maj

[canny.git] / experiments.tex

diff --git a/experiments.tex b/experiments.tex
index c92062c01027a8f4eed07bcf6fcf9b4e835d9192..0c08d6924a78df9cce07ca0dd0cb947f944d7021 100644 (file)
--- a/experiments.tex
+++ b/experiments.tex
@@ -1,39 +1,47 @@
-For whole experiments, a set of 500 images is randomly extracted 
-from the database taken from the BOSS contest~\cite{Boss10}. 
+For whole experiments, the whole set of 10000 images 
+of the BOSS contest~\cite{Boss10} database is taken. 

 In this set, each cover is a $512\times 512$
 In this set, each cover is a $512\times 512$

-grayscale digital image.
+grayscale digital image in a RAW format. 
+We restrict experiments to 
+this set of cover images since this paper is more focused on 
+the methodology than benchmarking.    
+Our approach is always compared to Hugo~\cite{DBLP:conf/ih/PevnyFB10}
+and to EAISLSBMR~\cite{Luo:2010:EAI:1824719.1824720}.
+

 
 
 
 

-\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}.
+
+\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.
 
 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.
+The higher it is, the larger the message length that can be inserted is.

 Practically, a set of edge pixels is computed according to the 
 Canny algorithm with an high threshold.
 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.
+The message length is thus defined to be 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.
 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 choose the subset of pixels to modify by 
+This method is further referred to 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.
 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.
+In our experiments and with the adaptive scheme, 
+the average size of the message that can be embedded is 16,445 bits.

 Its corresponds to an  average payload of 6.35\%. 
 
 
 
 
 In the latter, the embedding rate is defined as a percentage between the 
 Its corresponds to an  average payload of 6.35\%. 
 
 
 
 
 In the latter, the embedding rate is defined as a percentage between the 

-number of the modified pixels and the length of the bit message.
+number of modified pixels and the length of the bit message.

 This is the classical approach adopted in steganography.
 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
+Practically, the Canny algorithm generates  
+a set of edge pixels related to a 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.
 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.


@@ -44,63 +52,78 @@ Otherwise, pixels are again randomly chosen with BBS.
 The visual quality of the STABYLO scheme is evaluated in this section.
 For the sake of completeness, four metrics are computed in these experiments: 
 the Peak Signal to Noise Ratio (PSNR), 
 The visual quality of the STABYLO scheme is evaluated in this section.
 For the sake of completeness, four metrics are computed in these experiments: 
 the Peak Signal to Noise Ratio (PSNR), 

-the PSNR-HVS-M family~\cite{PSECAL07,psnrhvsm11} , 
-the BIQI~\cite{MB10,biqi11}, and 
+the PSNR-HVS-M family~\cite{psnrhvsm11}, 
+%the BIQI~\cite{MB10}, 
+and 

 the weighted PSNR (wPSNR)~\cite{DBLP:conf/ih/PereiraVMMP01}.
 The first one is widely used but does not take into
 account the Human Visual System (HVS).
 the weighted PSNR (wPSNR)~\cite{DBLP:conf/ih/PereiraVMMP01}.
 The first one is widely used but does not take into
 account the Human Visual System (HVS).

-The other last ones have been designed to tackle this problem.
+The other ones have been designed to tackle this problem.

 
 

-\begin{table}
+
+
+
+\begin{table*}

 \begin{center}
 \begin{center}

-\begin{tabular}{|c|c|c||c|c|}
-\hline
-Schemes & \multicolumn{3}{|c|}{STABYLO} & HUGO\\
+\begin{tabular}{|c|c|c||c|c|c|c|c|}

 \hline
 \hline

-Embedding &   \multicolumn{2}{|c||}{Adaptive} & Fixed & Fixed \\
+Schemes & \multicolumn{3}{|c|}{STABYLO} & \multicolumn{2}{|c|}{HUGO}& \multicolumn{2}{|c|}{EAISLSBMR} \\

 \hline
 \hline

-Rate &   + STC &  + sample & 10\% & 10\%\\ 
+Embedding &   Fixed & \multicolumn{2}{|c|}{Adaptive} &  \multicolumn{2}{|c|}{Fixed}& \multicolumn{2}{|c|}{Fixed} \\

 \hline
 \hline

-PSNR &  66.55 & 63.48  & 61.86  & 64.65   \\ 
+Rate &   10\% &  + sample & + STC  &  10\%&6.35\%& 10\%&6.35\%\\ 

 \hline
 \hline

-PSNR-HVS-M & 78.6 & 75.39 & 72.9 & 76.67\\ 
+PSNR & 61.86 & 63.48 &  66.55 (\textbf{-0.8\%})     & 64.65 & {67.08} & 60.8 & 62.9\\ 

 \hline
 \hline

-BIQI & 28.3 & 28.28 & 28.4 & 28.28\\ 
+PSNR-HVS-M & 72.9 & 75.39 & 78.6 (\textbf{-0.8\%})    & 76.67 & {79.23} & 61.3  & 63.4\\ 
+%\hline
+%BIQI & 28.3 & 28.28 & 28.4 & 28.28 & 28.28 & 28.2 & 28.2\\ 

 \hline
 \hline

-wPSNR & 86.43& 80.59 & 77.47& 83.03\\ 
+wPSNR & 77.47 & 80.59 & 86.43(\textbf{-1.6\%})  & 83.03 & {87.8} & 76.7 & 80.6\\ 

 \hline
 \end{tabular}
 \hline
 \end{tabular}

+
+\begin{footnotesize}
+\vspace{2em}
+Variances given in bold font express the quality differences between 
+HUGO and STABYLO with  STC+adaptive parameters.
+\end{footnotesize}
+

 \end{center}
 \end{center}

-\caption{Quality Measures of Steganography Approaches\label{table:quality}} 
-\end{table}
+\caption{Quality Measures of Steganography Approaches\label{table:quality}}
+\end{table*}
+
+

 
 

-Let us give an interpretation of these experiments.
+Results are summarized into the Table~\ref{table:quality}.
+Let us give an interpretation of these first 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 
 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 relevant.
+for the latter.

 These results are not surprising since the adaptive strategy aims at 
 These results are not surprising since the adaptive strategy aims at 

-embedding messages whose length is decided according to a higher threshold
+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.
 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.      
+However our approach always outperforms EAISLSBMR since this one may modify 
+the two least significant bits whereas STABYLO only alter LSB.
+
+If we combine \emph{adaptive} and \emph{STC} strategies 
+(which leads to an average embedding rate equal to 6.35\%)
+our approach  provides equivalent metrics than HUGO.
+The quality variance between HUGO and STABYLO for these parameters
+is given in bold font. It is always close to 1\% which confirms 
+the objective presented in the motivations:
+providing an efficient steganography approach with a lightweight manner.

 
 
 Let us now compare the STABYLO approach with other edge based steganography
 
 
 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.
+approaches, namely~\cite{DBLP:journals/eswa/ChenCL10,Chang20101286}.
+These two schemes focus on increasing the
+payload while the PSNR is acceptable, but do not 
+give quality metrics for fixed embedding rates from a large base of images. 

 
 
 
 
 
 


@@ -109,7 +132,7 @@ algorithm.
 
 
 
 
 
 

-The quality of our approach has been evaluated through the two 
+The steganalysis quality of our approach has been evaluated through the two 

 AUMP~\cite{Fillatre:2012:ASL:2333143.2333587}
 and Ensemble Classifier~\cite{DBLP:journals/tifs/KodovskyFH12} based steganalysers.
 Both aims at detecting hidden bits in grayscale natural images and are 
 AUMP~\cite{Fillatre:2012:ASL:2333143.2333587}
 and Ensemble Classifier~\cite{DBLP:journals/tifs/KodovskyFH12} based steganalysers.
 Both aims at detecting hidden bits in grayscale natural images and are 


@@ -117,36 +140,45 @@ 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 an adaptive Asymptotically Uniformly Most Powerful
 (AUMP) test is designed (theoretically and practically), to check whether
 The former approach is based on a simplified parametric model of natural images.
 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.  
+an image has stego content or not.
+This approach is dedicated to verify whether LSB has been modified or not.

 In the latter, the authors show that the 
 In the latter, the authors show that the 

-machine learning step, (which is often
-implemented as support vector machine)
-can be favorably 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{table*}

 \begin{center}
 \begin{center}

-\begin{tabular}{|c|c|c|c|c|}
+%\begin{small}
+\begin{tabular}{|c|c|c|c|c|c|c|c|}

 \hline
 \hline

-Schemes & \multicolumn{3}{|c|}{STABYLO} & HUGO\\
+Schemes & \multicolumn{3}{|c|}{STABYLO} & \multicolumn{2}{|c|}{HUGO}& \multicolumn{2}{|c|}{EAISLSBMR}\\

 \hline
 \hline

-Embedding &   \multicolumn{2}{|c|}{Adaptive} & Fixed & Fixed \\
+Embedding & Fixed &   \multicolumn{2}{|c|}{Adaptive}  & \multicolumn{2}{|c|}{Fixed}& \multicolumn{2}{|c|}{Fixed} \\

 \hline
 \hline

-Rate &   + STC &  + sample & 10\% & 10\%\\ 
+Rate & 10\% &  + sample &   + STC   & 10\%& 6.35\%& 10\%& 6.35\%\\ 

 \hline
 \hline

-AUMP & 0.39  & 0.33  & 0.22     &  0.50     \\
+AUMP & 0.22 & 0.33 & 0.39         &  0.50 &  0.50 & 0.49 & 0.50 \\

 \hline
 \hline

-Ensemble Classifier & 0.47 & 0.44 & 0.35     & 0.48     \\
+Ensemble Classifier & 0.35 & 0.44 & 0.47       & 0.48 &  0.49  &  0.43  & 0.46 \\

 
 \hline
 \end{tabular}
 
 \hline
 \end{tabular}

+%\end{small}

 \end{center}
 \caption{Steganalysing STABYLO\label{table:steganalyse}} 
 \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.   
+\end{table*}
+
+
+Results are summarized in Table~\ref{table:steganalyse}.
+First of all, STC outperforms the sample strategy for the two steganalysers, as 
+already noticed in the quality analysis presented in the previous section. 
+Next, our approach is more easily detectable than HUGO, which
+is the most secure steganographic tool, as far as we know. 
+However by combining \emph{adaptive} and \emph{STC} strategies
+our approach obtains similar results than HUGO ones.
+However due to its 
+huge number of features integration, it is not lightweight, which justifies 
+in the authors' opinion the consideration of the proposed method.