Let us recall too that this drawback
can be fixed by considering the LSB matching (LSBM) subcategory, in which
-the $+1$ or $-1$ is randomly added to the cover pixel's LSB value
+a $+1$ or $-1$ is randomly added to the cover pixel's LSB value
only if this one does not correspond to the secret bit.
%TODO : modifier ceci
By considering well-encrypted hidden messages, the probabilities of increasing or decreasing the value of pixels are equal. Then usual statistical approaches
directional filter. Thus, similarly, the distortion function is
the sum of the differences between these wavelet coefficients
computed from the cover and from the stego images.
-
-
Due to this distortion measures, HUGO, WOW and UNIWARD allow
to embed messages that are $7$ times longer than the former
ones with the same level of
indetectability as LSB matching.
However, this improvement has a larger computation cost, mainly due to
the distortion function
-calculus.
+computation.
There remains a large place between random selection of LSB and feature based modification of pixel values.
We thus propose to take advantage of this optimized embedding, provided they are not too time consuming.
In the latter, an hybrid edge detector is presented followed by an ad hoc
embedding.
-The Edge detection is computed by combining fuzzy logic~\cite{Tyan1993}
+The Edge detection is computed by combining fuz\-zy 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.
Contrarily, we argue that some images should not be taken
as a cover because of the nature of their signals.
Consider for instance a uniformly black image: a very tiny modification of its
-pixels can be easily detectable.
+pixels can be easily detected.
Practically speaking, if Alice would send
a hidden message to Bob, she would never consider
such kind of image and a high embedding rate.
long message in the cover signal.
Practically speaking, our approach is efficient enough for
payloads close to 0.06 bit per pixel which allows to embed
-messages of length larger than 16000 bits in an
+messages of length larger than 15,728 bits in an
image of size $512\times 512$ pixels.
% Message extraction is achieved by computing the same
will not be able to obtain the original message content.
Doing so makes our steganographic protocol, to a certain extend, an asymmetric one.
-To sum up, in this research work, well-studied and experimented
+To sum up, well-studied and experimented
techniques of signal processing (adaptive edges detection),
coding theory (syndrome-trellis codes), and cryptography
-(Blum-Goldwasser encryption protocol) are combined
-to compute an efficient steganographic
-scheme, whose principal characteristic is to take into
+(Blum-Goldwas\-ser encryption protocol) are combined in this research work.
+The objective is to compute an efficient steganographic
+sche\-me, whose principal characteristic is to take into
consideration the cover image and to be compatible with small computation resources.
The remainder of this document is organized as follows.
