How to find the entropy value of an RGB image after histogra equalization in Y plane.?

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arun kumar
arun kumar on 17 Dec 2015
Commented: arun kumar on 17 Dec 2015
I am finding entropy value of an RGB image after histogram processing in Y plane, as follows:
i % the original image
y1=rgb2ycbcr(i); y=y1(:,:,1);cb=y1(:,:,2);cr=y1(:,:,3); he1=histeq(y); r1=cat(3,he1,cb,cr); r1=ycbcr2rgb(r1);
g1=rgb2gray(r1); e1=entropy(g1):
Now I followed the procedure:
imwrite(r1,'temp1.jpg'); i2=imread('temp1.jpg'); g2=rgb2gray(i2); e2=entropy(g2)
But now e1 and e2 are different. Why it is so?

Accepted Answer

Guillaume on 17 Dec 2015
How much different?
Do you know that the jpg format is a lossy compression format? Every time you save an image as jpg, some of the pixel values are slightly changed.
If you use a non-lossy compression format such as png, does the entropy change?
  1 Comment
arun kumar
arun kumar on 17 Dec 2015
Thank you so much Guillaume. Now I saved the image with 'jpg' extension in 'lossless' mode. Now getting the same values of e1 and e2. Even with 'png' also I can get same values.
Thank you once again

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