答案1
一种快速简便的方法是使用tikz
:
\documentclass{beamer}
\usepackage{tikz}
\begin{document}
\begin{frame}
\frametitle{test}
\includegraphics{example-image-duck}
\begin{onlyenv}<2->
\begin{tikzpicture}[remember picture,overlay]
\fill[black,opacity=0.5] (current page.south west) rectangle (current page.north east);
\node[draw=orange,fill=black,font=\Huge\color{orange}] at (current page.center) {Some text};
\end{tikzpicture}
\end{onlyenv}
\end{frame}
\end{document}