MATLAB: How to calculate the entropy

entropy

How can I calculate the entropy of a sentence and selected sentence of a string. Thanks

Best Answer

Suppose you have a string

str = 'A quick brown fox';

1. If you have image processing toolbox, then try

ent = entropy(uint8(str))

2. Otherwise, you can also download this FEX submission: https://www.mathworks.com/matlabcentral/fileexchange/38295-compute-the-entropy-of-an-entered-text-string

ent = ComputeEntropy(str);

3. You can also write the following code which does not require any other toolbox

p = sum(str.'==unique(str))./length(str);
ent = -sum(p.*log2(p));

Same result for all three options

ent =
    3.6901

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MATLAB: Does the Image Processing Toolbox (R2007a) ENTROPY command return a value of zero when the image is cast as a double

Some of the Image Processing Toolbox functions have to assume a particular dynamic range. By convention, this range is [0,1] for data of type 'double', but [0,255] for data of type 'uint8'. Therefore, the IM2DOUBLE function should be used as it handles this scaling automatically. For example, your code thus becomes:

I = rgb2gray(ColorImage);           % use any true color image
ent1 = entropy(I);
I = im2double(I);
ent2 = entropy(I);

Both 'ent1' and 'ent2' should be equal.

Best Answer

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