Placing sub-figures captions in top and left-handed

The way I am using to collect many sub-figures in one figure is like that:

MWE:

\begin{figure}[b!]
\begin{center}
$% \begin{array}[t]{cc} \text{\includegraphics{PHDImages/Chapitre2/gamma-variate.eps}} & \text{% \includegraphics{PHDImages/Chapitre2/gamma-variate.eps}} \\ \text{(a)} & \text{(b)} \\ \text{\includegraphics{PHDImages/Chapitre2/gamma-variate.eps}} & \text{% \includegraphics{PHDImages/Chapitre2/gamma-variate.eps}} \\ \text{(c)} & \text{(d)}% \end{array}%$%
\end{center}
\caption{title}
\label{fig:FIGURE2.8}
\end{figure}


and the result:

but what I want actually is to put sub-figures captions in the top (BOLD left-handed) like in the following image:

how can I do that?

• Welcome to TeX.SE! Please extend your code snippet to complete small document, which we can copy and compile as it is. – Zarko Jul 4 at 18:26
• Welcome to TEX-SE! Please always provide a complete example that starts with \documentclass and ends with \end{document}. Otherwise we do not know which packages you are using. Also you may be interested in this post. – user121799 Jul 4 at 18:28

I wouldn't use an array environment to position the graphs. Instead, I would load the subcaption package and use its machinery to arrange the graphs and associated captions.

\documentclass[demo]{article} % omit 'demo' option in real doc.
\usepackage[T1]{fontenc}
\usepackage{subcaption,graphicx}
\captionsetup[subfigure]{skip=0.25\baselineskip,justification=raggedright,
font={footnotesize,bf},labelsep=space,labelformat=simple}
\renewcommand\thesubfigure{\Alph{subfigure}}

\begin{document}
\begin{figure}
\begin{subfigure}[b]{0.475\textwidth}
\caption{flow\,=\,damped oscilator, CMRO2 coupled}
\includegraphics[width=\textwidth]{PHDImages/Chapitre2/gamma-variate1.eps}
\end{subfigure}\hfill
\begin{subfigure}[b]{0.475\textwidth}
\caption{flow\,=\,gamma variate convolutions, CMRO2 coupled}
\includegraphics[width=\textwidth]{PHDImages/Chapitre2/gamma-variate2.eps}
\end{subfigure}

\begin{subfigure}[t]{0.475\textwidth}
\caption{\dots}
\includegraphics[width=\textwidth]{PHDImages/Chapitre2/gamma-variate3.eps}
\end{subfigure}\hfill
\begin{subfigure}[t]{0.475\textwidth}
\caption{\dots}
\includegraphics[width=\textwidth]{PHDImages/Chapitre2/gamma-variate4.eps}
\end{subfigure}

\caption{title}
\label{fig:FIGURE2.8}
\end{figure}
\end{document}