Image compression in signal-dependent noise.

The performance of an image compression scheme is affected by the presence of noise, and the achievable compression may be reduced significantly. We investigated the effects of specific signal-dependent-noise (SDN) sources, such as film-grain and speckle noise, on image compression, using JPEG (Joint Photographic Experts Group) standard image compression. For the improvement of compression ratios noisy images are preprocessed for noise suppression before compression is applied.

Volterra series modeling of spatial light modulators.

We present a multiple-input, single-output, weakly nonlinear model of spatial light modulators by use of a second-order Volterra series and describe an experimental method to measure the nonlinear transfer functions by means of sinusoidal perturbation and synchronous detection with a lock-in amplifier. We also present an application of this method to a liquid-crystal light valve.

M-type thick holograms in bacteriorhodopsin films with a high-divergence reference beam.

The capacity to use differing read and write wavelengths for reconstructing volume holograms recorded in a shift-multiplexing geometry is analyzed and realized for M-type volume holograms recorded on bacteriorhodopsin films. The intensity distribution in the reconstructed wave is calculated as a function of the parameters of the recording and readout beams. Optimal recording and retrieving geometries, as well as a precise method for tuning the readout setup, are suggested.

Digital stereo image analyzer for generating automated 3-D measures of optic disc deformation in glaucoma.

The major limitations of precise evaluation of retinal structures in present clinical situations are the lack of standardization, the inherent subjectivity involved in the interpretation of retinal images, and intra- as well as interobserver variability. While evaluating optic disc deformation in glaucoma, these limitations could be overcome by using advanced digital image analysis techniques to generate precise metrics from stereo optic disc image pairs. A digital stereovision system for visualizing the topography of the optic nerve head from stereo optic disc images is presented.

Throughput analysis of digital partitioning with error-correcting codes for optical matrix-vector processors.

Digital partitioning and error-correcting codes provide a technique for achieving high-accuracy computations with analog optical matrix-vector processors. We present the results of a detailed throughput analysis of this technique. The results indicate that using one processor per submatrix provides the best compromise between system throughput and hardware requirements over a range of matrix sizes.

Reliability characteristics of quadratic Hebbian-type associative memories in optical and electronic network implementations.

The performance capability of quadratic Hebbian type associative memories (QHAM's) in the presence of interconnection faults is examined, and equations for predicting the probability of direct convergence P(dc) given a fraction of interconnection faults are developed. The interconnection faults considered are the equivalent of open circuit and short circuit synaptic interconnections in electronic implementations. Our results show that a network with open circuit interconnection faults has a higher probability of direct convergence P (dc) than a network with short circuit interconnection faults, when the fraction of failed interconnections p is small and the short circuit signal G is large.

Temporal intensity noise characteristics and discrete numeric accuracy of analog liquid-crystal-based spatial light modulators.

We investigate the temporal intensity noise characteristics of analog liquid-crystal-based spatial light modulators and how they affect the device's achievable discrete numeric accuracies in an optical computing system. First we present an analytical development that defines the concept of precision in analog computing systems, then we define a noise metric and a precision-optimal quantizer for determining the discrete numeric characteristics of the devices. Second we present an experimental discussion in which a low-noise test facility constructed for this investigation is described, and the noise characteristics of three commercially available liquid-crystal-based modulators are measured and analyzed.

Error-correction coding for accuracy enhancement in optical matrix-vector multipliers.

Error-correcting codes provide a technique for enhancing the accuracy of optical matrix-vector multipliers (OMVM's). The effects of signal-independent and signal-dependent noise on the performance of OMVM's that employ error-correcting codes are studied through the use of computer simulations. Noise present in the matrix results in random errors that can be corrected by these codes.

Characteristics of Hebbian-type associative memories having faulty interconnections.

The performance of Hebbian-type associative memories (HAMs) in the presence of faulty (open- and short-circuit) synaptic interconnections is examined and equations for predicting network reliability are developed. The results show that a network with open-circuit interconnection faults has a higher probability of direct convergence than a network with short-circuit interconnection faults when the fraction of failed interconnections is small and the short-circuit signal is large. The results are extended to the case where network attraction radius is considered.

On the Characteristics of the Autoassociative Memory with Nonzero-Diagonal Terms in the Memory Matrix.

A statistical method is applied to explore the unique characteristics of a certain class of neural network autoassociative memory with neurons and first-order synaptic interconnections. The memory matrix is constructed to store = α vectors based on the outer-product learning algorithm. We theoretically prove that, by setting all the diagonal terms of the memory matrix to be and letting the input error ratio ρ = 0, the probability of successful recall steadily decreases as α increases, but as α increases past 1.

Noise limitations in optical linear algebra processors.

A general statistical noise model is presented for optical linear algebra processors. A statistical analysis which includes device noise, the multiplication process, and the addition operation is undertaken. We focus on those processes which are architecturally independent.

Outer product processor using polarization encoding.

An architecture capable of performing the outer product operation followed by a weighting of the resultant elements is presented in this paper. By using a polarization encoding technique, the spatial capacity is increased by a factor of four over implementations using other techniques. The use of space-integrating photodiodes as detectors permits the evaluation of second-order polynomials.

Two-dimensional optical Clos interconnection network and its uses.

A 2-D optical three-stage Clos interconnection network, which is made up of a number of feasible crossbars of medium size, is implemented for dynamic data communications. The network is nonblocking and can handle a large number of communication lines (compared with crossbar networks of realizable size). Doth one-to-one and one-to-many routing algorithms are discussed.

Automated method for fundus image registration and analysis.

Automated detection of subtle changes in sequential images requires development of procedures that ensure true subtraction of two images by proper registration and normalization of illumination. The difference image can then be further processed to analyze the spectral components and the gray level variations. An innovative and generalized approach to accurate image subtraction incorporating illumination normalization and correction for translation, rotation, and scale difference in two sequential images is considered.

Power cepstrum and spectrum techniques applied to image registration.

The use of power cepstrum analysis in image registration is explored. Rotational shifts and translational shifts are corrected separately. The technique involves two main ideas.

Image restoration by transformation of signal-dependent noise to signal-independent noise.

A transformation to convert signal-dependent noise corrupting an image to additive Gaussian signal-independent noise is derived in this paper. Wiener filtering techniques using a Markovian covariance model for the image signal are applied to the transformed data followed by an inverse transformation to restore the degraded image. An ad hoc technique using contrast manipulation to adaptively convert signal-dependent noise to signal-independent noise is also described.

Image recovery from signal-dependent noise.

It is well known that the noise processes corrupting an image are, in general, signal dependent. Under low signal to-noise-ratio situations, the amount of signal information present in the signal-dependent noise may become a significant fraction of the total signal information. A simple technique designed to demonstrate the potential for signal extraction from signal-dependent noise is presented.

Hybrid electrooptical power cepstrum analyzer.

The power cepstrum (power spectrum of the log of the power spectrum) of a signal in a multipath environment provides information on echo amplitudes and delay times. An electrooptical power cepstrum analyzer, which displays this information in real time, is described. The basic system approach is to use optics to provide the power spectrums and electronics to provide the logarithm function.

Estimation in signal-dependent film-grain noise.

Optimal estimators are derived for a signal-dependent film-grain noise model, and the effect of signal-dependence on the estimators's structures is investigated. Due to the mathematical complexity of these optimal estimators, various suboptimal estimators are proposed. Computer simulations are then presented which compare the optimal and suboptimal estimators with regard to mean square estimation error, sensitivity to signal-dependence, and robustness with respect to the a priori signal probability density function.

Multiplex holography for space-variant processing: a transfer function sampling approach.

Several techniques for the holographic representation of any bandlimited space-variant system by spatially sampling the input plane and multiplexing the respective system transfer functions have been previously described. This paper describes an alternative multiplexing technique in which the transfer functions are sampled in the Fourier plane to produce the multiplexed holograms. Various techniques for generating multiple copies of the input function that are required during playback are considered.