Cryptography Reference
In-Depth Information
10.5.2 Watermarking Schemes
In order to solve the problems of watermarking techniques used for the ap-
plications of print-to-web linking technology using mobile phone camera, the
only way for us is to make the watermark more robust at the cost of reducing
image quality within the perceptible tolerance of human eyes. As a general
method for robust watermarking techniques, it is common to generate water-
mark into patterns that have the low perceptibility and have high correlation
properties.
Many watermarking methods have been proposed for the applications of
print-to-web linking technology using a mobile phone camera. These can be
divided into 4 categories as follows:
(1) Watermarking in the frequency domain.
(2) Watermarking in the spatial domain.
(3) Watermarking in the color domain.
(4) Watermarking in the special design.
10.5.3 Frequency Domain Methods
A watermark generated in frequency domain is a method that inserts some
special components into an image frequency domain. It then generates the wa-
termark pattern by inverse-transforming the pattern into the spatial domain.
We know that the major merit of a watermark generated in the frequency
domain is the robustness to geometrical transform [15]. Fig. 10.8 shows an
example of watermark generated in frequency domain. A similar method was
proposed by a company in Japan. The drawback of this method is that it is
time consuming during the watermark extraction process.
Fig. 10.8.
An example of the watermark generated in frequency domain, and the
right one is an expanded area in the left image.
