章节标题和图表间隙问题！

Question

我有以下代码：

\begin{document}
\appendix
\input{appendix1/appendix1.tex}
\input{appendix2/appendix2.tex}
\end{document}

附录2包含以下代码：

\chapter{APPENDIX B }
\label{chp:appendixB}
\section{Grouped Test Images with Their Histograms}
\subsection*{Portrait}
\begin{figure}[h!]
\begin{subfigure}[h!]{\textwidth}
  %\includegraphics[width=10cm, height=4.5cm]{einstein_image&histogram.jpg}
  \includegraphics[width=\linewidth]{einstein_image&histogram.jpg}
  \centering
  \caption{Einstein Image and Histogram}
  \label{fig:3_9_1}
  \caption*{Source: Courtesy of Gonzales \& Woods \cite{data_e} }
  \end{subfigure}
\begin{subfigure}[h!]{\textwidth}
 \includegraphics[width=\linewidth]{lena_image&histogram.jpg}
  \centering
 \caption{Lena Image and Histogram}
  \label{fig:3_9_2}
       \caption*{Source: Image Databases, Standard Test Images \cite{data_lwpcmphlwj}}
 \end{subfigure}
 \caption{Images and Histograms belong to Portrait Class}
 \end{figure}

我附上了结果：

为何“附录B”有重复？为什么标题之间有很大差距？

谢谢，