clc
RGB=imread('buzz.jpg');
gray=rgb2gray(RGB);
A=im2double(gray);
[U,S,V]=svd(A);
sz=size(A);
Approx=zeros(sz);
r=50
for i=1:r
u=U(:,i);
s=S(i,i);
v=V(:,i);
Approx=Approx+s*u*v';
end
Approx;
subplot(1,2,1),imshow(A),title('original');
subplot(1,2,2),imshow(Approx),title(['low rank r=',num2str(r)]);