This PDF file contains the editorial “Engineering at Home” for OE Vol. 46 Issue 06

We propose a new scheme of computer-generated hologram (CGH) watermarking to resist rotation and scaling. To embed the inverse log-polar mapping of a mark pattern's CGH into a cover image, the twin image of the mark pattern can be directly reconstructed by fast Fourier transformation from the log-polar mapping of the watermarked image after rotation and scaling, not requiring a registration step in the extracting procedure. In an experiment, the information position of the twin image is located in the high-frequency domain and the redundant information of the low-frequency component is properly eliminated, so the contrast of the twin image is appropriately enhanced and the basic information of the mark pattern is effectively preserved to be recognized. The experimental results show that the mark-pattern's information can be effectively reconstructed when the watermarked image is scaled by 0.5 to 2 or rotated by any angle, so this watermarking scheme is effectively verified by experiment.

We experimentally demonstrate 4×2.5-Gbit/s all-optical frequency upconversion at 20 GHz, based on nonlinear polarization rotation in a highly nonlinear fiber. The demodulated signals are analyzed.

We present the design of a compact, wide-angle pushbroom imaging spectrometer suitable for exploration of solar system bodies from low orbit. The spectrometer is based on a single detector array with a broadband response that covers the range 400 to 3000 nm and provides a spectral sampling of 10 nm. The telescope has a 24-deg field of view with 600 spatially resolved elements (detector pixels). A specially designed convex diffraction grating permits optimization of the signal-to-noise ratio through the entire spectral band. Tolerances and design parameters permit the achievement of high uniformity of response through field and wavelength. The spectrometer performance is evaluated in terms of predicted spectral and spatial response functions and from the point of view of minimizing their variation through field and wavelength. The design serves as an example for illustrating the design principles specific to this type of system.

A novel arrayed-waveguide grating (AWG) based on unbent waveguides is proposed. Two graded-index planar waveguides (GISLAB) are used as input and output planar waveguides, respectively, and the arrayed waveguides are replaced by unbent waveguides, which are photosensitive waveguides exposed to UV light twice. Next, the 2-D semivectorial beam propagation method is adopted to simulate the light transmitting process in the device, and the simulation shows that this device and the design are feasible.

We study the changes in groove shape and depth that occur when holographic gratings are replicated in plastic. Specifically, we measure the groove profiles and spatial frequencies of electroplated metal shims made from sinusoidal holographic gratings, and also the same properties of the replicas made of polymethylmethacrylate (also metal shims). Nine samples are studied that have spatial frequencies in the range 600 to 2000 mm^-1. The shims of the replicated gratings have up to 30% shallower grooves and 13% lower diffraction efficiencies than the shims of the originals. The maximum measured diffraction efficiency for shims of the original gratings having 525-to 620-mm^-1 spatial frequencies correspond to a 0.22-μm groove depth, which agrees with the calculated value. We use this information to modify the groove shapes on the holographic gratings to make better plastic replicas.

This paper describes a novel phase error compensation method for reducing the measurement error caused by nonsinusoidal waveforms in phase-shifting methods. For 3-D shape measurement systems using commercial video projectors, the nonsinusoidal waveform of the projected fringe patterns as a result of the nonlinear gamma of projectors causes significant phase measurement error and therefore shape measurement error. The proposed phase error compensation method is based on our finding that the phase error due to the nonsinusoidal waveform depends only on the nonlinearity of the projector's gamma. Therefore, if the projector's gamma is calibrated and the phase error due to the nonlinearity of the gamma is calculated, a lookup table that stores the phase error can be constructed for error compensation. Our experimental results demonstrate that by using the proposed method, the measurement error can be reduced by 10 times. In addition to phase error compensation, a similar method is also proposed to correct the nonsinusoidality of the fringe patterns for the purpose of generating a more accurate flat image of the object for texture mapping. While not relevant to applications in metrology, texture mapping is important for applications in computer vision and computer graphics.

Device-quality single crystals of mercurous bromide were grown by the physical vapor transport method. Crystals transmitted light wavelengths up to 30 μm and did not show any absorption bands. Detailed x-ray Laue and x-ray diffraction studies were used to characterize and orient the crystals. Optical evaluation was performed by fabricating slabs of crystals. A design was developed to fabricate acousto-optic tunable filters with 10-deg off-axis orientation operating in the mid- and long-wavelength regions. An acousto-optic tunable filter (AOTF) was fabricated using a crystal with a 16-mm optical aperture for the 10-deg design. A theoretical tuning curve for a mercurous bromide crystal-based AOTF using this design was also computed for the first time. Experimentally measured data on frequency matching agreed well with the theoretical predictions, and the transducer thickness was suitable for filtering 7.58 μm with the fabricated AOTF.

Epitaxial single-crystal chemical-vapor-deposited diamond with (100) crystal orientation is obtained from Element Six (Ascot, United Kingdom) and Apollo Diamond (Boston, Massachusetts). Both companies supply 5×5-mm squares with thicknesses of 0.35 to 1.74 mm. Element Six also provides disks with a state of the art diameter of 10 to 11 mm and a thickness of 1.0 mm. The absorption coefficient measured by laser calorimetry at 1.064 μm is 0.003 cm^-1 for squares from Element Six and 0.07 cm^-1 for squares from Apollo. One Apollo specimen has an absorption coefficient near those of the Element Six material. Absorption coefficients of Element Six disks are 0.008 to 0.03 cm^-1. Each square specimen can be rotated between orientations that produce minimum or maximum loss of polarization of a 1.064-μm laser beam transmitted through the diamond. Minimum loss is in the range 0 to 11% (mean=5%) and maximum loss is 8 to 27% (mean=17%). Element Six disks produce a loss of polarization in the range 0 to 4%, depending on the angle of rotation of the disk. Part of the 0.04 to 0.6% total integrated optical scatter in the forward hemisphere at 1.064 μm can be attributed to surface roughness.

A theoretical model for the mode-locked hybrid soliton pulse source (HSPS) is developed by using a time domain solution of coupled-mode equations and rate equations. Numerical simulations show that grating must be both linearly chirped and apodized to be used in HSPS systems with a wide mode-locking frequency range (2.1 to 3 GHz) and transform-limited output pulses.

Advances in laser technology and nonlinear optical techniques can be effectively utilized for light detection and ranging (LIDAR) applications in space and atmospheric sciences to achieve better flexibility and control of the available optical power. Using such devices, one can achieve highly accurate and resolved measurement of the distribution for atmospheric scattering layers. In the present investigation, a diode-double-end-pumped high-repetition-rate, multiwavelength Nd:YAG laser is designed, fabricated, and various laser beam parameters are characterized for LIDAR applications. Nonlinear optical techniques are employed to generate higher harmonics like 532, 355, and 266 nm for various spectral studies. The studies of laser crystal parameters of Nd:YVO₄ and Nd:YAG are performed using a diode-double-end-pumped configuration to extract maximum output power in the fundamental mode. The fractional thermal loading and effective stimulated emission cross section for ⁴F_3/2 → ⁴I_11/2 transition of 1.1 at. % doped Nd:YVO₄ slab and 0.7% doped Nd:YAG rod is determined and compared using a convex-plane resonator configuration stabilized by pump-power-induced thermal lensing effect. Lower fractional thermal loading, larger effective stimulated emission cross section, and naturally polarized output enable these lasers to be more suitable for highly accurate and resolved measurement of the distribution for atmospheric scattering layers.

The characteristics of thermoplastic films, like low conductivity and high transparency, allow simplifying the prediction of the necessary engineering parameters in CO2 laser lap welding by the application of an energy balance approximation. The energy density evaluated by computation is experimentally applied to the welding of transparent high- and low-density polyethylene and polypropylene samples, with thicknesses between 10 and 100 μm. The comparison between prediction and experimental results is also made with an existing thermodynamic model. The latter is developed in accordance with the characteristics of transmission lap welding of the thermoplastics films considered in this work. Results show, for circa 80% of the analyses, a deviation lower than 20% between experimental and predicted values, highlighting the relevance of the energy balance approximation. Also, the similarity between predicted and experimental values confirms the main assumptions made in the development of the thermodynamic model. However, the action of thermal forces in the weld pool prove to be an important factor, restricting the minimum laser beam diameter over the sample. This limits one of the parameters to be evaluated by the energy balance approximation, but from an engineering point of view, its relevance and precision in the process modeling is preserved.

A photoacoustic (PA) leak detector on the base of a compact CO₂ laser is proposed for the detection of hydrogen leaks from cooling systems of electric power generators. Leak detection is based on a trace gas marker SF₆ registration, which is added to the gas carrier within the leakage area. Experimental results of SF₆ impurity detection in weak gas leakage using a PA detector with a differential ring cavity flow type are sited. The threshold sensitivity of the detector is measured at ~7.5·10^-10cm^-1. The effect of gas-flow rate through the detector is studied. The minimum reliably detectable flow is estimated to be ~1·10^-10 Pa·m³/s, which exceeds the sensitivity of commercial helium and halogen leak detectors. Description and specifications of the developed model of a portable laser leak detector, designed in accordance with experimental results, are given.

We investigate and demonstrate experimentally a two-stage erbium-based amplifier with a larger amplified-spontaneous-emission light source for a long-distance fiber sensor by using strain-induced fiber Bragg gratings in the fiber systems. In a 20-km-long fiber sensor system, the sensor has a maximal ≈ 2.28-nm wavelength shift under a 1500-μm/m strain.

Relations between fabrication conditions and optical characteristics of planar waveguides made by proton exchange in benzoic acid are documented in the literature, but reports on the characterization of waveguide fabrication processes, performed in a systematic way, could not be found, resulting in the need to combine data from several authors. Discrepancies among results from different researches are evident, resulting from different experimental methodologies and calibration of equipment. Therefore, aiming at extracting a consistent data set, optical characterization of the refractive index profile was employed to study series of samples. The objective was to develop a methodology for fabrication of proton-exchanged channel waveguides in LiNbO₃ operating in the single-mode regime at several wavelengths, with specific characteristics required to optimize integrated devices. To achieve this, it is necessary to obtain the relations between the optical characteristics of the waveguides and their fabrication conditions, and to introduce models of the waveguide formation process.

Second harmonic generation of coupled cavity structures (CCSs) fabricated in one-dimensional photonic crystals, which are composed of dispersive materials, is investigated. The fundamental wave is a localized mode, and the second harmonic wave is a traveling mode of the CCS. Using transfer matrix and effective refractive index methods, we analyze the localization and phase matching of the two modes. Using a nonlinear finite-difference time-domain method, we simulate the nonlinear process with a Gaussian pumping pulse, and both transmitted and reflected second harmonic signals are obtained. We investigate the effect of cavity number on the conversion efficiency and find the material dispersion can be compensated by the structural dispersion. For this reason, the conversion efficiency in a CCS is three orders larger than that in a bulk material of the coherence length.

Different modulation methods for optical wireless have different power and bandwidth efficiencies. Each approach has a direct bearing on the quality and effectiveness of wireless optical communications. As two prime examples, pulse position modulation (PPM) and pulse width modulation (PWM) are compared. The comparison includes the power and bandwidth efficiencies, the power spectrum distribution, and the ability to resist intersymbol interference. Compact system models of multilevel digital PPM (L-PPM), and multilevel digital PWM (L-PWM) are also introduced. The results show that L-PPM has advantages in power efficiency and an approximately uniform spectral distribution, whereas L-PWM has a greater ability to resist intersymbol interference.

A simple passive optical network with ring-type distributed optical networking units (ONUs) is proposed. The ring protection is performed by a clockwise and a counterclockwise circulating fiber. The protection-and-restoration time is measured to be less than 5 s, and depends on the optical switching and the autodiscovery process time. In spite of additional devices for protection, the system reliability is enhanced so that the expected downtime decreases from 41.3 to 28.9 min/yr. The optimum condition to support the maximum number of ONUs is derived and verified by an optical link simulation.

The authors investigate how to improve real transmission control protocol (TCP) performance over optical burst switching (OBS) networks, providing larger available bandwidth and reliability. Considering the acknowledgement (ACK) packet losses, a simple modified analytic model is studied to give the real steady-state TCP throughput over OBS networks. The effect of ACK losses is analyzed based on the calculation and simulation results, and it is concluded that eliminating or mitigating ACK losses should improve the performance. Then, at the OBS routers, two novel ACK-based assembly and scheduling mechanisms, viz. a timer-based ACK assembly scheme and an ACK priority scheduling scheme, are proposed. Simulation results demonstrate that compared with conventional assembly and scheduling algorithms, the two new mechanisms can improve TCP performance over OBS networks to great extent, meeting the requirements of grid networks, such as lower network burst loss probability to provide reliable performance, and higher TCP throughput to increase the available bandwidth. It is also seen through comparison that the novel ACK priority scheduling mechanism has better performance than the usual one.

Alignment of optomechanical components is important when designing and manufacturing optical systems. This study used an optical fiber as a case study to develop an alignment method. The core diameter of a single-mode fiber is about 9 µm, and any slight misalignment or deformation of the optical mechanism will cause significant optical losses in connections. Previous studies have shown that the currently used alignment methods are not efficient, and the precise position for the connection is not easy to locate. This study proposes a two-stage method to overcome these problems. In the first stage, the Nelder-Mead simplex method is used to move quickly to the optimum solution. In the second stage, a numerical optimization method is used to improve the accuracy. This study compares different numerical optimization method that can be used to find the ideal connection position. It can be concluded that the most stable method for the search direction is the steepest-descent method, because the light intensity distribution is similar to a Gaussian one, and the most efficient method for the step-size determination is polynomial interpolation. Therefore, the second stage uses the steepest-descent method with polynomial interpolation.

The paper reports a novel design for single-polarization single-mode (SPSM) operation at 1310 nm in photonic crystal fibers (PCFs), using a rectangular-lattice PCF with two lines of three central air holes enlarged. The proposed PCF, composed entirely of silica, is modeled by a full-vector finite-element method with anisotropic perfectly matched layers. Simulations show that wideband single-polarization operation can be easily realized with the proposed structure. This wideband SPSM operation, the low confinement losses, and the small effective mode area are the main advantages of the proposed fiber. The influence of varying PCF parameters on the SPSM operation is discussed, and numerical results show that the proposed fiber is a SPSM one with confinement loss less than 0.1 dB/km at wavelengths ranging from 1100 to 1460 nm and effective mode area about 4.3 μm² at 1310 nm.

A random access protocol that adopts stop-and-wait automatic repeat request (ARQ) is proposed for optical code-division multiple-access (CDMA) communication systems. A detailed state diagram and a mathematical model based on the equilibrium point analysis (EPA) technique are presented. Several performance measures are evaluated under different network parameters. In addition, the performance of the proposed protocol is compared to that of the round-robin receiver/transmitter (R³T) protocol, which is based on a go-back-n-technique. The ALOHA CDMA protocol is also considered. Finally, our protocol is analyzed when a queuing subsystem is added. Our numerical analysis shows that the proposed protocol is less complex and significantly outperforms the R³T protocol. We show that adding a single buffer to the system does not improve the performance much.

A theoretical analysis is developed to evaluate the conditional and average bit error rate (BER) performance degradation of an optical heterodyne continuous-phase frequency-shift keying (CPFSK) system caused by signal phase distortion due to polarization mode dispersion (PMD) in a single-mode fiber. The probability density function (pdf) of the random phase fluctuation due to PMD at the output of the receiver is determined analytically. The average BER performance results are evaluated at a bit rate of 10 Gb/s, considering Maxwellian distribution for the differential group delay (DGD) based on the pdf of the random phase fluctuation. The results show that the performance of the optical heterodyne CPFSK direct detection system suffers power penalties of 0.75, 1.95, 4.00, and 9.15 dB, corresponding to mean DGD of 20, 30, 40, and 60 ps, respectively, at a average BER of 10^-9 operating at 10 Gb/s. Furthermore, at increased values of the mean DGD, there occur BER floors above 10^-9, which cannot be lowered by further increasing the signal power. It is noticed that BER floors occur at about 2×10^-8, 10^-5, and 2.5×10^-4, corresponding to mean DGD of 60, 70, and 80 ps, respectively, at 10 Gb/s and a modulation index of 0.50. The effect of PMD is found to be more detrimental at higher modulation indexes and bit rates.

Different definitions of spot size and depth of focus in optical data storage systems are analyzed and compared numerically. It appears that the differences between the definitions become more significant as the numerical aperture of the optical system increases. The relationship between spherical aberration and axial intensity is studied, and a general definition of the depth of focus based on this analysis is proposed.

We present a method to fabricate in situ lens arrays on the edge of waveguide arrays that are embedded in a printed circuit board. This fabrication method can guarantee precise alignment between the lenslet and the waveguide arrays, by directly overlaying the lenslet pattern on the waveguide cores. Each fabricated lenslet has a numerical aperture of 0.1, and the beam through it has a divergence angle of 3.29 deg, close to that of a perfectly aligned commercial lenslet array.

Fluid vibrations in axisymmetric geometry according to the first harmonic in the circumferential direction are analyzed. This problem has a practical application in the analysis of transverse vibrations of fluid in an axisymmetric pipe. The numerical model is developed using finite-element techniques in axisymmetric geometry. Irrotational motions of ideal compressible fluid are analyzed. The finite-element model of the system is based on the approximation of nodal displacements via the shape functions. Thus the field of the amplitudes of the circumferential variation of the volumetric strain is calculated, exploiting conjugate approximation techniques. Obtained volumetric strains are used for the numerical construction of the interference pattern of the vibrating fluid. For this purpose the Abel transform, which is usually exploited in axisymmetric problems, is generalized for problems with circumferential variation of displacements. The obtained interference patterns are used in hybrid experimental–numerical procedures and help to interpret experimental results.

Terrestrial free space optical (FSO) links are based on the simple concept of a light beam carrying information, thus facilitating very high data rates. Fog remains the major hurdle in increasing the availability and reliability of terrestrial FSO links, as fog particles scatter the propagating light, causing nonnegligible attenuation. We present measurement results from our campaigns carried out at the continental city of Graz and at La Turbie near Nice, the southern coast of France. We perform a detailed analysis of the measurement results providing time-series analysis of these fog measurements and a comparison between maritime and continental fogs. Based on our measurement analysis, we provide insight into designing efficient FSO systems, with better performance and enhanced resilience.

For remote sensing over snow-covered surfaces, the bidirectional reflectance distribution function (BRDF) of snow plays an important role that should be considered in inverse algorithms for the retrieval of snow properties. However, to simplify retrievals, many researchers assume that snow is a Lambertian reflector. This "forward model" error affects the accuracy of retrieved snow parameters (such as albedo, snow grain size, and impurity concentration). To quantify this error and to compensate for it, we provide a simple yet accurate semi-empirical correction formula. It allows for easy conversion of top-of-the-atmosphere (TOA) reflectance arising from an anisotropically reflecting snow surface to an equivalent TOA reflectance for a Lambertian surface with the same albedo. Conversely, this correction can be used to translate TOA radiance computed with the Lambertian assumption into a more realistic value based on a BRDF treatment. The coefficients in this correction formula are stored in a look-up table (LUT), and a simple LUT interpolation program is provided to allow the user to extract TOA reflectances for any sun-satellite geometry by quick interpolation in the LUTs. For the first 8 channels of the VIIRS spectrometer, the R-square regression coefficient for fitting this correction formula is better than 0.95 for a wide range of sun-satellite geometries.

Airborne light detection and ranging (LIDAR) data filtering is the most time-consuming and expensive part in applications related to laser scanning. This paper proposed a fast facet-based LIDAR data filtering method. LIDAR point clouds are interpolated onto a regular grid, and the filtering of nonground points is implemented on the grid-based data. The simple, quadratic, and cubic facet models, which are respectively, based on the zero, second, and third orders of orthogonal polynomials, are used to estimate the underlying elevation surface trend, which is considered as the approximation of ground surface. As the ground measurements are generally below the objects, the nonground points are filtered by removing the points that are higher than the estimated elevation surface trend. The resulting holes are filled with the nearest remaining measurements. Iteratively filtering in this way, the estimated elevation surface trend converges at the real ground surface. The nonground points that are higher than the finally approximated ground surface are filtered and the ground points are extracted from the LIDAR data. Experimental results on the test data released from the International Society for Photogrammetry and Remote Sensing (ISPRS) demonstrate that the proposed approach is efficient and provides at least comparable performance with the accuracy reports published by ISPRS.

A novel algorithm for detecting and tracking extended target using the projection curves analysis and correlation tracking based on the maximum matching pel count (MPC) criterion is presented. First, the projection curves of the difference image of two consecutive frames are analyzed to find the approximate areas of moving target on the entire scenes. Then correlation tracking based on the improved MPC criterion is used for target tracking against the cluttered background. Experimental results show, as compared to the conventional approaches, the proposed algorithm is more robust, has higher precision, and has simplified computational complexity for tracking an extended target against a cluttered background.

Image fusion has gained importance with the advances in multispectral imaging. We examine four different fusion methods by comparing human observers' target detection performance with the resultant fused images. Three experiments with 89 participants were conducted. In the first experiment, images with multiple targets were presented to the participants. Quantitative measurements of participants' hit accuracy and reaction time were measured. In the second experiment, we implemented an approach that has not been generally used in the context of image fusion evaluation: we used the paired-comparison technique to qualitatively assess and scale the subjective value of the fusion methods. In the third experiment, participants' eye movements were recorded as the participants searched for targets. We introduce a novel method to compensate for eye-tracker precision limitations and to enable analysis of eye movement data of different image samples even for detection tasks with small targets. Results indicated that the false color and principal components fusion methods showed the best results over all experiments.

Backprojection is an essential step of the cone-beam reconstruction algorithm for computed tomography. Conventional backprojection maps a reconstructed voxel to the projection space by interpolating across adjacent detector channels and rows of a single projection. Although this approach is computationally efficient, both theoretical analysis and phantom experiments have shown that a significant degradation in z resolution can result. To overcome this shortcoming, we propose a conjugate cone-beam backprojection approach in which two projections that are 180 deg apart are backprojected simultaneously. By carefully selecting the helical pitch and designing the interpolation function, the z resolution of the reconstructed images can be significantly improved. The proposed conjugate backprojection algorithm has the potential to reduce data extrapolation artifacts due to limited detector size in step-and-shoot data acquisition. Extensive computer simulations and phantom experiments are used to demonstrate the efficacy of our approach.

This paper reviews the theory of the European article-number barcode (EAN-13) and describes the use of the bar-code pattern as watermarks for embedding into a cover image. The mechanisms that are used to construct a multiple-bar-code watermarking scheme, including the discrete Fourier transform (DFT), adaptive phase-shift keying (APSK), amplitude boost (AB), nearest-phase selection (NPS), and bar-code pattern size shrinking (BPSS), are also discussed. Compared with other watermarking techniques, our proposed method has four advantages: (a) We develop a BPSS mechanism to shrink the bar-code size and increase the amount of bar code to be embedded into the cover image. (b) We use the APSK mechanism to determine the phase modulation strength automatically according to the signal magnitude. This decreases the degradation of the cover image enormously. (c) Two strategies—AB and NPS—are used in the scheme. AB enhances the robustness, and NPS improve the imperceptibility. (d) A bar-code pattern error-correcting mechanism is adopted to correct the extracted watermarks. It enhances the robustness greatly. In order to demonstrate the effectiveness of the proposed scheme, simulations under various conditions were conducted. The results show that the proposed scheme can sustain most common attacks, including JPEG compression, rotation, resizing, cropping, painting, noising, and blurring.

Some algorithms for morphological multiscale contrast enhancement for gray and color images, based on a psychophysical model of contrast perception, are introduced. The color space for applying the transformations is the space of chromatic coordinates (u,v,Y). The brightness Y of the space is transformed separately to increase its contrast; subsequently, the gravity center law is used to enhance hue. One of the algorithms applied to Y is based on a composition of contrast mappings that are built by means of the openings and closings by reconstruction. This composition successfully finds the principal regions according to a morphological contrast criterion. This contrast criterion is consistent with Weber's law. The second approach is derived from the Retinex approach that uses a family of Gaussian transformations. Instead of working with Gaussian transformations, a family of openings by reconstruction is used. Again, Weber's law is used for building the operators, although this law is not used as a criterion for selecting the primitives but as a concept for building rational morphological operators. For color images, once the brightness is enhanced, the color is improved by increasing the saturation of the image.

We propose an alternative test for the characterization of fogging by organic compound of interior automotive materials and develop a semiautomated experimental prototype of a system for the acquisition and digital processing of images of droplets on glass substrates. We found optimal conditions of illumination of samples of fogging for the acquisition of images, achieving the resolution of 2 μm that is basically the limitation of the microscope used in the experiment. The list of parameters that characterize fogging was extended; in addition to size, we measure the shape, orientation, and distribution of droplets over the substrate. The shape of droplets on a substrate is given by equivalent ellipses. The following processes of the fogging characterization were automated: substrate positioning and image sampling at points selected randomly or on a regular lattice; acquisition, storage, and binarization of digital images; histograms of shape features, orientation, size, and deposition density of drops. As an example, we report the statistical analysis of drops of organic compounds. Two methods for the shape description of drops are evaluated and compared also.

The orthogonal subspace projection (OSP) algorithm, which is used to process mixed pixels in hyperspectral images, is discussed frequently in the remote sensing literature. A recent paper discussed ways to derive the OSP and the use of OSP as a target detector or for material abundance estimation. However, a technique called the constrained signal detector (CSD) outperforms the OSP technique. OSP is equivalent to the unconstrained least-squares estimate of the abundance of a particular material in a mixed pixel. CSD is equivalent to the constrained least-squares abundance estimate. It is shown through theory and simulation that the constrained method (CSD) outperforms the unconstrained technique (OSP) for the problems of target detection and material abundance estimation in mixed pixels.

A digital image copyright protection scheme based on visual cryptography (VC) and singular value decomposition (SVD) techniques is proposed. In the proposed scheme, a master share is first constructed by applying SVD to a host image. Then, the master share is used together with a secret image to construct an ownership share, according to a two-out-of-two VC scheme. The secret image for ownership identification can be revealed by stacking the master share, and the ownership share. The proposed scheme embeds the secret image without modifying the host image. In addition, the hidden secret image can be extracted without resorting to the original host image and the aid of computers. Experimental results show that the proposed scheme, compared with existing schemes, achieves stronger robustness against several common attacks.

This paper describes a three-dimensional (3-D) face recognition system based on two different 3-D sensors. These sensors were used to overcome pose variation problems that cannot be effectively solved when working with 2-D images. We acquired input data based on a structured light system and compared them with 3-D faces acquired by a 3-D laser scanner. Due to differing data structures, we generated a selection of probe images and stored images (not only for head pose estimation but also for face recognition). Given an unknown range image, we extracted invariant facial features based on facial geometry and utilized the previously developed error-compensated singular-value decomposition method to estimate a head pose. Distinctive facial shape indices were defined and extracted based on facial curvature characteristics. The extracted indices have a different number and different distribution on each face image. When multiple matching possibilities are involved, dynamic programming (DP) is useful matching algorithm. DP merges data points in order to achieve better point-to-point matching by finding a matching path at minimum cost. Experimental results show that the proposed method obtained a 96.8% face recognition rate when working with 300 individuals under different pose variations.

The testing and evaluation of a low cost system capable of estimating the position of a moving target within an extendible indoor area with low error is presented. Based on a recently developed system architecture, which makes use of a noise-sensitive indoor localization system made up of ir sensors, the position estimation error is based on comparing the number of the digital ir patterns received at the moving target with the expected one. To overcome the problem of instant noise that appears despite the effective system shielding, we employ a number of rules that take into consideration the previous position estimations. These rules are based on the fact that the speed of the target is always limited and its track is smooth most of the time. The test for the rules was made by running a series of experiments on the sensors system, and as a result, we verified that the maximum absolute error in the experimental results is approximately equal to the grid node distance. Moreover, the noise restrictions of the system were tested and recognized, allowing direct measurement of relevant parameters.

With the increasing awareness of personal and national safety, security and surveillance systems are commonly encountered in our everyday lives. Computer vision technologies such as modeling and recognition are the key components of current surveillance systems. Over the last few years, many studies have been conducted for facial recognition using data acquired by imaging systems such as video and laser scanning. With the advent of low-cost digital cameras, photogrammetry has emerged as a cost-effective and straightforward technique to accurately acquire three-dimensional facial measurements. For identification and verification purposes, generated facial models should undergo surface registration and matching procedures. In addition to facial recognition, the surface matching can be used for identifying resulting discrepancies from different facial expressions. The presented research introduces a novel approach for using low-cost digital cameras and surface matching to generate and recognize corresponding facial models. Preliminary experimental results showed that the proposed algorithms could successfully match and detect discrepancies between two facial models. The performance, advantages, and limitations of this preliminary study will be discussed, along with recommendations for future research.

Corner and junction detection is an important preprocessing step in image registration, data fusion, object recognition, and many other tasks. This work deals with corner and junction detection of characteristic features of the structure resulting from cross-pattern projection. The ultimate aim is to adapt the positions and orientation of the cross-pattern projections to what has been observed. The use of this projected light pattern in the framework of active vision allows us to identify certain points of interest on 3-D objects, to directly acquire a synthesis, which thus permits simplified detection, measurement, recognition, or tracking. We present detection methods for corners and junctions in the context of Hough transform detection.

A novel method to detect flames in infrared (IR) video is proposed. Image regions containing flames appear as bright regions in IR video. In addition to ordinary motion and brightness clues, the flame flicker process is also detected by using a hidden Markov model (HMM) describing the temporal behavior. IR image frames are also analyzed spatially. Boundaries of flames are represented in wavelet domain and the high frequency nature of the boundaries of fire regions is also used as a clue to model the flame flicker. All of the temporal and spatial clues extracted from the IR video are combined to reach a final decision. False alarms due to ordinary bright moving objects are greatly reduced because of the HMM-based flicker modeling and wavelet domain boundary modeling.

Maximum variance projection (MVP), as a novel subspace learning algorithm, is proposed. It is a linear discriminant algorithm that preserves local information by capturing the local geometry of the manifold. Two abilities of manifold learning and classification are combined into the properties of our algorithm. Since face images often belong to a submanifold of intrinsically low dimension, we carry out the MVP algorithm for face manifold learning and classification. Several experiments show the effectiveness of our developed algorithm.