Normalization of Thermal image with range 0 to 40

Question

I'm doing research about using thermal image for temperature measurement for medical purposes, I try to repeat methodology of paper "Face and eyes localization algorithm in thermal images for temperature measurement of the inner canthus of the eyes". They used Normalization of thermal image with range 0 to 40, and they got this results.

I tried the code below:

tt = imread('test.jpg');
figure, imshow(tt)
tt = double(tt);
normimg = uint8(zeros(size(tt))); 
for idx = 1 : 3
chan = tt(:,:,idx);
minvalue = min(chan(:));
maxvalue = max(chan(:));
normimg(:,:,idx) = uint8((chan-minvalue)*40/(maxvalue-minvalue)); 
end
figure, imshow(normimg)

and I got different results so what I should do to get same results Thank you in advance

Answer 1

You should first try to convert it to 2d matrix (Grayscale) then normalize it by the 40*(X-Min)/(Max-Min)

Answer 2

Your normalization is OK and the image is fine. The point is that "imshow" command assumes your image is in range [0~255] so if the maximum value of the image is 40, it will be dark in the figure. To see the image properly, put a "[]" in imshow command:

imshow(normimg,[])

And also you can do the whole job in just three lines:

tt = imread('test.jpg');
normimg = 40 * mat2gray(tt);
figure, imshow(normimg,[]);