I=randn(501,501);
A=autocorr2d(I);

figure;
subplot(1,2,1)
imagesc(I)
axis equal tight
box on
xlabel('X')
ylabel('Y')
title('Original Image')
colorbar

subplot(1,2,2)
imagesc(-250:1:250,-250:1:250,A,[-1,1])
axis equal tight
box on
xlabel('X')
ylabel('Y')
title('Spatial Autocorrelation')
colorbar


I=imread('i.png');
A=autocorr2d(I);

figure;
subplot(1,2,1)
imagesc(I)
axis equal tight
box on
xlabel('X')
ylabel('Y')
title('Original Image')
colorbar

subplot(1,2,2)
d_max=size(I,1)/2 +1;
imagesc(-size(I,1)/2:size(I,1)/2-1,-size(I,1)/2:size(I,1)/2-1,A,[-1,1])
axis equal tight
box on
xlabel('X')
ylabel('Y')
title('Spatial Autocorrelation')
colorbar