Finding the threshold of thermal images

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asaf omer 2022-2-15

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https://ww2.mathworks.cn/matlabcentral/answers/1650180-finding-the-threshold-of-thermal-images

评论： yanqi liu 2022-2-16

Hello.

I have some thermal images and i wanna find the optimal thresholds,is there a command that can can help with this?

So far I didnt find something usefull.

thanks

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Answer 1

Image Analyst 2022-2-15

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There is no optimal threshold. You have to decide what temperature range you're interested in. An image just has a bunch of temperatures in it. How could it possibly know that you're interested in the range from 240 degrees C and hotter? It can't. Only you would know that.

By the way, if you need to convert a pseudocolored image into a temperature image, see my attached demo.

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Image Analyst 2022-2-15

在 MATLAB Online 中打开

triangle_threshold.m

You can find the max of the histogram and fall down a certain amount from there, like until it gets to 2% of the max:

[counts, edges] = histcounts(thermalImage);
[maxCount, indexOfMax] = max(counts);
thresholdLevel = 0;
for k = indexOfMax : length(counts)
    if counts(k) < 0.02 * maxCount
        thresholdLevel = edges(k);
    end
end

or you could try my attached triangle threshold method, which is good at finding the "corner" of skewed histograms.

yanqi liu 2022-2-16

在 MATLAB Online 中打开

yes，sir，may be use cumsum to get the target rate

clc; clear all; close all;
thermalImage = imread('cameraman.tif');
[counts,centers] = hist(thermalImage(:), 0:255);
counts2 = cumsum(counts);
for k = 1 : length(counts2)
    if counts2(k) < 0.5 * counts2(end)
    else        
        % find 50% rate
        thresholdLevel = centers(k);
        break;
    end
end
bw = thermalImage < thresholdLevel;
figure; imshow(bw);