You should best make a separate PDF with your big image and include it in the main document using the pdfpages package. The \includepdf macro provided can insert one or multiple PDF pages either with the document page size or with the original page size. For the latter simply use the fitpaper option.
\documentclass[a4paper]{book}
\usepackage{graphicx}
\usepackage{pdfpages}
\usepackage{afterpage}
\usepackage{lipsum}
\begin{document}
\chapter{Test}
\lipsum% stands for some example paragraphs before the image
\afterpage{% to place it direkt after the next page break, not direct after the text, to avoid a larger empty space
\includepdf[fitpaper=true]{big_image}%
}
\lipsum% stand for some example paragraphs after the image. The first parapraphs can still be placed on the page before the image
\end{document}
Here I made the example image using the following document:
% big_image.tex
\documentclass[a0paper,landscape]{article}
\usepackage[margin=2cm]{geometry}
\usepackage{graphicx}
\pagestyle{empty}
\setlength{\parindent}{0pt}
\begin{document}
\includegraphics[width=.999\textwidth,height=.999\textheight]{example-image}%
\end{document}
geometrypackage?\clearpage\newgeomtry{a0paper,margin=1in}then insert the image followed by\clearpage\newgeomtry{a4paper,margin=1in}may be the solution. – Jun 11 '12 at 22:50