#separable-kernels

Question 1: Single choice

The Sobel kernel for horizontal changes factors as an outer product, $\begin{bmatrix}-1&0&1\\-2&0&2\\-1&0&1\end{bmatrix} = \begin{bmatrix}1\\2\\1\end{bmatrix}\begin{bmatrix}-1&0&1\end{bmatrix}$ . What does the $[1, 2, 1]^\top$ factor contribute?

It smooths vertically, along the edge, so the result is less sensitive to noise1
It takes a second derivative, so the kernel responds to the curvature of the edge profile2
It normalizes the kernel so that a flat region keeps its brightness3
It makes the kernel respond to horizontal edges as well as vertical ones4

Timed test