| Summary: | 碩士 === 國立臺灣大學 === 電機工程學研究所 === 99 === Digital watermarking is the process of embedding information into owner’s contents
that is difficult to remove. It can represent in several ways such as an embedded
tag, picture, signature or any digital information. Once a digital content has been
stolen, owner could use digital watermark to claim the copyright of ownership and
apply for compensation according to copyright law.
To improve the robustness of digital watermark, most techniques proposed to
use discrete cosine transform (DCT) to embed watermark information into the low-
frequency part of image since DC components have larger perceptual capacity than
AC components. These schemes perform very well under a general JPEG compres-
sion. However, when the watermarked images have been compressed with higher
compression ratio, the embedded watermark is destroyed.
In this thesis, we proposed an innovative DCT-based digital image watermarking
scheme that could enhance the robustness under higher JPEG compression with the
concept of modulus. We could also preserve the visual quality of watermarked
images.
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