This PDF file contains the editorial “Why are so few Communications published in OE?” for OE Vol. 39 Issue 04

In this work we consider the effect of the pixel active area geometrical shape on the modulation transfer function (MTF) of an image sensor. When designing a CMOS Active Pixel Sensor (APS), or a CCD or CID sensor for this matter, the active area of the pixel would have a certain geometrical shape which might not cover the whole pixel area. To improve the device performance, it is important to understand the effect this has on the pixel sensitivity and on the resulting MTF. We perform a theoretical analysis of the MTF for the active area shape and derive explicit formulas for the transfer function for pixel arrays with a square, a rectangular and an L shaped active area (most commonly used), and generalize for any connected active area shape. Preliminary experimental results of subpixel scanning sensitivity maps and the corresponding MTFs have also been obtained, which confirm the theoretical derivations. Both the simulation results and the MTF calculated from the Point Spread Function (PSF) measurements of the actual pixel arrays show that the active area shape contributes significantly to the behavior of the overall MTF. The results also indicate that for any potential pixel active area shape, the effect of its diversion from the square pixel could be calculated, so that tradeoff between the conflicting requirements, such as SNR and MTF, could be compared per each pixel design for better overall sensor performance.

A computationally efficient pyramid adaptive algorithm based on Fourier local phase matching is proposed to compute precise depth estimates for motion stereo. In general, the motion stereo uses intensity value as the matching primitive. To decrease the computational depth error, when the brightness of each moving picture is highly variable, we developed a method for motion stereo using the phase of Gabor filters instead of intensity. To implement the motion stereo more efficiently, a hierarchical method is also used, consisting of pyramidal data sequences. We present the experimental results demonstrating that our method gives more accurate depth estimates than the motion stereo algorithm based on intensity matching.

Methods for the analysis of continuously distorted quasiperiodic images are improved. Especially techniques of 2-D reconstruction are studied. The locally normalized correlation is used in the correlation-averaging method. To eliminate image distortion the function of the distortion is approximated step by step by the linear fractional function or by the Lagrange interpolation polynomials. The modification of the methods is illustrated in figures of cyanobacterial Slayers, namely, on negatively strained S layers of Synechocystis aquatilis Kovacik 1990/8 and Microcystis aeruginosa Hindak 1971/1 and the metal- shadowed S layer of Microcystis cf. wesenbergii Bitov 1994.

. Pulse infrared thermography is renowned as an effective and rapid method of nondestructive inspection. The primary difficulty in making useful interpretations of a thermal image is the presence of extraneous effects such as thermal noise, optical distortion through the thermal imaging system, and of most concern, non-uniform heating through the uneven excitation of the surface. A means for removal of background trends caused by uneven illumination is presented. It is based on a polynomial fitting technique applied to a rectangular infrared image on a line-by-line basis in either horizontal or vertical directions. The polynomial coefficients are found by choosing three key pixels through a conditional iterative technique. The proposed algorithm enables improvements in flaw visibility and assists the effective application of additional image processing techniques. The procedure is found to remove trends without distorting real flaw indications as long as the indication spans less than 67% of the interval under examination.

The evaluation of human detection performance of targets embedded in natural iR images is uniquely extended to deal with enhanced images. Various image metrics designed to describe global image clutter and local target-to-background contrast are presented. Agreement between experimental results, as obtained for both natural and enhanced iR images and image metrics, is evaluated by correlating the metric values with target detection results obtained from two psychophysical experiments, which were designed to record and measure human target detection performance and image quality judgments. Positive correlation values are generally obtained between the metric values and both the target detection (rate and probability) performance and the image quality scale values. More specifically, the local contrast metric is found to be the most suitable to the data recorded from the quality judgments experiment, while the global clutter metric is found to be the most suitable to the data recorded from the detection performance experiments. Further analysis of the relationship between the image metrics and the experimental results yield empirical classification thresholds that can be used to evaluate and predict human detection performance in similar cases. A method to evaluate the classification efficiency, is introduced and used to reconfirm the metrics appropriateness to describe detection performance and quality judgments of targets embedded in both natural and enhanced images. © 2000 Society ofPhoto-Optical Instrumentation Engineers. [S0091-3286(00)00202-6]

Multispectral/hyperspectral imaging spectrometry in earth remote sensing applications mostly focuses on determining the identity and abundance of materials in a geographic area of interest. Without any prior knowledge, however, it is generally very difficult to identify and determine how many endmembers reside in a scene. We cope with this limitation by estimating the number of endmembers using a noise- adjusted version of the transformed Gerschgorin disk approach (NATGD). This estimated result is then applied to a noise-adjusted version of fast independent component analysis (NAFICA). Experimental results indicate that NAFICA offers a new approach for unsupervised signature extraction and separation in hyperspectral images. © 2000 Society of Photo-Optical Instrumentation Engineers. [S0091-3286(00)02004-3]

The unsupervised Pappas adaptive clustering (PAC) algorithm is a well-known Bayesian and contextual procedure for pixel labeling. It applies only to piecewise constant or slowly varying intensity images that may be corrupted by an additive white Gaussian noise field independent of the scene. Interesting features of PAC include multiresolution implementation and adaptive estimation of spectral parameters in an iterative framework. Unfortunately, PAC removes from the scene any genuine but small region whatever the user-defined smoothing parameter may be. As a consequence, PAC's application domain is limited to providing sketches or caricatures of the original image. We present a modified PAC (MPAC) scheme centered on a novel class-conditional model, which employs local and global spectral estimates simultaneously. Results show that MPAC is superior to contextual PAC and stochastic expectation-maximization as well as to noncontextual (pixel- wise) clustering algorithms in detecting image details.

We propose a new algorithm to find the corpus callosum automatically from midsagittal brain MR (magnetic resonance) images using the statistical characteristics and shape information of the corpus callosum. We first extract regions satisfying the statistical characteristics (gray level distributions) of the corpus callosum that have relatively high intensity values. Then we try to find a region matching the shape information of the corpus callosum. In order to match the shape information, we propose a new directed window region growing algorithm instead of using conventional contour matching. An innovative feature of the algorithm is that we adaptively relax the statistical requirement until we find a region matching the shape information. After the initial segmentation, a directed border path pruning algorithm is proposed in order to remove some undesired artifacts, especially on the top of the corpus callosum. The proposed algorithm was applied to over 120 images and provided promising results.

A new nonuniformity correction scheme for an infrared (IR) camera is presented. The nonuniform response of the camera due to background IR radiation from the camera housing has been taken into account in the correction scheme, which can provide very uniform output characteristics for a wide range of camera temperature variation. The correction parameters have been obtained from two-step calibration processes. The calibration and correction algorithms are shown in detail.

A simple fiber optic thermal imaging system based on a thin and flexible IR waveguide is constructed. Two types of waveguides are used: silver halide fiber and hollow glass waveguide. The thermal image of a warm object is formed at the focal plane of an IR transmitting lens. The proximal end of the waveguide is fixed and attached to a pyroelectric IR detector. The distal end of the waveguide scans the thermal image in two directions. The IR radiation is transmitted through the waveguide to the detector. The signals from the detector are coupled into a suitable monitor, which produces a representation of the thermal image. In preliminary experiments, we attach a small magnet to the distal tip of the waveguide and move the tip using an electromagnetic field. For a target of spatial frequency 1.25 cycles/mm the modulation transfer function (MTF) of the system is 0.2 and for a target of spatial frequency of 0.1 cycles/mm the minimum resolvable temperature difference (MRTD) is 0.5°C. The system could be applied in industry or in medicine where imaging in the mid-IR and in a restricted space is required.

A new optical measurement method of a flow velocity distribution along the depth using low coherence interference techniques is proposed and demonstrated. In the proposed method, fluctuations of the interference signal formed with the reference and backscattering lights are detected by the optical heterodyne scheme. It is shown experimentally that the width of the spectrum of the interference signal is proportional to the flow velocity. The dynamic range is determined by the time constants of the fast Fourier transform (FFT) processor and lock-in amplifier used in the experiment.

We present a new computational method of white light scanning interferometry for 3-D surface mapping. This method accomplishes the task of detecting the true peak of the interference fringe in two steps. The first step is global search locating the envelope peak by fitting sampled intensity data directly to a symmetric quadratic polynomial. The second step is fine-tuning to precisely determine the fringe peak by compensating for the phase shift on reflection using the absolute fringe order identified by the envelope peak obtained in the first step. This two-step method offers an efficient means of computation to provide a good measuring accuracy with high noise immunity owing to its inherent reliance on least squares principles.

A modified Michelson interferometer is described by which three, by - ?/2, 0 and + ?/2 phase-shifted interferograms can be taken simultaneously by a single CCD camera using a binary diffraction grating and polarization optics. Hence measurements of dynamic events and in adverse conditions are possible. The experimental setup, first results and a mathematical error analysis are presented.

Phase-shifting interferometry is now used widely to map the deviations of optical surfaces from a reference plane or reference sphere. However, the accuracy of such measurements is limited by systematic errors due to several causes. These systematic errors can be minimized by a simple averaging technique.

A technique for measuring shapes containing gaps that combines optical fringe scanning with the fractional fringe order method is presented. The basic configuration is a Twyman-Green interferometer with collimated white-light illumination. The reference mirror is moved using a piezoelectric transducer at a phase interval of ?/2 during the measurement, and the fringe image is collected at every step. The surface shape is reconstructed by a four-frame scanning algorithm for each pixel for each selected wavelength. The absolute gap height is then identified by the fractional fringe order method, which can detect the 2? phase jumps accurately. The simultaneous measurement of both a gap of several wavelengths and a surface shape is also demonstrated. Finally, the influences of the spectral bandwidth of light and the central wavelength used in recording interferograms are discussed.

An efficient approach for the designing of ophthalmic lenses, based on the optimization of the aspherical surface coefficients is presented. We show that five optimization constraints are enough to both reduce the aberrations and prevent the development of inflection points along the aspherical surface. In particular, we solve the inflection point problem by counting the second derivative of the sag with respect to the height of the aspherical surface as one of the constraints. The design data indicate that nonconicoidal aspheric lenses can be made thinner and flatter than the equivalent spherical or conicoidal lenses. The traditional damped least-squares methods are used and design results are given for both aspherical negative lenses and aspherical positive lenses.

Diamond-like carbon (DLC) films were deposited directly on GaAs substrates by a capacitively coupled 13.56 MHz glow discharge in a CH4 plasma. The deposition process for antireflective DLC coating deposition on GaAs was optimized. DLC films of different thicknesses were deposited to investigate IR spectral characteristics. DLC films on GaAs increased microhardness from 500 kg/mm2 for the uncoated substrate to 1200 kg/mm2. The spectral transmittance of the bare and coated substrates in the 2.5 < ? < 16.5 ?m region was measured. DLC layer thickness affects the optical transmittance of the coated substrate. The peak transmittance with DLC coatings on both sides of the substrate reaches 95%, with about 1% absorption and 4% reflection.

We present a shift-invariant optoelectronic associative memory (OAM) which is realized in a cascade of correlators. The starting point is the OAM architecture proposed in 1995. Its crucial modification, which we propose, consists in the codification of each class of objects on the recognition filter by different carrier frequencies. This ensures the proper work of the system regardless of the location of the pattern in the input scene. As a result of such a filter design an additional intermediate layer has to be introduced into the OAM between the thresholder and reconstruction layer. We present a description and analysis of all elements of the modified OAM, with special regards to these subsystems (layers) which are particularly valid for the shift-invariant recognition and reconstruction. The final results of digital analysis of the behavior of the shift-invariant OAM are included.

A new data processing method is proposed for the damage detection of anisotropic composite materials. The wavelet transform and its phase space property are discussed to illustrate how the signal features are represented in the time-frequency plane. The terms in the expansion of the wavelet series that have the same time-frequency property as the original signal are then obtained by comparing the time- frequency space of the signal with the phase space of the wavelet transform. For wavelet neural networks, the training process can be very slow because the number of terms in the wavelet series is often too large for a reasonable search. Here we apply the Gram-Schmidt orthogonal- ization to remove the redundant wavelets in the series using the characteristics of sampled data. Moreover, the values of the features corresponding to different damage types are obtained by linear equations. Experiments on the damage detection of composites with various size cracks and delamination are conducted to demonstrate the feasibility of the proposed method. They show that the reconstructed curves obtained by the proposed approach can well approximate the original sampled curves and that the features corresponding to different damage types are identified.

A nonimaging optical system is developed for particle detection in an optical particle counter (OPC) with a large measurement plane, the kind of OPC required to control particle contamination in clean process gases used in chip manufacture. The measurement plane must cover the whole cross section of the gas pipe to be able to detect each particle. In a conventional OPC with imaging detection optics, local dependence of the particle signal is caused by the inhomogeneity of light intensity in the measurement plane as well as by local dependence of the angle of the detected scattered light. However, most important is the local signal dependence caused by the imaging detection optics. Using nonimaging elements reduces local dependence of the scattered light signal which is caused by the imaging optics. The work carried out on nonimaging light concentrators for particle detection is described. We discuss the advantages of using light concentrators, summarize the optical theory of light concentration and investigate the optical characteristics of light concentrators. Through theoretical as well as experimental tests, we show that the local deviation is less than ±25.6% for a homogenous light intensity distribution in the measurement plane.

A method of calculating the characteristics of noncollinear phase matching in both uniaxial and biaxial crystals is presented. Although significant work has been done to characterize collinear phase matching and to present many of its applications, noncollinear phase matching also has unique characteristics, leading to several useful applications. The method presented enables calculations of both the collinear and noncollinear cases, and enables a far larger set of nonlinear crystals and configurations to be studied.

In this paper, we describe the design and performance of a newly developed single-mode multifiber connector which employs an injection molded mechanically transferable (MT) type ferrule and a quick assembly technique. The connector is designed to be compatible with the MT connector. The ferrule is made using injection molded thermoplastic resin. This makes the ferrule production process easier, and also contributes to cost effectiveness. The ferrule can be assembled without polishing or heating by fixing cleaved fibers with a quick hardening adhesive. The ferrule assembly time is only 3 minutes. The fabricated 8-fiber ribbon connector exhibits a low insertion loss of 0.21 dB and a return loss of >45 dB with index-matching.

The feasibility of an all-optical fiber optic interface for sensors and actuators is demonstrated. The interface module converts optical power to electrical power for the use of the sensor or the actuator. In addition, the module provides bidirectional optical data transmission between the sensor or actuator and a control unit by using the powerfeeding fiber as a data transmission media. Optical power and data is transmitted to the sensor or actuator via a single multimode fiber. The system comprises of a customized 10-cell photovoltaic array illuminated by the use of a customized 1 x 10 integrated optics coupler. A 41% optical-to-electrical power conversion efficiency was obtained for the photovoltaic array, and a 27% total optical-to-electrical power conversion efficiency was attained for the system. When a single element in the array was biased as an LED, a -33 dBm optical power was coupled to the multimode fiber.

We examine the effect of fiber surface oxyfluorination on the interfacial bonding between acrylic coated optical fiber and a cementitious matrix and polyester resin respectively. The optical fiber is surface oxyfluorinated through a gas reaction process at room temperature in which elemental oxygen and fluorine are introduced into the acrylic molecular chain to replace the hydrogen atoms partially. After surface fluo- rination, the wettability of the optical fiber improves. Through an optical fiber embedment pull-out test, it is found that the surface oxyfluorination treatment improves on average the adhesional shear bond strength between the optical fiber and the cementitious matrix by 22% and the interfacial bonding between the optical fiber and the polyester resin matrix by 66%. The debonding of the unmodified optical fiber and the polyester matrix exhibits catastrophic failure characteristics, whereas that of the oxyfluorinated optical fiber with the polyester matrix is more gradual and there is still a substantial bond at the interface after the interfacial adhesive bond is broken. The mechanisms for the increase in interfacial bonding between the oxyfluorinated acrylic coated optical fiber and the cementitious and polyester resin matrices are proposed.

Incoherent-to-coherent converters using an induced self- pumped phase conjugator and using a mutually pumped phase conjuga- tor are demonstrated in a Ba1_xSrxTiO3 crystal. Resolution of 28 line pairs/mm has been obtained for the two incoherent-to-coherent converters. An notable advantage for the latter converter is that the converted image with amplified intensity can be obtained easily. © 2000 Society of Photo-Optical Instrumentation Engineers. [S0091-3286(00)01503-8]

Remote sensing of factory stack plumes may provide unique information on the constituents of the plume. Potential information on the chemical composition of the factory products may be gathered from thermal emission/absorption in the infrared. We have developed a new model for generating synthetic images of plumes as viewed from a hyperspectral sensor using DIRSIG, a radiometrically based ray-tracing code. Existing plume models that describe the characteristics of the plume (constituents, concentration, and temperature) are used for input into DIRSIG. Ray-tracing is done for the scene that accounts for radiance from the plume, atmosphere and background, as well as any transmissive effects. Observations are made on the interaction between the plume and its background and possible effects for remote sensing. Images of gas plumes using a hyperspectral sensor are illustrated. Several sensitivity studies are done to demonstrate the effects of changes in plume characteristics on the resulting image. Inverse algorithms that determine the plume effluent concentration are tested on the plume images. A validation is done on the gas plume model using experimental data collected on a SF6 plume. Results show the integrated plume model to be in good agreement with the actual data from five to one hundred meters from the stack exit. The validity and limitations of these models are discussed as a result of these tests.

Adaptive optics (AO) combines technologies that enable the correction of the wavefront distortion caused by the earth's atmospheric turbulence in real time. Adaptive secondary mirror (ASM) systems have been proposed and are now being developed. ASMs have advantages over conventional AO systems in terms of throughput, polarization and IR emissivity. Previously, we reported the design of an ASM demonstrator along with its predicted performance. We now report the construction techniques and the results from the preliminary static and dynamic testing of such a demonstrator. In particular, assembly methods that preserve the optical quality of the mirror are presented along with experimentally measured mirror influence functions and closed loop tip/tilt performance.

The Multi-Spectral Solar Telescope Array (MSSTA) is a sounding rocket-borne observatory composed of a set of normal- incidence multilayer-coated telescopes that obtained selected bandpass spectroheliograms (44 to 1550 Å) of the solar atmosphere. These spec- troheliograms were recorded on specially fabricated XUV and FUV 70-mm Kodak film. Rocket launches of this instrument payload took place in 1991 (MSSTA I) and 1994 (MSSTA II) at the White Sands Missile Test Range in New Mexico, sponsored by the National Aeronautics and Space Administration (NASA) sounding rocket experiment program. Immediately prior to the 1994 launch, visible light focusing tests of each telescope were performed in situ using a 1951 standard Air Force high- resolution test target, to measure optical resolution performance. We determined that the MSSTA II telescopes performed at diffraction-limited resolutions down to 0.70 arcsec at visible wavelengths. Based on these measurements, we calculate an upper bound to the focusing errors that incorporate the sum of all uncorrelated system focus errors that affect resolution performance. Coupling these upper bound estimates with the in-band diffraction limits, surface scattering errors and payload pointing jitter, we demonstrate that 11 of 19 MSSTA II telescope-having negligible figures of focus errors in comparison to the corresponding visible diffraction limits-performed at sub arcsecond resolution at their operational FUV/EUV/XUV wavelengths during flight. We estimate the in-band performance down to 0.14± 0.08 arcsec.

The Mallat algorithm for finite length signals is equivalent to a matrix transform on vector space, and the transform matrix is a finite 2-circular matrix. As a new concept, a minimal matrix, which is also a 2-circular matrix, is put forward. Through new developments of definitions and theorems for a minimal matrix, new algorithms for constructing wavelets filters are obtained. Employing these algorithms, we give several examples of orthonormal and biorthogonal wavelet filters. The methods avoid using a Z-transform or Fourier transform, so it is relatively simple to construct FIR wavelet filters. Because many filters constructed go beyond traditional wavelets, the new concept of discrete hyperwavelets transforms is put forward. Finally, an application in image compression is discussed briefly.

The notion of moment-patterns in the Radon space is introduced. A moment pattern of order k, in the Radon space, is the set of moments (of order k) associated with the projections of an image. Some of the interesting properties of the moment patterns are studied. A method of rendering the patterns invariant to translation, scaling, and rotation, within the Radon space, is developed. The resulting set of 1-D invariant moment patterns constitutes a descriptor of an object invariant to geometric transformations. When the data is available in the Radon space, as in computed tomography, the invariants can be constructed within the Radon space. An extension of the technique to 3-D is presented.

Based on optical Fourier transform, the online measurement of the sizes of standard wire sieves is described. Compared with other traditional methods, this system has more advantages, such as operating efficiently and precisely on line and in real time. The measuring system, composed of a laser, an optical Fourier transform system, a CCD camera, an image acquisition system, and a personal computer, can offer averaged sizes and percentage of apertures exceeding the specified size of standard wire sieves in two-dimensional directions. The experimental results are also presented.

Estimation of a long-term dc drift behavior is essential for the application of LiNbO3 optical intensity modulators to fiber communication systems. Therefore temperatureaccelerated tests are carried out using a feedback-biascontrol operation system, and the results are converted into a duration at ordinary device operation temperatures, e.g., 50°C.