对下列matlab函数或语句解释正确的是____。 f_average = fspecial('average',[3 3]); f_sobel = fspecial('sobel'); f_laplacian = fspecial('laplacian',0); A = mat2gray(imread('moon.tif')); B1 = imfilter(A,f_average); B2 = imfilter(A,f_sobel); B3 = imfilter(A,f_laplacian); figure; subplot(221);imshow(A); subplot(222);imshow(B1); subplot(223);imshow(B2); subplot(224);imshow(-B3); figure; subplot(221);imshow(A); subplot(222);imshow(A-B1); subplot(223);imshow(A-B2); subplot(224);imshow(A-B3);