[Tex/LaTex] Subfigure captions not centered

captionssubcaptionsubfloats

Having trouble getting captions in my subfigures centered. I've played around with the caption and subcaption packages a little bit and it seems like the subfigure captions are being treated like normal captions. For instance, when I add \usepackage[font=bf]{caption} to my preamble, all of the subcaptions are bolded, not just the main caption. If I add any options to \usepackage{subcaption}, they don't have any effect on anything. Here is what I'm doing right now:

\documentclass[12pt]{article}

\usepackage{mathptmx}
\usepackage{amsmath}
\usepackage{graphicx}
\usepackage[margin=0.9in]{geometry}
\usepackage{gensymb}
\usepackage{subcaption}
\usepackage{adjustbox}

\begin{document}

Petroporphyrins, as shown in Figure \ref{fig:porphyrinexamples}, are constituted of four cyclically-bonded pyrroles with various aliphatic, cylcic, and aromatic moieties. The nitrogen of each pyrrole is oriented to the center of the porphyrin, which is where the nickel or vanadium, in the form of vanadium (IV) oxide, coordinates.

\begin{figure}
\begin{adjustbox}{varwidth=\textwidth,fbox,center}
  \centering
\begin{subfigure}{.45\textwidth}
  \centering
  \includegraphics[width=.5\linewidth]{Porphyrin.png}
  \caption{Unsubstituted Demetalated Porphyrin}
  \label{fig:porphyrin}
\end{subfigure}
\begin{subfigure}{.45\textwidth}
  \centering
  \includegraphics[width=.5\linewidth]{VPorphyrin.png}
  \caption{Unsubstituted Vanadyl Porphyrin}
  \label{fig:vporphyrin}
\end{subfigure}
\\
\vspace{18pt}
\begin{subfigure}{.45\textwidth}
  \centering
  \includegraphics[width=.5\linewidth]{VDPEP.png}
  \caption{Vanadyl DPEP}
  \label{fig:vdpep}
\end{subfigure}
\begin{subfigure}{.45\textwidth}
  \centering
  \includegraphics[width=.5\linewidth]{VEtio.png}
  \caption{Vanadyl Etioporphyrin}
  \label{fig:vetio}
\end{subfigure}
\\
\vspace{18pt}
\begin{subfigure}{.45\textwidth}
  \centering
  \includegraphics[width=.5\linewidth]{VBenzoEtio.png}
  \caption{Vanadyl Benzoetioporphyrin}
  \label{fig:vbenzoetio}
\end{subfigure}
\begin{subfigure}{.45\textwidth}
  \centering
  \includegraphics[width=.5\linewidth]{VTHBEtio.png}
  \caption{Vanadyl Tetrahydrobenzoetioporphyrin}
  \label{fig:vthbetio}
\end{subfigure}
\end{adjustbox}
\caption{Several Basic Petroporphyrin Configurations}
\label{fig:porphyrinexamples}
\end{figure}

\end{document}

Best Answer

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The problem comes from the adjustbox; if you replace it with a minipage surrounded with an \fbox, the subcaptions are centered again:

\documentclass[12pt]{article}
\usepackage{mathptmx}
\usepackage{amsmath}
\usepackage[demo]{graphicx}
\usepackage[margin=0.9in]{geometry}
\usepackage{gensymb}
\usepackage{subcaption}
\usepackage{adjustbox}

\captionsetup[figure]{font=bf}
\captionsetup[subfigure]{font=rm}

\begin{document}

Petroporphyrins, as shown in Figure \ref{fig:porphyrinexamples}, are constituted of four cyclically-bonded pyrroles with various aliphatic, cylcic, and aromatic moieties. The nitrogen of each pyrrole is oriented to the center of the porphyrin, which is where the nickel or vanadium, in the form of vanadium (IV) oxide, coordinates.

\begin{figure}
\fbox{\begin{minipage}{\dimexpr\textwidth-2\fboxsep-2\fboxrule\relax}
\centering
\begin{subfigure}{.45\textwidth}
  \centering
  \includegraphics[width=.5\linewidth]{Porphyrin.png}
  \caption{Unsubstituted Demetalated Porphyrin}
  \label{fig:porphyrin}
\end{subfigure}%
\begin{subfigure}{.45\textwidth}
  \centering
  \includegraphics[width=.5\linewidth]{VPorphyrin.png}
  \caption{Unsubstituted Vanadyl Porphyrin}
  \label{fig:vporphyrin}
\end{subfigure}
\\
\vspace{18pt}
\begin{subfigure}{.45\textwidth}
  \centering
  \includegraphics[width=.5\linewidth]{VDPEP.png}
  \caption{Vanadyl DPEP}
  \label{fig:vdpep}
\end{subfigure}%
\begin{subfigure}{.45\textwidth}
  \centering
  \includegraphics[width=.5\linewidth]{VEtio.png}
  \caption{Vanadyl Etioporphyrin}
  \label{fig:vetio}
\end{subfigure}
\\
\vspace{18pt}
\begin{subfigure}{.45\textwidth}
  \centering
  \includegraphics[width=.5\linewidth]{VBenzoEtio.png}
  \caption{Vanadyl Benzoetioporphyrin}
  \label{fig:vbenzoetio}
\end{subfigure}%
\begin{subfigure}{.45\textwidth}
  \centering
  \includegraphics[width=.5\linewidth]{VTHBEtio.png}
  \caption{Vanadyl Tetrahydrobenzoetioporphyrin}
  \label{fig:vthbetio}
\end{subfigure}
\end{minipage}}
\caption{Several Basic Petroporphyrin Configurations}
\label{fig:porphyrinexamples}
\end{figure}

\end{document}

Regarding the second question, you can use the optional argument for \captionsetup to have different formatting foe figures and subfigures; in my example code I used

\captionsetup[figure]{font=bf}
\captionsetup[subfigure]{font=rm}

for illustration purposes.

The demo option for graphicx simply replaces actual figures with black rectangles; do not use that option in your actual document.

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