clear
format compact

%%
% We use an image that is built into MATLAB.
load('mandrill', 'X')
[m, n] = size(X)
figure(1)
image(X)
colormap(gray(256))
axis equal
title('Original image')

%%
% We define the one-dimensional tridiagonal blurring matrices.
v = [1/4 1/2 1/4];
B = spdiags(repmat(v,m,1), -1:1, m, m);
C = spdiags(repmat(v,n,1), -1:1, n, n);

%%
% Finally, we show the results of using k=12 repetitions of the blur in
% each direction.
blur = @(X, k) B^k * X * C^k;
nbl = 16;
figure(2)
colormap(gray(256))
image(blur(X, nbl))
axis equal
title('Blurred image')