This PDF file contains the editorial “Editorial: Open Access” for OE Vol. 44 Issue 09

A robust global motion model estimation method is proposed by fitting the optical flow field for aerial imagery. Considering the outlier-sensitive defect of traditional least-squares regression technique, we put forward a simple optical flow valuation mechanism to choose a small set of reliable flows for fitting. Since flow outliers that are unfit for fitting are almost completely removed, the final global motion estimation result is highly improved. Experimental results show the robustness and applicability of our method.

A new device for measuring surface vibrations of musical instruments is presented. The architecture of the device is based on a quasi-Fourier digital holography setup with inexpensive commercial elements capable of recording large digital holograms. Experimental results showing vibration modes for several musical instruments are given. The results demonstrate fringe pattern quality as well as the testing possibilities in tuning the musical instruments.

A two-user, 10-Gbits/s optical code-division multiple-access system implemented by using cascaded long-period fiber gratings formed in a dispersion-compensating fiber (DCF) is demonstrated. Our results show that the sensitivity of cladding modes to the refractive index change on the cladding surface is greatly reduced by utilizing the inner-cladding mode of the DCF. Two pairs of encoder/decoder are constructed and the performance is evaluated by measuring bit error rate (BER). With an interferer, a BER of 1.5×10^–12 is measured at a received optical power of –6 dBm.

We propose and demonstrate a versatile holographic storage system using a single-mode polarization-maintained (PM) fiber guided reference beam. By properly allocating the output coupler of the single-mode fiber, the system provides the ability of angular multiplexing recording with no upper limit of the angle tuning range of the reference beam. In addition, this system can easily achieve different holographic storage architectures including transmission, reflection, and 90-deg geometries.

Laser frequency stabilization is notably one of the major challenges on the way to a space-borne gravitational wave observatory. The proposed Laser Interferometer Space Antenna (LISA) is presently under development in an ESA, NASA collaboration. We present a novel method for active laser stabilization and phase noise suppression in such a gravitational wave detector. The proposed approach is a further evolution of the "arm-locking" method, which in essence consists of using an interferometer arm as an optical cavity, exploiting the extreme long-run stability of the cavity size in the frequency band of interest. We extend this method by using the natural interferometer arm length differences and existing interferometer signals as additional information sources for the reconstruction and active suppression of the quasi-periodic laser frequency noise, enhancing the resolution power of space-borne gravitational wave detectors.

We present a method to accurately measure the radius of curvature of a concave spherical mirror with a phase-measuring interferometer and a laser tracker. Use of a laser tracker eases the alignment of the testing system, eliminates the need to move the test piece during the measurement, and improves the accuracy of the distance measurement. Using this method, we measured the radius of curvature of a spherical mirror 0.5 m in diameter and about 2.5 m in radius of curvature. The accuracy of the measurement is better than ±20 µm.

We propose a new algorithm to determine the multifocus image fusion from several polychromatic images captured from the best focusing region where the best in focus image is included from a biological sample. This focusing region is built by including several images up and down starting from the Z position of the best image in focus. These captured RGB images are converted to YCbCr color space to have the color CbCr and intensity Y channels separated with the objective to preserve the color information of the best in focus image. Several approaches have been developed to fuse images, like those algorithms based on the wavelets transform, Laplacian, ratio, contrast or morphological pyramids selection, fusion by averaging, Bayesian methods, fuzzy sets, and artificial networks. However, this algorithm utilizes the Fourier approach by using the Y channel frequency content via analyzing the Fourier coefficients to retrieve the high frequencies to obtain the best possible characteristics of every captured image. After the completion of this process, we continue to construct the fused image with these coefficients and color information for the optimum in focus image in the YCbCr color space; as a result, we obtain a precise final RGB fused image.

We describe a high performance optomechanically scanned millimeter-wave imager intended to monitor the ground movement of aircraft in adverse weather conditions. It employs two counter-rotating mirrors that are tilted about their axes of rotation. They simulate the linear scan of a single high speed, large aperture flapping mirror. When used with a linear receiver array, they can produce a 2-D scan of the scene at TV rates. In the present application, they were used with a single receiver and a large flapping mirror to produce a 2-D scan of the scene ±10 deg vertically and 60 deg horizontally. One of the rotating mirrors has a concave surface and acts as the focusing element in the imager. The two mirrors are driven from a single servo motor using timing belts and toothed pulleys. The flapping mirror is slaved to the motion of the rotating disks using an electronic cam. The single channel 94-GHz receiver consisted of an InP LNA followed by a down converter and a detector. The video output passes to an A/D converter and is displayed on a conventional PC. This system has virtually 100% transmission and can be used at any waveband.

The paper describes an algorithm of photoelastic tomography and its application for residual stress measurement in glass articles of complicated shape. The algorithm is based on a linearized solution of the equations of integrated photoelasticity. The problem of tensor field tomography is decomposed into several problems of scalar field tomography for normal stress components of the stress tensor. The method is implemented with an automated polariscope supplied with a rotary stage. Software for the control of tomographic measurements and for the calculation of the stress fields has been elaborated. Several examples illustrate application of the method.

This paper deals with 3-D object reconstruction using a structured light system (SLS). The SLS is composed of a camera and a laser projector that illuminates spots on the scene of interest. The basic problem of such a system is the correspondence problem. If the correct correspondence between the imaged spots and the projected laser rays is found, the 3-D coordinates of the physical points associated with these spots can be calculated. We propose a method that automatically provides SLS configurations (i.e., the relative positions of both camera and laser projector with respect to the object to be analyzed) that allow performing an unambiguous and direct correspondence procedure. Experimental results are presented that show the validity and the effectiveness of the proposed method.

We realized a laser profilometer module using low temperature cofired ceramics technology. The device consists of a vertical-cavity surface-emitting laser as the light source and a complementary metal oxide semiconductor image sensor as the detector. The laser transmitter produces a thin light stripe on the measurable object, and the receiver calculates the distance profile using triangulation. Because the design of optoelectronic modules, such as the laser profilometer, is usually carried out using specialized software, its electronic compatibility is very important. We developed a data transmission network using commercial optical, electrical, and mechanical design software, which enabled us to electronically transfer data between the designers. The module electronics were realized with multilayer ceramics technology that eases component assembly by providing precision alignment features in the substrate. The housing was manufactured from aluminum using electronic data transfer from the mechanical design software to the five-axis milling workstation. Target distance profiles were obtained from 100 points with an accuracy varying from 0.1 mm at a 5-cm distance to 2 cm at 1.5 m. The module has potential for distance measurement in portable devices where small size, light weight, and low power consumption are important.

Detection of small objects in image data is fundamental to many image processing applications. Spatial domain detection of small objects is the key process of the detect before track (DBT) method for moving object detection. Most of the existing spatial detection methods are filter-based ones. We present a novel and efficient approach to spatial detection of small objects in image data, which combines the local signal-to-noise ratio (SNR) characteristic and appearance characteristic of small objects. In such a detection scheme, the nonlinear principal component analysis (NLPCA) neural network (NN) is used for modeling the appearance of small objects and constructing a saliency measure function. Based on this function and the feature vector extracted at each pixel position using the principal component analysis (PCA) technique, a small object saliency map is formed by lexicographically scanning the input image, then the saliency map is thresholded to obtain the intermediate object location map. We also treat such a saliency map as a spatially filtered result of the input image. Compared to several filter-based detection methods, experiments show that the proposed algorithm outperforms these methods.

Shadow and projection moiré are the oldest forms of moiré to be used in actual technical applications. In spite of this fact and the extensive number of papers that have been published on this topic, the use of shadow moiré as an accurate tool that can compete with alternative devices poses very many problems that go to the very essence of the mathematical models used to obtain contour information from fringe pattern data. In this paper some recent developments on the projection moiré method are presented. Comparisons between the results obtained with the projection method and the results obtained by mechanical devices that operate with contact probes are presented. These results show that the use of projection moiré makes it possible to achieve the same accuracy that current mechanical touch probe devices can provide.

We present the application of a portable radial in-plane speckle interferometer to the measurement of residual stresses when local heating is used as a stress relaxation technique. We also present a numerical method to calculate the residual stresses from the radial in-plane displacement field that is measured subsequent to the heating and cooling of the interrogated spot. A finite element analysis of the thermomechanical response of the specimen under test is performed to adjust the model used for residual stress determination. To evaluate the performance of this technique, results obtained using several preloaded specimens are compared with the stress introduced in them. It is shown that the speckle interferometer and local heating combined system allows the measurement of residual stresses with an average deviation of approximately 7% for a range of uniaxial stresses from 25 up to 75% of the yield stress of the material.

We report a diode-end-pumped 1064-nm Nd:YVO₄ laser passively cw mode-locked by a semiconductor saturable absorber mirror. We designed a long cavity with relatively small mode size in the gain medium so that stable passive mode locking without Q-switching instabilities became possible under low pump power. At 2.42 W of pump power a mode-locked fundamental-mode average output power of 742 mW was attained with an overall optical-optical efficiency of 31%. The pulse duration was 9.1 ps as measured at the repetition rate of 58 MHz.

A high-average-power β-BaB₂O₄ (BBO) optical parametric oscillator pumped by the second harmonic of a Nd:YAG laser is demonstrated at the pulse repetition frequency of 0.5 kHz. Average power of 5.4 W (10.8 mJ per pulse) with an energy conversion efficiency of 45% is obtained for a type I BBO optical parametric oscillator. The output power can be increased, and undesirable thermal effects are not observed.

We use two Pockels cells in series to achieve simple temporal pulse shaping. This technique is used in our optical parametric chirp pulse amplification (OPCPA) system to optimize the temporal shape of the pump pulse. It also offers a low cost alternative to arbitrary waveform generators.

A highly uniform multiwavelength erbium-doped fiber ring laser with an intracavity sine phase modulator is demonstrated. The flat output spectrum is achieved by optimizing the cavity structure, modulation amplitude, and frequency of the sine phase modulator. Fifteen lasing lines with wavelength spacing of 0.9 nm appear simultaneously and stably with power differences less than 2 dB and side-mode suppression ratio higher than 32 dB. In addition, the proposed cavity can support unidirectional operation without optical isolators. An output power difference of about 20 dB is realized between the counterclockwise and clockwise directions, which is almost independent of the pump power and lasing wavelengths.

The heat generation in a flashlamp-pumped Nd:glass disk amplifier is studied by the simulation of the whole pumping process, which is based on the ray-tracing method. The results of temperature rise distribution as well as gain distribution are presented. The evolution of heat generation in disk during the pumping process is discussed in detail. Some main factors related with the thermal effect, such as the quantum efficiency, fluorescence lifetime, and pulse duration, are investigated through studying the ratio of the heat generation to energy storage in the gain medium. The influence of each parameter on heat generation is studied carefully, and the results provide ways to decrease the heat generation during the pumping process.

This paper focuses on the integration of InGaAsSb photodetectors along with micro-optics in order to realize a prototype system that can achieve a stronger response during atmospheric profiling and spectroscopy measurements. The integration of the detector was executed using a novel conductive-adhesive-based flip-chip integration process. The design, fabrication, and integration of the constituent technologies and experimental results from their characterization are presented.

We demonstrate the use of a pair of mechanically induced long period gratings (LPGs) for sensing the refractive index and concentration of liquids for which NaCl solutions of different concentrations and standard refractive index liquids are studied. The effect of varying the refractive index and/or concentration is reflected in changing output power loss values at resonance wavelengths. For a concentration change from 5 to 20 g per 100 ml, the maximum variation detected in optical output power is 20 pW, while for a refractive index variation from 1.446 to 1.458, it is 11 pW. These studies are quite useful for chemical, pharmaceutical, biological, and process control sensing applications.

A Tl₃AsSe₃ (TAS) acousto-optic tunable filter (AOTF) hyperspectral imaging system is designed and demonstrated that enables real-time imaging of ambient temperature scenes at wavelengths around 10 µm. The predicted sensitivity improvement is a factor of 46 compared to previous TAS AOTF systems, and is accomplished by increasing the spectral passband, improving the AOTF diffraction efficiency, and using a higher sensitivity camera. Optical system designs are also developed and tested for reducing AOTF aberrations and producing pixel-limited resolution.

Modeling the process of ion exchange in glass requires accurate knowledge of the self-diffusion coefficients of the incoming and outgoing ions. Furthermore, correlating the concentration profile of the incoming ions to a change in refractive index requires knowledge of the correlation coefficient. We present a method by which these three parameters can be quickly determined experimentally, using a genetic algorithm. Comparison with published data is presented.

A study of laser (near- and mid-infrared) pulse dispersion in hollow waveguides is presented. We developed an analytical model to describe the pulse dispersion in hollow waveguides and compared our theoretical calculations with measurements done by us and also by two other groups. The pulse dispersion was experimentally measured for a short Q-switched Er:YAG laser in the nanosecond range and for femtosecond Ti:sapphire laser pulses transmitted by hollow optical waveguides. For analytical calculation of the pulse dispersion in these waveguides, a refined ray tracing program was developed. This approach took into account roughness of the internal reflecting and refracting inner layers. A comparison analysis between the measurements and calculations conducted at identical parameters demonstrates good correlation between theoretical and experimental results.

Optical add-drop multiplexers (OADMs) based on grating-assisted null couplers are excellent candidates for low-cost wavelength division multiplexed (WDM) systems. These devices potentially offer exceptional operating characteristics in a compact layout that does not require circulators. Optimization analysis has been already presented. However, inherent fabrication errors either in the null coupler or in the grating increase the crosstalk at the drop port. In this paper, a simple model that relates the optical signal-to-noise ratio (OSNR) of the OADM to the null-coupler and grating parameters is presented. Based on that model, we propose two new approaches to increase the OSNR at the drop at output ports, when fabrication errors are present. One approach optimizes the grating angle to minimize the noise produced by spurious reflection without mode conversion. The other shifts these reflections out of the bandwidth used by the WDM system. The advantages and limitations of these approaches are analyzed.

We investigate the process of generating graded-index plastic optical fibers by thermal diffusion of dopants in multistep-core fibers formed by layered extrusion. The layer thicknesses and their dopant concentrations are varied for two-step-core fibers to determine the values that, after the completion of the diffusion process, result in a desired dopant distribution optimized for maximum bandwidth of graded-index fibers. Our solution of the relevant diffusion equation by the explicit finite-difference method is verified against an analytical solution from the literature and two cases of fibers with diffused profiles, one with a two-step and the other with six-step core. The conclusions reached provide a guideline for the design of graded-index plastic fibers and enable prediction of the fiber bandwidth.

We experimentally analyze power excursions on a surviving data channel due to praseodymium-doped fluoride fiber amplifier (PDFFA) gain transients. These transients are a result of the equivalent time-varying power for adding or dropping up to 15 wavelength division multiplexed (WDM) signals from a 16-channel WDM system at 1310 nm. We find that power excursions for the surviving 10-Gbit/s data channel increase with an increase in the number of channels added or dropped from the system. Bit error rate (BER) measurements on the surviving channel indicate that a power penalty of up to 3.5 dB as compared to the steady-state condition results from a 15-channel add-drop event. These results provide indication of the applicability of PDFFA amplification to dynamic reconfigurable optical networks in future DWDM systems that incorporate wavelengths in the 1310-nm region.

We propose a microlens for improving the coupling efficiency between a Lambertian emitter and an optical fiber with small numerical aperture. The nonimaging lens uses refraction in the central part for light rays emitted at small angles, and reflection in the peripheral part for rays emitted at large angles. In this way, the high numerical aperture of the source can efficiently be converted into the small numerical aperture of the fiber. Arrays of these lenses can be fabricated on a wafer scale using grayscale lithography. Simulation results for the coupling efficiency and alignment tolerances are presented for coupling to a standard multimode fiber with a core diameter of 62.5 µm and numerical aperture of 0.275. For small fiber core diameter to source diameter ratios, improvements in the coupling efficiency very close to the theoretical limit are predicted. For a light-emitting diode (LED) with a diameter of 25 µm, an improvement factor of 6 is observed in comparison to simple butt coupling, and a factor of more than 2 as compared to a standard spherical microlens.

A comprehensive study of the oblique frozen modes in a finite 1-D anisotropic photonic crystal is presented. The most attractive property of these waves is near-zero axial group velocity in conjunction with small reflection from the lattice interface. We use a characteristic matrix analysis to describe both monochromatic wave and pulse propagation in a 1-D anisotropic photonic crystal of finite length. Using a layered structure consisting of air and an example of a suitable material, SbSI, we demonstrate the slow down factor, intensity enhancement, bandwidth, and transmission coefficient of axially frozen modes.

A systematic investigation of glass forming tendency and crystallization kinetics of the Ag_x-Sb_2(1–x)-Te_3(1–x) (x=0.16, 0.18, and 0.20) is reported. The alloy of the Ag-Sb-Te glass system, obtained by the rapid quenching technique, is characterized by calorimetric measurements and different thermal analysis for different heating rates. Variation in two important parameters, namely, glass transition temperature T_g and glass forming tendency K_gl, are studied with the variation of Ag content. By analyzing the results that occur with the increase in Ag content, we see that the glass-forming tendency K_gl also increases. However, with the increase in heating rates, the glass transition helps us to find the suitability of an alloy to be used in phase change optical memories/switches. The results are analyzed using Kissinger's equation for the nonisothermal crystallization of materials.

We describe the fabrication of an intrinsic fiber Fabry-Pérot interferometer meant to be used in white light interferometry sensing experiments. It requires the elaboration of a cavity exhibiting a finesse of about 2, and therefore, cavity mirrors with a reflection coefficient of about 23%. The different steps involved in the fabrication of the cavity are addressed. We discuss the optical properties of the e-beam deposited TiO₂ and SiO₂ multilayer mirrors used for the fabrication of the cavity. In this part, a convenient method for measuring the complex refractive index of the materials is proposed, as well as an in situ monitoring technique used to accurately control the film properties. We next study the evolution of the mirror reflectivity with the splicing procedure, and we propose a modeling of the mirror composition after splicing. Then, the fabrication of a 20-mm-long Fabry-Pérot cavity exhibiting a visibility of 0.5 is presented. In this section, an efficient signal processing is proposed to reduce any measurement noise.

Thermal blooming is a major effect in high power laser beams transmitting through gaseous medium as well as the atmosphere. Due to this effect, the beam pattern is deformed through the propagation path. In this work, a ring pattern beam from a high-power CO₂ laser with an unstable resonator is evaluated when propagating through a high-pressure CO₂ gas, and the results are compared with those of the Gaussian beam. The results show that unlike the initial Gaussian beam from which a ring pattern formed when propagating through an absorbing medium, for the initial ring pattern beam, in the absence of the gas flow, a symmetrical two-fold pattern is formed due to the blooming effect. The results also show that such symmetry can be deformed in the presence of gas flow.

We describe an experiment where we made a direct measurement of the bit-error rate of a low-order adaptive optics laser communications system. The adaptive optics system consisted of a two-axis tip-tilt corrector. In the paper we describe the driver system for the tilt aberration generator, the tilt sensor, the control system for the corrector mirror, and the diagnostic electronics for measuring and recording the bit-error rate. Finally, we present results of a closed-loop experiment where we report bit-error rate improvement up to a factor of 42.

We describe an experiment where we made a direct measurement of the bit-error rate of a high-order adaptive optics laser communications system. We describe a quantitative characterization of a repeatable atmospheric turbulence aberration generator and both static and dynamic characterizations of a 19-channel adaptive optics system. We show a reduction of the bit-error rate by a factor of 41.5 under specific laboratory conditions.

We propose a two-color infrared counter-countermeasure (IRCCM) in a crossed-array tracker for efficient target tracking under infrared countermeasure (IRCM) conditions. The proposed two-color IRCCM uses two detection bands in the mid and near IR regions for target and IRCM detections, respectively. The ratio of the incident signals passing the two detection bands is calculated, and a threshold ratio is determined to distinguish the target signal from the target-IRCM mixed signal, i.e., to generate a target pulse signal without IRCM effects. Our IRCCM also adopts target position prediction to make provision against wrong target detection. To evaluate the performance of the proposed IRCCM, we construct a simulator and perform target tracking under various conditions. The simulation results show that the proposed IRCCM allows efficient target tracking by minimizing the IRCM effects.

The high-voltage condensers in a polarity-inversion two-stage Marx surge generator are charged from –50 to –70 kV by a power supply, and the electric charges in the condensers are discharged to an x-ray tube after closing gap switches in the surge generator with a trigger device. The x-ray tube is a demountable diode, and the turbomolecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Clean silver Kα lines are produced using a 30-μm-thick palladium filter, since the tube utilizes a disk cathode and a rod target, and bremsstrahlung rays are not emitted in the opposite direction to that of electron acceleration. At a charging voltage of –70 kV, the instantaneous tube voltage and current are 90 kV and 0.8 kA, respectively. The x-ray pulse widths are approximately 80 ns, and the instantaneous number of generator-produced Kα photons is approximately 4×10⁷photons/cm² per pulse at 0.3 m from the source 3.0 mm in diameter.

The cerium-target x-ray tube is useful for performing cone beam K-edge angiography, because K-series characteristic x-rays from the cerium target are absorbed effectively by iodine-based contrast media. The x-ray generator consists of a main controller and a unit with a high-voltage circuit and a fixed anode x-ray tube. The tube is a glass-enclosed diode with a cerium target and a 0.5-mm-thick beryllium window. The maximum tube voltage and current are 65 kV and 0.4 mA, respectively, and the focal-spot sizes are 1.3×0.9 mm. Cerium K-series characteristic x-rays are left, using a 3.0-mm-thick aluminum filter, and the x-ray intensity is 19.9 μGy/s at 1.0 m from the source with a tube voltage of 60 kV and a current of 0.40 mA. Angiography is performed with a computed radiography system using iodine-based microspheres 15 μm in diameter. In angiography of nonliving animals, we observe fine blood vessels of approximately 100 μm with high contrasts.

Diffraction limit imaging from the ground on a 2-arcmin field of view is about to be real with the demonstration of a new generation of multiconjugate adaptive optics, to be installed at Paranal in Chile in 2006. The layer-oriented part of the multiconjugate adaptive optics demonstrator (MAD) selects up to eight natural guide stars over the field of view, allowing a uniform correction. Using the layer-oriented concept and two deformable mirrors conjugated to the ground and 8.5 km, we determine multiconjugate adaptive optics (MCAO) performance on an 8-m-class telescope. We describe initially the optical constraints, the adopted solutions, and several optomechanical approaches used to build such a system. Alignment procedures are indicated with some useful details in the last section.

A regularized wavelet-based image super-resolution reconstruction approach is presented. The super-resolution image reconstruction problem is an ill-posed inverse problem. Several iterative solutions have been proposed, but they are time-consuming. The suggested approach avoids the computational complexity limitations of existing solutions. It is based on breaking the problem into four consecutive steps: a registration step, a multichannel regularized restoration step, a wavelet-based image fusion and denoising step, and finally a regularized image interpolation step. The objective of the wavelet fusion step is to integrate all of the data obtained from the multichannel restoration step into a single image. The wavelet denoising is performed for the low-SNR cases to reduce the noise effect. The obtained image is then interpolated using a regularized interpolation scheme. The paper explains the implementation of each of these steps. The results indicate that the proposed approach has succeeded in obtaining a high-resolution image from multiple degraded observations with a high peak SNR. The performance of the proposed approach is also investigated for degraded observations with different SNRs. The proposed approach can be implemented for large-dimension low-resolution images, which is not possible in most published iterative solutions.

There have been many techniques that manipulate a compressed image in the discrete cosine transform (DCT) domain for MPEG and JPEG standards, and we have proposed a model-based discontinuity evaluation technique in the DCT domain that has problems with rotated or nonideal discontinuities. To enhance the effectiveness of the discontinuity detection method in the DCT domain while preserving the advantage of efficiency, we propose a fuzzy filtering technique that consists of height fuzzification, direction fuzzification, and fuzzy filtering of discontinuities. The enhancement achieved by the fuzzy filtering includes the linking, thinning, and smoothing of discontinuities in the DCT domain. Although the detected discontinuities are rough in a low-resolution image for the size (8×8 pixels) of the DCT block, experimental results show that this technique is fast and stable to enhance the quality of discontinuities.

A new spindle error measurement system is described. It employs a specially designed rotational fixture with a corner cube to replace the precision reference master ball used in the traditional method. A two-dimensional position-sensitive detector (PSD) is used to replace the noncontact sensor for measuring the motion error of the rotating spindle. The rotational fixture is held on the tool holder, and the PSD is mounted on an adjustable holder to detect the position of an incident laser beam reflected from the corner cube. When the spindle rotates, the spindle error changes the direction of the reflective beam and also the positions of the spots on the PSD. Thus, the radial runout of the spindle can be obtained via the PSD outputs. The theoretical analysis to eliminate the setup error and eccentricity-induced error, as well as the error analysis, is given. This system is proposed as a new instrument and method for spindle metrology.

We propose a lossless compression method based on a chain code composed of only three symbols. The method is applicable to compress 2-D binary object shapes, and it consists of representing the orthogonal direction changes of the discrete contour, corresponding to each object binary shape, by three bits of a chain code. According to our experimental results, we find that this method is suitable for the representation of bilevel images. The results are about 25% more efficient in compression than the Freeman chain code method, and an average of 29% better than the Joint Bilevel Image Experts Group (JBIG) compressor.

We analyze the design issues for the SPIHT (set partitioning in hierarchical trees) coding, one of the best-regarded embedded-wavelet-based algorithms in the literature. Equipped with the multiresolution decomposition, progressive scalar quantization, and adaptive arithmetic coding, SPIHT generates highly compact scalable bitstreams suitable for real-time multimedia applications. The design parameters at each stage of SPIHT greatly influence its performance in terms of compression efficiency and computational complexity. We first evaluate two important classes of wavelet filters, orthogonal and biorthogonal. Orthogonal filters are energy-preserving, while biorthogonal linear-phase filters allow symmetric extension across the boundary. Among the various properties of wavelets pertaining to coding, we investigate the effects of energy compaction, energy conservation, and symmetric extension, respectively. Second, the magnitude of biorthogonal wavelet coefficients may not faithfully reflect their actual significance. We explore a scaling scheme in quantization that minimizes the overall mean squared error. Finally, the contribution of entropy coding is measured.

Low bandwidth and high error rates are characteristic properties of mobile multimedia communication environments. Therefore there is a high demand for higher coding efficiency and advanced error resilience tools in these applications. These requirements have been addressed by the latest video coding standard, H.264/AVC. This paper reviews some of the new coding techniques and error resilience tools that are possible with this video coding standard and discusses some experimental results to demonstrate its performance.

A distortion-invariant class-associative pattern recognition technique is proposed, where a class of objects may be defined as a group of objects with similarity and dissimilarity among them. The fractional power fringe-adjusted joint transform correlation technique as well as the synthetic discriminant function concept has been effectively utilized to achieve the distortion-invariant detection of multiple dissimilar targets simultaneously present in the input scene. Simulation results prove that the proposed scheme is an effective tool for the detection of multiple dissimilar targets in both binary and gray-level input scenes corrupted by distortion and noise.

The ability of certain performance metrics to quantify how well a target recognition system under test (SUT) can correctly identify targets and non-targets is investigated. The SUT, which may employ optical, microwave, or other inputs, assigns a score between zero and one that indicates the predicted probability of a target. Sampled target and nontarget SUT score outputs are generated using representative sets of beta probability densities. Two performance metrics, the area under the receiver operating characteristic (AURC) and the confidence error (CE), are analyzed. The AURC quantifies how well the target and nontarget distributions are separated, and the CE quantifies the statistical accuracy of each assigned score. The CE and AURC were generated for many representative sets of beta-distributed scores, and the metrics were calculated and compared using continuous methods as well as discrete (sampling) methods. Close agreement in results with these methods for the AURC is shown. While the continuous and the discrete CE are shown to be similar, differences are shown in various discrete CE approaches, which occur when bins of various sizes are used. A method for an alternative weighted CE calculation using maximum likelihood estimation of density parameters is identified. This method enables sampled data to be processed using continuous methods.

Arrays of micromirrors are used to correct residual wavefront aberrations in optical systems. Each micromirror typically has either one or three actuators so it can locally correct either the piston error in the wavefront, or the piston error plus the tip and tilt errors. An array of 1000 piston-only micromirrors is compared with an array of 333 piston-tip-tilt micromirrors with the same number of actuators. The piston-tip-tilt micromirror arrays are better in all comparisons. They reduce defocus and astigmatism by 300×versus 30× for piston-only (Zernike terms Z4, Z5, and Z6). The wavefront error due to third-order spherical (Z9) is reduced by 33×versus 6×, and the fifth-order spherical (Z16) is reduced by 6×versus 2×. The micromirror array pattern is also studied. Hexagonal arrays reduce the aberrations roughly 10% more than do square arrays.