说明：  P0304：直方图均匀化P0305：模拟图像受高斯白噪声和椒盐噪声的影响P0306：采用二维中值滤波函数medfilt2对受椒盐噪声干扰的图像滤波P0309：运用5种不同的梯度增强法进行图像锐化
(P0304: Histogram of homogenization P0305: analog image by Gaussian white noise and salt and pepper noise P0306: A two-dimensional median filtering function medfilt2 of interference by salt and pepper noise image filtering P0309: the use of five kinds of different gradient method to enhance image Sharpen)