Recently, a novel wavelet method to reduce speckle noise in synthetic aperture radar images was presented. The method, based on the thresholding of the wavelet coefficients of the transformed image, is computationally efficient and maintains sharp image features. The application of a similar method is explored to reduce speckle noise in TV holography fringes, which is a very important problem in the quantitative analysis of transient phenomena. Several thresholding approaches are used to test the noise reduction algorithm on computer-simulated fringes and results are assessed through the evaluation of two comparative parameters: the image fidelity and the speckle index. It is shown that the method achieves the highest speckle reduction when speckle grains have the same average size of the image pixels.

The properties of a liquid crystal television to be used as a spatial modulator of the polarization of a laser beam are studied. It is found that the model most commonly used for the display description does not adequately reproduce the transmission through crossed polarizers. A new model is proposed that takes into account additional birefringence effects resulting from border effects near the television windows. With this correction, the anomalous behavior of the television is explained and the throughput for different configurations is properly predicted.

Laser backscattering is an excellent tool to investigate size and concentration of suspended particles. It was successfully applied to the analysis of erythrocyte aggregation. A method is proposed that applies laser backscattering to the evaluation of the strength of the immunologic erythrocyte agglutination by approaching the energy required for the mechanical dissociation of agglutinates. Mills and Snabre have proposed a theory of laser backscattering for erythrocyte aggregation analysis. It is applied here to analyze the dissociation process of erythrocyte agglutinates performed by imposing a constant shear rate to the agglutinate suspension in a couette viscometer until a dispersion of isolated red cells is attained. Experimental verifications of the method were performed on the erythrocytes of the ABO group reacting against an anti-A test serum in twofold series dilutions. Spent energy is approached by a numerical process carried out on the backscattered intensity data registered during mechanical dissociation. Velocities of agglutination and dissociation lead to the calculation of dissociation parameters. These values are used to evaluate the strength of the immunological reaction and to discriminate weak subgroups of ABO system.

The modal distribution at the output of a multimode optical fiber behaves as a speckle pattern. Further, a speckle pattern carries information on the pupil diameter of the optical system exit aperture. Pupil measurements by speckle size determination may not be an easy task, because of the statistical nature of the speckle phenomena. The measurement of a multimode fiber core is proposed using a speckle autocorrelation algorithm to obtain the minimum speckle diameter present in the pattern generated by the fiber. Both computer simulations and actual pupils are used to test its performance. Core diameter measurements are carried out showing good agreement with the specifications supplied by the fiber manufacturer.

In dual-plate speckle photography, the images corresponding to both deformation states are recorded on separate photographic plates. In this way, two major limitations of speckle photography, large rigid body displacements of the specimen and the 180-deg displacement direction ambiguity, can be overcome. When both photographic plates are placed with the glass base of one of them between the emulsions and they are illuminated by a narrow laser beam, a pattern of circular fringes is generated. Displacements can be measured by evaluating the distance between the center of the fringe pattern and the undiffracted laser beam. A new algorithm for the fully automatic analysis of such fringe patterns is presented. Its performance is tested using computer-simulated fringes and compared with performance obtained using a previously developed algorithm.

A very simple dye laser cavity generates stable single pulses of less than 300-ps duration and several microjoules of energy when pumped by about 50 µJ of an 8-ns pulse from a low-pressure nitrogen laser. The pulses are produced by a mechanism similar to the "quenched" resonator setup. A theoretical description is given, showing good agreement with the observed results. Achievable improvements are described, which would reach the tens of picosecond range.

Spatial filtering, spectral matched inhibition, and recovering of defocused images are implemented by modulation of the induced birefringence of a BSO crystal. The intensity distribution received by the crystal modulates the induced birefringence and the ellipticity of the transmitted light is then modified as it propagates through the crystal. To describe the processor, a 4-f optical system is used. A simple physical model is introduced and numerical and experimental results are presented.

Measurement of optical absorbance is used to study the relaxation of acrylic film doped with Disperse Red 1 and poled with an electric field produced by the corona effect. Time variation of dichroism is studied over 10 days and results are adjusted with different time functions. Second-harmonic generation is presented as a test of the lack of symmetry of the poled film resulting from the orientation process.

Three optical methods for sizing polymer particles are instrumented to be used in the leather industry. One method is based on the measurement of the light scattered intensity for several angles, and the other two are monochromatic or spectral extinction methods. Uniform latex particles and two commercial products used in leather finishing are measured. Advantages compared with electronic microscopy are discussed.

The full width at half maximum (FWHM) is sometimes used to characterize the autocorrelation function of the time history of a speckle pattern. We propose to include more autocorrelation points to diminish the variability of the measurement. The width of the equivalent rectangle (WER) and the X*LOG X measurements are defined and some simulations and experimental results obtained are shown.

An interesting way to display the temporal evolution of a speckle pattern produced by a slowly changing perturbation is presented. It is based on digital speckle pattern interferometry (DSPI) concepts applied to 1-D slices of each frame of the time-evolving perturbation. The time history of a column of an image is depicted as a function of time. Correlation fringes are obtained by subtracting an unperturbed state from consecutive or alternate columns. Applications are suggested.

A fruitful approach to the studies of a liquid free surface is demonstrated. Using optical interferential techniques, the free surface of nonvolatile and volatile confined liquids are analyzed. Various wall container types are investigated. Besides the classical plane wall, experiments are performed by using cylindrical and toroidal walls. In these last cases, the meniscus effect that affects the free surface of the liquid is compensated. Then, it is possible to obtain completely flat free surfaces of liquids up to 80% of their total. Interferometric experiments are also described to measure the inclination of the site with respect to the local horizon, represented by the liquid flat free surface, and to follow the temporal evolution of such free surfaces affected by different conditions.

The performance of four methods for feature enhanced mammographic images—optimal adaptive neighborhood imaging, automatic spatial filtering, adaptive histogram equalization imal contrast pixel to pixel—are compared. Each method is te a database of 50 mammographic images, which included similar shaped nodules. A contrast parameter was used to compare the performance of each processing method. It was found that the ma trast pixel-to-pixel method gives the highest contrast value. A mamogram including a real subtle lesion is used to illustrate the use of this last contrast enhancement method in clinical diagnosis.

Extraction efficiency in a folded resonator with overlapping between neighboring beams is analyzed in terms of number of mirrors, small-signal gain, and active length. The medium is assumed to be homogeneously broadened and saturated by the sum of overlapping irradiances, supposed to be uniform across each beam. Extraction efficiency is presented as a function of output coupler reflectivity, total gain, and reflectivity of folding mirrors. Optimum coupling is also computed for a range of gains per amplifying section and folding mirror reflectivities. Finally, efficiencies calculated with this model are compared with those obtained with a nonoverlapping model, showing higher figures, with maximum values shifted to the low-output coupler reflectivity for the presented model.

A homemade TEA CO2 multimode line-tunable laser was used as a radiation source to study the IR absorption of O3 in pure samples and in O3 – M mixtures (M=O2, N2, and air) at the initial steps of the excitation by direct calorimetric measurements. The fluence and pressure dependence of the O3 absorption cross section and the number of photons absorbed n were determined for all the available rotational lines P(4) through P(58) of the 9.5-µm emission band. The dependence of n on added nonreactive gas pressure over the range 0 to 750 Torr was studied for three different fluences of the P(30) line.

The analysis of light propagation in optical systems composed of periodic arrays of identical apertures is performed using the diffraction properties of the Walsh functions. By taking into account three main features of these functions, namely, completeness, binary nature, and self-imaging properties, the successive interactions between each aperture and the diffracted field can be adequately explained through the Walsh–Hadamard spectrum associated with the transmitted amplitude distribution.

MPEG4 is a natural extension of audiovisual coding, and yet from many perspectives breaks new ground as a standard. New coding techniques are being introduced, of course, but they will work on new data structures. The standard itself has a new architecture, and will use a new operational model when implemented on equipment that is likely to have innovative system architecture. The author introduces the background developments in technology and applications that are driving or enabling the standard, introduces the focus of MPEG4, and enumerates the new functionalities to be supported. Key applications in interactive TV and heterogeneous environments are discussed. The architecture of MPEG4 is described, followed by a discussion of the multiphase MPEG4 communication scenarios, and issues of practical implementation of MPEG4 terminals. The paper concludes with a description of the MPEG4 workplan. In summary, MPEG4 has two fundamental attributes. First, it is the coding of audiovisual objects, which may be natural or synthetic data in two or three dimensions. Second, the heart of MPEG4 is its syntax: the MPEG4 Syntactic Descriptive Language—MSDL.

The International Telecommunications Union (ITU) has prepared a series of draft recommendations defining a multimedia video-conferencing/videophone terminal transmitting over the Public Switched Telephone Network (PSTN). Recommendation H.324 defines the overall system structure and therefore the device commonly known as an H.324 terminal. The author outlines the key technical characteristics of the entire set of five draft recommendations–H.324, G.723, H.263, H.246, and H.223. Of particular interest is the new H.263 video coding algorithm, which outperforms the H.261 video coder by approximately 2 or 3 to 1. The H.263 coder employs a wide range of advanced coding techniques, including half-pel motion compensation, 8 × 8-pel motion vectors, over-lapped block motion compensation, and PB frames. It is likely that the H.263 recommendations will be used for other applications at higher bit rates as well as for the H.324 PSTN. The ITU has also begun work to adapt the H.324 PSTN terminal for mobile radio applications. The primary effort is the addition of error control measures to the multiplexer (and possibly the source coders) to address the more challenging error characteristics in the mobile environment.

Image coding using quadtrees is useful in many applications and is well known in computer vision and graphics. We draw a parallel between quadtrees and rational languages that are recognizable by finite state automata (FSA), also known as automata. The FSA are shown to be an interesting alternative to the corresponding quadtrees. Binary image (0=black, 1=white) coding using a FSA follows these two steps: (1) automaton construction based on the image quadtree, (2) automaton minimization. The display of the coded image is simply obtained by stepping through the automaton. We demonstrate how simple image operations can be efficiently implemented directly with FSA. Examples are also presented to illustrate the relationship between the FSA complexity and the coded images. Finally, the generalization of this approach to gray-level images, color images, and volume data is discussed. We believe that this automaton coding approach will be useful in developing efficient image and data compression algorithms.

The discrete sine and cosine transforms (DSTs and DCTs) are powerful tools for image compression. They would be even more useful if they could be used to perform convolution. As we have recently shown, these transforms do possess a convolution-multiplication property and therefore can be used to perform digital filtering. The convolution is a special type, called symmetric convolution. This paper reviews the concepts of symmetric convolution and then elaborates on how to use the operation, and thereby DSTs and DCTs, to implement digital filters for images. An indication of how to compute the transforms and what is the complexity of their use is also given.