How to calculate the entropy of a grayscale image.

Hi can you help me to calculate the entropy of a grayscale image using Matlab? Here I've shown below the code that I tried. The code was working but I got the value of the entropy of my image as 'NaN'. So, please help me to find the entropy value of a grayscale image correctly.

I = imread('152.bmp');
x = entropy(I);
%functionH = MyEntropy(x);

imshow(x);
figure()

[Height,Width] = size(x);

[m,Binsx]=imhist(x);
m = m/(Height*Width);

sprintf('the sum of the histogram value is = %g',sum(m));
figure,plot(Binsx,m,'k')
xlabel('pixel value'),ylabel('relative count')

H = sum(-m.*log2(m));
sprintf('the entropy of the image is = %g',H)

[Image Analyst]

I don't know why people always give us code but not the data to run it with. How are we supposed to run it??? Oh well, good luck.

[Anurag ch]

Please suggest me the use of m=m/(Height*Width) step in the above code as soon as possible.

[Walter Roberson]

Normalization so that m becomes fractions of the image size instead of absolute image counts.

[Anurag ch]

Thank you sir,Please suggest whether it is necessary to perform normalization and also specify me the definition of it.

[Walter Roberson]

Yes normalization is needed there. The definition of entropy depends upon probability, which for event counts becomes the number of similar events divided by the total number of events .

[Anurag ch]

sir,can you give me the correct definition of normalization

[Walter Roberson]

1. Statistics: Standardization of data obtained from different sources at different periods, through peer review or comparison against the objectives of data collection.

Source: http://www.businessdictionary.com/definition/normalization.html

Answer 1

[Miriam]

Hi Ishara,

It looks like you are trying to find the height, width, and histogram using the entropy value you found. Maybe try:

[Height,Width] = size(I);
[m,Binsx] = imhist(I);

[Ishara Nipuni]

Thanks a lot for your help. I got the entropy of my image with the help of the above code. Thank you again. I need to get the entropy value to a graph. Can you please help me on that?

[Miriam]

I'm not sure I understand. The entropy of your image is a single number, what do you want to plot?

[Image Analyst]

There is an entropyfilt() that finds the entropy in a sliding window. Why do you think you want entropy anyway? What's the use case?