Hi, I'm new with Matlab and while doing my coding for canny edge detection, I got this error from the line that I bold.Can someone help me with this error? Thank you in advanced. "Subscript indices must either be real positive integers or logicals."

%Hysteresis Thresholding
T_Low = T_Low * max(max(BW));
T_High = T_High * max(max(BW));

T_res = zeros (pan, leb);

for i = 1  : pan
    for j = 1 : leb
        if (BW(i, j) < T_Low)
            T_res(i, j) = 0;
        elseif (BW(i, j) > T_High)
            T_res(i, j) = 1;
       % Using 8-connected components
       elseif ( BW(i+1,j)>T_High || BW(i-1,j)>T_High || BW(i,j+1)>T_High || BW(i,j-1)>T_High || BW(i-1, j-1)>T_High || BW(i-1, j+1)>T_High || BW(i+1, j+1)>T_High || BW(i+1, j-1)>T_High)  %THIS LINE
            T_res(i,j) = 1;
        end
    end
end

Answer 1

[Ameer Hamza]

In your code, you are trying to access values like

BW(i-1,j)

so when i=1 this becomes B(0,j). In MATLAB index zero is not allowed. Therefore you are getting the error the subscript must be a real positive integer.

Answer 2

[Image Analyst]

See the FAQ for a good explanation: http://matlab.wikia.com/wiki/FAQ#How_do_I_fix_the_error_.22Subscript_indices_must_either_be_real_positive_integers_or_logicals..22.3F

What is your definition of hysteresis thresholding? It looks like you're simply doing thresholding and dilation:

binaryImage = T_res > T_high;
binaryImage = imdilate(binaryImage, true(3));

It seems that is essentially what your loop boils down to.