Extract data from a histogram

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elTurco 2023-4-7

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https://ww2.mathworks.cn/matlabcentral/answers/1943409-extract-data-from-a-histogram

编辑： Image Analyst 2023-4-7

I have a 256 x 256 pixel gray image. I drew the histogram of this image in matlab. I need to find the total number of pixels in each of the 0-64,64-128,128-192 and 192-255 gray levels. I've plotted the histogram but I can't get the pixel values. Is anyone you help?

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Answer 1

Image Analyst 2023-4-7

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https://ww2.mathworks.cn/matlabcentral/answers/1943409-extract-data-from-a-histogram#answer_1211639

在 MATLAB Online 中打开

Try this:

grayImage = imread('cameraman.tif');

subplot(2, 1, 1);

imshow(grayImage, []);

subplot(2, 1, 2);

imhist(grayImage); % Display histogram

grid on;

edges = [0 : 64 : 255, 255]

edges = 1×5

0 64 128 192 255

[counts, edges] = histcounts(grayImage, edges)

counts = 1×4

16032 10445 37886 1173

edges = 1×5

0 64 128 192 255

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elTurco 2023-4-7

Thank you very much for the help...I need to find the mean and standard deviation of the pixels in each range (0-64,64-128,128-192,192-255). how can I find that?

Image Analyst 2023-4-7

编辑：Image Analyst 2023-4-7

在 MATLAB Online 中打开

For example, for one range:

mask = (grayImage >= 0) & (grayImage <= 64);
numPixelsInRange = nnz(mask)
stdDev = std(grayImage(mask))
theMean = mean(grayImage(mask))

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Answer 2

dpb 2023-4-7

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1943409-extract-data-from-a-histogram#answer_1211629

移动：Image Analyst 2023-4-7

Use histcounts as direct solution instead. The data are inside the histogram but you've got to go "handle diving" to retrieve them if you didn't save the object handle when called it; if you did then see the 'Properties' section of the doc for it (link to in the 'See Also') section. All in all, it's easier to just use histcounts