This PDF file contains the editorial “2001 in Review” for OE Vol. 41 Issue 02

The quantum-noise-limited sensitivity is derived for a two-beam interferometer, which uses a phase generated carrier demodulation scheme. For surface-disturbancedetecting sensors, this sensitivity limit is expressed in terms of the smallest displacement that may be detected if the signal-to-noise ratio is unity. We determine the quantumnoise- limited displacement of the classical Michelson interferometer to be 5 pm.

Good results on rain pattern tracking are achieved by merging the information extracted from a weather radar data sequence, using both a correlation and shape analysis approach. The two methods, namely the tracking radar echoes by correlation corrected by continuity (COTREC) and the modal matching shape representation are both applied to the problem. This choice allows us to exploit the advantages of both a global and a more local approach to a motion-based interpretation of rain events. By combining the two methods, we may work on a global frame analysis based on correlation matching and add a local analysis of the shape of the cells to find a more refined motion vector field. Some results are shown, extracted from data sequences recorded by a C-band weather radar in Northern Italy.

We present a display to distinguish loci of equal activity in samples showing dynamic speckle patterns. Regions differing in their activity are shown as different gray levels. We define the generalized differences and the weighted generalized difference operations and we compare the results with previously reported methods. Results obtained with seeds are shown.

A novel composite material based on medium-density polyethylene and thermoplastic chalcogenide glass has been produced. Both materials are highly transparent in the middle and far IR, but their refractive indices differ dramatically. The polymer and the glass have nearly equal viscosities at the temperature of polyethylene processing. This fact allowed the use of extrusion for homogenization. Single- and twin-screw extrusion processes yielded compositions that contain up to 40% of chalcogenide glass particles, which were dispersed in the polymer matrix. Highly homogeneous compositions that contain perfectly spherical glass particles 1 to 2 ?m in diameter dispersed in the polymer matrix were obtained. Highly oriented structures involving chalcogenide glass fibers immersed in the polymer matrix were prepared at high stretch speeds. It was established that it is possible to produce a composite that is opaque in the visible and near IR, and highly transparent in the 2 to 25-?m wavelength band. The use of oriented films as IR laser light-shaping diffusers is possible. The composite films obtained were tried successfully as immersion adhesive layers for the contacting of IR fibers.

Marginal rays are used to study the limitations of the spatial and angular extents of light beams by stops and apertures in tapered gradient-index lenses. The results are applied to two kinds of taper functions and compared to selfoc lenses.

To enhance the security of a dot-matrix hologram (DMH), a method to hide an image inside the DMH is proposed. The hidden image, which does not depress the visibility and the dynamic-effect feature of the DMH, is invisible but can be reconstructed by illuminating the DMH with a specified laser beam. The reconstructed hidden image is invariable to the lateral shift between the laser beam and DMH. Two experiments are carried out to illustrate the applicability of the proposed method.

Design of a simple diffuser, in which the absolute value of the phase difference between the diffuser's adjacent samples is constant, is considered. A condition is imposed in the design so that the diffuser is suitable for use with the iterative method based on the iterative Fourier transform algorithm for calculating a two-dimensional complex amplitude function that possesses a bandlimited and smooth spectrum. A method for effectively designing this diffuser is proposed, and its application in the field of digital holography is presented.

In conventional fractal image coding (FIC) schemes, domain blocks are constrained to be twice as large as range blocks to ensure the convergence of their iterative decoding stage. However, this constraint has limited the fractal encoder to exploit the self-similarity at the same resolution scale of natural images. To overcome the shortcoming, a novel scheme using same-sized range and domain blocks is proposed. Further, a recursive scheme feeding the coding results back to the input during the encoding procedure is used to improve the decoded image quality. Experimental results show our method gives significant improvement over Fisher's FIC.

Among a context of three pixels, the present JPEG-LS produces predicted values based on whether a vertical edge or a horizontal edge is detected. When a diagonal edge exists, however, experiments and observation reveal that such a prediction will generate large predictive errors. By applying the triangle inequality to the analysis of predictive templates in JpEG-LS, we propose a diagonal-edge detection scheme to reduce the predictive error and hence provide an improvement on the prediction accuracy. Experiments are carried out to test the proposed scheme for a group of sample images. In comparison with the current JPEG-LS prediction, our scheme produces lower prediction errors, in terms of both MSE measurement and visual comparison of error images.

Junctions convey rich information and are often used to identify objects in the scene or for stereoscopic matching or displacement vector measuring. In a previous work, an accurate wavelet-based corner detection method has been proposed. This work is an extension of the work on junction characterization and detection in real images. We first perform an analytical study for a general junction model that allows us to better understand the behavior of junctions in the wavelet domain. Two new properties, including the scale proportion property of the modulus and the scale invariant property of orientation in the wavelet domain, are derived. These properties are applied to accurately detect junctions. Several promising experimental results have been carried out using noisy and noisy-free real images. These results show that our approach is a general methodology for accurate detection of discrete surface intersection.

Image segmentation is a process for dividing a given image into meaningful regions with homogeneous properties. A new two step approach is proposed for medical image segmentation using a fuzzy Hopfield neural network based on both global and local gray-level information. The membership function simulated with neuron outputs is determined using a fuzzy set, and the synaptic connection weights between the neurons are predetermined and fixed to improve the efficiency of the neural network. The proposed method needs initial cluster centers. The initial centers can be obtained from the global information about the distribution of the intensities in the image, or from prior knowledge of the intensity of the region of interest. It is shown by experiments that the proposed fuzzy Hopfield neural network approach is better than most previous approaches. We also show that the global information can be used by applying the hard c-means to estimate the initial cluster centers.

Two fundamental motivations exist for designing remote sensing systems that are undersampled: (1) SNR considerations that motivate larger detectors to collect more photoevents per frame time and (2) the desire to maximize the field of view with a finite number of detectors. As a result, many remote sensing systems do not satisfy the Nyquist sampling criterion, leading to measured images corrupted with a defect called aliasing. We describe a localized subpixel motion sensing algorithm that is used to properly place small blocks of the sequence of images in an upsampled space. Localized motion sensing enables dealiasing to be performed on image sequences with more complicated relative motion than simple translation. The presented results show improvements in both the edge response and subjective image quality.

The demand for high-resolution images is gradually increasing, whereas many imaging systems have been designed to enable a certain level of aliasing during image acquisition. in this sense, digital image processing approaches have recently been investigated to reconstruct a high-resolution image from aliased low-resolution images. However, since the subpixel motion information is assumed to be accurate in most conventional approaches, the satisfactory high-resolution image cannot be obtained when the subpixel motion information is inaccurate. Hence, we propose a new algorithm to reduce the distortion in the reconstructed high-resolution image due to the inaccuracy of subpixel motion information. For this purpose, we analyze the effect of inaccurate subpixel motion information on a high-resolution image reconstruction, and model it as zero-mean additive Gaussian errors added respectively to each low-resolution image. To reduce the distortion, we apply the modified multichannel image deconvolution approach to the problem. The validity of the proposed algorithm is demonstrated both theoretically and experimentally.

In imaging systems the detector arrays deliver at the output time-discrete signals, where the spatial frequencies of the object scene are mapped into the electrical signal frequencies. Since the spatial frequency spectrum cannot be bandlimited by the front optics, the usual detector arrays perform a spatial undersampling and as a consequence aliasing occurs. A means to partially suppress the backfolded alias band is bandwidth limitation in the reconstruction low-pass, at the price of resolution loss. By utilizing a bilinear detector array in a pushbroom-type scanner, undersampling and aliasing can be overcome. For modeling the perception, the theory of discrete systems and multirate digital filter banks is applied, where aliasing cancellation and perfect reconstruction play an important role. The discrete transfer function of a bilinear array can be imbedded into the scheme of a second-order filter bank. The detector arrays already build the analysis bank and the overall filter bank is completed with the synthesis bank, for which stabilized inverse filters are proposed, to compensate for the low-pass characteristics and to approximate perfect reconstruction. The synthesis filter branch can be realized in a so-called ‘‘direct form,’’ or the ‘‘polyphase form,’’ where the latter is an expenditure-optimal solution, which gives advantages when implemented in a signal processor. This paper attempts to introduce well-established concepts of the theory of multirate filter banks into the analysis of scanning imagers, which is applicable in a much broader sense than for the problems addressed here. To the author’s knowledge this is also a novelty.

We have successfully developed a near-infrared photoncounting system using an InGaAs avalanche photodiode. By investigating the characteristics of the InGaAs avalanche photodiode in the analog detection mode and the photon-counting mode, we have optimized its operating condition as a photon-counting detector. The multiplication factor shows a maximum at 193 K, and the detection efficiency shows a maximum at 173 K. However, the signal-to-noise ratio shows a maximum at 153 K. On the optimum operating condition, the wide dynamic range of about 50 dB (1.0x 10-16 W to 1.0x 10-11 W) and the minimum detectable power of 100 aW (1.0x 10-16 W) are achieved at 1.5 ?m. The detection efficiency depends on the incident optical power, and 15% for 1 pW is achieved at 1.5 ?m. In the near-infrared range between 0.9 and 1.55 ?m, moderate detection efficiency is obtained. Finally, we have demonstrated a 1.54-?m eye-safe photon-counting lidar using a Raman shifted Nd:YAG laser and the photon-counting system. Some light signals backscattered from clouds and the atmosphere are obtained. The experimental results show that the photon-counting system is very practical and attractive.

An algorithm for stitching together a set of individual phase measurements into a unified larger phase map is presented. The set of individual phase maps results from scanning a component over the interferometer aperture and acquiring a measurement at each position. The algorithm is based on an iterative approach, where singular value decomposition is used to solve the rigid body movement problem between the different phase maps. The algorithm has been tested in numerical experiments and has been successfully applied to real data.

We perform computer simulation and experimental work to investigate how the surface topography of reflecting mirrors affects the optical performance of the thin-film micromirror array (TMA) designed for projection display. We reveal that the form accuracy of mirror surface specified by the peak to valley should be less than 0.3 ?m, so that the reflecting efficiency becomes more than 95%. We also find that the micromirrors should be tilted in a diagonal mode so as to maximize the contrast ratio that is defined by the ratio of the maximum amount of through light to the minimum.

The sequential steps of conversion of data gathered by a full-field 3-D shape measurement optical system into CAD/CAM and multimedia environments are discussed. The complete triangulation algorithm, which automatically creates the triangle mesh from the input cloud of points, is described. Each block of this algorithm is explained in detail with special attention paid to the parameters controlling the quality of the data conversion process. The adaptive process of reducing the number of the triangles based on a second derivative of local curvature of an objects’ surface is explained. The error analysis is discussed at each step of the cloud data processing in dependency of the algorithm initial parameters. The three algorithms that process additional color information (R,G,B) into the texture mapped on the triangle mesh is presented. The usefulness of the complete conversion process is proved by the manufacturing of an exemplary object, exporting a human 3-D face to the Internet and an example object into a 3-D virtual environment.

We present a new signal processing method, extracting the phase information from the spatial interference pattern, for precise displacement measurement. This method is to measure the fringe movement by detecting the fringe peak positions, which are linearly proportional to the displacement of an object. The proposed method is simple and robust compared to conventional techniques, but it has several significant error sources: the optical and electrical random noises, the wavefront distortion, and the tilt motion of the target mirror. Thus, we need the error analyses and computer simulations about the effect of these factors and propose the compensation method.

For a medical application, we are interested in an estimation of optical flow on a patient's face, particularly around the eyes. Among the methods of optical flow estimation, gradient estimation and block matching are the main methods. However, the gradient-based approach can only be applied for small displacements (one or two pixels). Generally, the process of block matching leads to good results only if the searching strategy is judiciously selected. Our approach is based on a Markov random field model, combined with an algorithm of block matching in a multiresolution scheme. The multiresolution approach allows detection of a large range of speeds. The large displacements are detected on coarse scales and small displacements are detected successively on finer scales in a coarse to fine strategy. The Markov random fields allow the initialization and control of motion estimation across all scales. The tracking of motion is achieved by a block matching algorithm. This method gives the optical flow, whatever the amplitude of motion is, if pertaining to the range defined by the multiresolution approach. The results clearly show the complement of Markov random field estimation and block matching across the scales.

We present a system for 3-D shape measurement in large volumes based on combined digital-fringe-Gray-code projection. With the help of a new calibration procedure, the system provides accurate results despite its crossed-axis configuration and unknown aberrations of the digital light projector and CCD camera. Also, the separate clouds of points captured from different directions are automatically merged into the main cloud. The system delivers results in the form of (x,y,z) coordinates of the object points with additional (R G,B) color information about their texture. Applicability of the system is proven by presenting sample results of measurements performed on complex objects. The uncertainty of the system was estimated at 10-4 of the measurement volume.

A method and tools recently applied in animation are presented, and the associated problems connected with combining the real and the virtual world are described. Approaches include creating computer graphics libraries of realistic 3-D objects and describing their animation in 3-D space. The presented method simplifies the process of virtual-object generation and provides the shape and movement of the monitored object. Optical structured-light methods supported by photo- grammetry are proposed for gathering the information about a shape, deformations of shape, and shifts of 3-D objects. The authors apply the spatiotemporal approach, in which the spatial analysis of fringe pattern delivers information about the shape of the object, while the temporal analysis of the intensity variation l(t) at a given pixel provides information about shape variations and out-of-plane displacement. The function I(t) is analyzed by the Fourier-transform method. Rigid-body motion of the object is determined by a photogrammetry-based marker tracking method. The methodology of measurement is presented, together with experimental results.

As in the lens optimization process, ophthalmic lens designers have usually constructed error functions with 0.5, 0.7, and 1.0 at only three oblique fields. This seems enough to achieve a balanced trade-off with the astigmatic error, the power error, and the distortion all being considered simultaneously. However, for high-power ophthalmic lenses, the aberration curves show serious violations even if aspherical coefficients are involved. The analytical results indicate that a field error suppression of up to 7 points may even be required in some cases. The suppression effects are excellent and examples of both positive and negative lenses are designed.

In this study, an optical method is developed for the determination of the mechanical properties of polymers. The proposed method utilized the transmitted and reflected caustics. Thus, it can be used in a typical optical stress analysis laboratory. The mechanical properties of an optically isotropic material are determined using thin specimens with a central hole that are loaded in tension. The diffraction effects were considered using a digital image-analysis system. The effect of the hole size on the determination of the mechanical property is investigated. Excellent results were obtained using the proposed method.

We report the theory of operation and time domain model (TDM) simulation results for a two-section Fabry-Pe´ rot sampled grating distributed Bragg reflector (FP/SGDBR), 100-GHz, step-tunable laser [sidemode suppression rate (SMSR)>38 dB]. Although the main idea, the Vernier effect, was previously published, we present for the first time these two-section combinations for this specific sort of application.

We present a method for calibrating a range finder system composed of a camera and a structured light source. The system is used to reconstruct the three-dimensional (3-D) surface of an object. This is achieved by projecting a pattern, represented by a set of regularly spaced spots, on the surface of the object using the structured light source. An image of the illuminated object is next taken and by analyzing the distortion of the projected pattern, the 3-D surface of the object can be reconstructed. This reconstruction operation can be envisaged only if the system is calibrated. Instead of using a classical calibration method, which is based on the determination of the matrices that characterize the intrinsic and extrinsic parameters of the system, we propose a fast and easy to set up methodology, consisting of taking a sequence of images of a plane in translation on which a set of regularly spaced spots is projected using the structured light projection system. Next, a relationship between the position of the plane and the coordinates of the spots in the image is established. Using this relationship, we are able to determine the 3-D coordinates of a set of points on the object's surface knowing the 2-D coordinates of the spots in the image of the object taken by the range finder system. Finally, from the 3-D coordinates of the set of points, the 3-D surface of the object is reconstructed.

Wideband radar can obtain much target information due to its high-range resolution. Because its size is smaller than the resolution of conventional radar, for an airplane, it can be regarded as a point. However, for wideband radar with a bandwidth of several hundred megahertz, the range resolution is less than a meter, and airplane echoes of one impulse form a high-resolution range profile (HRRP), which includes the shape information of a target that can be used for automatic target recognition (ATR). A range profile can be divided into many range resolution cells, each of which still contains the echoes of many scatterers. The complex amplitude of one range cell echo can be regarded as the sum of these echoes. A small aspect of change will lead to a big change of the complex amplitude, since, although the variation of the range of each scatterer to radar is very small, it is still large enough compared to the small wavelength and may cause a big phase change. Hence, the range profiles are very sensitive to the aspect angle, which makes the ATR based on HRRPs a well-known challenging problem. The properties of range profiles are investigated and a preprocessing scheme is presented to obtain stable range profiles for ATR.

However, problems still remain in conveying this video data to the end users. Limiting factors are the resource capabilities in distributed architectures and the features of theals. The efficient use of image processing, video indexing, and analysis techniques can provide users with solutions or alternatives. We see the video stream as a sequence of correlated images containing in its structure temporal events such as camera editing effects and presents a new algorithm for achieving video segmentation, indexing, and key framing tasks. The algorithm is based on color histograms and uses a binary penetration technique. Although much has been done in this area, most work does not adequately consider the optimization of timing performance and processing storage. This is especially the case if the techniques are designed for use in run-time distributed environments. Our main contribution is to blend high performance and storage criteria with the need to achieve effective results. The algorithm exploits the temporal heuristic characteristic of the visual information within a video stream. It takes into consideration the issues of detecting false cuts and missing true cuts due to the movement of the camera, the optical flow of large objects, or both. We provide a discussion, together with results from experiments and from the implementation of our application, to show the merits of the new algorithm as compared to the existing one.

Silicon wafers that are fabricated by the Czochralski technique contain pyramidal pits, which are referred to in more general terms as crystal-originated particles (COPs). Because wafer inspection systems now benefit from the predictability of scattering from particles of known size, shape, and composition, it is of interest to achieve the same level of predictability for surface breaking defects such as pits. A model, valid for s-polarization and a high incidence angle, is based on the Fraunhoffer approximation for the diffraction from a square aperture, and is enhanced by an empirically derived term that accounts for the scatter component attributed to facets. Measurements and the model show that (using the prescribed optics configuration) a characteristic peak occurs between 20 and 45 deg in the forward scatter region, which increases in magnitude and moves forward with increasing pit size. This kind of information can be used to improve an instrument's ability to distinguish between surface particles and COPs by strategically positioning detectors accordingly. Furthermore, the model can be used as a check against numerical models that are designed to predict scatter from pyramidal pits that are of size equal to a wavelength or much smaller.

A conventional Shack-Hartmann wavefront sensor cannot be used for the measurement of wavefronts with steep slopes if the spots leave their respective subapertures. In an earlier paper [N. Lindlein, J. Pfund, and J. Schwider, ''Expansion of the dynamic range of a Shack- Hartmann sensor by using astigmatic microlenses," Opt. Eng. 39(8), 2220-2225 (2000)], we described a method to expand the dynamic range of a Shack-Hartmann wavefront sensor by marking the spots using astigmatic microlenses. We present experimental results for this method and describe how this special sensor can be interpreted as a combination of several Shack-Hartmann sensors with enlarged subapertures.

Based on the principle of Shack-Hartmann wavefront sensors (SHWFS), the differential angle-of-arrival fluctuation coefficient, the slope structure-correlation coefficient, the generalized slope correlation coefficient, the variance of the angle-of-arrival fluctuation, the slope structure function, and the slope structure-correlation function are used to evaluate the power law exponent ? of the phase power spectrum and the generalized atmospheric coherence length p0 for non-Kolmogorov turbulence. These methods used to evaluate the atmospheric parameters are compared by introducing the additive measurement noise of SHWFS. The differential angle-of-arrival fluctuation coefficient, the slope structure-correlation coefficient, and the generalized slope correlation coefficient are only related to ? and independent of p0. The slope structure-correlation coefficient and the slope structure-correlation function can remove the effect of the measurement noise. The SHWFS data in the atmospheric experiments for laser beam propagation through a 1000-m horizontal path are utilized to evaluate ? and p0 according to the methods.