Hey, i'm new to matlab please help me understand the following statement.

Ix = [diff(S,1,2) , S(:,1,:) - S(:,end,:)];

Note: S is an image

[Walter Roberson]

is class(S) double or is it uint8 ?

Answer 1

[Jonathon Gibson]

diff(S,1,2) will return the difference between each adjacent pair of columns in S, this is approximating the x-derivative of the image using finite differences, f(x+1)-f(x). But if your matrix is m x n, then diff will return an m x (n-1) matrix. So what the second part, S(:,1,:) - S(:,end,:), is doing is concatenating another column to get an m x n matrix back. That last column in Ix is the difference between the first and the last column of S, effectively doing the same thing that diff did, but wrapping around the edge of the image.