Cryptography Reference
In-Depth Information
10.5.4 Spatial Domain Methods
A watermark generated in the spatial domain is a method that generates
watermark patterns using some noise patterns that possess correlation prop-
erties. For example m-sequences. The watermark patterns are then embedded
into an image in spatial domain. Fig. 10.9 shows an example of a watermark
pattern generated in spatial domain. A similar method was proposed by a
company in Japan. The major merit of this method is fewer calculations in
the process of watermark extraction. The drawback of this method is that
in the process of watermark detection, the existence of the image itself will
reduce the rate of detection of embedded noise patterns. Therefore, as shown
in Fig. 10.9, the images are generally designed with a wide blank background
where the noise patterns are embedded.
Fig. 10.9.
An example of a watermark generated in spatial domain, and the right
one is an expanded area in the left image.
10.5.5 Color Domain Methods
The watermark generated in the color domain is a method that generates the
watermark patterns using colors that are hard to perceive by the human eye. It
embeds the watermark patterns into an image in the spatial domain. Fig. 10.10
shows an example of a watermark generated using yellow colors. A similar
method was proposed by a company in Japan. As shown in Fig. 10.10(b), the
yellow domain of an image Fig. 10.10(a) was divided into small blocks and
two adjoining blocks were indexed from left to right horizontally. These are
embedded with 1 bit of information in the following way. If a bit information
1 is embedded,
• then the average yellow in left block is adjusted to be larger than that in
right block.
