NL-MEANS图像去噪算法。 该算法对于灰度图像的高斯白噪声的去除效果极好，但是在计算时间上耗时较高。本程度对于256*256的灰度图像，约在30s以上。 运行，请输入“main”。-NL-means algorithm is a good way for grey image denoising on AWN, but it has high cost on the computation. The program here may cost beyond 30s for 256