Problem with centering Images in a column (beamer)

Question

I have a strange problem centering an image in a column.

I m going to create a presentation with Beamer and I created a slide with 2 columns.

The idea (conceptually) is to display the first image, then the second and then comes the last one which should replace the first 2 BUT be vertically centered I don t know how, but my last image goes at the bottom of the slide.

Here is the code:

\documentclass{beamer}
\usepackage[utf8x]{inputenc}
\usepackage{default}
\usepackage{amsmath,amsfonts,amssymb}
\usepackage{graphicx}
\usepackage{xmpmulti}
\graphicspath{{bilder_pre/}}
\usetheme{Warsaw}
\setbeamercovered{transparent}
\setbeamertemplate{items}[ball]
\begin{document}
\begin{frame}{TEXT - \textsl{TEXT TEXT TEXT}}

 \begin{block}{Auswirkung der dcckbcskjcbsc}
      Kommentar
 \end{block}

 \begin{columns}
      \begin{column}{0.33\textwidth}

                \visible<1-2>{\includegraphics[scale=0.2]{foto1}}
                \visible<2>{\includegraphics[scale=0.2]{foto2}}%
                \llap{\includegraphics<3->[scale=0.2]{foto3}}

      \end{column}

      \begin{column}{0.33\textwidth}
%                   \includegraphics<1->[scale=0.2]{Abbildung4_2}
      \end{column}

      \begin{column}{0.33\textwidth}
 %                   \includegraphics<1>[scale=0.2]{Abbildung4_1}
      \end{column}
 \end{columns}

\end{frame}


\end{document}

I tried every combination: \centering{}, \parbox, \begin{overlayarea} and \begin{overprint}. No matter...

What could I do?

Answer 1

Here you are a solution with \parbox and \only:

\PassOptionsToPackage{demo}{graphicx}
\documentclass{beamer}
\usepackage{graphicx}
\usepackage{framed}
\usetheme{Warsaw}

\begin{document}
\begin{frame}{TEXT - \textsl{TEXT TEXT TEXT}}
\begin{block}{Auswirkung der dcckbcskjcbsc}
Kommentar
\end{block}

\begin{columns}
\begin{column}{0.33\textwidth}

%better than scale: width + height + keepaspectratio

\parbox[c][.6\textheight][c]{\columnwidth}{%
\only<1-2>{\includegraphics[width=\columnwidth,%
    height=.3\textheight,keepaspectratio]{foto1}\\%
\visible<2>{\includegraphics[width=\columnwidth,%
    height=.3\textheight,keepaspectratio]{foto2}}%
}
\only<3>{\includegraphics[width=\columnwidth,%
    height=.3\textheight,keepaspectratio]{foto3}%
}}

\end{column}
\begin{column}{0.33\textwidth}
\end{column}
\begin{column}{0.33\textwidth}
\end{column}
\end{columns}
\end{frame}
\end{document}