+\subsection{Adaptive Embedding Rate}
+
+Two strategies have been developed in our scheme with respect to the rate of
+embedding which 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 considered.
+Practically, a set of edge pixels is computed according to the
+Canny algorithm with high threshold.
+The message length is thus defined to be the half of this set cardinality.
+The rate between available bits and bit message length is then more than two.This constraint is indeed induced by the fact that the efficiency
+of the STC algorithm is unsatisfactory under that threshold.
+
+
+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.
+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 an STC step is again applied.
+Otherwise, pixels are randomly chosen from the set of pixels to build the
+subset with a given size. The BBS PRNG is again applied there.
+
+
+
+
+\subsection{Image Quality}
+The visual quality of the STABYLO scheme is evaluated in this section.
+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 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 other last ones have been designed to tackle this problem.
+
+\begin{table}
+\begin{center}
+\begin{tabular}{|c|c|c|}
+\hline
+Embedding rate & Adaptive & 10 \% \\
+\hline
+PSNR & 66.55 & 61.86 \\
+\hline
+PSNR-HVS-M & 78.6 & 72.9 \\
+\hline
+BIQI & 28.3 & 28.4 \\
+\hline
+wPSNR & 86.43& 77.47 \\
+\hline
+\end{tabular}
+\end{center}
+\caption{Quality measures of our steganography approach\label{table:quality}}
+\end{table}
+
+
+Let us compare the STABYLO approach with other edge based steganography
+schemes with respect to the image quality.
+First of all, wPSNR and PSNR of the Edge Adaptive
+scheme detailed in~\cite{Luo:2010:EAI:1824719.1824720} are lower than ours.
+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.
+
+
