[Tex/LaTex] Vertical centering of figure

Question

I understand from other posts that a single float should automatically be centered vertically on the page; however, this does not seem to be the case in my code. Why?

I use the book class.

Both examples below result in the figures being placed on the top of the page.

\clearpage
\begin{figure}[ht]
\renewcommand{\figurename}{Picture}
\centering
\includegraphics[scale=1.0,clip]{pic1.eps}
\caption{pic1}
\label{pic1}
\end{figure}

\clearpage
\begin{figure}[H]
\renewcommand{\figurename}{Picture}
\centering
\includegraphics[scale=0.6,clip]{pic2.eps}
\caption{pic2}
\label{pic2}
\end{figure}
\clearpage

Answer 1

The problem is solved by using

\begin{figure}[p]