Cryptography Reference
In-Depth Information
the commonly employed scheme is to embed the watermark into Least
Significant Bits (LSB). This is done in the frequency domain as a Dis-
crete Cosine Transform (DCT) domain or Discrete Wavelet Transform
(DWT) domain. The tendency is to embed the watermark into the
higher frequency band coe cients. However, this causes the water-
mark to become vulnerable to common image processing techniques
such as Low-Pass Filtering (LPF).
2. Watermark robustness means the capability that the watermarked media
can withstand intentional or unintentional media processing, known as
attacks . These can include filtering, transcoding, resizing, or rotation.
There are also benchmarks to objectively examine the watermark robust-
ness, such as Stirmark [25]. It is generally agreed that robustness plays
an important role in the design of watermarking algorithm. To speak
heuristically, in order to gain more robustness, the watermark needs to
be embedded into the Most Significant Bits (MSB) in the spatial domain.
Alternatively, this may be done in the lower frequency band coe cients
in the transform domain. By doing so, the watermarked image quality
can be seriously degraded, and others may suspect to the existence of the
watermark. The tradeoff between watermark imperceptibility and water-
mark robustness is to embed the watermark into the middle frequency
bands in the transform domain [26].
3. Watermark capacity refers to the number of bits embedded into the orig-
inal media. That is, the size of watermark. Generally speaking, if more
bits can be embedded, the watermarking algorithm is supposed to be
more robust; however, under these conditions, the quality of watermarked
media is degraded, and the existence of a watermark becomes more per-
ceptible. Authors in [17, 19] have derived theoretical bounds for watermark
capacity.
The fundamental concepts of digital watermarking and data hiding, may
be further explored in the advanced topics relating to data hiding and appli-
cations in the subsequent chapters.
1.3 Summary
A general concept for multimedia signal processing and watermarking is pre-
sented in this chapter. Topics included in this topic are also considered. In
subsequent chapters, the authors will discuss the two themes of this topic.
These include fundamental concepts, algorithms and applications in detail.
We hope readers will find them of value.
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