Centering wide 2x2 figure using adjustbox

Question

I have four large figures which I would like to tile 2x2. These figures will need to go beyond the \textwidth boundaries but I still want the 2x2 tile centered in the page. Looking at Center figure that is wider than \textwidth I've only been able to get the \centerfloat command from this answer to produce the desired outcome.

I'd like to be able to do this with the adjustbox package as described in this answer, but I'm having trouble getting creating the two rows of figures. Is it possible to get this functionality from the adjustbox package? I was trying to use the minipage option but haven't had success. This is what I currently get.

\documentclass{article}

\usepackage{subcaption}

\usepackage{mwe}% for this example only

\usepackage{adjustbox}

\begin{document}

\begin{figure}
    \begin{adjustbox}{center}
    \centering
    \begin{subfigure}{.6\textwidth}
        \includegraphics[width=1.0\linewidth]{example-image}
    \end{subfigure}%
    \begin{subfigure}{.6\textwidth}
        \includegraphics[width=1.0\linewidth]{example-image}
    \end{subfigure}
    \begin{subfigure}{.6\textwidth}
        \includegraphics[width=1.0\linewidth]{example-image}
    \end{subfigure}%
    \begin{subfigure}{.6\textwidth}
        \includegraphics[width=1.0\linewidth]{example-image}
    \end{subfigure}
    \end{adjustbox}
\end{figure}

\end{document}

Answer 1

Here is a version using \makebox.

Note: a minipage would reset \textwidth, but a \parbox doesn't.

\documentclass{article}
\usepackage{graphicx}
\usepackage{subcaption}
\usepackage{showframe}% MWE only

\begin{document}

\begin{figure}
\makebox[\textwidth][c]{\parbox{1.2\textwidth}{%
  \begin{subfigure}{.6\textwidth}
      \includegraphics[width=\linewidth]{example-image}
  \end{subfigure}%
  \begin{subfigure}{.6\textwidth}
      \includegraphics[width=\linewidth]{example-image}
  \end{subfigure}
  \begin{subfigure}{.6\textwidth}
      \includegraphics[width=\linewidth]{example-image}
  \end{subfigure}%
  \begin{subfigure}{.6\textwidth}
      \includegraphics[width=\linewidth]{example-image}
  \end{subfigure}
}}
\caption{A $2\times2$ arrangement}
\end{figure}
\end{document}

---

Here is a version using adjustbox.

\documentclass{article}
\usepackage[export]{adjustbox}
\usepackage{subcaption}
\begin{document}

\begin{figure}
  \begin{adjustbox}{center}
  \parbox{1.2\textwidth}{\lineskip=0pt
    \begin{subfigure}{.6\textwidth}
      \includegraphics[width=\linewidth]{example-image}
    \end{subfigure}%
    \begin{subfigure}{.6\textwidth}
      \includegraphics[width=\linewidth]{example-image}
    \end{subfigure}
    \begin{subfigure}{.6\textwidth}
      \includegraphics[width=\linewidth]{example-image}
    \end{subfigure}%
    \begin{subfigure}{.6\textwidth}
      \includegraphics[width=\linewidth]{example-image}
    \end{subfigure}}
  \end{adjustbox}
  \caption{Caption}
  \label{fig:key}
\end{figure}
\end{document}

---

Here is a version using neither,

\documentclass{article}
\usepackage{graphicx}
\usepackage{subcaption}
\begin{document}

\begin{figure}
  \leftskip=-0.1\textwidth
  \rightskip=-0.1\textwidth
  \lineskip=0pt
  \begin{subfigure}{.6\textwidth}
      \includegraphics[width=\linewidth]{example-image}
  \end{subfigure}%
  \begin{subfigure}{.6\textwidth}
      \includegraphics[width=\linewidth]{example-image}
  \end{subfigure}
  \begin{subfigure}{.6\textwidth}
      \includegraphics[width=\linewidth]{example-image}
  \end{subfigure}%
  \begin{subfigure}{.6\textwidth}
      \includegraphics[width=\linewidth]{example-image}
  \end{subfigure}
  \caption{Caption}
  \label{fig:key}
\end{figure}
\end{document}

Answer 2

You need subfigure only in case you have subcaptions. Otherwise, just treat the images as if they were big letters.

\documentclass{article}
\usepackage{graphicx}

\begin{document}

\begin{figure}
\centering
%%% local settings
\renewcommand{\arraystretch}{0}
\setlength{\tabcolsep}{0pt}

\begin{tabular}{cc}
\includegraphics[width=0.4\linewidth]{example-image} &
\includegraphics[width=0.4\linewidth]{example-image} \\
\includegraphics[width=0.4\linewidth]{example-image} &
\includegraphics[width=0.4\linewidth]{example-image}
\end{tabular}

\caption{A $2\times2$ arrangement}

\end{figure}

\end{document}

By locally removing the interline spacing between rows (\renewcommand{\arraystretch}{0} and the intercolumn padding (\setlength{\tabcolsep}{0pt}) in the tabular, the images are placed next to each other with no space. Since the settings are done in a group (the figure environment), the values will be restored after \end{figure}, no need to reset them manually.

If you want oversized pictures, put the tabular in a box:

\makebox[\linewidth]{%
  \begin{tabular}{cc}
    \includegraphics[width=0.6\linewidth]{example-image} &
    \includegraphics[width=0.6\linewidth]{example-image} \\
    \includegraphics[width=0.6\linewidth]{example-image} &
    \includegraphics[width=0.6\linewidth]{example-image}
  \end{tabular}%
}