How to find local minima in a image histogram?

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Dani D 2017-10-20

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编辑： Image Analyst 2017-10-20

Hello, I have few search about it in google. but i'm confused :( I would like to search for the first (leftmost) local minimum in the image histogram. For example the attached image is histogram of sample image. and we need local minima. I need just one number. Thanks

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Image Analyst 2017-10-20

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https://ww2.mathworks.cn/matlabcentral/answers/362250-how-to-find-local-minima-in-a-image-histogram#answer_286758

编辑：Image Analyst 2017-10-20

在 MATLAB Online 中打开

Use diff() to get the difference between the n+1st bin and the nth bin. Then use find to get the index

[counts, grayLevels] = imhist(grayImage);
index = find(diff(counts) >= 0, 1, 'first');
minGL = grayLevels(index);

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Walter Roberson 2017-10-20

That would not be uncommon. Suppose an image had no true black, then the first histogram entry would be a count of 0. The very first shade that did occur would have a non-zero entry, which is an increase. You would have a local minimum of 0 from the first bin to the first bin that had some data, at which point you would have an increase.

Image Analyst 2017-10-20

编辑：Image Analyst 2017-10-20

Yes, that's the first place where the histogram is flat. Perhaps you want findpeaks() where you get more control over how big a peak or valley you detect.

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