X-Git-Url: https://bilbo.iut-bm.univ-fcomte.fr/and/gitweb/canny.git/blobdiff_plain/b335b39d3ad21e598f9a7172a3e95ffe0d48a736..e556b479316abe0d4183c94c28a84f07f9f64c9c:/experiments.tex diff --git a/experiments.tex b/experiments.tex index 11af844..21d813d 100644 --- a/experiments.tex +++ b/experiments.tex @@ -1,12 +1,107 @@ +For whole experiments, a set of 500 images is randomly extracted +from the database taken from the BOSS contest~\cite{Boss10}. +In this set, each cover is a $512\times 512$ +grayscale digital image. + + +\subsection{Adaptive Embedding Rate} + +Two strategies have been developed in our scheme, depending on the embedding rate that is either \emph{adaptive} or \emph{fixed}. + +In the former the embedding rate depends on the number of edge pixels. +The higher it is, the larger is the message length that can be inserted. +Practically, a set of edge pixels is computed according to the +Canny algorithm with an high threshold. +The message length is thus defined to be the half of this set cardinality. +In this strategy, two methods are thus applied to extract bits that +are modified. The first one is a direct application of the STC algorithm. +This method is further referred as \emph{adaptive+STC}. +The second one randomly chooses the subset of pixels to modify by +applying the BBS PRNG again. This method is denoted \emph{adaptive+sample}. +Notice that the rate between +available bits and bit message length is always equal to 2. +This constraint is indeed induced by the fact that the efficiency +of the STC algorithm is unsatisfactory under that threshold. +On our experiments and with the adaptive scheme, +the average size of the message that can be embedded is 16445. +Its corresponds to an average payload of 6.35\%. + + + + +In the latter, the embedding rate is defined as a percentage between the +number of modified pixels and the length of the bit message. +This is the classical approach adopted in steganography. +Practically, the Canny algorithm generates a +a set of edge pixels with threshold that is decreasing until its cardinality +is sufficient. If the set cardinality is more than twice larger than the +bit message length, a STC step is again applied. +Otherwise, pixels are again randomly chosen with BBS. + + \subsection{Image Quality} The visual quality of the STABYLO scheme is evaluated in this section. -Three metrics are computed in these experiments : +For the sake of completeness, four metrics are computed in these experiments: the Peak Signal to Noise Ratio (PSNR), -the PSNR-HVS-M~\cite{PSECAL07,psnrhvsm11} and the BIQI~\cite{MB10,biqi11}. +the PSNR-HVS-M family~\cite{PSECAL07,psnrhvsm11}, +the BIQI~\cite{MB10,biqi11}, and +the weighted PSNR (wPSNR)~\cite{DBLP:conf/ih/PereiraVMMP01}. The first one is widely used but does not take into -account Human Visual System (HVS). -The two last ones have been designed to tackle this problem. +account the Human Visual System (HVS). +The other ones have been designed to tackle this problem. + +\begin{table} +\begin{center} +\begin{tabular}{|c|c|c||c|c|} +\hline +Schemes & \multicolumn{3}{|c|}{STABYLO} & HUGO\\ +\hline +Embedding & \multicolumn{2}{|c||}{Adaptive} & Fixed & Fixed \\ +\hline +Rate & + STC & + sample & 10\% & 10\%\\ +\hline +PSNR & 66.55 & 63.48 & 61.86 & 64.65 \\ +\hline +PSNR-HVS-M & 78.6 & 75.39 & 72.9 & 76.67\\ +\hline +BIQI & 28.3 & 28.28 & 28.4 & 28.28\\ +\hline +wPSNR & 86.43& 80.59 & 77.47& 83.03\\ +\hline +\end{tabular} +\end{center} +\caption{Quality Measures of Steganography Approaches\label{table:quality}} +\end{table} + +Let us give an interpretation of these experiments. +First of all, the adaptive strategy produces images with lower distortion +than the one of images resulting from the 10\% fixed strategy. +Numerical results are indeed always greater for the former strategy than +for the latter, except for the BIQI metrics where differences are not really relevant. +These results are not surprising since the adaptive strategy aims at +embedding messages whose length is decided according to an higher threshold +into the edge detection. +Let us focus on the quality of HUGO images: with a given fixed +embedding rate (10\%), +HUGO always produces images whose quality is higher than the STABYLO's one. +However, our approach nevertheless provides better results with the strategy +\emph{adaptive+STC} in a lightweight manner, as motivated in the introduction. + + +Let us now compare the STABYLO approach with other edge based steganography +schemes with respect to the image quality. +First of all, the Edge Adaptive +scheme detailed in~\cite{Luo:2010:EAI:1824719.1824720} +executed with a 10\% embedding rate +has the same PSNR but a lower wPSNR than ours: +these two metrics are respectively equal to 61.9 and 68.9. +Next, both the approaches~\cite{DBLP:journals/eswa/ChenCL10,Chang20101286} +focus on increasing the payload while the PSNR is acceptable, but do not +give quality metrics for fixed embedding rate from a large base of images. +Our approach outperforms the former thanks to the introduction of the STC +algorithm. + @@ -20,14 +115,39 @@ and Ensemble Classifier~\cite{DBLP:journals/tifs/KodovskyFH12} based steganalyse Both aims at detecting hidden bits in grayscale natural images and are considered as the state of the art of steganalysers in spatial domain~\cite{FK12}. The former approach is based on a simplified parametric model of natural images. -Parameters are firstly estimated and a adaptive Asymptotically Uniformly Most Powerful -(AUMP) test is designed (theoretically and practically) to check whether -a natural image has stego content or not. +Parameters are firstly estimated and an adaptive Asymptotically Uniformly Most Powerful +(AUMP) test is designed (theoretically and practically), to check whether +an image has stego content or not. In the latter, the authors show that the -machine learning step, (which is often -implemented as support vector machine) -can be a favourably executed thanks to an Ensemble Classifiers. +machine learning step, which is often +implemented as support vector machine, +can be favorably executed thanks to an ensemble classifier. + + + +\begin{table} +\begin{center} +\begin{tabular}{|c|c|c|c|c|} +\hline +Schemes & \multicolumn{3}{|c|}{STABYLO} & HUGO\\ +\hline +Embedding & \multicolumn{2}{|c|}{Adaptive} & Fixed & Fixed \\ +\hline +Rate & + STC & + sample & 10\% & 10\%\\ +\hline +AUMP & 0.39 & 0.33 & 0.22 & 0.50 \\ +\hline +Ensemble Classifier & 0.47 & 0.44 & 0.35 & 0.48 \\ + +\hline +\end{tabular} +\end{center} +\caption{Steganalysing STABYLO\label{table:steganalyse}} +\end{table} +Results show that our approach is more easily detectable than HUGO, which +is the most secure steganographic tool, as far as we know. However due to its +huge number of features integration, it is not lightweight, which justifies +in authors' opinion the consideration of the proposed method. -\JFC{Raphael, il faut donner des résultats ici} \ No newline at end of file