Charles D. Creusere

A new method of robust image compression based on the embedded zerotree wavelet algorithm

We propose a wavelet-based image compression algorithm that achieves robustness to transmission errors by partitioning the transform coefficients into groups and independently processing each group using an embedded coder. Thus, a bit error in one group does not affect the others, allowing more uncorrupted information to reach the decoder.

A simple method for designing high-quality prototype filters for M-band pseudo QMF banks

Discusses a new method for designing the prototype filters necessary to implement M-band pseudo QMF banks. This method does not rely on the traditional nonlinear optimization used in past work but rather optimizes a single parameter on a convex error surface, consistently delivering the best equiripple filter possible while minimizing the overlapped passband distortion. A very simple algorithm for designing lowpass prototype filters suitable for use in pseudo QMF banks is described. To illustrate the applicability of this algorithm, two different filters are designed, both for such applications as wideband audio coding that require high quality reconstructed signals. >

Polarization-based index of refraction and reflection angle estimation for remote sensing applications

A passive-polarization-based imaging system records the polarization state of light reflected by objects that are illuminated with an unpolarized and generally uncontrolled source. Such systems can be useful in many remote sensing applications including target detection, object segmentation, and material classification. We present a method to jointly estimate the complex index of refraction and the reflection angle (reflected zenith angle) of a target from multiple measurements collected by a passive polarimeter. An expression for the degree of polarization is derived from the microfacet polarimetric bidirectional reflectance model for the case of scattering in the plane of incidence. Using this expression, we develop a nonlinear least-squares estimation algorithm for extracting an apparent index of refraction and the reflection angle from a set of polarization measurements collected from multiple source positions. Computer simulation results show that the estimation accuracy generally improves with an increasing number of source position measurements. Laboratory results indicate that the proposed method is effective for recovering the reflection angle and that the estimated index of refraction provides a feature vector that is robust to the reflection angle.

An Objective Metric of Human Subjective Audio Quality Optimized for a Wide Range of Audio Fidelities

The goal of this paper is to develop an audio quality metric that can accurately quantify subjective quality over audio fidelities ranging from highly impaired to perceptually lossless. As one example of its utility, such a metric would allow scalable audio coding algorithms to be easily optimized over their entire operating ranges. We have found that the ITU-recommended objective quality metric, ITU-R BS.1387, does not accurately predict subjective audio quality over the wide range of fidelity levels of interest to us. In developing the desired universal metric, we use as a starting point the model output variables (MOVs) that make up BS.1387 as well as the energy equalization truncation threshold which has been found to be particularly useful for highly impaired audio. To combine these MOVs into a single quality measure that is both accurate and robust, we have developed a hybrid least-squares/minimax optimization procedure. Our test results show that the minimax-optimized metric is up to 36% lower in maximum absolute error compared to a similar metric designed using the conventional least-squares procedure.

Audio quality assessment using the mean structural similarity measure

Efficient transmission and storage of digital audio signals can be accomplished using a wide variety of compression algorithms. To compare and optimize the performance of such algorithms, objective metrics are often used to measure the quality of such compressed audio signals since subjective testing is extremely time consuming. In this paper, we consider the application of the structural similarity measure, originally developed for image quality assessment, to the problem of audio quality assessment. Specifically, we study two different implementations of the structural similarity index: the first applies it to short and fixed time-domain frames of an audio sequence while the second decomposes the audio signals into a non-redundant, time-frequency map and then compares the structural similarity in the resulting 2-dimensional domain. We compare the accuracies of the two structural similarity measures with those of other accepted objective audio quality metrics relative to MUSHRA-based subjective audio evaluations.

Image coding using wavelets based on perfect reconstruction IIR filter banks

This paper re-examines modulated polyphase filter banks which use reverse-time subfilters to achieve perfect reconstruction and studies their performance for image coding when used to form a wavelet decomposition. To code the wavelet coefficients, we use the embedded zerotree wavelet (EZW) algorithm developed by Shapiro (1993) which is reasonably simple and yet achieves very good rate-distortion performance. The problem of eliminating filter transients is thoroughly studied and optimal results are derived in both the absence and presence of subband coefficient quantization. Using this analysis as a starting point, we develop a new method of coding the filter states (required to eliminate edge transients) for transmission to the receiver which efficiently exploits interscale redundancy and is easily incorporated into the zerotree algorithm. Comparing this direct transmission method to circular convolution, we find that it achieves superior rate-distortion performance in a wide range of cases. Coding comparisons between two infinite impulse response (IIR) wavelets and a number of biorthogonal wavelets are presented. These comparisons indicate that the performance of the polyphase allpass wavelet is comparable to that of the best finite impulse response (FIR) biorthogonal wavelets with considerably reduced computational complexity.

Efficient audio coding using perfect reconstruction noncausal IIR filter banks

We consider the problem of implementing perfect reconstruction modulated polyphase filter banks having infinite impulse response (IIR) subfilters in systems that must process infinite length 1-D inputs. This task is complicated by the fact that the synthesis bank needed to ensure perfect reconstruction in such a system generally has noncausal or reverse-time filter sections. To overcome this limitation, we develop a number of unique buffering schemes that make possible the implementation of such reverse-time filters with infinite length signals. For the important special case when the polyphase subfilters are allpass, we also present a method that allows for very efficient implementation of tree-structured filter banks and wavelet transforms. We then describe a wideband coding algorithm based largely on work done by Lokhoff (1991) and Johnston (1980, 1988). Using this algorithm, we compare the performance of IIR filter banks with that of more conventional pseudo-QMF and tree-structured QMF banks. The results of these comparisons indicate that one of our filter banks-a tree-structured allpass bank-achieves slightly better performance than equivalent FIR banks in terms of rate and distortion (both objectively and subjectively measured) while requiring lower computational complexity.

Assessing the Quality of Audio Containing Temporally Varying Distortions

In this paper, we consider the problem of characterizing the quality of audio that is impaired by time-varying distortions. Specifically, the quality of such audio must be characterized by a time-dependent function. We first study issues associated with the human subjective testing which must be addressed in order to create such a function, and we conclude that the best approach for achieving both high temporal resolution and high accuracy is most likely a combination of two testing methodologies. Using the collected subjective data, we then design an objective metric that attempts to replicate the subjective responses. The proposed metric uses as its core a subset of the model output variables that are part of the ITU perceptual evaluation of audio quality (PEAQ) recommendation as well as the structural similarity measure and the segmental signal to noise ratio. Depending on the dataset used in its design, we find that the estimated quality has an average correlation coefficient relative to the ground truth curves of between 0.887 and 0.933. Furthermore, we also find that it is possible to reduce the complexity of this metric considerably while only degrading its performance by between 0.3% and 1.6%. In addition, the reduced complexity metric appears to be more robust than the original one.

Passive Polarimetric Imagery-Based Material Classification Robust to Illumination Source Position and Viewpoint

Polarization, a property of light that conveys information about the transverse electric field orientation, complements other attributes of electromagnetic radiation such as intensity and frequency. Using multiple passive polarimetric images, we develop an iterative, model-based approach to estimate the complex index of refraction and apply it to target classification.

Evaluating low bitrate scalable audio quality using advanced version of PEAQ and energy equalization approach

ITU-R BS.1387-1 gives a method for objective measurement of perceived audio quality known as PEAQ (perceptual evaluation of audio quality). This algorithm has been developed for measuring the quality of mid and high quality audio. We show that the advanced version of PEAQ performs poorly when compared to the previously developed energy equalization approach (EEA) for evaluating the quality of low bitrate scalable audio. We also show that including an energy equalization parameter as one of the model output variables (MOVs) of the advanced version improves its performance significantly; the performance of this modified version is superior to that of EEA.