  This short paper proposes to use the statistical analysis of the correlation
between DCT coefficients to design a new synchronization strategy that can be
used for cost-based steganographic schemes in the JPEG domain. First, an
analysis is performed on the covariance matrix of DCT coefficients of
neighboring blocks after a development similar to the one used to generate
BossBase. This analysis exhibits groups of uncorrelated coefficients: 4 groups
per block and 2 groups of uncorrelated diagonal neighbors together with groups
of mutually correlated coefficients groups of 6 coefficients per blocs and 8
coefficients between 2 adjacent blocks. Using the uncorrelated groups, an
embedding scheme can be designed using only 8 disjoint lattices. The cost map
for each lattice is updated firstly by using an implicit underlying Gaussian
distribution with a variance directly computed from the embedding costs, and
secondly by deriving conditional distributions from multivariate distributions.
The covariance matrix of these distributions takes into account both the
correlations exhibited by the analysis of the covariance matrix and the
variance derived from the cost. This synchronization scheme enables to obtain a
gain of PE of 5% at QF 95 for an embedding rate close to 0.3 bnzac coefficient
using DCTR feature sets.
