Matrix Figure Alignment

Question

I'm trying to replicate Figure 3.15 as shown here so that I can display 3 matrices side by side with captions:

Anyone know of a simple way to get the formatting right? This is what I'm currently using just so that I have something:

\begin{figure}
\centering
\begin{subfigure}{.5\textwidth}
\centering
\subcaption{Image matrix, $f(x,y)$}
{$\begin{matrix}
0 & 0 & 0 & 0 & 0 \\
0 & 0 & 0 & 0 & 0 \\
0 & 0 & 1 & 0 & 0 \\
0 & 0 & 0 & 0 & 0 \\
0 & 0 & 0 & 0 & 0 \\
\end{matrix}$}
\label{fig:sub1}
\end{subfigure} \vspace{5mm}

\begin{subfigure}{.5\textwidth}
\centering
\subcaption{Spatial Mask, $w(x,y)$}
$\begin{matrix}
1 & 2 & 3 \\ 
4 & 5 & 6 \\ 
7 & 8 & 9 \\ 
\end{matrix}$
\label{fig:sub1}
\end{subfigure} \vspace{5mm}

\begin{subfigure}{.5\textwidth}
\centering
\subcaption{Convolved image}
$\begin{matrix}
0 & 0 & 0 & 0 & 0 \\
0 & 1 & 2 & 3 & 0 \\
0 & 4 & 5 & 6 & 0 \\
0 & 7 & 8 & 9 & 0 \\
0 & 0 & 0 & 0 & 0 \\
\end{matrix}$
\label{fig:sub1}
\end{subfigure}

\end{figure}

Answer 1

Here is a rough start. Alignment is done by putting the matrices in a minipage[b] or minipage[t] as required. The matrix environment doesn't have a vertical positioning parameter, so maybe it would be better to use array and put the positioning there, thus giving the opportunity to eliminate the minipage. Or use tikz for positioning, etc. Lots of possibilities for refinement.

\documentclass{article}

\usepackage{subcaption}
\usepackage{amsmath}

\begin{document}
\small
\setlength{\arraycolsep}{2pt}
\begin{figure}

\begin{subfigure}[b]{.3\textwidth}
    Origin of $f(x,y)$\\
  \begin{minipage}[b]{0.5\linewidth}
    $\begin{matrix}
        0 & 0 & 0 & 0 & 0 \\
        0 & 0 & 0 & 0 & 0 \\
        0 & 0 & 1 & 0 & 0 \\
        0 & 0 & 0 & 0 & 0 \\
        0 & 0 & 0 & 0 & 0 \\
      \end{matrix}$
      \vspace{0pt}
  \end{minipage}
  \begin{minipage}[b]{0.2\textwidth}
    $w(x,y)$\\
    $\begin{matrix}
      1 & 2 & 3 \\
      4 & 5 & 6 \\
      7 & 8 & 9 \\
    \end{matrix}$
    \vspace{0pt}
  \end{minipage}
\caption{}\label{fig:sub1}
\end{subfigure}
%
\begin{subfigure}[b]{0.3\textwidth}
  \begin{minipage}[b]{\linewidth}
    Padded $f$\\
    $
    \begin{matrix}
      0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\
      0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\
      0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\
      0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\
      0 & 0 & 0 & 0 & 1 & 0 & 0 & 0 & 0 \\
      0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\
      0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\
      0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\
      0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\
    \end{matrix}$\vspace{0pt}
  \end{minipage} 
  \caption{}
\end{subfigure}
\vspace{2\baselineskip}

\begin{subfigure}[t]{0.3\textwidth}
  \begin{minipage}[t]{\textwidth}
        Initial position for $w$\\
    $\begin{matrix}
      \cline{1-3}
      |1 & 2 & 3| & 0 & 0 & 0 & 0 & 0 & 0 \\
      |4 & 5 & 6| & 0 & 0 & 0 & 0 & 0 & 0 \\
      |7 & 8 & 9| & 0 & 0 & 0 & 0 & 0 & 0 \\
      \cline{1-3}
      0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\
      0 & 0 & 0 & 0 & 1 & 0 & 0 & 0 & 0 \\
      0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\
      0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\
      0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\
      0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\
    \end{matrix}$\vspace{0pt}
  \end{minipage} 
  \caption{}
\end{subfigure}
%
\begin{subfigure}[t]{0.3\textwidth}
  \begin{minipage}[t]{\textwidth}
        `full' correlation result\\
    $\begin{matrix}
      0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\
      0 & 0 & 0 & 0 & 1 & 0 & 0 & 0 & 0 \\
      0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\
      0 & 0 & 0 & 9 & 8 & 7 & 0 & 0 & 0 \\
      0 & 0 & 0 & 6 & 5 & 4 & 0 & 0 & 0 \\
      0 & 0 & 0 & 3 & 2 & 1 & 0 & 0 & 0 \\
      0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\
      0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\
      0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\
    \end{matrix}$\vspace{0pt}
  \end{minipage} 
  \caption{}
\end{subfigure}
\begin{subfigure}[t]{.3\textwidth}
      `same'~correlation~result\\
$\begin{matrix}
0 & 0 & 0 & 0 & 0 \\
0 & 1 & 2 & 3 & 0 \\
0 & 4 & 5 & 6 & 0 \\
0 & 7 & 8 & 9 & 0 \\
0 & 0 & 0 & 0 & 0 \\
\end{matrix}$
\vspace{4\baselineskip}
\caption{}\label{fig:sub1}
\end{subfigure}

\end{figure}
\end{document}