二阶高斯低通滤波器，实现对图像的平滑处理，-Gaussian second-order low-pass filter, to achieve the smoothing of images,

高斯低通滤波器设计，并画出过滤波器之前之后的信号时域图和频域图-Gaussian low-pass filter design, and had been painting of filter before and after the signal time domain and frequency domain