A Piecewise Nonlinear Enhancement Method of Side Scan Sonar Images

Side scan sonar(SSS) imaging is an essential technology for the prospection, monitoring and location of underwater vehicles in marine environment. However, original SSS images are usually poor contrast and contain large amounts of noise, so they can't be directly used and need to be enhanced. To address these problems, a novel spatial domain enhancement method has been proposed in this paper. We firstly suppress speckle noise with neighborhood smoothing. Through the statistical features of the SSS image histogram, the low-gray region, the middle-gray region and the high-gray region of the SSS image are determined. Then, the three regions are enhanced through a piecewise function according to the imaging characteristics. Our method is easy to be implemented and the parameters can be adjusted automatically. The experiments show that our method has a greater improvement in Peak Signal to Noise Ratio (PSNR) and Structural Similarity Index (SSIM) than existing spatial domain methods, and performs faster processing speed compared to other frequency domain methods. Moreover, the method enhances the gray-value contrast between any adjacent regions and so it is favorable for the subsequent processing.