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im2bw get different binary results on same data between double and uint8 in R2016a

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raym
raym on 8 Dec 2020
Hi, I am using im2bw to convert a RGB image to binary, but get very different results when image was in uint8 or double format.
How does this difference appear?
which results should I trust?
Thanks.
a= [];
a(:,:,1) = [ 1 2 6 7 6;
1 1 8 7 8;
1 1 9 6 7;
1 2 7 8 6;
1 2 6 8 7];
a(:,:,2) = [ 0 0 0 0 0;
0 0 0 0 0;
0 0 0 0 0;
0 0 0 0 0;
0 0 0 0 0];
a(:,:,3) = [0 0 0 0 0;
0 0 0 0 0;
0 0 0 0 0;
0 0 0 0 0;
0 0 0 0 0];
graythresh(a)%0.4980
imshow(im2bw(a)) % shows a normal binary image
graythresh(uint8(a)) %0.0137
imshow(im2bw(uint8(a))) % shows only black. All information is lost.

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