Hard space in figure/table caption

Question

I have a problem with figure captions. Since I have very long words in figure and table captions (names of chemical compounds) the space between caption label, caption number and first word of caption is not constant. It looks like this:

While I would like to have hard space between caption label, caption number and first word of caption so it would look more or less like this:

I am using own document class I didn't put any code for captions there except of two lines in the preamble:

\usepackage[labelfont=bf]{caption}
\captionsetup{labelsep=period}

a piece of code from class that may be of some importance for the question:

\def\@baseclass{report}
\DeclareOption*{\PassOptionsToClass{\CurrentOption}{\@baseclass}}
\PassOptionsToClass{a4paper,twoside,openright,12pt}{\@baseclass}
\ProcessOptions

\LoadClass{\@baseclass}

Is there a simple way to do it (get hard spaces in the caption label)?

Answer 1

Perhaps one of these solutions will be more or less what you want: I defined a hardspace caption label format that ensures a normal space between caption name and caption number. A fixed space between label and first word can be achieved with the RaggedRight option (which enables some hyphenation). However, as the whole caption is centred with respect to text width, its placement may look odd, depending on the effective width of the figure, and it may be better to have caption width equal to figure width and have caption on the left side rather than centred. This can be achieved with the measuredfigure environment from the threeparttable package.

So I propose 4 variants, according to justification and use of this environment or not:

\documentclass[11pt, a4paper]{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage{mathtools}
\usepackage{caption}
\usepackage{threeparttable}

\DeclareCaptionLabelFormat{hardspace}{\mbox{#1~#2}}
\DeclareCaptionLabelSeparator{hardspace}{.~}
\captionsetup{labelformat = hardspace, labelfont = bf,justification = RaggedRight}
\usepackage[demo]{graphicx}

\usepackage{chngcntr}
\renewcommand\thesection{\Alph{section}}
\counterwithin{figure}{section}
\setcounter{section}{1}
\setcounter{figure}{21}

\begin{document}
\noindent\texttt{Justification = RaggedRight: }

\begin{figure}[!h]
\centering
\begin{measuredfigure}
{\includegraphics[width =0.9\linewidth]{myfigure}}
\caption{The $\prescript{1}{}{\text{H-NMR}}$ spectrum of \textbf{12},4-bis(2,2’-bithienyl-(4-hydroxypenyl)methane thymine-1-acetate, in deuterated chloroform.}
\end{measuredfigure}
\end{figure}

\begin{figure}[!h]
\centering
\includegraphics[width =0.9\linewidth]{myfigure}
\caption{The $\prescript{1}{}{\text{H-NMR}}$ spectrum of \textbf{12},4-bis(2,2’-bithienyl-(4-hydroxypenyl)methane thymine-1-acetate, in deuterated chloroform.}
\end{figure}

\clearpage
\noindent\texttt{Justification = justified: }

\captionsetup{justification = justified}
\begin{figure}[!h]
\centering
\begin{measuredfigure}
{\includegraphics[width =0.9\linewidth]{myfigure}}
\caption{The $\prescript{1}{}{\text{H-NMR}}$ spectrum of \textbf{12},4-bis(2,2’-bithienyl-(4-hydroxypenyl)methane thymine-1-acetate, in deuterated chloroform.}
\end{measuredfigure}
\end{figure}

\begin{figure}[!h]
\centering
\includegraphics[width =0.9\linewidth]{myfigure}
\caption{The $\prescript{1}{}{\text{H-NMR}}$ spectrum of \textbf{12},4-bis(2,2’-bithienyl-(4-hydroxypenyl)methane thymine-1-acetate, in deuterated chloroform.}
\end{figure}

\end{document}