# How to find energy of image ?

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Rastislav Textóris on 1 Mar 2020
Answered: Image Analyst on 1 Mar 2020
Hello, i have to find energy of an image in matlab. I want to compare energy of decomoposition levels in DWT. I am looking for number of this energy.
Thank you

Subhadeep Koley on 1 Mar 2020
If you want to calculate "Energy" as defined from the gray level co-occurrence matrix of the image then the following code might help.
% Create gray-level co-occurrence matrix from image
glcms = graycomatrix(img);
% Calculate properties of gray-level co-occurrence matrix
stats = graycoprops(glcms);
% Display energy values
disp(['Energy = ', num2str(stats.Energy)]);

Image Analyst on 1 Mar 2020
Light falls onto a sensor with units of watts per square meter, and a pixel has an area of square meters, and the illumination is collected for some number of seconds, so you can see that the signal (gray level) is a unit of energy. Just do the math on the units. Since a watt is a joule per second:
[joules/(sec * m^2)] * m^2 * sec = joules.
So one definition of energy could be to simply sum up all the gray levels
energy = sum(grayImage(:));
Of course that's a proportionality - the value is not the number of joules directly.