Entropy

clear all;
close all;
clc;

x = imread('circuit.tif');

p = imhist(x);
[m,n] = size(p);

E = 0;
for i = 1:m
    for j = 1:n
        if(p(i,j) > 0)
            E = E - (p(i,j) * log2(p(i,j)));
        end
    end
end

ex = entropy(p);

Why E and ex having different values ? How we can solve it ?

[Walter Roberson]

I do not have access at the moment to check: I wonder what the datatype of p is? If it turns out to be one of the integer data types, your expressions probably do not compute what you expect.

[Image Analyst]

p is a 1D variable since it's the counts. Also you didn't normalize p by dividing by numel(x).

Answer 1

[Image Analyst]

Try this:

p(p==0) = [];
E2 = -sum(p .* log2(p))
E3 = entropy(x)