>> im = imread('ny.png');
>> r = im(:,:,1);
>> g = im(:,:,2);
>> b = im(:,:,3);
>> imshow(r), imshow(g),imshow(b);
分别显示有颜色的
>> r1 = cat(3, r, zeros(size(r)), zeros(size(r)));
>> g1 = cat(3, zeros(size(g)), g, zeros(size(g)));
>> b1 = cat(3, zeros(size(b)), zeros(size(b)), b);