Transparent shading for Singapore theme

[samcarter]

It might be nice to change the shading of the Singapore theme to transparent

\documentclass{beamer}

\usetheme{Singapore}

\setbeamertemplate{background canvas}{\includegraphics[width=\paperwidth]{example-grid-100x100bp}}

\begin{document}
\section{test}
\begin{frame}
content...
\end{frame}
\end{document}

(would also be a nice option to get rid of the \AtBeginDocument{\setbeamercolor{section in head/foot}{bg=}} which causes problems for some footlines)