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Macbeth key revision
A full guide of Macbeth revision notes containing key quotes, character analysis, sample paragraphs and video links
£6.25 Preview RemoveDigital Watermarking
Introduction 1.1 Digital Watermarking Watermarking techniques are usually preferred for copyright ownership declaration, creator/authorship declaration, copyright violation detection (fingerprinting function), copyright violation deterrence, copy control, media authentication, and media data integrity functions. They are also devised for variety of media viz., text, digital audio, digital image and digital video. 1.2 Spread Spectrum (SS) Watermarking 1.2.1 Spread Spectrum Spread Spectrum techniques for watermarking purposes have aroused a lot of interest in today because of it’s using in Steganography. Generally the message use to watermark is a narrow band signal compared to the wide band of the cover image. Spread spectrum techniques applied to the message allow the frequency bands to be matched before transmitting the message (Watermark) through the covert channel (image). Furthermore, high frequencies are relevant for the invisibility of the watermarked message but are inefficient as far as robustness is concerned, whereas low frequencies are of interest with regards to robustness but are useless because of the unacceptable visible impact. Spread spectrum can reconcile these conflicting points by allowing a low energy signal to be embedded in each one of the frequency bands. Spread spectrum techniques also offer the possibility of protecting the watermark privacy using a secret key to control a pseudo noise generator. 1.2.2 Mathematical form of SS Watermarking encoding and Decoding Cox proposed a watermarking scheme that is based on the spread spectrum (SS) communication .In this scheme, the discrete cosine transform (DCT) is performed on a whole image and then the watermark is embedded in a predetermined range of low frequency components as shown in Figure 2.1. The embedded watermark signal consists of a sequence of real numbers that are normally distributed and it is scaled according to the signal strength of the frequency components. It is a simple watermarking scheme with perceptual weighting consideration.
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