I am attempting to insert a full-page figure into my slides, see the MWE below.
The first experience, that 'Title' and 'subtitle' appear
at their normal position. With the option 'plain' I expected to not appear.
The second one, that if I uncomment the 'section' command, I do have an extra slide, with section 'title' as frame title, on the top of the background figure, although the template is local. Do I misunderstand something?
\documentclass{beamer}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{graphicx}
\begin{document}
%\section{sec}{title}
{
\usebackgroundtemplate{\includegraphics[width=\paperwidth]{YourFigureHere}}%
\begin{frame}[plain]{Title}{Subtitle}
\end{frame}
}
\end{document}
Best Answer
The first question has already been addressed in comments.
Here, I address the second, together with the related question you asked in comments.
The template is local. But the frame on which the stray text appears is not complete when the group containing the template specification opens. So the template is set while material is being collected for that frame. When you start the next frame properly, the previous one is finished and shipped out with the background template.
If you add stray text following the frame, but before the group is closed, you can see the reverse effect. The stray text is put into a new frame. At this point, the background is active. However, the group is closed while material is still being collected for the frame. So the background setting is switched off while that material is being collected. When the next frame begins outside of the local group, the previous frame is ended and the frame is shipped out with the current, default background template.
This is easier to show than to explain...