Adjust the caption to figures on minipage

Using minipage, is posible to split the (a) (b) letters above any figures, in order to perfectly center them?

\begin{figure}[tpb]
\subfloat[]{
\begin{minipage}{0.45\linewidth}   %tamaño
\includegraphics[width=1\columnwidth,keepaspectratio]{matlab/pdr_12345_p.pdf}
\end{minipage}}
\subfloat[]{
\hspace{5mm}    \begin{minipage}{0.45\linewidth}
\includegraphics[width=1\columnwidth,keepaspectratio]{matlab/pdr_11111_p.pdf}

\end{minipage}}
\end{figure}

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You could use the subcaption package to induce an automatic line break between the caption's "number" (letter, actually) and text. The subcaption package also provides the environment subfigure (plus subtable); using it allows you to combine \subfloat directive and minipage environment into a single environment.

The following MWE shows how this may done. (Note that I haven't provided a caption for the overall figure float as your example didn't seem to require one.)

\documentclass[a4paper,twoside]{report}
\usepackage{subcaption}
\captionsetup[sub]{labelsep=newline}
\usepackage[demo]{graphicx} % remove '[demo]' for real version
\begin{document}
\begin{figure}
\begin{subfigure}{0.45\linewidth}
\includegraphics[width=\columnwidth,keepaspectratio]{matlab/pdr_12345_p.pdf}
\caption{First Subfigure}
\end{subfigure}
\hspace{\fill}   % separate the two subfigures as much as possible
\begin{subfigure}{0.45\linewidth}
\includegraphics[width=\columnwidth,keepaspectratio]{matlab/pdr_11111_p.pdf}
\caption{Second Subfigure}
\end{subfigure}
\end{figure}

\end{document}

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