\usepackage[left=15mm, right=15mm, top=15mm, bottom=20mm, b5paper,mag=1193,
            nohead ]{geometry}

\usepackage{graphicx}
\usepackage{rotating}

\def\bigimg#1{\hspace{-0.05\textwidth}\includegraphics[width=1.05\textwidth]{#1}}
\def\Bigimg#1{\hspace{-0.15\textwidth}\includegraphics[width=1.2\textwidth]{#1}}
\def\img#1#2{{\begin{center}\includegraphics[width=#2\textwidth]{#1}\end{center}}}

\newenvironment{midlepage}{
      \setlength\paperwidth{2\paperwidth}
      \setlength\textwidth{2\textwidth}}{
      \newpage
      \setlength\paperwidth{0.5\paperwidth} 
      \setlength\textwidth{0.5\textwidth}}

%\if@twoside
% \oddsidemargin -0.4 in      %   Note that \oddsidemargin = \evensidemargin
% \evensidemargin -0.4 in
%\fi
