[Tex/LaTex] How to achieve top-alignment of images in subfigure

subfloatsvertical alignment

There are some threads about subfigures and alignment, but I could not find a solution for my problem. I want to have two figures side by side, both with their own capture (a and b) and below one capture for both. Using

\documentclass{article}
\usepackage{subcaption}
\usepackage{graphicx}

\begin{document}
\begin{figure}
    \centering
    \begin{subfigure}[b]{.49\textwidth}
        \centering
        \includegraphics[width=6cm]{example-image-a}
        \caption{Caption describing fig a}
        \label{fig:figure_a}
    \end{subfigure}\hfill%
    \begin{subfigure}[b]{.49\textwidth}
        \centering
        \includegraphics[width=7cm]{example-image-b}
        \caption{Caption describing fig b}
        \label{fig:figure_b}
    \end{subfigure}
    \caption{Caption for both images}
    \label{fig:Filter_L_LCL}
\end{figure}
\end{document}

gives me this:
enter image description here

and using my graphics I get this, so it is quite the similar situation:

enter image description here

Exactly what I want, expect the image alignment. I'd like to have them top-aligned and captions bottom-aligned (the image size must not be changed since image and document font size match). How can this be done? Any solution without manually shifting?

Best Answer

You can obtain it with the floatrow package:

\documentclass{article}
\usepackage{geometry}
\usepackage{subcaption}
\usepackage{graphicx, floatrow}

\begin{document}

\begin{figure}
\floatsetup{valign=t, heightadjust=all}
\ffigbox{%
\begin{subfloatrow}
\ffigbox{\includegraphics[width=6cm]{example-image-a}}{\caption{Caption describing fig a \label{fig:figure_a}}}
\ffigbox{\includegraphics[width=7cm]{example-image-b}}{\caption{Caption describing fig b} \label{fig:figure_b}}
    \end{subfloatrow}}
    {\caption{Caption for both images}
    \label{fig:Filter_L_LCL}}
\end{figure}

\end{document} 

enter image description here