Quantization-Based Digital Image Watermarking
Date Issued
2005
Date
2005
Author(s)
Chen, Jun-Horng
DOI
en-US
Abstract
The computer networks and mass storage devices make the exchange and spread of digital multimedia content more easy than before, yet challenge the copyright protection and obstruct the development of creative work. In addition, many fantastic software can tamper the digital content imperceptibly, and thus raise the difficulty of authentication. Consequently, watermarking techniques are extensively discussed with the aim to address these issues and provide the DRM (Digital Rights Management) with a firm basis.
This dissertation presents a preliminary discussion of watermarking systems. Each part of a generic watermarking scheme is discussed essentially. In the invisible watermarking systems, three important properties: transparency, robustness, and capacity, are typically evaluated to criticize the performance of a watermarking system. However, these properties are demanded different extents depending on what applications the watermarking systems are applied.
Many researches regarded the watermark as the message to be sent over a digital communications system, and the transmitting will inevitably sustain the interference from the host signal and the superimposed noise from attacks. However, this viewpoint ignores the fact that the host signal is known to the watermark embedder. The quantization-based watermarking has the inherent advantage that the host signal is taken into account for rejecting the interference from it, where the QIM (Quantization Index Modulation) is the representative approach. This study analyzes and compares a variety of improving skills for quantization-based watermarking. The experimental results have shown that those improving skills more or less accomplished their expectation in some restricted scenarios, but not for all the cases. In this dissertation, the non-centric quantization is proposed to improve the robustness of quantization-based watermarking. The simulation results have demonstrated that the proposed scheme outperforms the convectional quantization-based watermarking for most of the applicable cases.
This study also presents the watermarking schemes based on vector quantization (VQ), which inherently have the feature of joint watermarking and compression (JWC). A modified binary tree splitting method (BTSM) is proposed to generate the codebook for VQ, and the watermark message is thus embedded by the replacement of the representative index when the host vector is encoded. The performance superiority over other watermarking schemes based on VQ is presented. Notably, the lightness of computation cost of the proposed scheme enhances its applicability.
Most of the watermarking approaches are proposed for the host images in gray-level. As for the color host images, the most intuitive approach is directly applied the methods designed for gray-level images to the tri-channel signals of the host images. This study evaluates the performances of the watermark messages embedded into different channels of the color host image. The experimental results have shown that the answer to "which channel of the color host image is suitable for embedding watermark message?" is indecisive, yet should be answered according to the attack to which the watermarked images will resist. The color quantization based on the Fibonacci lattice has been proven to be competitive to other approaches for its good visual quality and the simplicity of color palette generation at decoder end. A novel image watermarking approach, Fibonacci Lattice Index Modulation (FLIM), is specifically proposed for the color image watermarking in this study. FLIM unobtrusively embeds a fragile watermark into the chromatic component for the purpose of authentication. With another robust watermark embedded into the luminance component by the QIM approach, the hybrid watermarking system embeds two watermark messages with different purposes concurrently, and can thus be applied to a variety of scenarios.
Subjects
數位影像浮水印
量化
向量量化
費伯納契晶格
強健性
Digital Image Watermarking
Quantization
Vector Quantization
Fibonacci Lattice
Robustness
Type
thesis
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