Trying to insert a background image via TikZ results in extra white-space around the corners

Question

I am trying to insert a background image in my beamer template as follows:

\documentclass[10pt,c,aspectratio=169,a4paper]{beamer}
\usepackage{tikz}


\setbeamertemplate{background}{
    \begin{tikzpicture}%
     \node {\includegraphics[width=\paperwidth,height=\paperheight,keepaspectratio]{example-image-a}};
    \end{tikzpicture}
}

\begin{document}

    \section{Introduction}

    \begin{frame}

\end{frame}
\end{document}

this results in

as you can see, due to some sort of bounding box around the inserted image, there is a space from the north-west corner of the image in (x-y). However, I would like to position the image in the starting at the north-west corner.

Answer 1

You need to set inner sep=0pt.

\documentclass[10pt,c,aspectratio=169,a4paper]{beamer}
\usepackage{tikz}


\setbeamertemplate{background}{
    \begin{tikzpicture}%
     \node[inner sep=0pt] {\includegraphics[width=\paperwidth,height=\paperheight,keepaspectratio]{example-image-a}};
    \end{tikzpicture}
}

\begin{document}

    \section{Introduction}

    \begin{frame}

\end{frame}
\end{document}