Automatically bold first sentence of a floats caption

Question

How to bold automatically the first sentence of the float caption and second sentence is normal?

\begin{figure}[t]
\centering
\caption{First sentence. Second sentence.}
\end{figure}

Output should be:

Figure 1. First sentence. Second sentence.

Answer 1

You can use the approach described in Customize text format of captions by parsing content of \@caption, namelly

\documentclass{article}
\usepackage{xstring}
\usepackage{etoolbox}
\usepackage{caption}

\captionsetup{labelfont=bf,tableposition=top}

\makeatletter
\newcommand\formatlabel[1]{%
    \noexpandarg
    \IfSubStr{#1}{.}{%
      \StrBefore{#1}{.}[\firstcaption]%
      \StrBehind{#1}{.}[\secondcaption]%
      \textbf{\firstcaption.} \secondcaption}{%
      #1}%
      }


\patchcmd{\@caption}{#3}{\formatlabel{#3}}
\makeatother

\begin{document}

\begin{figure}[t]
\centering
test test
\caption{First sentence. Second sentence.}
\end{figure}

\end{document}

Answer 2

A non-automatic way would be to define:

\newcommand{\bcaption}[2]{\caption{\textbf{#1} #2}}

and using the 'bf' option to the package caption.

Here a working example:

\documentclass{article}
\usepackage[bf]{caption}
\newcommand{\bcaption}[2]{\caption{\textbf{#1} #2}}
\begin{document}
\begin{figure}[t]
\centering
 \bcaption{First sentence.}{Second sentence.}
\end{figure}
\end{document}