If \(f\) is a \(5\times5\) image with a 1 at the center and zeros elsewhere, and \(h\) is a \(3\times3\) kernel of ones, what is the total sum of the output, ignoring padding borders?
Each input pixel contributes its value times the full kernel, whose sum is \(9\). With a single 1 in the input, the total output sum is \(1\times 9 = 9\).
2D convolution is the operation that combines an image \(f(x,y)\) with a kernel \(h(x,y)\) by sliding the kernel and summing products at each position.