This PDF file contains the editorial “Dark Data” for OE Vol. 47 Issue 01

We report an integrated all-fiber variable optical attenuator (VOA) for dynamic control of a device by achieving optimized taper and axial compression of an index-guiding holey fiber. We experimentally demonstrate a VOA device with dynamic ranges of 18 dB over the spectral range from 1450 to 1650 nm and a low insertion loss of 0.5 dB.

We present a theoretical analysis of the total collectible optical power of an arbitrarily shaped multimode optical fiber probe for contact sensing where the signal from the analyte is emitted or scattered on the outside surface of the fiber tip. Calculation results and optimization parameters are given for spherical, parabolic, and cone-shaped fiber probes. This analysis can be used to guide the design and optimization of various fiber sensors, including fluorescence, surface plasmon resonance, and surface enhanced Raman sensors.

A novel algorithm based on an improved power-law detector is proposed to detect moving small dim targets against heavy cluttered background in IR image sequences. As the gray-scale value of a pixel in an image fluctuates when a target passes by, this fluctuation can be viewed as a weak transient signal, and can be detected by the power-law detector, which performs well for transient signal detection. The experimental results illustrate that the proposed algorithm is effective and adaptable for moving small dim target detection in image sequences with heavy clutter

We develop new visualization and diagnostics techniques for the analysis of the mechanical causes of second-order scattered light, applying these to the stray-light analysis of the MONS space telescope, whose scientific aim is the measurement of low-amplitude photometric oscillations in stars. The telescope is designed to detect amplitudes of 1 part per million, requiring a high stray-light rejection factor, and is thus an ideal subject for this work. The analysis involved determining stray-light cases and then using an innovative approach to efficient high-order ray tracing to produce detailed predictions of the stray-light flux distributions. In addition to demonstrating the utility of the approaches developed here, the results of the analysis show that the MONS space telescope design meets the stray-light rejection requirements.

Optical analysis is critical to the evaluation of a light-emitting diode (LED) street lamp, especially when the lamp is still in its early stage of development and applications and when optimization is needed for making use of unique characteristics of LEDs. In this study, optical analysis of an 80-W LED street lamp was conducted. Experimental research on such a lamp was first undertaken. The results demonstrated that the average illumination was about 8.25 lx and the total uniformity was 0.364 for a 20-m-long and 10-m-wide test area at a height of 8 m, which is acceptable for the current standard for a submain road. Numerical simulation was also conducted; the feasibility of the numerical model was proven by comparison of the simulations with the experimental data, which will be used for future optimization study and other novel designs of the optical system of street lamps. Through the simulations and the corresponding analysis, it was found that the tested 80-W LED street lamp had reasonable performance in average illumination, but multiple shadows existed, which would need to be removed in future designs. Improvements are suggested to reduce the number of optical elements, to reduce the lamp's volume, and to enhance the illumination performance. Two design methods for LED street lamps are summarized, based on the optical analysis.

We have experimentally demonstrated and report on the results of crystal growth, fabrication, design, development, and performance for the long-wavelength infrared (LWIR) hyperspectral imager based on an acousto-optic tunable filter (AOTF) utilizing an efficient crystal, thallium arsenic selenide (Ti₃AsSe₃ TAS). Results on the growth of 40-mm-diameter, 15-cm-long crystal boules, to fabricate 4.0-cm-long AOTF devices, and on the system design and performance are presented. To achieve an 8-cm^-1-resolution AOTF, we developed a design utilizing growth at 10.6 deg off from the c axis of the crystal and achieved >37% efficiency. A system concept was developed with high efficiency, resolution, and throughput utilizing this TAS AOTF. The test setup consisted of an LWIR camera (microbolometer), the AOTF, and a blackbody radiative source (hot filament), and represents the first time AOTF imaging has been achieved with a microbolometer camera. The filament was placed ≈25 cm in front of the AOTF, and the camera was aligned to the first-order diffracted beam of the AOTF. The AOTF was tuned to 10.6-μm wavelength by applying a 13.9-MHz rf signal to the transducer. Preliminary experimental results obtained for SF₆ gas utilizing this system are reported.

As the number of fielded sensors proliferates, sensors are being implemented in sensor networks with wired or wireless exchange of information. To handle the expanding load of data with limited network bandwidth resources, both still and moving imagery can be highly compressed. However, high levels of compression are not error-free, and the resulting images contain artifacts that may adversely affect the ability of observers to detect or identify targets of interest. This paper attempts to quantify the effect of image compression on observer tasks such as target identification. We addressed two typical compression algorithms, at two levels of compression, in a series of controlled perception experiments to isolate and quantify the effects on observer task performance. We find that the performance loss caused by image compression is well modeled by the use of an effective per-pixel blur, and give those blurs for the cases we used.

An x-ray microscope is a useful tool in medicine and biology. The performance of an x-ray microscope critically depends on its x-ray optics. In this paper, a Wolter type-I x-ray mirror is considered for biological applications. It was fabricated using an epoxy replication method. Fabrication tolerances (figure error and surface roughness) of the soft x-ray mirror were examined. A master mandrel was prepared using single-point diamond turning and polishing, and a mirror with axial symmetry was successfully manufactured by coating of a parting agent, epoxy molding, and separation steps. The replicated mirror showed 1.4-nm rms surface roughness and 160-nm peak-to-valley (and 34.3-nm rms) figure error. Several mirrors were manufactured from only one master mandrel.

This paper presents a novel scanning-path determination method to choose a next best view, using a combination of the shape-from-silhouette and convex-hull methods to ensure the accuracy and integrity of measured object surface data. A backlight system is used to illuminate the scene to acquire silhouettes from different viewpoints, from which an approximate 3-D surface model can be deduced. The scanning path is determined according to the convex hull of the approximate model so as to specify the movement of a three-axis motion table to achieve automatic measurement. With a mathematical model of a sensor equipped with a color CCD and a line-structured laser, 3-D color data of the object can be obtained integrally and accurately.

Radial runout measurement on a spindle, based on laser autocollimation, is susceptible to reflection surface irregularities because an irregularity occurring in the reflected laser beam rotates with the spin of the reflection target. This, study proposes an error correction method for the influences of reflection surface irregularities by applying the three-point method, which separates the radial runout of the spindle and the out-of-roundness of the reference cylinder attached to the spindle by using three displacement sensors. The principle of the proposed method is described, and its validity is confirmed in a computer simulation and experiment.

This paper introduces a high-resolution 3-D scanning system for objective evaluation of fabric fuzziness using laser range-sensing technology. This system consists of a laser range sensor, a 2-D mechanical stage, and a computer with dedicated software. The paper covers the process of surface digitization from 3-D scanning, image-processing techniques for surface feature description, and methods for characterization of fabric fuzziness. It also reports a preliminary test on a set of fabrics that were treated in different laundering cycles to gain different levels of fuzziness. The test demonstrates that this system has great potential for discriminating among fabric fuzziness levels in a quantitative and reliable manner.

A structured light system for three-dimensional shape measurement with single camera has the shortcoming of camera occlusion. To alleviate this problem, this paper introduces a structured light system with dual cameras for three-dimensional shape measurement. We discuss (1) system description, (2) system calibration, (3) three-dimensional data registration using the iterative closest-point (ICP) algorithm, and (4) three-dimensional data merging using holoimage. The principle of the system is introduced, and experiments are presented to verify its performance.

We discuss the possibilities of a far-field beam profiling technique for the determination of the near-focal profiles of laser beams focused beyond the paraxial approximation. The analysis is based on the rigorous vectorial Fourier synthesis of the fields and includes polarization effects. The wave-vector distribution can be calculated either a priori using the radius of the impinging laser beam and the data of the objective, or by obtaining its parameters from profiling at different z positions far behind the objective. For such measurements we designed a profiling system suitable for in situ application in microscopy. The device consists of a fiber optic taper bonded onto the chip of a CMOS camera, allowing taking pictures in the working medium in planes sufficiently close to the focus. The near-focal profiles obtained by these two approaches show good agreement, but only if the measured effective numerical aperture NA_eff is used. We have further readdressed the effect of filling the objective pupil on the near-focal fields. The small improvement in focusing by the commonly practiced overfilling is hardly worth the significant loss of power. Moreover, overfilling above an optimal beam radius a_opt results in an increase of aberrations when focusing through an optical interface.

We investigate nondegenerate four-wave mixing and the resulting high efficiency of wavelength conversion in a semiconductor-optical-amplifier integrated distributed feedback laser, which is one of the latest achievements of photonics technology. For analyzing the amplifier we use a finite-difference beam propagation method based on solution of a modified nonlinear Schrödinger equation, and for the laser we use a coupled-wave approach. We investigated wavelength conversion up to 4-THz pump-probe detuning with lossless conversion up to 400-GHz detuning and a conversion efficiency of -4.8 dB at 1-THz pump-probe detuning. For calibration and verification of the software developed in this study, we have used experimental measurements reported from MIT electronics and Fujitsu research laboratories on a similar device. We have successfully estimated the conversion efficiency of the tested device.

The design requirements of a high-stability narrowband dye laser with a curved dye cell, pumped by a copper vapor laser, are discussed. The design is simple and easy to fabricate at low cost. It is shown that the curved dye-cell geometry, with hydraulic diameter varying from 23 to 1 mm and curvature ratio varying from 1 to 81, creates flow conditions that meet the requirements of a stable narrowband tunable dye laser. It is shown numerically that the eddy sizes, temperature fluctuations, and associated energies in boundary layer are responsible for the fluctuations in the output. A dye laser based on this geometry was operated from Reynolds number 184 to 1100. The numerical results agree with the experimental results showing better dye laser stability at higher Reynolds number.

Brillouin optical time-domain reflectometry (BOTDR) and Brillouin optical time-domain analysis (BOTDA) are considered to be promising and practical sensing techniques for large structures. However, there is still a major obstacle to applying BOTDR or BOTDA on large-scales; the high cost and unreliability associated with sensor installation and failure. We report a novel, low-cost, and highly reliable BOTD sensor using a rebar consisting of a bare optical fiber (OF) packaged in fiber-reinforced polymer (FRP) and named BOTD-FRP-OF. We investigate the surface bonding and its mechanical strength scanning-electron-microscope and intensity experiments. Considering the strain difference between OF and host matrix, which may result in measurement error, the strain transfer from host to OF has been studied theoretically. Furthermore, the sensing properties of glass FRP-OFs for strain and temperature at different gauge lengths were tested under different spatial and readout resolutions using commercial BOTDA. Finally, an absolute dual-BOTD-FRP-OF temperature compensation method is proposed and has been tested. This novel FRP-OF rebar shows both high strength and good sensing properties, which can be used in long-term structural health monitoring for civil infrastructure.

This paper reports the development of a novel InSb infrared photovoltaic sensor (PVS) operating at room temperature. The PVS consists of an InSb p⁺p^-n⁺ structure grown on semi-insulating GaAs(100) substrate, with a p⁺-Al_0.17In_0.83Sb barrier layer between the p⁺ and p^- layers to reduce diffusion of photoexcited electrons. Photodiodes were fabricated by wet etching, and, using a 500-K blackbody, we obtained detectivity D^*=2.8×10⁸ cm Hz^1/2/W and responsivity R_V=1.9 kV/W at room temperature. The SNR was improved with the serial connection of 700 photodiodes patterned on a 600×600-μm² chip. On increasing the number N of connected photodiodes, the SNR was improved by a factor of N^1/2. The responsivity was constant for signals ranging from dc to 500 Hz. From spectral response measurements a cutoff wavelength of 6.8 μm was obtained. The PVS was flip-chip bonded on pre-amplifier IC, allowing the shortest possible connection between the PVS and the pre-amplifier, making the system immune to electromagnetic noise. The system was finally encapsulated in a dual flat nonleaded package with a window, which exposes the back of the GaAs substrate, allowing the infrared light incidence. The device is small (2.2×2.7×0.7 mm³), operates at room temperature, and is able to detect human body radiation in the middle IR range.

For reducing the material consumption of optical waveguides for chip-scale optical interconnects, we propose a material-saving optical waveguide fabrication process based on light-assisted selectively occupied repeated transfer (LA SORT). LA SORT enables device elements to be selectively transferred onto a substrate with designed arrangements at one time, using all-photolithographic methods. In the proposed process, optical waveguides are fabricated by transferring cores selectively onto final substrates from a picking-up substrate, on which a high-density core array is placed. Since one picking-up substrate can provide cores to a plurality of final substrates, drastic reduction of waveguide material consumption is expected. The process can also construct complete air-cladding waveguides for fine-pattern optical interconnects. By LA SORT, using films coated with UV-curable material, selective transfers of polymer device elements were achieved. A selective transfer of 32-μm-wide, 3-cm-long polymer cores duplicated by the built-in mask method was demonstrated to provide the proof of concept of the process. We also succeeded in fabricating 4-μm-wide polymer cores with tapered mirrors, and making air-cladding waveguides by transferring the cores. Possible applications of the proposed process to nanoscale optical circuit integration are discussed.

Optical coupling from a strip waveguide to a two-dimensional photonic crystal (PC) slab waveguide in the slow light regime is investigated. Group-velocity mismatch between optical modes is responsible for large coupling loss. Typical devices based on a W1 PC waveguide, with strip input and output waveguides on each side, are studied using finite-difference time-domain and plane-wave expansion calculations. Compact tapers based on PC lattice parameter tuning are proposed to reduce the coupling loss. At 1.6 μm, for an optical mode with group velocity v_g/c=0.054, the transmission can be enhanced from 18% without tapers to 95% with a 3.4-μm-long taper on each side of the PC.

A novel optical single-sideband modulator consisting of eight-phase modulator waveguides is proposed. It features an ideal output signal-to-noise ratio (SNR) when used as a wavelength converter. The calculated results indicate that the wideband wavelength conversion with ideal output SNR can be realized by using this modulator in a fiber loop.

All-optical NOR and OR gates using the same setup, based on cross-polarization modulation in a single semiconductor optical amplifier, have been demonstrated experimentally at 10 Gbit/s with two and three input signals. The results show good dynamic extinction ratios of 13.2 and 11.0 dB for NOR and OR outputs, respectively. The logic output performance of this logic configuration versus input signal and probe power have been investigated experimentally.

We propose a novel static primary routing algorithm, called ALB Dijkstra (Adaptive Load Balancing Dijkstra), which introduces new concepts and methods into the traditional Dijkstra algorithm to improve its performance with respect to burst drop probability in optical burst switching networks. This new algorithm has a basic version and an extended version, which are applicable to networks with and without wavelength converters, respectively. By introducing two new concepts of virtual link cost and virtual link-wavelength cost, the new algorithm is able to take account of the influence of actual topology and traffic load distribution in its adaptive searching procedure. ALB Dijkstra offers a fast approach to optimized path selection so that link resources can be utilized efficiently. Numerical simulations show that the overall network performance is significantly improved over the ordinary shortest-path routing strategy.

The signal intensity as a function of range is considered for optical communication systems that utilize time-coincident pairs (or larger sets) of photons for information encoding. Two systems are examined: one that generates pairs of photons that have an entangled quantum state, and another where the pairs of photons are generated from a pair of pulsed photon sources. The signal intensity as a function of range is analyzed as a qualitative first-order approximation for these two techniques. For the first time, to this author's knowledge, it is shown that pairs of photons that share a quantum state, and hence have highly correlated momenta, can produce communication systems that have a high degree of noise immunity and are useful for ranges significantly beyond the collimated range of the transmitter, which up until now has been considered the maximum range. As an example, it is shown that a transmitter with a 1-m aperture and a pair of pulsed photon sources will be effective for about 200 km, while a transmitter with the same aperture and a quantum-entangled photon source will have an effective range greater than 60,000 km.

We propose a fiber ring laser that operates in a single longitudinal mode by incorporating unpumped erbium-doped fiber as a saturable absorber filter. This laser can be discretely tuned to a 25-GHz-spacing grid that precisely matches ITU-T (International Telecommunication Union, Telecommunication Standardization Sector) grids, which are reference frequencies for optical communication systems. This laser has a signal-to-source spontaneous emission ratio higher than 60 dB, and the lasing frequencies of 361 channels are matched to ITU-T grids with excellent power flatness. With one channel of this fiber laser, we place the reference frequency near the absolute frequency reference (AFR, 193.1 THz). The relative frequency stability of the laser and the frequency offset from the AFR were less than 1.6×10^-8 (integrated time, 5 min) and 30 MHz, respectively.

This paper presents a new synthesis method for designing complex fiber Bragg gratings (FBGs). The method is based on a multiobjective Lagrange-multiplier-constrained optimization (LMCO), to which various constraints on the designed filters can be added in consideration of practical application demands and fabrication requirements. The maximum amplitude of the index modulation profiles of the designed FBGs can be substantially reduced under constrained conditions. In contrast with the layer-peeling (LP) algorithm, the LMCO method can easily incorporate different types of requirements in terms of a user-defined cost function. Compared to stochastic approaches such as genetic algorithms, the proposed method is likewise a direct optimization method, but without using random numbers, and therefore has a smoother coupling coefficient profile as well as faster convergence. A theoretical model and investigation have been made in this study. A narrowband dispersionless FBG filter for optical fiber communication was designed, and its simulation results were compared with those of the LP algorithm. The study results demonstrate that the LMCO algorithm can provide an alternative for practical and complex fiber grating filters.

A stabilizing technique has been developed for a 3×3-coupler-based Mach-Zehnder interferometer, and the interferometer is used to interrogate a fiber Bragg grating (FBG) sensor. The fluctuation of an output can be removed by using the technique. New arithmetic is also introduced to recover the wavelength shifts of the FBG. The experimental results show that stable wavelength shifts of the FBG were obtained. The accurate calculation of modulation amplitude was also demonstrated.

We examine the effects of transmission error on the digital holograms in phase-shifting digital holography. It is evident that the reconstruction object image is vulnerable to transmission errors from the noise channel. An estimation-based reconstruction algorithm is used to detect the error points and the largest-error hologram of the error points. Based on the detection result, the adaptive algorithm reconstructs the digital hologram by removing the noise effect on the largest-error hologram. With accurate detection, the proposed algorithm is able to reconstruct an object image from a digital hologram with severe transmission errors.

The Stokes method provides a seminal method for the determination of the state of polarization of a beam of light using measurable quantities. This paper presents a methodology for the rapid acquisition of the four Stokes parameters. We have been able to acquire images at the rate of 500 images per second using a high-speed video camera. Using the camera, an optical chopper, a computer system containing a framegrabber, and software to coordinate all elements of the system, the four Stokes parameters have been acquired in 6 ms. Included in this paper is a description of all elements of the system, the calibration of the camera and polarization elements, the design of the imaging chopper polarimeter, and corrections related to rotation of polarization elements during exposure. A discussion of errors includes variations in pixel sensitivity, ill-conditioning of the Stokes parameters, aperture clipping, quasimonochromatic approximation, and variations in the Stokes parameters during data acquisition. Validation and testing of the methodology includes a comparison of empirical and theoretical skylight polarization parameters and values related to known, rapidly changing polarization states using several different bandwidth filters.

It is envisioned that the next generation of ultrahigh-speed laser communication systems will utilize compact optical antennas equipped with advanced beam tracking and effective fiber coupling mechanisms. Such laser communication systems will be used not only for space communications but also to provide optical links for long-distance terrestrial communications. We present the design of a high-speed laser communication system developed utilizing compact optical antennas with off-axis free-form surface (FFS) mirrors. We describe FFS optical devices and their design contribution in realizing compact optical antennas. Furthermore, an innovative fiber coupling device made from a glass ferrule and fiber is introduced, and with this device it is possible to couple the laser beam seamlessly to a single-mode fiber. We also present a fine tracking mechanism that uses a miniature fine pointing mirror (FPM) incorporated in the antenna. The machanism functions by feeding back the incident angle of the signal detected by a quadrant detector (QD) to the FPM. The achievable actuator response frequency for tracking is approximately 2 kHz, and it has been demonstrated to effectively mitigate the effects of laser beam angle-of-arrival fluctuation as a result of atmospheric turbulence.

A free-space optical communication channel suffers degraded performance due to blurring and scintillation of the received signal caused by atmospheric turbulence. Adaptive optics (AO) improves the communication performance of such a channel by concentrating the received power on the detector. The degree of improvement with AO correction depends on the modulation format, and on the modulation order when pulse position modulation is utilized. Gains of up to 6 dB with AO have been experimentally validated in a laboratory test bed under simulated atmospheric conditions involving turbulence and background light. The fade statistics of the turbulent atmospheric channel have also been analyzed with and without AO correction.

A laboratory turbulence simulation based on irregular micro-optical structures has been studied. The phase distributions are derived from Kolmogorov spectra with different Fried parameters r₀ by using the fast Fourier transform technique. A mask-shifting method has been invented for generating the designed irregular phase on a quartz substrate. The fabricated element is rotated by a motor to construct a turbulence generator. The dynamic phase produced by the generator is measured in real time with Shack-Hartmann sensor. The resulting power spectrum and the Fried parameter agree with the expected ones. Some issues associated with the simulation of turbulence are discussed.

Robustness and tracking speed are two important indices for evaluating the performance of real-time 3-D tracking. We propose a new approach to fuse sensing data of the most current observation into a 3-D visual tracker with particle techniques. With the proposed data fusion method, the importance density function in the particle filter can be designed to represent posterior states by particle crowds in a better way. This makes the tracking system more robust to noise and outliers. On the other hand, because particle interpretation is performed in a much more efficient fashion, the number of particles used in tracking is greatly reduced, which improves the real-time performance of the system. Simulation and experimental results verified the effectiveness of the proposed method.

Cone-beam computed tomography can reproduce a digital volume for an object that can be completely put inside the scan field of view (SFOV). In practice, the detector may not be wide enough to receive the projection, or the incident beam aperture may be confined to part of the object being scanning. Such cases cause width-truncated projections. With a dataset of width-truncated cone-beam projections, we can reconstruct a local volume in the object domain by using a convolution backprojection method. For the width-truncated projections, when the projection width is wider than the kernel length, we find that there exists, at the center of the object domain, a small region that can be tomographically reconstructed just as well as if there had been no truncation. Given the reconstruction kernel length, we propose a simple boundary extension technique to augment the SFOV, i.e., padding the truncated portions beyond the boundary. A continuous extrapolation beyond the boundary can effectively reduce the Gibbs effect, thereby enabling the reconstruction of a subvolume encompassing the SFOV. We demonstrate convolution-backprojection-based local cone-beam tomography by a breast phantom experiment, where the cone-beam projection is truncated by adjusting the x-ray collimator.

We consider the use of Zernike moments (ZMs) for rotation- and scale-invariant classification of images. It is well known that ZMs are rotation-invariant only. We make use of the major benefit of the Fourier-Mellin (FM) transformation, which changes the rotation and the scale into translation. We introduce a new algorithm, which fuses the ZMs with the FM transform and is invariant under both rotation and scaling. Two sets of images were used to test the proposed algorithm. Experimental results reveal that the proposed algorithm has much better recognition rate than using ZMs within a variation of rotation between 0 and 360 deg, and scaling down and up between 25% and 400% of the original size.

This paper presents generalized explicit schemes (GESs) for coherence-enhancing diffusion (CED) filtering, which is one of a wide variety of nonlinear diffusion filtering schemes. Unlike the traditional standard explicit scheme, which updates the diffusion coefficients in each iteration, the generalized ones use several new updating types, including fixed diffusion coefficients and the uniform-interval update (UIU) and optimized interval update (OIU) of diffusion coefficients. The GESs significantly improve efficiency by reducing the computational cost of updating the diffusion coefficients, compared with the existing acceleration methods, and by enlarging the time step, as in implicit or semi-implicit schemes or a scheme with larger mask of spatial discretization. Also, the OIU may allow the GES to achieve high accuracy by using only two to four updates of the diffusion coefficients during the whole process. Experiments demonstrate that the efficiency of the GESs is comparable to those of existing acceleration methods; nevertheless, the GESs with the OIU outperforms the other methods in the efficiency-accuracy trade-off.

A novel image enhancement algorithm for faint pavement cracks is proposed, based on the finite ridgelet transform (FRIT). In high-resolution FRIT subbands, typical linear singularities of the image are represented by a few coefficients, while randomly located noisy singularities are unlikely to produce significant coefficients. The parameters of an enhancement function can be determined through analyzing the distribution of the high-resolution FRIT coefficients. Therefore, a scheme based on modifying FRIT coefficients should be very effective in enhancing the linear singularities and suppressing the noise. In general, an entire pavement crack is a curve. A smooth partition method is proposed to divide a pavement crack image into local windows where the crack looks straight. Then the FRIT-based enhancement method can be applied to each piece of the whole crack. Experiments verify that faint crack signals submerged in the complicated background can be displayed efficiently by this algorithm.

We devise a segmentation scheme aimed at extracting edge information from speckled images using a maximum likelihood edge detector. The scheme is based on finding a threshold for the probability density function of the summing average field over a neighborhood set and, in a general context, is founded on a likelihood random field model (LRFM). A rigorous stochastic analysis is used to derive an exact expression for the cumulative density function of the likelihood of the averaging sum image. Based on this, an accurate probability of error is derived and the performance of the scheme is analyzed. The segmentation performs reasonably well for both simulated and real images. The LRFM scheme is also compared with standard edge detection methods to quantify the significant gains obtained from the optimized edge detector. The importance of this work lies in the development of a stochastic-based segmentation, allowing an accurate quantification of the probability of false detection. Nonvisual quantification and misclassification in speckled images, such as synthetic aperture radar and medical ultrasound, is relatively new and is of interest to remote sensing human observers and clinicians.

Wavefront coding technology can extend the depth of focus of a well-corrected three-mirror anastigmatic optical system by about ten times, but the image obtained directly by charge-coupled devices blurs at the same time. An effective image restoration must be applied to these blurred images. This paper describes an innovative method that restores the blurred image, which combines the optical design software and mathematical software. The point spread function of system with wavefront coding technology is quite different from the usual and difficult to simulate by a disk function or other simple function in most cases. The commercial optical design software is applied to obtain the point spread function. If a 1×1-pixel image with brightness 255 is set as the point source of a optical system, the result of calculation software using a ray tracing algorithm will itself be the digital point spread function. This is proven to be a simple and effective way to acquire the complicated point spread functions of unusual optical systems such as those using wavefront coding technology. A regularization factor and contrast-adjusting factors are introduced into the classical Wiener filter, which achieves good restored images: the root-mean-square error is less than 0.0193, while the peak signal-noise ratio is higher than 23.7. Some parameters of the filter can be adjusted so that the restored image is more suitable for evaluation by eye. It is also shown that a single filter can restore all the images within the extended depth of focus.

We address the problem of image superresolution and present a novel approach to single-frame superresolution using fractal image coding. The proposed approach takes great advantage of the properties of fractals-resolution independence, similarity preservation, and nonlinear operation-which are suited for image superresolution, specifically for image restoration and magnification. The idea of our work is to estimate the fractal code of the original image from its degraded (blurred and noised) observation and decode it at a higher resolution, and all the strategies are performed in the fractal image coding framework. To achieve this, we employ an adaptive fractal coding scheme in the frequency domain, and further, we introduce an overlapping partition scheme to remove the blocky artifacts and improve the reconstruction quality. Experiments on simulated and real images show that the resulting fractal-based superresolution method yields superior performance to conventional single-frame superresolution methods.

This research explores the automated detection of surface blemishes that fall across two different background textures in a light-emitting-diode (LED) chip. Water-drop blemishes, commonly found on chip surfaces, impair the appearance of LEDs as well as their functionality and security. Automated inspection of a water-drop blemish is difficult, because the blemish has a semi-opaque appearance and a low intensity contrast with the rough exterior of the LED chip. Moreover, the blemish may fall across two different background textures, which further increases the difficulties of defect detection. We first use the one-level Haar wavelet transform to decompose a chip image and extract four wavelet characteristics. Then, the T² statistic of multivariate statistical analysis is applied to integrate the multiple wavelet characteristics. Thus, the wavelet-based T² approach judges the existence of water-drop blemishes. Finally, we compare the defect detection performance among the wavelet-based T² method and traditional methods. Experimental results show that the proposed method achieves a 95.8% probability of accurately detecting the existence of water-drop blemishes, and an approximate 92.6% probability of correctly segmenting their regions.

A robot scanning system consisting of a portable laser 3-D scanner and an industrial robot is demonstrated. In this system, the scanner is precalibrated by the traditional nonlinear two-step approach. In addition, by using a criterion sphere as the calibration object, a new robot tool center point (TCP) calibration approach is proposed for calibrating the relation between the precalibrated laser 3-D scanner and the robot. In this approach, two different translational motions of the robot are first made to determine the rotation part, and then at least three different rotational motions are made to determine the translation part. During the process, the extrinsic camera parameters are not recalibrated for each robot motion, so the calibration errors brought by camera calibration can be decreased. Moreover, the calibration error due to robot positioning error can be decreased by making use of the differences of different robot positions in calculations. An experiment was performed on a portable laser 3-D scanner and an ABB IRB-4400 industrial robot to test the validity of the proposed calibration approach. The experimental results show that this approach is simple and accurate compared to the conventional robot TCP calibration approach.

Object recognition can be formulated as matching image features to model features. When recognition is patch-based, the feature correspondence is one to one. However, due to noise, repetitive structures, and background clutter, features do not match one to one, but one to many. By using the multiscale feature point technique, a new object recognition algorithm is presented to identify the center, scale, and orientation of the objects in the images. This approach recognizes the objects the presence of translation, scale variation, rotation, partial occlusion, and changed viewpoint. It does not require that features match one to one, and maintains the structure information of the object. This is accomplished by voting on the object's center, scale factor, and orientation for each match point. Experimental results demonstrate that the method works well with translation, rotation, scale changes, and partial occlusion, but gives less accurate results when the viewpoint is altered.

This paper introduces an effective representation method for 3-D shape and texture, to be called DOC/TOC ("Depth/texture on cylinder"), and a depth estimation algorithm that is appropriate to representation in an image-based rendering environment using multiview input images. In this framework, we show that this representation is also useful for object reconstruction. While previous reconstruction methods focus on the estimation of 3-D information only, we consider compactness and effectiveness of the information, and reconstruction results as well. DOC/TOC represents 3-D information on a 2-D cylinder surface by projection on that surface. The inner-boundary loss of the projection is complemented by using multiple depth values. This method is also a good starting point for mesh generation for 3-D reconstruction. Experimental results show that the proposed methods successfully represent and reconstruct the shape and texture of 3-D objects without information loss. Results of this research are applicable to other various types of intermediate surface.

The omnidirectional camera system with its wide view angle is widely utilized for camera calibration and 3-D reconstruction due to its advantage that a large amount of environmental information can be obtained using a small number of images. Since the straight-line features of the environment are projected as contours by the omnidirectional camera model, the corresponding contours among views can be effectively used for camera calibration. This paper presents a two-step calibration algorithm to estimate the extrinsic parameters of the omnidirectional camera by using the corresponding contours. The first step involves obtaining camera parameters by minimizing an angular error function between the epipolar plane and back-projected vectors of end points on the corresponding contours. With this, the final parameters minimizing a distance error between the computed and the real contours in the third view are estimated. Our experiments on synthetic and real images demonstrate that the algorithm precisely estimates the extrinsic parameters of the camera.

Effects of the threshold value on the multiple-target detection performance of a modified amplitude-modulated joint transform correlator are studied on the basis of computer simulations, using human fingerprint and face images. Correlation outputs are quantitatively measured by means of a primary-to-secondary peak ratio and a peak-to-correlation-deviation ratio. The simulation results reveal that the detection of high-contrast targets can be optimized by using a low-threshold. In the case of low-contrast targets, the optimization depends on spatial-frequency contents and noise.

Coherence-free microwave photonic filter configurations are presented. The configurations are based on a Sagnac loop interferometer containing an electro-absorption modulator (EAM) without a nonreciprocal bias unit. Notch responses are obtained by modulating the clockwise and counterclockwise propagating waves inside the Sagnac loop at different times. Measured results verify the theoretical expressions and demonstrate a robust notch filter response extending to high frequency without reducing notch depth.

An updated algorithm is described for the subpixel localization of synthetic references in digital images by use of an augmented search template. The new algorithm is easier to implement than the one originally conceived for this problem, while offering similar performance.