How can I compute the probability of a pixel intensity of the image in Matlab??

Question

ghada sandoub 2019-3-19

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https://ww2.mathworks.cn/matlabcentral/answers/450942-how-can-i-compute-the-probability-of-a-pixel-intensity-of-the-image-in-matlab

评论： Walter Roberson 2022-5-29

I have an enhanced image and I want to measure the amount of information in the enhanced image using the following metric:

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??

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Adam 2019-3-19

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

ghada sandoub 2019-3-19

Ie is the enhanced image of dimmed image. Ie is color image. and I want to measure the amount of enhancement in the enhanced image by using DE which measures the amount of information in the enhanced image by estimating the probability of a pixel intensty in this image. but I didn't know how to make this in matlab.

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Answer 1

Image Analyst 2019-3-19

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https://ww2.mathworks.cn/matlabcentral/answers/450942-how-can-i-compute-the-probability-of-a-pixel-intensity-of-the-image-in-matlab#answer_366112

在 MATLAB Online 中打开

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;

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Aaron Charles Alday 2020-2-20

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 2022-5-28

@Aaron Charles Alday, that's not my code. I didn't use imhist, I used histogram. imhist does not take those arguments.

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Answer 2

KALYAN ACHARJYA 2019-3-19

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https://ww2.mathworks.cn/matlabcentral/answers/450942-how-can-i-compute-the-probability-of-a-pixel-intensity-of-the-image-in-matlab#answer_366116

编辑：KALYAN ACHARJYA 2019-3-19

在 MATLAB Online 中打开

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>>

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ghada sandoub 2019-3-19

Thanks alot

KALYAN ACHARJYA 2019-3-20

编辑：KALYAN ACHARJYA 2019-3-20

Is the problem solved? I have written simple code based on your question. If not. Check the comment of Image Anaalyst sir

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Answer 3

Ganesha Thondilege 2022-5-28

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https://ww2.mathworks.cn/matlabcentral/answers/450942-how-can-i-compute-the-probability-of-a-pixel-intensity-of-the-image-in-matlab#answer_973255

在 MATLAB Online 中打开

I hope this will help you.

grayImage = imread('cameraman.jpg');
subplot(1,2, 1);
imshow(grayImage);
subplot(1,2, 2);
imhist(grayImage);

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Ganesha Thondilege 2022-5-28

在 MATLAB Online 中打开

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);

Walter Roberson 2022-5-29

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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