John D. Villasenor

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The discrete wavelet transform (DWT) decomposes an image into bands that vary in spatial frequency and orientation. It is widely used for image compression, measures of the visibility of DWT quantization errors are required to achieve optimal compression. Uniform quantization of a single band of coefficients results in an artifact that we call DWT uniform(More)
1 2 Abstract A radar interferometric technique for topographic mapping of surfaces promises a high resolution, globally consistent approach to generation of digital elevation models. One implementation approach, that of utilizing a single synthetic aperture radar system in a nearly repeating orbit, is attractive not only for cost and complexity reasons but(More)
This letter explains the effect of graph connectivity on error-floor performance of low-density parity-check (LDPC) codes under message-passing decoding. A new metric, called extrinsic message degree (EMD), measures cycle connectivity in bipartite graphs of LDPC codes. Using an easily computed estimate of EMD, we propose a Viterbi-like algorithm that(More)
Choice of filter bank in wavelet compression is a critical issue that affects image quality as well as system design. Although regularity is sometimes used in filter evaluation, its success at predicting compression performance is only partial. A more reliable evaluation can be obtained by considering an L-level synthesis/analysis system as a single-input,(More)
This work explains the relationship between cycles, stopping sets, and dependent columns of the parity check matrix of low-density parity-check (LDPC) codes. Furthermore, it discusses how these structures limit LDPC code performance under belief propagation decoding. A new metric called extrinsic message degree (EMD) measures cycle connectivity in bipartite(More)
We describe a new image coding approach in which a 4-ary arithmetic coder is used to represent signiicant coeecient values and the lengths of zero runs between coeecients. This algorithm works by raster scanning within subbands, and therefore involves much lower addressing complexity than other algorithms such as zerotree coding that require the creation(More)
Although arithmetic coding offers extremely high coding efficiency, it provides little or no security as traditionally implemented. We present a modified scheme that offers both encryption and compression. The system utilizes an arithmetic coder in which the overall length within the range [0,1) allocated to each symbol is preserved, but the traditional(More)
Binary arithmetic coding involves recursive partitioning the range [0,1) in accordance with the relative probabilities of occurrence of the two input symbols. We describe a modification of this approach in which the overall length within the range [0,1) allocated to each symbol is preserved, but the traditional assumption that a single contiguous interval(More)
We present an automated methodology for producing hardware-based random number generator (RNG) designs for arbitrary distributions using the inverse cumulative distribution function (ICDF). The ICDF is evaluated via piecewise polynomial approximation with a hierarchical segmentation scheme that involves uniform segments and segments with size varying by(More)
The International Telecommunications Union (ITU) recently adopted reversible variable length codes (RVLCs) for use in the emerging H.263+ video compression standard. As the name suggests, these codes can be decoded in two directions and can therefore be used by a decoder to enhance robustness in the presence of transmission bit errors. In addition, these(More)