I tried centering horizontally using the "adjustwidth" environment, but unfortunately, it's not very accurate. Also my captions are not centered under my figures anymore.
I have no idea how to use the area above my minipage. I tried using vspace, but I can't seem to move the minipage upwards.
Following image illustrates my issue:
Following piece of code (MWE) shows what I tried to do:
\documentclass[11pt, a4paper, openright]{book} %oneside option
\usepackage{etex}
\usepackage{tocbibind}
%PACKAGES
%\usepackage{times}
\usepackage[dvips]{graphicx}
\usepackage{chngpage}
\usepackage{url}
\usepackage[english]{babel}
\usepackage[T1]{fontenc}
\usepackage[all]{xy}
\usepackage{amssymb}
\usepackage{amsmath}
\usepackage{psfrag} %laprint
\usepackage{color}
\usepackage[usenames]{xcolor}
\usepackage[pdf,usenames,dvipsnames]{pstricks}
\usepackage{tikz}
\usepackage{auto-pst-pdf}
\usepackage{epsfig}
\usepackage{pst-grad} % For gradients
\usepackage{pst-plot} % For axes
\usepackage{epstopdf}
\usepackage{float}
\usepackage{pdfpages}
\usepackage{subfigure}
\usepackage{mathabx}
\usepackage[chapter]{algorithm}
\usepackage[small,bf,hang]{caption}
\renewcommand{\captionfont}{\small\itshape}
\usepackage{natbib}
\bibpunct{[}{]}{;}{n}{,}{,} % Numerical system
\usepackage{listings}
%LAYOUT
\bibliographystyle{ieeetr}
\usepackage{chngcntr}
\setcounter{secnumdepth}{4}
\setcounter{tocdepth}{1}
\setlength{\textheight}{237mm} %A4 - 297
\setlength{\textwidth}{160mm} %A4 - 210
\setlength{\topmargin}{-0.54cm} %A4
\setlength{\headheight}{15pt} %A4
\setlength{\oddsidemargin}{0.46cm} %A4 Centers text.
\setlength{\evensidemargin}{-.54cm} %A4
%
%Left margin 30 mm, right margin 20 mm, top margin 20 mm, bottom margin 20 mm.
%2,54
\usepackage{fancyhdr}
\pagestyle{fancy}
% with this we ensure that the chapter and section
% headings are in lowercase.
\renewcommand{\chaptermark}[1]{%
\markboth{#1}{}}
\renewcommand{\sectionmark}[1]{%
\markright{\thesection\ #1}}
\fancyhf{} % delete current header and footer
\fancyhead[LE,RO]{\bfseries\thepage}
\fancyhead[LO]{\bfseries\rightmark}
\fancyhead[RE]{\bfseries\leftmark}
\renewcommand{\headrulewidth}{0.5pt}
\renewcommand{\footrulewidth}{0pt}
\addtolength{\headheight}{0.5pt} % space for the rule
\fancypagestyle{plain}{%
\fancyhead{} % get rid of headers on plain pages
\renewcommand{\headrulewidth}{0pt} % and the line
}
\parskip 6pt % sets spacing between paragraphs
\parindent 0pt % sets leading space for paragraphs
\newtheorem{definition}{Definition}[chapter]
\newenvironment{remark}[1][Remark]{\begin{trivlist}
\item[\hskip \labelsep {\bfseries #1}]}{\end{trivlist}}
\newcommand{\vectornorm}[1]{\|#1\|}
%Locally remove natural indent of itemize
\usepackage{enumitem}
\usepackage{hyperref}
\hypersetup{
colorlinks,%
citecolor=black,%
filecolor=black,%
linkcolor=black,%
urlcolor=black
}
\begin{document}
\begin{figure}[p]
\makebox[\textwidth][c]{%
\begin{minipage}[b]{0.565\linewidth}
\centering
\includegraphics[scale=0.7]{plots/Reflex_128_Plot_xRemovals_yCPUsecondsEncoding.eps}
\caption{Reflex: $128 \times 128$ - Encoder}
\label{plot:encoding_decoding_cpu_time_2a}
\end{minipage}%
\begin{minipage}[b]{0.565\linewidth}
\centering
\includegraphics[scale=0.7]{plots/Reflex_128_Plot_xRemovals_yCPUsecondsDecoding.eps}
\caption{Reflex: $128 \times 128$ - Decoder}
\label{plot:encoding_decoding_cpu_time_2b}
\end{minipage}}%
\makebox[\textwidth][c]{%
\begin{minipage}[b]{0.565\linewidth}
\centering
\includegraphics[scale=0.7]{plots/Lena_128_Plot_xRemovals_yCPUsecondsEncoding.eps}
\caption{Lena: $128 \times 128$ - Encoder}
\label{plot:encoding_decoding_cpu_time_3a}
\end{minipage}%
\begin{minipage}[b]{0.565\linewidth}
\centering
\includegraphics[scale=0.7]{plots/Lena_128_Plot_xRemovals_yCPUsecondsDecoding.eps}
\caption{Lena: $128 \times 128$ - Decoder}
\label{plot:encoding_decoding_cpu_time_3b}
\end{minipage}}%
\makebox[\textwidth][c]{%
\begin{minipage}[b]{0.565\linewidth}
\centering
\includegraphics[scale=0.7]{plots/Fruits_128_Plot_xRemovals_yCPUsecondsEncoding.eps}
\caption{Fruits: $128 \times 128$ - Encoder}
\label{plot:encoding_decoding_cpu_time_4a}
\end{minipage}%
\begin{minipage}[b]{0.565\linewidth}
\includegraphics[scale=0.7]{plots/Fruits_128_Plot_xRemovals_yCPUsecondsDecoding.eps}
\centering
\caption{Fruits: $128 \times 128$ - Decoder}
\label{plot:encoding_decoding_cpu_time_4b}
\end{minipage}}%
\end{figure}
\end{document}
Thanks in advance for your help!