删除子图标题而不删除标签

Question

我尝试根据下面显示的代码对这四幅图像使用子图以及标题。

\begin{figure}[H]
%\centering
\begin{subfigure}[t]{0.49\textwidth}
    %\centering
    \includegraphics[width=\linewidth]{g1_2}
    \caption{\SI{10}{\nano\meter}$\times$\SI{10}{\nano\meter} raw image of the surface of epitaxial graphene, $\left(U_T=+\SI{100}{\milli\volt}, I_T=\SI{500}{\pico\ampere}\right)$, $z=0\to\SI{34.768}{\pico\meter}$}
    \label{figp1a}
\end{subfigure}%
\hfill
\begin{subfigure}[t]{0.49\textwidth}
    %\centering
    \includegraphics[width=\linewidth]{g2_2}
    \caption{\SI{10}{\nano\meter}$\times$\SI{10}{\nano\meter} raw image of the surface of epitaxial graphene, $\left(U_T=+\SI{100}{\milli\volt}, I_T=\SI{500}{\pico\ampere}\right)$, $z=0\to\SI{45.534}{\pico\meter}$}
    \label{figp1b}
\end{subfigure}

\begin{subfigure}[t]{0.49\textwidth}
    %\centering
    \includegraphics[width=\linewidth]{g_bilayer_2}
    \caption{\SI{6.5}{\nano\meter}$\times$\SI{6.5}{\nano\meter} raw image of the surface of epitaxial graphene, $\left(U_T=+\SI{100}{\milli\volt}, I_T=\SI{500}{\pico\ampere}\right)$, $z=0\to\SI{47.548}{\pico\meter}$}
    \label{figp1c}
\end{subfigure}%
\hfill
\begin{subfigure}[t]{0.49\textwidth}
    %\centering
    \includegraphics[width=\linewidth]{g_bilayer_zoom_2}
    \caption{\SI{2.3}{\nano\meter}$\times$\SI{2.3}{\nano\meter} zoomed in section from fig.\ref{figp1c}, $\left(U_T=+\SI{100}{\milli\volt}, I_T=\SI{500}{\pico\ampere}\right)$}
    \label{figp1d}
\end{subfigure}

\caption{STM imaging of different areas of the epitaxial graphene sample, prior to the deposition.}\label{figp1}
\end{figure}

图像结果如下。

我希望获得结果十字的边界作为一条新路径，可以绘制或填充。

因此，我尝试删除标题，然后使用此代码重试

\begin{figure}[H]
%\centering
\begin{subfigure}[t]{0.49\textwidth}
    %\centering
    \includegraphics[width=\linewidth]{g1_2}
    %\caption{\SI{10}{\nano\meter}$\times$\SI{10}{\nano\meter} raw image of the surface of epitaxial graphene, $\left(U_T=+\SI{100}{\milli\volt}, I_T=\SI{500}{\pico\ampere}\right)$, $z=0\to\SI{34.768}{\pico\meter}$}
    \label{figp1a}
\end{subfigure}%
\hfill
\begin{subfigure}[t]{0.49\textwidth}
    %\centering
    \includegraphics[width=\linewidth]{g2_2}
    %\caption{\SI{10}{\nano\meter}$\times$\SI{10}{\nano\meter} raw image of the surface of epitaxial graphene, $\left(U_T=+\SI{100}{\milli\volt}, I_T=\SI{500}{\pico\ampere}\right)$, $z=0\to\SI{45.534}{\pico\meter}$}
    \label{figp1b}
\end{subfigure}

\begin{subfigure}[t]{0.49\textwidth}
    %\centering
    \includegraphics[width=\linewidth]{g_bilayer_2}
    %\caption{\SI{6.5}{\nano\meter}$\times$\SI{6.5}{\nano\meter} raw image of the surface of epitaxial graphene, $\left(U_T=+\SI{100}{\milli\volt}, I_T=\SI{500}{\pico\ampere}\right)$, $z=0\to\SI{47.548}{\pico\meter}$}
    \label{figp1c}
\end{subfigure}%
\hfill
\begin{subfigure}[t]{0.49\textwidth}
    %\centering
    \includegraphics[width=\linewidth]{g_bilayer_zoom_2}
    %\caption{\SI{2.3}{\nano\meter}$\times$\SI{2.3}{\nano\meter} zoomed in section from fig.\ref{figp1c}, $\left(U_T=+\SI{100}{\milli\volt}, I_T=\SI{500}{\pico\ampere}\right)$}
    \label{figp1d}
\end{subfigure}

\caption{STM imaging of different areas of the epitaxial graphene sample, prior to the deposition.}\label{figp1}
\end{figure}

现在图像结果如下

这个图像概念对我来说没问题，但不幸的是，这四幅图像的标签\label{figp1a}，即\label{figp1b}，\label{figp1c}和\label{figp1d}似乎不再起作用，因为我注释了子图中的标题。我需要第二幅带有标签的图像。

Answer 1

为了让@Mico高兴。subcaption 包有一个用于此的命令，即\phantomsubcaption。

\documentclass{article}
\usepackage{todonotes}
\usepackage{subcaption}
\begin{document}
\begin{figure}
\begin{subfigure}[t]{0.49\textwidth}
    \missingfigure[figwidth=\linewidth]{marmots are cute}
    \phantomsubcaption
    \label{figp1a}
\end{subfigure}%
\hfill
\begin{subfigure}[t]{0.49\textwidth}
    \missingfigure[figwidth=\linewidth]{koala bears are also cute}
    \phantomsubcaption
    \label{figp1b}
\end{subfigure}

\begin{subfigure}[t]{0.49\textwidth}
    \missingfigure[figwidth=\linewidth]{but in this forum, people love ducks}
    \phantomsubcaption
    \label{figp1c}
\end{subfigure}%
\hfill
\begin{subfigure}[t]{0.49\textwidth}
    \missingfigure[figwidth=\linewidth]{I dunno why}
    \phantomsubcaption
    \label{figp1d}
\end{subfigure}
\caption{Marmots, koala bears and ducks.}
\end{figure}
The most important message is the one of Figure~\ref{figp1a}. But you may also
like the one of Figure~\ref{figp1b}. Figure~\ref{figp1d} contains a question.
\end{document}