The crack edge enhancement of straddle-type monorail track beam surface based on non-subsampled contourlet transform

This article introduces a new algorithm of crack edge enhancement of straddle-type monorail track beam surface based on non-subsampled contourlet transform (NSCT). According to the characteristics that the low frequency can be retained and mid-frequency can be enhanced by fractional differential approach non-linearly, a new enhancement method that the smooth subband of NSCT domain can be enhanced by fractional differentiation has been proposed; while in the high-frequency subbands of NSCT domain, each pixel of high-frequency subband is divided into strong edge, weak edge and noise on the basis of direction sensitivity characteristics, then the weak edge can be enhanced non-linearly, strong edge be retained, and noise be removed by a new constructed non-linear function. Experimental results show that the method proposed in this paper has greatly improved visual effects and larger contrast improvement index (CII) as compared with other enhancement methods, and the enhancement effect is very good.