答案:解:20(1)加入2%的椒盐噪声并显示5I = imread('raptor.jpg');%原图像J1 = imnoise(I,'salt & pepper',0.02);%加入椒盐噪声figure;%分别显示四种噪声的效果subplot(121), imshow(I); subplot(122), imshow(J1);(2) I = imread('raptor.jpg');%原图像 5J1 = imnoise(I,'salt & pepper',0.02);%加入椒盐噪声L = medfilt2(J,[3 3]);% 中值滤波figure;subplot(121), imshow(I); subplot(122), imshow(J1);subplot(123), imshow(L);(3)I = imread('raptor.jpg');%原图像 5h1 = [0,-1,0;-1,5,-1;0,-1,0];%fspecial('laplacian');I2 = imfilter(I,h1);subplot(121), imshow(I); subplot(122), imshow(I2,[]);(4)使用Sobel算子,选择合适的阈值,对图像进行边缘提取并显示结果J = imread('raptor.jpg'); 5I=RGB2GRAY(J);I1 = edge(I,'sobel',0.2);I2 = edge(I,'sobel',0.4);I3 = edge(I,'sobel',0.6);subplot(221), imshow(I);subplot(222), imshow(I1);subplot(223), imshow(I2);subplot(224),imshow(I3);