How can I compute the probability of a pixel intensity of the image in Matlab??
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ghada sandoub
on 19 Mar 2019
Commented: Walter Roberson
on 29 May 2022
I have an enhanced image and I want to measure the amount of information in the enhanced image using the following metric:
![Capture.JPG](https://www.mathworks.com/matlabcentral/answers/uploaded_files/209216/Capture.jpeg)
where p(Ie) denotes the probability of a pixel intensity in the enhanced image Ie . now I want to know how to estimate the probability of a pixel intensity. Does anyone know how to do this in Matlab??
2 Comments
Adam
on 19 Mar 2019
Which pixel intensity? The probablity of being exactly a given intensity or of being higher than a given intensity or lower? It doesn't make sense without additional context.of what Ie is
Accepted Answer
Image Analyst
on 19 Mar 2019
ghada:
Use histogram() with the 'Normalization' option of 'probability'.
You might also be interested in the entropy() function (which computes your formula directly from the image), or entropyfilt() function (which does an entropy computation in a moving window).
Demo below:
grayImage = imread('cameraman.tif');
subplot(2, 1, 1);
imshow(grayImage);
subplot(2, 1, 2);
histObject = histogram(grayImage, 256, 'Normalization', 'probability')
grid on;
xlabel('Gray Level', 'FontSize', 20);
ylabel('Probability', 'FontSize', 20);
% Extract probabililty of each gray level into a vector "p".
p = histObject.Values;
![0001 Screenshot.png](https://www.mathworks.com/matlabcentral/answers/uploaded_files/209230/0001%20Screenshot.png)
4 Comments
Aaron Charles Alday
on 20 Feb 2020
Your code didn't work to my matlab sorftware the command window shows this message....why?
"Error in imhist (line 60)
[a, n, isScaled, top, map] = parse_inputs(varargin{:});
Error in Test_Run_2 (line 8)
[pixelCounts, white_value] = imhist(grayImage, 256, 'Normalization', 'probability')"
Image Analyst
on 28 May 2022
@Aaron Charles Alday, that's not my code. I didn't use imhist, I used histogram. imhist does not take those arguments.
More Answers (2)
KALYAN ACHARJYA
on 19 Mar 2019
Edited: KALYAN ACHARJYA
on 19 Mar 2019
gray_image=rgb2gray(imread('test.jpg'));
[rows colm]=size(gray_image);
[pixelCounts, gray_value]=imhist(gray_image);
prob=pixelCounts(:)./(rows*colm);
prob=nonzeros(prob);
log_prob=log(prob);
DE=-sum(prob.*log_prob);
fprintf('\n The DE value is: %.2f',DE);
Command Window:
The DE value is: 3.50>>
2 Comments
KALYAN ACHARJYA
on 20 Mar 2019
Edited: KALYAN ACHARJYA
on 20 Mar 2019
Is the problem solved? I have written simple code based on your question. If not. Check the comment of Image Anaalyst sir
Ganesha Thondilege
on 28 May 2022
I hope this will help you.
grayImage = imread('cameraman.jpg');
subplot(1,2, 1);
imshow(grayImage);
subplot(1,2, 2);
imhist(grayImage);
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1013975/image.jpeg)
3 Comments
Ganesha Thondilege
on 28 May 2022
Try this to get the probabilities of each gray_value
grayImage = imread('cameraman.jpg');
[l,m]=size(grayImage);
subplot(1,2, 1);
imshow(grayImage);
[pixelCounts, gray_value]=imhist(grayImage);
prob=pixelCounts(:)./(l*m);
subplot(1,2,2);
plot(gray_value,prob);
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1014005/image.jpeg)
Walter Roberson
on 29 May 2022
what advantages would this have compared to https://www.mathworks.com/matlabcentral/answers/450942-how-can-i-compute-the-probability-of-a-pixel-intensity-of-the-image-in-matlab#answer_366112
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