It takes into account so-called SPAM features (whose size is larger than $10^7$) to avoid overfitting a particular
steganalyser. Thus a distortion measure for each pixel is individually determined as the sum of differences between
features of SPAM computed from the cover and from the stego images.
-Thanks to this feature set, HUGO allows to embed $7\times$ longer messages with the same level of
+Thanks to this features set, HUGO allows to embed $7\times$ longer messages with the same level of
indetectability than LSB matching.
However, this improvement is time consuming, mainly due to the distortion function
computation.
There remains a large place between random selection of LSB and feature based modification of pixel values.
We argue that modifying edge pixels is an acceptable compromise.
Edges form the outline of an object: they are the boundary between overlapping objects or between an object
-and the background. A small modification of pixel value in the stego image should not be harmful to the image quality:
-in cover image, edge pixels already break its continuity and thus already contain large variation with neighboring
+and the background. When producing the stego-image, a small modification of some pixel values in such edges should not impact the image quality, which is a requirement when
+attempting to be undetectable. Indeed,
+in cover image, edges already break the continuity of pixels' intensity map and thus already present large variations with theirs neighboring
pixels. In other words, minor changes in regular area are more dramatic than larger modifications in edge ones.
-Our proposal is thus to embed message bits into edge shapes while preserving other smooth regions.
+Our first proposal is thus to embed message bits into edge shapes while preserving other smooth regions.
-Edge based steganographic schemes have been already studied in~\cite{Luo:2010:EAI:1824719.1824720} and \cite{DBLP:journals/eswa/ChenCL10}.
+Edge based steganographic schemes have been already studied, the most interesting
+approaches being detailed in~\cite{Luo:2010:EAI:1824719.1824720} and \cite{DBLP:journals/eswa/ChenCL10}.
In the former, the authors show how to select sharper edge regions with respect
to a given embedding rate: the larger the number of bits to be embedded, the coarser
the edge regions are.
Then the data hiding algorithm is achieved by applying LSBMR on pixels of these regions.
The authors show that their proposed method is more efficient than all the LSB, LSBM, and LSBMR approaches
thanks to extensive experiments.
-However, it has been shown that the distinguish error with LSB embedding is lower than
+However, it has been shown that the distinguishing error with LSB embedding is lower than
the one with some binary embedding~\cite{DBLP:journals/tifs/FillerJF11}.
We thus propose to take benefit of these optimized embedding, provided they are not too time consuming.
In the latter, an hybrid edge detector is presented followed by an ad hoc
-embedding approach.
+embedding.
The Edge detection is computed by combining fuzzy logic~\cite{Tyan1993}
and Canny~\cite{Canny:1986:CAE:11274.11275} approaches. The goal of this combination
is to enlarge the set of modified bits to increase the payload of the data hiding scheme.
The approach we propose is thus to provide a self adaptive algorithm with a high payload, which depends on the
cover signal.
-For some applications it might be interesting to have a reversible procedure to compute the same edge detection pixel set for the cover and the stego image. For this, we propose to apply the edge detection algorithm not on all the bits of the image, but to exclude the LSBs.
-
+Additionally, in the steganographic context, the data hiding procedure is often required
+to be a reversible one. We thus need to be able to compute the same edge detection pixels set for the cover and the stego image. For this, we propose to apply the edge detection algorithm not on all the bits of the image, but to exclude the LSBs.
+Finally, even if the steganalysis discipline
+has done great leaps forward these last years, it is currently impossible to prove rigorously
+that a given hidden message cannot be recovered by an attacker.
+This is why we add to our scheme a reasonable
+message encryption stage, to be certain that,
+even in the worst case scenario, the attacker
+will not be able to obtain the message content.
-\JFC{Christophe : énoncer la problématique du besoin de crypto et de ``cryptographiquement sûr'', les algo déjà cassés....
-l'efficacité d'un encodage/décodage ...}
-To deal with security issues, message is encrypted...
In this research work, we thus propose to combine tried and
tested techniques of signal theory (the adaptive edge detection), coding (the binary embedding), and cryptography
