Andrew Z. Tirkel

Bio: Andrew Z. Tirkel is an academic researcher from Monash University. The author has contributed to research in topics: Digital watermarking & Watermark. The author has an hindex of 10, co-authored 40 publications receiving 1661 citations. Previous affiliations of Andrew Z. Tirkel include Monash University, Clayton campus.

A digital watermark

Abstract: The paper discusses the feasibility of coding an "undetectable" digital water mark on a standard 512/spl times/512 intensity image with an 8 bit gray scale. The watermark is capable of carrying such information as authentication or authorisation codes, or a legend essential for image interpretation. This capability is envisaged to find application in image tagging, copyright enforcement, counterfeit protection, and controlled access. Two methods of implementation are discussed. The first is based on bit plane manipulation of the LSB, which offers easy and rapid decoding. The second method utilises linear addition of the water mark to the image data, and is more difficult to decode, offering inherent security. This linearity property also allows some image processing, such as averaging, to take place on the image, without corrupting the water mark beyond recovery. Either method is potentially compatible with JPEG and MPEG processing. >

Key independent watermark detection

Abstract: Many types of pseudo-random signals have been used to embed signatures as watermarks, with spread spectrum signal techniques used to recover the signature from the encrypted data. Legendre sequences are a suitable candidate for signature encryption as they exhibit 'perfect' two level auto-correlation. Additionally Legendre sequences have the unusual and interesting property of invariance under Fourier transformation; the spatial and frequency representation of each sequence is identical up to a phase factor. The presence of a Legendre-based watermark, embedded in the pixel or transform domain, can be detected by cross-correlating a sequence-encrypted image with its Fourier transform. This property enables verification of the presence of a watermark (of specified length), without requiring prior knowledge of the sequence type or key used for the encryption.

Millimeter wave array for UAV imaging MIMO radar

Abstract: High resolution imaging radars at millimeter-wave frequencies for obstacle avoidance for Unmanned Aerial Vehicles (UAV) utilize a large antenna aperture and sequential mechanical scanning of the aperture to form images with high fidelity. Planar arrays are an attractive alternative. They do not require mechanical scanning, and images are formed digitally using beamforming techniques [1]. To achieve image quality comparable to mechanically scanned radars, fully populated arrays require inordinate numbers of elements. These are costly, a challenge to design, and difficult to produce. Thinned or sparse arrays are a potential solution to this problem. MIMO (Multiple Input Multiple Output) techniques are an efficient method of thinning an array using spreading sequences to create an overlay of paired transmitter and receiver elements, without sacrificing image quality. The use of MIMO techniques to thin an array is a relatively recent development [2]. To be of practical use at millimeter-wave frequencies, MIMO techniques require the development of novel array geometries and architecture. This paper presents designs for the implementation of millimeter-wave planar arrays which have been thinned using MIMO techniques and considerers the limitations on the length of spreading sequences due to the increasingly pronounced effect of Doppler at higher frequencies. These considerations have led to the first instance of the use of the Moreno-Tirkel sequence Family B for high resolution imaging radar.

Algebraic construction of a new class of quasi-orthogonal arrays for steganography

Abstract: Watermark recovery is often based on cross-correlating images with pseudo-noise sequences, as access to un-watermarked originals is not required. Successful recovery of these watermarks is determined by the (periodic or aperiodic) sequence auto- and cross-correlation properties. This paper presents several methods of extending the dimensionality of 1D sequences in order to utilize the advantages that this offers. A new type of 2D array construction is described, which meets the above requirements. They are constructed from 1D sequences that have good auto-correlation properties by appending rows of cyclic shifts of the original sequence. The sequence values, formed from the roots of unity, offer additional diversity and security over binary arrays. A family of such arrays is described which have low cross-correlation and can be folded and unfolded, rendering them robust to cryptographic attack. Row and column products of 1D Legendre sequences can also produce equally useful 2D arrays (with interesting properties resulting from the Fourier invariance of Legendre sequences). A metric to characterize all these 2D correlation based watermarks is proposed.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

New optimal low correlation sequences for wireless communications

Abstract: This paper presents three new sets of frequency hopping sequences, which are converted into sequences for CDMA. One of the CDMA sequence families is optimal with respect to the Welch bound, and two are nearly optimal. Our sequences are available for more lengths, and have much higher linear complexity than other CDMA sequences. They have a similar structure to the small Kasami set, but are balanced. The CDMA sequences are constructed using a composition method, which combines new shift sequences with pseudonoise columns to form an array. The array dimensions are relatively prime, so it is unfolded using the Chinese Remainder Theorem. Each of our constructions gives rise to two additional families with larger family sizes but worse correlation as explained in Section 4.2.

Secure spread spectrum watermarking for multimedia

Abstract: This paper presents a secure (tamper-resistant) algorithm for watermarking images, and a methodology for digital watermarking that may be generalized to audio, video, and multimedia data. We advocate that a watermark should be constructed as an independent and identically distributed (i.i.d.) Gaussian random vector that is imperceptibly inserted in a spread-spectrum-like fashion into the perceptually most significant spectral components of the data. We argue that insertion of a watermark under this regime makes the watermark robust to signal processing operations (such as lossy compression, filtering, digital-analog and analog-digital conversion, requantization, etc.), and common geometric transformations (such as cropping, scaling, translation, and rotation) provided that the original image is available and that it can be successfully registered against the transformed watermarked image. In these cases, the watermark detector unambiguously identifies the owner. Further, the use of Gaussian noise, ensures strong resilience to multiple-document, or collusional, attacks. Experimental results are provided to support these claims, along with an exposition of pending open problems.

Digital Watermarking

Abstract: Digital watermarking is a key ingredient to copyright protection. It provides a solution to illegal copying of digital material and has many other useful applications such as broadcast monitoring and the recording of electronic transactions. Now, for the first time, there is a book that focuses exclusively on this exciting technology. Digital Watermarking covers the crucial research findings in the field: it explains the principles underlying digital watermarking technologies, describes the requirements that have given rise to them, and discusses the diverse ends to which these technologies are being applied. As a result, additional groundwork is laid for future developments in this field, helping the reader understand and anticipate new approaches and applications.

Information hiding-a survey

Abstract: Information-hiding techniques have recently become important in a number of application areas. Digital audio, video, and pictures are increasingly furnished with distinguishing but imperceptible marks, which may contain a hidden copyright notice or serial number or even help to prevent unauthorized copying directly. Military communications systems make increasing use of traffic security techniques which, rather than merely concealing the content of a message using encryption, seek to conceal its sender, its receiver, or its very existence. Similar techniques are used in some mobile phone systems and schemes proposed for digital elections. Criminals try to use whatever traffic security properties are provided intentionally or otherwise in the available communications systems, and police forces try to restrict their use. However, many of the techniques proposed in this young and rapidly evolving field can trace their history back to antiquity, and many of them are surprisingly easy to circumvent. In this article, we try to give an overview of the field, of what we know, what works, what does not, and what are the interesting topics for research.

Quantization index modulation: a class of provably good methods for digital watermarking and information embedding

Abstract: We consider the problem of embedding one signal (e.g., a digital watermark), within another "host" signal to form a third, "composite" signal. The embedding is designed to achieve efficient tradeoffs among the three conflicting goals of maximizing the information-embedding rate, minimizing the distortion between the host signal and composite signal, and maximizing the robustness of the embedding. We introduce new classes of embedding methods, termed quantization index modulation (QIM) and distortion-compensated QIM (DC-QIM), and develop convenient realizations in the form of what we refer to as dither modulation. Using deterministic models to evaluate digital watermarking methods, we show that QIM is "provably good" against arbitrary bounded and fully informed attacks, which arise in several copyright applications, and in particular it achieves provably better rate distortion-robustness tradeoffs than currently popular spread-spectrum and low-bit(s) modulation methods. Furthermore, we show that for some important classes of probabilistic models, DC-QIM is optimal (capacity-achieving) and regular QIM is near-optimal. These include both additive white Gaussian noise (AWGN) channels, which may be good models for hybrid transmission applications such as digital audio broadcasting, and mean-square-error-constrained attack channels that model private-key watermarking applications.

Digital Watermarking and Steganography

Abstract: Digital audio, video, images, and documents are flying through cyberspace to their respective owners. Unfortunately, along the way, individuals may choose to intervene and take this content for themselves. Digital watermarking and steganography technology greatly reduces the instances of this by limiting or eliminating the ability of third parties to decipher the content that he has taken. The many techiniques of digital watermarking (embedding a code) and steganography (hiding information) continue to evolve as applications that necessitate them do the same. The authors of this second edition provide an update on the framework for applying these techniques that they provided researchers and professionals in the first well-received edition. Steganography and steganalysis (the art of detecting hidden information) have been added to a robust treatment of digital watermarking, as many in each field research and deal with the other. New material includes watermarking with side information, QIM, and dirty-paper codes. The revision and inclusion of new material by these influential authors has created a must-own book for anyone in this profession. *This new edition now contains essential information on steganalysis and steganography *New concepts and new applications including QIM introduced *Digital watermark embedding is given a complete update with new processes and applications