This work considers digital images as covers and foundation is
spatial least significant-bit (LSB) replacement.
-I this data hiding scheme a subset of all the LSB of the cover image is modified
+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.
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
-and thus by steganalysis methods~\cite{DBLP:journals/tsp/DumitrescuWW03,DBLP:conf/mmsec/FridrichGD01,Dumitrescu:2005:LSB:1073170.1073176}
+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
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.
-This scheme deals with pairs of pixels instead of individual ones.
-It thus allows to decrease the number of modified bits per cover pixel
-for the same payload compared to LSB replacement and LSBM and
-and avoids the LSB replacement style asymmetry. Unfortunately,
-detectors referenced above are able to distinguish between
-stego content images and cover images.
+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.
+
+
+
+In such a way, the modification
+rate of pixels can decrease from 0.5 to 0.375 bits/pixel
+(bpp) in the case of a maximum embedding rate, meaning fewer
+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
+LSBM approach. % based on our experiments
+
+
+
+
Instead of (efficiently) modifying LSBs, there is also a need to select pixels whose value
modification minimizes a distortion function.
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
-pixels. In other words, minor changes in regular area is more dramatic than larger modifications in edge ones.
+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.
Edge based steganographic schemes have bee already studied~\cite{Luo:2010:EAI:1824719.1824720,DBLP:journals/eswa/ChenCL10}.
and compare them to state of the art steganographic schemes.
Finally, concluding notes and future works are given in section~\ref{sec:concl}
-theory : ?
+
