Beamer: \usebackgroundtemplate + \only: problem duplicated frame and index shifted by 1

Question

I'm trying to put \only<1>{...} images in the background slide of beamer. However, I need to add +1 to all values in \only, i.e. I need to write \only<2>{...} to display the image on the first frame. Despite being not practical, the problem is that it also duplicate the last slide 2 times, which creates without any reason an additional, unwanted slide...

Any reason for that? How can I come back to normal numbering, and remove this last unwanted frame?

Thanks!

MWE:

\documentclass[table,aspectratio=169]{beamer}
\useoutertheme[footline=institutetitle,subsection=false]{miniframes}
\usecolortheme{beaver}
\begin{document}
{\usebackgroundtemplate{%
    % Why do I need to add 1 to get the correct value for only, and how can I remove the last, doubled, slide?
    \only<2>{\includegraphics[width=\paperwidth,height=\paperheight]{example-image-a}}%
    \only<3>{\includegraphics[width=\paperwidth,height=\paperheight]{example-image-b}}%
    \only<4>{\includegraphics[width=\paperwidth,height=\paperheight]{example-image-c}}%
  }
  \begin{frame}[t]
    \begin{itemize}
      \item \onslide<1>{A}
      \item \onslide<2>{B}
      \item \onslide<3>{C (see that on the next slide there is an empty slide...)}
    \end{itemize}
  \end{frame}
}
\end{document}

-- EDIT -- The problem of the solution given in this thread is that it create additional pages instead of putting all slides in a single page...

\documentclass{beamer}
\useoutertheme[footline=institutetitle,subsection=false]{miniframes}
\usecolortheme{beaver}
\setbeamercolor{separation line}{use=structure,bg=darkred!80!black}
\begin{document}
\section{test}
{
  \setbeamertemplate{background}{\includegraphics[height=\paperheight,width=\paperwidth]{example-image-a}}
  \begin{frame}<1>[label=myframelabel]
    \begin{itemize}
      \item<+-> a
      \item<+-> b
      \item<+-> c
      \item<+-> d
      \item<+-> e
    \end{itemize}
  \end{frame}
  \setbeamertemplate{background}{\includegraphics[height=\paperheight,width=\paperwidth]{example-image-b}}
  \againframe<2>{myframelabel}
  \setbeamertemplate{background}{\includegraphics[height=\paperheight,width=\paperwidth]{example-image-c}}
  \againframe<3>{myframelabel}
  \setbeamertemplate{background}{\includegraphics[height=\paperheight,width=\paperwidth]{example-image-a}}
  \againframe<4->{myframelabel}
}
\begin{frame}
  Hello, I'm a new empty frame
\end{frame}
\end{document}

Change Beamer frame background between slides in same itemize seems to be related. — leandriis, May 16 '21 at 11:40
@leandriis Thanks a lot, the solutions proposed here does work. Thanks a lot! Feel free to write an answer if you want and I can accept it. — tobiasBora, May 16 '21 at 16:37
It's just a bit sad, one solution creates one new page per slide, and one solution is not super proper as it tries to enlarge the picture a bit more to avoid having margins. — tobiasBora, May 16 '21 at 16:59

score 2 · Accepted Answer · answered May 16 '21 at 18:41

you are overdoing with the \only in the background template. You can simply retrieve the slide number and choose your graphic based on its value:

\documentclass[table,aspectratio=169]{beamer}
\useoutertheme[footline=institutetitle,subsection=false]{miniframes}
\usecolortheme{beaver}
\begin{document}
\ExplSyntaxOn
\usebackgroundtemplate{%
\tl_set:Nx \l_tmpa_tl {example-image-\int_to_alph:n{\insertslidenumber}}
\includegraphics[width=\paperwidth,height=\paperheight]{\l_tmpa_tl}}
\ExplSyntaxOff

  \begin{frame}[t]
    \begin{itemize}
      \item \onslide<1>{A}
      \item \onslide<2>{B}
      \item \onslide<3>{C (see that on the next slide there is an empty slide...)}
    \end{itemize}
  \end{frame}
\end{document}

Thanks a lot, it works great! I also added a new answer that improves slighly the readability of the code and that allows ranges like <1-3> (I used newcommand, I'm not sure if it's great to mix that with ExplSyntax, but at least it seems to work nicely). — tobiasBora, May 17 '21 at 08:08

score 0 · Answer 2 · answered May 17 '21 at 08:07

After Ulrich's answer, I came out with this code to also handle ranges like <4-5>, and to factorize a bit the repetitive code. So I don't bring any new idea, but I just wanted to provide it for reference. I'm not sure if it's great practice to mix newcommand with ExplSyntax... but it seems to really nicely, thanks a lot! It also works with miniframes, pages...

\documentclass[table,aspectratio=169]{beamer}
\useoutertheme[footline=institutetitle,subsection=false]{miniframes}
\usecolortheme{beaver}
\ExplSyntaxOn
\newcommand{\addBackgroundOne}[2]{
    \bool_if:nT {\int_compare_p:n{\insertslidenumber=#1}}{%
      \includegraphics[width=\paperwidth,height=\paperheight]{#2}
    }
}
\newcommand{\addBackgroundSlice}[3]{
    \bool_if:nT {\int_compare_p:n{\insertslidenumber>=#1} && \int_compare_p:n{\insertslidenumber<=#2}}{%
      \includegraphics[width=\paperwidth,height=\paperheight]{#3}
    }
}
\ExplSyntaxOff
\begin{document}
{
  \usebackgroundtemplate{%
    \addBackgroundOne{1}{example-image-a}
    \addBackgroundSlice{2}{3}{example-image-b}
    \addBackgroundOne{4}{example-image-c}
  }
  \begin{frame}[t]
    \begin{itemize}
      \item A
            \pause
      \item B
            \pause
      \item B
            \pause
      \item C
    \end{itemize}
  \end{frame}
}
\end{document}

Beamer: \usebackgroundtemplate + \only: problem duplicated frame and index shifted by 1

2 Answers2

Linked