Browsing by Author "Orchard, Michael"
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Item On The Problem of Simultaneous Encoding of Magnitude and Location Information(2002-11-20) Castro, Rui; Wakin, Michael; Orchard, Michael; Digital Signal Processing (http://dsp.rice.edu/)Modern image coders balance bitrate used for encoding the location of signicant transform coefficients, and bitrate used for coding their values. The importance of balancing location and value information in practical coders raises fundamental open questions about how to code even simple processes with joint uncertainty in coefficient location and magnitude. This paper studies the most basic example of such a process: a 2-D process studied earlier by Weidmann and Vetterli that combines Gaussian magnitude information with Bernoulli location uncertainty. The paper offers insight into the coding of this process by investigating several new coding strategies based on more general approaches to lossy compression of location. Extending these ideas to practical coding, we develop a trellis-coded quantization algorithm with performance matching the published theoretical bounds. Finally, we evaluate the quality of our strategies by deriving a rate-distortion bound using Blahut's algorithm for discrete sources.Item Phase and Magnitude Perceptual Sensitivities in Nonredundant Complex Wavelet Representations(2003-11-01) Wakin, Michael; Orchard, Michael; Baraniuk, Richard G.; Chandrasekaran, Venkat; Digital Signal Processing (http://dsp.rice.edu/)The recent development of a nonredundant complex wavelet transform allows a novel framework for image analysis. Work on this representation has recognized that the phase and magnitude of complex coefficients can be related to important geometric properties in images. Existing work on human visual system (HVS) sensitivity offers little guidance in understanding the relative importance of noise (e.g., introduced by lossy coding) in phase components and magnitude components. The distinct geometric significance of the two components would suggest that their respective errors relate to different types of image structure, and thus each would have its own unique HVS sensitivity. In this paper, we extend the study of just-noticeable-differences (JND) to magnitude/phase sensitivities in complex wavelet representations and outline and report on preliminary experiments characterizing them.Item Robust Privacy-Preserving Fingerprint Authentication(2016-01-08) Zhang, Ye; Koushanfar, Farinaz; Veeraraghavan, Ashok; Orchard, MichaelThis paper presents the first scalable, efficient, and reliable privacy-preserving fingerprint authentication based on minutiae representation. Our method is provably secure by leveraging the Yao's classic Garbled Circuit (GC) protocol. While the concept of using GC for secure fingerprint matching has been suggested earlier, to the best of our knowledge, no prior reliable method or implementation applicable to real fingerprint data has been available. Our technique achieves both accuracy and practicability by customizing a widely adopted minutiae-based fingerprint matching algorithm, Bozorth matcher, as our core authentication engine. We modify the Bozorth matcher and identify certain sensitive parts of this algorithm. For these critical parts, we create a sequential circuit description which can be efficiently synthesized and customized to GC using the TinyGarble framework. We show evaluations of our modified matching algorithm on a standard fingerprint database FVC2002 DB2 to demonstrate its reliability. The implementation of privacy-preserving fingerprint authentication using Synopsis Design Compiler on a commercial Intel processor shows the efficiency and scalability of the proposed methodologies.Item Transmit Diversity with Channel Feedback(2001-09-20) Mukkavilli, Krishna Kiran; Sabharwal, Ashutosh; Orchard, Michael; Aazhang, Behnaam; Center for Multimedia Communications (http://cmc.rice.edu/)Transmit diversity in the presence of channel feedback at the transmitter is analyzed in this paper. We first consider perfect channel feedback and summarize the beamforming solution which minimizes the codeword error probability. We note that the error probability minimizing scheme is different from the mutual information maximizing scheme. We then present a scheme with partial channel feedback in the form of relative phases of channel vectors. This scheme achieves performance comparable to the beamforming with much less information about the channel, which in turn requires less resources for feedback. The new scheme presented in this paper is a generalization of a well known scheme for two transmit and one receive antenna, using the phase difference of the channel coefficients.