Gradient of Image using window size

I am new to MATLAB and trying to calculate the magnitude of the gradient using a specified window size but I receive the error: Attempted to access img(0,5); index must be a positive integer or logical. I am not sure how to solve this. Does anyone have any suggestions?

img = imread('image.png');

img = im2double(img);

[row, col] = size(img);

windowSize = 5;

for x = 1:row

for y = 1:col

if (x >= windowSize && x < row - windowSize && y >= windowSize && y < col - windowSize)

gradient(x,y) = abs(img(x+windowSize,y) - img(x-windowSize,y)) + abs(img(x,y+windowSize) -img(x,y-windowSize));

else

 gradient(x,y) = 0;

end end end

Answer 1

[Image Analyst]

Just use imgradient(img). Why go to all the trouble of doing it yourself when there's a built-in function that does it for you?