I = imread('after-384x288.jpg');

[counts,x] = imhist(I);

plot(x,counts, 'b')
hold on

k=5;

C = [ zeros(k,1); counts; zeros(k,1)  ];
Csmooth = zeros( size(counts) );

for i=1:size(counts,1)
  C(i:i+2*k);
  Csmooth(i) = mean( C(i:i+2*k) );
end

plot(x, Csmooth, 'r')
hold off