#laplacian

Question 1: Select all that apply

The discrete Laplacian kernel $\begin{bmatrix}0&1&0\\1&-4&1\\0&1&0\end{bmatrix}$ is applied at the centre pixel of each $3 \times 3$ patch below. For which patches is the response exactly 0? Select all that apply.

$\begin{bmatrix}50&50&50\\50&50&50\\50&50&50\end{bmatrix}$ 1
$\begin{bmatrix}10&20&30\\10&20&30\\10&20&30\end{bmatrix}$ 2
$\begin{bmatrix}0&10&20\\10&20&30\\20&30&40\end{bmatrix}$ 3
$\begin{bmatrix}0&0&0\\0&90&0\\0&0&0\end{bmatrix}$ 4
$\begin{bmatrix}0&0&90\\0&0&90\\0&0&90\end{bmatrix}$ 5

Timed test