# How can i calculate the entropy of the region of interest of an RGB image?

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Sadia Iffat on 19 Aug 2017
Commented: Sadia Iffat on 20 Aug 2017
I know how to calculate the entropy of an RGB image.First ,vectorize the image and finally use it as a parameter of the entropy() function.
image_vector = double(original_RGB_image(:));
entropy_of_the_image = entropy(image_vector);
But what should we do to calculate the entropy of the region of interest of image?
I know one approach.Somehow,convert it into a black-white image(white=1) and use the inverse of the black-white image as a parameter of the original RGB image.I think,then the background color will be black .But it doesnot work.The background(sourrounding) became blue(something like that) instead of black? what should i do? Here is my code...
a=imresize(a,[300 300]);
mkr=a;
figure,
imshow(mkr);
im=rgb2gray(a);
level=graythresh(im);
a=im2bw(im,level);
figure,
imshow(a);
mkr(a)=nan;
figure,
imshow(mkr);

Image Analyst on 19 Aug 2017
Edited: Image Analyst on 19 Aug 2017
You can do this:
You might also want to look at entropyfilt() for a spatial filter based on entropy.
Sadia Iffat on 20 Aug 2017
So,why entropy is used for image classification? How can i understand when i should measure entropy for the classification problem?

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