How not to show caption of figure but only of subfigure in list of figures

Question

I have a similar problem to How to change the display of subfigures in List of Figures?.

I'm using the subcaption package. I dont need to show the caption of all figures but for some figures which have subfigures I want to show only the caption of the subfigure. How can I achieve this?

So I want to come from currently this:

2.1   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     a Subcaption 1 . . . . . . . . . . . . . . . . . . . . . . . . . 6
     b Subcaption 2 . . . . . . . . . . . . . . . . . . . . . . . . . 6

to have it displayed like this:

2.1  a  Subcaption 1 . . . . . . . . . . . . . . . . . . . . . . . . . 6
     b  Subcaption 2 . . . . . . . . . . . . . . . . . . . . . . . . . 6

The code would look like this:

\documentclass{scrbook}

\usepackage{graphicx}
\usepackage{caption}
\usepackage[list=true]{subcaption}

\begin{document}
\begin{figure}[H]
  \begin{subfigure}{\textwidth}
    \includegraphics[width=textwidth]{subfigure1.jpg}
    \caption{subcaption 1}
  \end{subfigure}%
  \begin{subfigure}{\textwidth}
    \includegraphics[width=\textwidth]{subfigure2.jpg}
    \caption{subcaption 2}
  \end{subfigure}
  \caption[~]{Caption}
\end{figure}

\end{document}

Answer 1

To get this to work, you can NOT use \caption inside the figure. In another figure, fine. Just not this one.

\firstsubcaption puts the figure number into the lof, while \nextsubcaption just puts the subfigure into the lof. \dummycaption looks like a figure caption, but otherwise does nothing.

These captions are not quite as flexible in format, but they will be centered until they reach \textwidth, then switch to hanging indentation. Feel free to play with \makecaption until you are happy.

\documentclass{scrbook}

\usepackage{graphicx}
\usepackage{caption}% not needed, but compatible
\usepackage[list=true]{subcaption}% not needed, but compatible
\usepackage{mwe}

\makeatletter
\@ifundefined{c@subfigure}{%
  \newcounter{subfigure}[figure]%
  \renewcommand{\thesubfigure}{\alph{subfigure}}%
 }{}%
\makeatother

\newlength{\tempwidth}
\newsavebox{\tempbox}

\newcommand{\makecaption}[2]% #1 = caption head, #2 = caption text
{\savebox{\tempbox}{#1#2}%
 \ifdim\wd\tempbox>\textwidth
   \settowidth{\tempwidth}{#1}%
   \savebox{\tempbox}{\parbox{\textwidth}%
    {\hangindent=\tempwidth
     \hangafter=1
     \makebox[\tempwidth][l]{#1}#2}}%
 \fi
 \vskip\abovecaptionskip
 {\centering\usebox{\tempbox}\par}%
 \vskip\belowcaptionskip\hbox{}}

\newcommand{\firstsubcaption}[2][\empty]% #1 = short caption (optional), #2 = caption
{\refstepcounter{figure}%
 \refstepcounter{subfigure}%
 \ifx#1\empty
   \addcontentsline{lof}{figure}{\string\numberline {\thefigure}{\hbox to .5in{\thesubfigure}\ignorespaces #2 \relax}}%
 \else
   \addcontentsline{lof}{figure}{\string\numberline {\thefigure}{\hbox to .5in{\thesubfigure}\ignorespaces #1 \relax}}%
 \fi
 \makecaption{(\thesubfigure) }{#2}}

\newcommand{\nextsubcaption}[2][\empty]% #1 = short caption (optional), #2 = caption
{\refstepcounter{subfigure}%
 \ifx#1\empty
   \addcontentsline{lof}{figure}{\string\numberline { }{\hbox to .5in{\thesubfigure}\ignorespaces #2 \relax}}%
 \else
   \addcontentsline{lof}{figure}{\string\numberline { }{\hbox to .5in{\thesubfigure}\ignorespaces #1 \relax}}%
 \fi
 \makecaption{(\thesubfigure) }{#2}}

\newcommand{\dummycaption}[1][\empty]% #1 = caption text (optional)
{\ifx#1\empty\makecaption{Figure \thefigure}{}%
 \else\makecaption{Figure \thefigure: }{#1}%
 \fi}

\begin{document}
\listoffigures

\begin{figure}[H]
  \centering%
  \begin{subfigure}{.8\textwidth}
  \includegraphics[width=\textwidth]{example-image-a}%
  \firstsubcaption{subcaption 1}
  \end{subfigure}
  \begin{subfigure}{.8\textwidth}
  \includegraphics[width=\textwidth]{example-image-b}%
  \nextsubcaption{subcaption 2}
  \end{subfigure}
  \dummycaption
\end{figure}

\end{document}