Manual threshold_ What is wrong?

img = imread('cameraman.tif');
%Threshold the image at the intensity level 128
%make all the values in the image less than 128 to 0 and equal or greater than 128 to 255

imgT = img;

[M N]=size(img);
for i=1:M
    for j=1:N
        if (img(i,j)==128 || img(i,j)>128)
            imgT(i,j)=1;
        else
            imgT(i,j)=0;
        end
    end
end
figure;
subplot(1,2,1)
imshow(img)
subplot(1,2,2)
imshow(imgT, [])
imgT=uint8(imgT);

Answer 1

[DGM]

This is another case of creating improperly-scaled images.

The incoming image img is uint8, and the output image imgT inherits its class from img. The loop sets output pixels to either 0 or 1, but in uint8, 0 is black and white is 255. The end result is a binarized image that's essentially black. Casting imgT to uint8 does nothing, because it's already uint8.

The code can be simplified.

% the image
inpict = imread('cameraman.tif');

% a binarized image of logical class
outpict = inpict >= 128;

% the output
imshow(outpict)

The result is a logical-class image that can directly be used for array indexing and other processing tasks. If the goal is to create a binarized image of uint8 class, then use im2uint8() to cast and scale the image properly for the output class.