How to make appear semi transparent the following parts of a presentation?

Question

Hello I am using a template called: Radboud University Beamer(Version1), https://www.sharelatex.com/templates/presentations, I am customizing it a little.

Since I want to use an image at the first slide I changed the background, however in order to make visible the text inside I changed the default behavior of beam for this as follows:

\setbeamercolor{author}{fg=red!80!black,bg=red!20!white}

The problem with this is that the image is not visible I would like to use not a solid color instead a semi transparent color, so I would like to appreciate advices to get this,

there is a question related with this:

How to make a block transparent for a background image

And I tried with this approach as follows:

\addtobeamertemplate{block begin}{\pgfsetfillopacity{0.8}}{\pgfsetfillopacity{1}}
 \addtobeamertemplate{block alerted begin}{\pgfsetfillopacity{0.9}}{\pgfsetfillopacity{1}}
 \addtobeamertemplate{block example begin}{\pgfsetfillopacity{0.9}}{\pgfsetfillopacity{1}}

Using a template, I failed since this is only changing the behavior of the blocks, not parts such as \author, \subtitle, \title, that are just macros to store the information, not to use them I would like to appreciate any help to overcome this situation, thanks any how.

Answer 1

You have to use the code where the information of title, author etc are inserted in the document, in this case the title page.

\documentclass[compress]{beamer}
\usecolortheme{rose}

\usebackgroundtemplate{\centering
        \includegraphics[width=\paperwidth,height=\paperheight]{example-image}}

\addtobeamertemplate{title page}{\pgfsetfillopacity{0.5}}{\pgfsetfillopacity{1}}


\title{test}
\author{bla}

\setbeamercolor{title}{fg=white, bg=red}
\setbeamercolor{author}{fg=white, bg=red}
\setbeamercolor{date}{fg=white, bg=red}

\begin{document}
  \begin{frame}
        \titlepage
  \end{frame}
\end{document}