the detection environment of tunnel cracks,such as concrete mud,dirt,water seepage area,etc..This results in low contrast between background and small cracks.Therefore,it is easy to miss cracks by using conventional morphological methods.In order to solve this problem,this paper proposed a crack detection method based on fractional Fourier transform.In this me-thod,the image is mapped to different time-frequency domains by different order fractional Fourier transform,which is helpful to extract the filth feature in the crack image.The background contrast of the image is balanced by compensating the filth region with the background information.The fractional differential method is used to enhance the image and the connected domain method is used to extract the cracks.Experimental results show that the proposed method can effectively remove the filth region and detect tunnel cracks with low contrast.

Key words: Crack detection, Fractional fourier transform, Image enhance, Low-contrast