I have two images C and B and I need to sum the total difference A = C-B.

Now, I got the solution sum(A), but I also read that sum(sum(A)) has also been used for a rating function. Can someone explain me what the difference is?

CodePudding user response：

The function sum sums over the first non-singleton dimension of the matrix. A singleton dimension is one of size 1. So for a 2D matrix, it will sum over columns, yielding a row vector. Calling sum with this result will sum over the one row, yielding a single value.

Thus, sum(sum(A)) is the sum over the full 2D matrix A.

The same can be done with sum(A(:)), or, in more recent versions of MATLAB, with sum(A,'all').