[m n]=size(I)subplot(2,1,1),imshow(I);title({'原图像'});y1=I(4,:);y2=I(5,:);y3=I(6,:);y4=I(7,:);y5=I(8,:);y6=I(9,:);y7=I(10,:);y8=I(20,:)*2;subplot(212)plot(1:n,y8)

[m n]=size(I)subplot(2,1,1),imshow(I);title({'原图像'});y1=I(4,:);y2=I(5,:);y3=I(6,:);y4=I(7,:);y5=I(8,:);y6=I(9,:);y7=I(10,:);y8=I(20,:)*2;subplot(212)plot(1:n,y8)
[m n]=size(I)subplot(2,1,1),imshow(I);title({'原图像'});y1=I(4,:);y2=I(5,:);y3=I(6,:);y4=I(7,:);y5=I(8,:);y6=I(9,:);y7=I(10,:);y8=I(20,:)*2;subplot(212)plot(1:n,y8)

[m n]=size(I)subplot(2,1,1),imshow(I);title({'原图像'});y1=I(4,:);y2=I(5,:);y3=I(6,:);y4=I(7,:);y5=I(8,:);y6=I(9,:);y7=I(10,:);y8=I(20,:)*2;subplot(212)plot(1:n,y8)
size返回的m*n是矩阵i的维数;subplot(2,1,1),表示话2行1列的图,把imshow放在第一个位置
imshow(I)就是直接按I的灰度级画出图.y8=I(20,:)*2表示y8是I的第20行的数据的2倍
最后会把矩阵I的第20行的数据的2倍（即为y8）画出来