\subsection{Preprocessing}
\begin{frame}{Preprocessing}
    \begin{columns}[T] % contents are top vertically aligned
    \begin{column}[T]{5cm} % each column can also be its own environment
        \begin{itemize}
            \item<1-> Normalizing
            \begin{itemize}
                \item<2-> Scaling
                \item<2-> Shifting
                \item<3-> Resampling
            \end{itemize}
            \item<1-> Noise reduction
            \begin{itemize}
                \item<4-> Smoothing (e.g. moving average)
                \item<5-> Dot reduction
                \item<6-> Filtering (by distance, speed or angle)
                \item<7-> Stroke connection
            \end{itemize}
        \end{itemize}
    \end{column}
    \begin{column}[T]{6cm} % alternative top-align that's better for graphics
        \only<2>{\includegraphics[width=6cm, keepaspectratio]{scale-and-shift.png}}
        \only<3>{\includegraphics[width=6cm, keepaspectratio]{resampling.png}}
        \only<4>{\includegraphics[width=6cm, keepaspectratio]{smooth-1-1-1.png}}
        \only<7>{\includegraphics[width=6cm, keepaspectratio]{interrupted-stroke.png}}
    \end{column}
    \end{columns}


\end{frame}