Cryptography Reference
In-Depth Information
The aim is to transmit watermarked images over noisy channels. Our pro-
posed schemes for embedding single or multiple watermarks using tabu search
can effectively overcome channel impairments and reproduce a good recon-
structed image, while still retaining the capability for ownership and copyright
protection.
12.2 Backgrounds of Multiple Description Coding
and Its Generic Model
During transmissions of data, losses are inevitable due to channel errors or
lost packets under different types of transmission channels. In contrast to the
conventional schemes such as progressive transmission, Multiple Description
Coding (MDC) offers an alternative method for the effective transmission of
compressed multimedia information.
MDC is an error resilient coding technique, which can be used as a source
coding method for a channel whose end-to-end performance includes uncor-
rected erasures. This channel is encountered in a packet communication sys-
tem that has effective error detection but does not have the features which
permit the retransmission of incorrect or lost packets. MDC uses diversity
to overcome channel impairments so that a decoder, which receives an ar-
bitrary subset of the channels, may reproduce a useful reconstruction [23].
Information-theoretic issues of MDC have been studied extensively since the
early eighties [24, 25]. In Multiple Description (MD) coders, the same source
material is coded into several chunks of data, called
descriptions
, such that
each description can be decoded independently in order to obtain minimum
fidelity. It also combines with other descriptions to achieve a better quality.
The goals for MDC and channel coding are to make effective transmission
of data, the MDC offers a totally different perspective from that of channel
coding [26].
MDC is suitable for transmission with noisy channels with long bursts
of errors. To gain robustness of the loss of descriptions in spite, MDC must
sacrifice some compression e
ciency while still retaining the capability of er-
ror resilience. Fig. 12.1 depicts the generic model for MD source coding with
two channels and three decoders. The Encoder is denoted by α
0
. Decoder
0, denoted by β
0
, is called the
central decoder
, and Decoders 1 and 2, are
denoted by β
1
and β
2
respectively, are the
side decoders
. The Euclidean dis-
tance between X and X
(0)
is the
central distortion
, while the errors between
X and X
(i)
,i =1, 2, are the
side distortions
. It suggests a situation in which
there are three separate users or three classes of users, which could arise when
broadcasting on two channels. The same abstraction holds if there is a sin-
gle user that can be in one of three states depending on which descriptions
are received. Generally speaking, if we extend the number of transmission
channels in Fig. 12.1 to K, there will be 2
K
−1 receivers that decode with
