Calculation of entropy shows " the entropy of the image is = NaN", please help

Img = imread('test1.jpg');
I=rgb2gray(Img);
[Height,Width] = size(I);
[m,Binsx] = imhist(I);
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)

Answer 1

[Image Analyst]

Use entropy():

H = entropy(I)

[ushamary sharma]

thankyou

Answer 2

[Walter Roberson]

H = sum(-m.*log2(m));

The problem with the code is that you have some entries which are 0. You should only be calculating based upon the non-zero entries.

mp = m(m>0);
H = sum(-mp.*log2(mp));