How to find out the different intensity values that are used in the image and make out a list of them.Then find the freq. of occurence (probability) of each of intensity values in the image?

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Anushka 2015-7-30

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回答： Image Analyst 2015-7-30

How to find out the different intensity values that are used in the image and make out a list of them. Then find the freq. of occurrence (probability) of each of intensity values in the image?

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John D'Errico 2015-7-30

Convert to L*a*b*, then make a histogram of the L* channel?

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Answer 1

Walter Roberson 2015-7-30

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grayImage = rgb2gray(YourImage);
[unique_vals, ~, idx] = unique(grayImage(:));
counts = accumarray(idx(:), 1);
probs = counts ./ sum(counts);
bar(unique_vals, probs);

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Answer 2

Image Analyst 2015-7-30

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You can use

grayImage = rgb2gray(rgbImage);
[pixelCounts, grayLevels] = imhist(grayImage);
grayLevelFrequency = pixelCounts / numel(grayImage);

It depends on what you mean by intensity or how accurate you want to be. It would be best to calibrate your system using a Color Checker Chart and then convert to LAB and take the histogram of the L channel. This is what I do, and what John suggested above. If you just want to get an idea of graylevels for thresholding or something, then you don't need to go through all that.