Finding the threshold of thermal images
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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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Answers (1)
Image Analyst
on 15 Feb 2022
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.
3 Comments
Image Analyst
on 15 Feb 2022
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
on 16 Feb 2022
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);
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