中文说明：
四种图像去噪程序，给原图像分别加上高斯噪声，椒盐噪声，乘性噪声，脉冲噪声后进行去噪，输出去噪后的图像。
English Description：
Four kinds of image denoising procedures, add Gaussian noise, salt and pepper noise, multiplicative noise, impulse noise to the original image respectively, then denoise, and output the denoised image.