entropy.m

Image = imread('Cameraman256.bmp');
Frequency = zeros(256);
Samples = 256 * 256;

for i = 1:256
    for j = 1:256
        % convert 0-255 to index-wise
        IntensityIndex = Image(i,j) + 1; 
        Frequency(IntensityIndex) = Frequency(IntensityIndex) + 1;
    end
end

FinalEntropy=0;
for i = 1:256
    Probability = Frequency(i) / Samples;
    if Probability ~= 0
        Entropy = -1 * Probability * log2(Probability);
        FinalEntropy = FinalEntropy + Entropy;
    end
end
FinalEntropy