-This work considers digital images as covers and foundation is
+This work considers digital images as covers and it is based on
spatial least significant-bit (LSB) replacement.
-In this data hiding scheme a subset of all the LSB of the cover image is modified
-with a secret bit stream depending on to a key, the cover, and the message to embed.
+In this data hiding scheme a subset of all the LSBs of the cover image is modified
+with a secret bit stream depending on a key, the cover, and the message to embed.
This well studied steganographic approach never decreases (resp. increases)
pixel with even value (resp. odd value) and may break structural symmetry.
-These structural modification can be detected by statistical approaches
+These structural modifications can be detected by statistical approaches
and thus by steganalysis methods~\cite{DBLP:journals/tsp/DumitrescuWW03,DBLP:conf/mmsec/FridrichGD01,Dumitrescu:2005:LSB:1073170.1073176}.
This drawback is avoided in LSB matching (LSBM) where
the $+1$ or $-1$ is randomly added to the cover pixel LSB value
only if this one does not match the secret bit.
-Since probabilities of increasing or decreasing pixel value are the same, statistical approaches
-cannot be applied there to discover stego-images in LSBM.
-The most accurate detectors for this matching are universal steganalysers such as~\cite{LHS08,DBLP:conf/ih/2005,FK12}
+Since probabilities of increasing or decreasing the pixel value are the same, statistical approaches
+cannot be applied here to discover stego-images in LSBM.
+The most accurate detectors for this matching are universal steganalysers such as~\cite{LHS08,DBLP:conf/ih/2005,FK12},
which classify images thanks to extracted features from neighboring elements of noise residual.
-LSB matching revisited (LSBMR)~\cite{Mielikainen06} have been recently introduced.
+LSB matching revisited (LSBMR) has been recently introduced in~\cite{Mielikainen06}.
For a given pair of pixels, in which the LSB
of the first pixel carries one bit of secret message, and the relationship
(odd–even combination) of the two pixel values carries
another bit of secret message.
-
+\CG{Je pige pas cette phrase, et je comprends pas l'explication du LSBMR :/}
In such a way, the modification
changes to the cover image at the same payload compared to
LSB replacement and LSBM. It is also shown that such a new
scheme can avoid the LSB replacement style asymmetry, and
-thus it should make the detection slightly more difficult than the
+thus it should make the detection slightly more difficult than in the
LSBM approach. % based on our experiments
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 contains large variation with neighbouring
+in cover image, edge pixels already break its continuity and thus already contain large variation with 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.
However, it has been shown that the distinguish error with LSB embedding is fewer than
the one with some binary embedding~\cite{DBLP:journals/tifs/FillerJF11}.
We thus propose to take benefit of these optimized embedding, provided it is not too time consuming.
-In the latter, an hybrid edge detector is presented followed by an ad'hoc
+In the latter, an hybrid edge detector is presented followed by an ad hoc
embedding approach.
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
produce stego content
with only considering the payload, not the type of image signal: the higher the payload is,
the better the approach is said to be.
-Contrarely, we argue that some images should not be taken as a cover because of the nature of their signal.
+Contrarily, we argue that some images should not be taken as a cover because of the nature of their signal.
Consider for instance a uniformly black image: a very tiny modification of its pixels can be easily detectable.
The approach we propose is thus to provide a self adaptive algorithm with a high payload, which depends on the
-cover signal.
+cover signal.
+For some applications it might be interesting to be 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 only on all the bits without taking into consideration the LSB.
\JFC{Christophe : énoncer la problématique du besoin de crypto et de ``cryptographiquement sûr'', les algo déjà cassés....
scheme, which takes into consideration the cover image
an which is amenable to be executed on small devices.
-The rest of the paper is organised as follows.
+The rest of the paper is organized as follows.
Section~\ref{sec:ourapproach} presents the details of our steganographic scheme.
Section~\ref{sec:experiments} shows experiments on image quality, steganalytic evaluation, complexity of our approach
and compare them to state of the art steganographic schemes.
