I have always wondered whether the impact factor was a reasonable metric to describe the journal performance of Optical Engineering. This month, I have had some pretty good discussions with SPIE staff and some of the other SPIE journal editors about the topic.

A generic reconstruction algorithm is proposed, which is obtained by using a phase-shifting technique with an arbitrary number of phase shifts between intensity measurements. The generic algorithm entirely describes the structure of known phase-shifting algorithms and permits the construction of new ones with an arbitrary number of phase shifts.

We have developed a thin quarter-wave plate (QWP) operating at low terahertz frequency of 0.51 THz by etching micro-grating on a silicon substrate. The grating period is 30 μm, and the etching depth is 156 μm. Stokes parameters are used to characterize the QWP. The QWP shows a high transmission coefficient of 0.93 and a low polarization dependent loss (PDL) of 1.4 dB at 0.51 THz.

Our correlation analysis has shown promising and surprisingly good dependence of optical signal attenuation on sonic temperature, which is shown and discussed in this study. This discovered dependence is derived from measurements (periods with fog and rain events were excluded) and presented in the form of scatter plots. It is possible to express roughly that the attenuation decreases with the sonic temperature (negative correlation coefficient). Trying to understand our results, we added the explanation of the physical quantity sonic temperature in this contribution.

With the rapid growth of wind turbines and focus on maintenance costs structural measurements are becoming essential. Fiber-optical sensors have physical properties that make them suitable for embedding in wind turbine blades, such as small size and immunity to electrical interferences. Fiber-optical grating sensors can be utilized to provide important information regarding strain, temperature, and curvature of the blades, which can be applied in condition-monitoring to detect fatigue failure and furthermore for optimization of the production from the wind turbine. We provide an overview of the current status and a discussion on research and implementation of fiber Bragg gratings and long-period gratings in wind turbine blade sensors.

Based on a customized time-domain optical coherence tomography (OCT) system, a series of signal processing approaches have been designed and reviewed. To improve demodulation accuracy and image quality, demodulation approaches such as median filter, Hilbert transform, and envelope detector were investigated with simulated as well as experimental data. Without noise, the Hilbert transform has the best performance, but after considering the narrow-band noise in the modulated signal, the envelope detector was selected as the ideal demodulation technique. To reduce noise and enhance image contrast, digital signal processing techniques such as a bandpass filtering and two-dimensional median filtering were applied before and after the demodulation, respectively. Finally with integration of the customized OCT setup and designed signal processing algorithms, aerospace materials, such as polymer coatings and glass-fiber composites, were successfully characterized. The cross-sectional images obtained clearly show the microstructures of the materials.

One of the most remarkable issues of modular large format digital cameras is that the image which is photogrammetric processed (for example, is the input to aerial triangulation) results from the composition of images physically acquired by a sensor. This “artificial” image is produced through a given principal distance and principal point and is corrected from distortions up to a certain amount (usually 2 μm). Therefore, it becomes unavoidable to monitor the adequate behavior of the camera and images, so self-calibration is one of the main procedures related to the efficient management of these devices. In this context, to calibrate this type of sensor and assess its performance, a two-height flight, with ground sample distance of 0.075 and 0.150 m, over a test field has been projected and executed. The issues that have been checked are: the misalignment between the inertial motion unit and the camera, the actual value of both the principal distance and principal point and the influence of the so-called additional parameters on the behavior of the image residuals.

It is shown that electron heating by electromagnetic radiation in mercury-cadmium-telluride (MCT) layers can be used for designing of uncooled terahertz (THz)/sub-THz detectors with appropriate for active imaging characteristics (noise equivalent power ∼2.6×10 ⁻¹⁰W/Hz ^1/2 at ν∼140  GHz ) and these detectors can be manufactured within well established MCT technologies. This narrow-gap semiconductor can be considered as a material for THz/sub-THz detectors with possibility to be assembled into arrays. The characteristics of those detectors can be controlled and improved by selection of parameters of initial layers, substrate properties, and antenna configuration. For field effect transistor detectors, even for transistors with rather long channels (∼1  μm ), rather similar characteristics at ν∼140  GHz can also be obtained.

Potassium dihydrogen phosphate (KDP) crystals, which are widely used in high-power laser systems, are required to be free of defects on fabricated subsurfaces. The depth of subsurface defects (SSD) of KDP crystals is significantly influenced by the parameters used in the single point diamond turning technique. In this paper, based on the deliquescent magnetorheological finishing technique, the SSD of KDP crystals is observed and the depths under various cutting parameters are detected and discussed. The results indicate that no SSD is generated under small parameters and with the increase of cutting parameters, SSD appears and the depth rises almost linearly. Although the ascending trends of SSD depths caused by cutting depth and feed rate are much alike, the two parameters make different contributions. Taking the same material removal efficiency as a criterion, a large cutting depth generates shallower SSD depth than a large feed rate. Based on the experiment results, an optimized cutting procedure is obtained to generate defect-free surfaces.

We review our recent progress on the fabrication of x-ray diffractive optical elements (DOEs) by combining complementary advantages of electron beam, x-ray, and proximity optical lithography. First, an electron beam lithography tool with an accelerating voltage of 100 kV is used to expose initial x-ray mask based on SiC membrane with a low aspect ratio. Second, x-ray lithography is used to replicate x-ray DOEs and amplify the aspect ratio up to 14:1. Third, proximity optical lithography is used to fabricate a large-scale gold mesh as the supporting structures. We demonstrate that this method can achieve high aspect ratio metal nanometer structures without the need of a complicated multilayer resist process. A large number of x-ray DOEs have been fabricated with feature sizes down to 100 nm for the purpose of laser plasma fusion applications. Among them, the ninth-order diffraction peak on the positive side of the zeroth order can be observed for both 3333 and 5000  lines/mm x-ray gold transmission gratings.

We present an absolute testing of a spherical reference surface of a Fizeau interferometer with the method of shift-rotation, which relies on the decomposition of the surface deviation into rotationally asymmetric and symmetric components. With a new procedure to measure the rotationally asymmetric component and an iterative algorithm to calculate the symmetric component, the method can calibrate the spherical reference surface with high accuracy. An experiment is presented to verify the validity of the absolute testing method. The reference surface deviation measured with the absolute testing method agrees well with that of random-ball-averaging testing method; the root mean square of the residual figure between them is ∼0.8  nm .

A new approach to estimate the point spread function (PSF) of remotely sensed images is proposed here based on multiple natural point-like sources, i.e., subimages of the observed image. First the conditional subimages are extracted, and then a blind deconvolution technique is used to derive the PSF from these subimages. For a sampled imaging system with signal-to-noise ratio <20  dB , this method can provide a relatively accurate PSF result. Moreover, the estimated PSF can be applied to image restoration using Wiener filtering or other nonblind restoration methods.

We demonstrate a comprehensive and broadly applicable methodology for the optimal in situ configuration of bendable soft x-ray Kirkpatrick-Baez mirrors. The mirrors used for this application are preset at the Advanced Light Source Optical Metrology Laboratory prior to beamline installation. The in situ methodology consists of a new technique for simultaneously setting the height and pitch angle of each mirror. The benders of both mirrors were then optimally tuned in order to minimize ray aberrations to a level below the diffraction-limited beam waist size of 200  nm (horizontal)×100  nm (vertical) . After applying this methodology, we measured a beam waist size of 290  nm (horizontal)×130  nm (vertical) with 1 nm light using the Foucault knife-edge test. We also discuss the utility of using a grating-based lateral shearing interferometer with quantitative wavefront feedback for further improvement of bendable optics.

The bulge test has been utilized extensively in determining the mechanical properties of thin film materials. We develop a bulge-test system that consists of three main components, including an optical system, a loading system, and a control system. A telecentric lens is adopted as an imaging camera in an optical system to provide high imaging quality along with a constant angle of view across the entire field of view. The out-of-plane deformation is obtained by projecting a sinusoidal fringe pattern onto a specimen surface and analyzing recorded images with a digital image correlation algorithm. A least-squares polynomial fitting is presented to solve the problem that the out-of-plane calibration coefficient is not a constant. Experiments were performed to validate the availability and reliability of this proposed bulge-test system in the measurement of a dynamic microscopic deformation of membrane. The measuring range of deformation is from several microns to hundreds of microns with an accuracy of 0.6 μm.

The dependences of the 294 and 10 K mobility μ and volume carrier concentration n on thickness (d=25 to 147 nm) are examined in aluminum-doped zinc oxide (AZO). Two AZO layers are grown at each thickness, one with and one without a 20-nm-thick ZnON buffer layer. Plots of the 10 K sheet concentration n_s versus d for buffered (B) and unbuffered (UB) samples give straight lines of similar slope, n=8.36×10²⁰ and 8.32×10²⁰  cm⁻³, but different x-axis intercepts, δd=−4 and +13  nm, respectively. Plots of n_s versus d at 294 K produce substantially the same results. Plots of μ versus d can be well fitted with the equation μ(d)=μ(∞)/[1+d*/(d−δd)], where d* is the thickness for which μ(∞) is reduced by a factor 2. For the B and UB samples, d*=7 and 23 nm, respectively, showing the efficacy of the ZnON buffer. Finally, from n and μ(∞) we can use degenerate electron scattering theory to calculate bulk donor and acceptor concentrations of 1.23×10²¹  cm⁻³ and 1.95×10²⁰  cm⁻³, respectively, and Drude theory to predict a plasmonic resonance at 1.34 μm. The latter is confirmed by reflectance measurements

The Near-Infrared Spectrograph (NIRSpec) is one of the four science instruments of the James Webb Space Telescope. Its focal plane consists of two HAWAII-2RG sensors operating in the wavelength range of 0.6 to 5.0 µm and, as part of characterizing NIRSpec, the noise properties of these detectors under dark and illuminated conditions were studied. Under dark conditions, and as already known, 1/f noise in the detector system causes somewhat higher noise levels than can be accounted for by a simple model that includes white read noise and shot noise on integrated charge. More surprisingly, for high levels of accumulated charge, significantly lower total noise than expected was observed. This effect is shown to be due to pixel-to-pixel correlations introduced by signal-dependent interpixel crosstalk, with an interpixel coupling factor, α , that ranges from ∼0.01 for zero signal to ∼0.03 close to saturation.

A versatile wavefront sensor is described, using a two-dimensional acousto-optic modulator (AOM) driven with double radio frequencies in both the orthogonal directions. Inserted in the spectral plane in a 4-f system, the AOM acts like a moving double-frequency crossed grating. The proposed wavefront sensor inherits the advantages of a double-frequency grating lateral shearing interferometer in the aspects of high-resolution slope estimations and structure compactness. The sensor naturally performs as a heterodyne detection system, thanks to the inherent property of traveling waves in acousto-optic modulators. Variable shear can be acquired conveniently by electronically adjusting the driving frequencies, with the optimal performance achieved under different circumstances involving parameters such as accuracy, dynamic range, and signal-to-noise ratio. Beyond the proposed concept, theory analysis is presented in detail, and simulations are carried out to demonstrate the principle and validation of the proposed wavefront sensor.

Metallic photonic crystals (MPCs) with different periods have been fabricated by solution-processed method. Scanning electron microscopy images show that the structures with their period larger than 400 nm can easily maintain their morphologies during the high temperature lift-off process. The optical properties of the waveguided MPCs with different periods have been investigated. With an increase in the period, high-order coupling between particle plasmon resonance and the waveguide resonance modes can be observed in the spectra. We found that the ±2 orders coupling of the structure with its period of 880 nm has similar tuning properties to the ±1 st orders coupling of the 430 nm period structures, which infers us that we can use the structures with larger period that can be controllably fabricated to replace the ones with smaller period. The results we obtained in this work provide reference for further applications of the MPCs.

An optical single sideband (OSSB) modulation radio over a fiber system, by using an acousto-optic filter (AOF), is proposed and demonstrated. In the AOF, a uniform fiber Bragg grating is etched and modulated by an axially propagating acoustic wave. Due to the acousto-optic superlattice modulation, two secondary reflection peaks, centered on the primary reflection peak, are generated. In the scheme, an optical double-sideband signal passes though the AOF to realize OSSB modulation. Because the reflect depth of the primary peak is much deeper than those of the secondary peaks, the carrier experiences higher attenuation than the upper sideband, which means the carrier-to-sideband ratio (CSR) can be optimized at the same time. We demonstrate this scheme via simulations, and successfully reduce the CSR from 9.73 to 2.9 dB. As a result, the receiving sensitivity improved from −23.43 to −31.18  dBm at BER of 10⁻⁹ with 30 km long SMF.

This paper presents an overview of integrated optical signal routing based on the principle of electro-optic effects. There are some specific types of materials whose refractive index changes due to the application of the electric field. Lithium-niobate (LiNbO₃ ) and gallium arsenide are some important electro-optic materials. Due to the application of the voltage across electrode present in one of the arms of Mach-Zehnder interferometer (MZI), the electric field changes, hence, phase change in the signal present in one of the arms. Depending upon the phase change introduced, signal shifts from one waveguide to the other waveguide. Hence, this paper provides the detailed description of 1×4 signal router, using three MZI, and its construction using beam propagation method. Finally, the results are verified by the MATLAB-based results.

The chirp properties of semiconductor optical amplifiers in all-optical switches are numerically investigated using a field propagation model. The chirp dynamics in the blue-shift and red-shift sideband are analyzed under the injection of random optical pump pulses. We also analyze the impact of the blue-detuned filtering scheme that is used to eliminate the pattern effect and enhance the operating speed of the optical switching. The reason for overshoots in eye diagrams in the blue-detuned filtering scheme is explained. We find that overshoots result from the ultrafast blue chirp induced by carrier heating and two-phonon absorption. These results are very useful for semiconductor optical amplifier-based ultrafast all-optical signal processing.

An experimental investigation on an S-tapered photonic crystal fiber interferometer is presented. The whole fabrication process was carried out using a standard splicing machine. The interferometer shows a compact and stable structure with a waist diameter of 110 μm, taper length of 280 μm, and axial offset of 40 μm. The transmission spectra indicated that it is highly sensitive to the surrounding refractive index (RI) and insensitive to temperature. Resolutions of 3.3×10 ⁻⁴ and 8.0×10 ⁻⁵ RI units were achieved in the 1.33 to 1.38 and 1.38 to 1.44 range, respectively. Furthermore, its temperature dependence was only 4  pm/°C .

An all-optical realization of a two-tap complex-coefficient microwave photonic filter, working under incoherent mode, is proposed and demonstrated. The complex coefficient is realized by simply adjusting the bias voltage applied to the dual-electrode Mach–Zehnder modulator. The real coefficient is controlled by adjusting the power of the two taps. As a result, the frequency response of the filter can be continuously tuned, over a full free spectral range, without changing the shape of the filter.

Polarizing Panda-type W-fibers, practical realizations are presented for fiber-optic gyroscope (FOG) sensing coil (500-m length, 8-μm fundamental mode field diameter) and for polarization/modal filtering at the FOG loop interferometer input (∼1-m length, 10-μm fundamental mode field diameter). Using these fibers, two different mathematical models for light propagation are tested and applied for further dichroism spectral band spreading of polarizing W-fibers with fundamental mode field diameter (MFD) of 6 to 10 μm for FOG coil and at least with MFD=8 to 10 μm for input filtering in loop interferometer. Also, some fibers with large MFD are considered, which may be useful for high-power fiber lasers, requiring the low nonlinear effects. One is a practically realized single-mode 200-m W-fiber Panda with dichroism and MFD=12.4  μm at 1.06 μm, which is bend resistant for 60-mm diameters. For further MFD increase a straight 100-mm length modal and polarization filters are suggested with MFD=30 to 70 μm at 1.06 μm, based on a pure silica core fiber, narrow/shallow fluorine cladding, and stress-applying parts. The latter are used for core refractive index regulation by birefringence (W-profile forming), which is more precise than with core germanium doping.

A high-efficiency tunable refractive lens based on liquid crystals with concentric electrode rings and a simple unique design of a resistor network is reported, and used to assess the performance of an optimized electrically tunable lens. It has a large number of phase control points to be able to accurately control the phase profile and produce high efficiency. The lens design uses resistors between neighboring electrodes to minimize external connections. The lens optical path difference is measured as a near perfect parabolic shape and the Strehl ratio of about 80% is obtained (comparing to a high-quality glass lens). Image evaluations show a good image quality with diffraction limited resolution, but the contrast is lowered by a large-area haze. The lens design also shows a good switching speed, and adjustable power, allowing it to be used in many applications. An example lens with a diameter of 2.4 mm and a 5 diopter tunable range is used in the evaluations.

An acoustic birefringence suppression scheme for acoustic fiber gratings has been proposed and experimentally demonstrated. Experimental observation of the transmission characteristics of the single-mode-fiber-based (SMF-based) acoustic grating confirms that introduction of one segment of solid-core photonic crystal fiber (PCF) with air-hole array in the cladding region helps to eradicate resonance peak splitting induced by acoustic birefringence, which has been explained by our theoretical analysis from the acoustic wave modulation method and fiber cross-section structure. Moreover, experimental results indicate that the introduction of the solid-core PCF does not have a considerable impact on the frequency dependence of resonance wavelength for the SMF-based acoustic fiber grating, which ensures the performances of the PCF-assisted SMF-based acousto-optic tunable filter for practical applications.

Optical-electrical printed wiring boards were fabricated featuring mechanical transfer (MT)-compatible interconnections for out-of-plane optical signal routing with an average optical link loss of 10.7 dB. Commercially available components were integrated into an optical layer for out-of-plane optical routing, including light turning devices that feature spherical micro lens arrays, a total internal reflection mirror, and alignment slots compatible with standard MT connectors. The feasibility of the optical-electrical printed wiring board is discussed in detail to demonstrate its compatibility with common printed circuit board manufacturing processes. The optical-electrical printed wiring board prototypes survived thermal cycling (−40°C to 85°C) and humidity exposure (95% humidity) showing an overall degradation of <3  dB of optical performance. Operational failure (<18  dB ) occurred after environmental aging life testing at 110°C for 216 h.

A novel approach for all-optical digital encoder for both binary-to-gray code and gray-to-binary code have been proposed. Design is based on the basic concept of digital encoder using the exclusive OR (XOR) addition. The XOR gate used in these encoders has been implemented using differential phase modulation between two arms of the Mach-Zehnder interferometer (MZI), in which a semiconductor optical amplifier is placed symmetrically in both arms of MZI. For the most severely degraded output bit, i.e., least significant bit for gray-to-binary encoder, the extinction ratio obtained is 2.35 while the minimum bit error rate is zero at 10  GB/s . For the second most significant bit of gray-to-binary encoder and for all the three bits except the most significant bit of binary-to-gray encoder, the extinction ratio obtained is around 27 dB. For the most significant bit, as input and output bits are same, the extinction ratio is very high, approaching infinity.

We suggest combining several optical methods for remote sensing and characterization of crude oil films and emulsions. These are coherent fringe projection illumination (CFP), holographic in-line interferometry (HILI), and laser-induced fluorescence. The combined methods of CFP and HILI are described in the frame of coherent superposition of partial interference patterns. It is shown that in addition to detection and identification of oil, laser illumination in the green-blue region can also degrade oil. This finding indicates that properly structured laser clean-up can be an alternative method of decontamination.

Calibration of phase in spatial light modulators is a prerequisite for applications where a prespecified phase distribution needs to be implemented over the surface of the modulator. The present work proposes a full-field polarization phase shifting interferometric technique, based on the Twyman-Green interferometer, for the purpose.

Testing with lateral and radial shears is becoming standard in optical shops. Of late, holographic optical elements have proven to be easy and simple to set up, and can be used in both a collimated and convergent beam. However, there is very little work on making quantitative measurements using a symmetric radial shear. We demonstrate a simple method of obtaining both asymmetric and symmetric radial shears, and use the inherent tilt in the wavefronts to perform spatial Fourier transformation to extract phase maps. This radial shear interferometer is also suitable for static and dynamic situations.

We report the experimental results of geometric parameter measurement of the single-mode fiber by use of digital holographic microtomography technology. Tomography of the single-mode fiber is performed by a filtered back-projection algorithm and a Fourier diffraction algorithm, respectively, to reconstruct the three-dimensional (3-D) map of refractive index. According to this map, we can further get the dimensions of the single-mode fiber by the relate edge detection algorithm of image processing. Experimental results show that compared to the filtered back-projection reconstruction, diffraction tomography based on the Rytov approximation resembles the dimensions of the single-mode fiber. It provides a new way for the nondestructive and on-site measurement of tiny weakly diffracting objects with a cylindrically symmetric structure, such as the single-mode fiber.

We consider an optical beam propagated through the atmosphere and incident on an object causing a temperature rise. In clear air, the physical characteristics of the optical beam transmitted to the object surface are influenced primarily by the effect of atmospheric turbulence, which can be significant near the ground or ocean surface. We use a statistical model to quantify the expected power transfer through turbulent atmosphere and provide guidance toward the threshold of thermal blooming for the considered scenarios. The bulk thermal characteristics of the materials considered are used in a thermal diffusion model to determine the net temperature rise at the object surface due to the incident optical beam. These results of the study are presented in graphical form and are of particular interest to operators of high power laser systems operating over large distances through the atmosphere. Numerical examples include a CO ₂ laser (λ=10.6  μm ) with: aperture size of 5 cm, varied pulse duration, and propagation distance of 0.5 km incident on 0.1-mm copper, 10-mm polyimide, 1-mm water, and 10-mm glass/resin composite targets. To assess the effect of near ground/ocean laser propagation, we compare turbulent (of varying degrees) and nonturbulent atmosphere.

We propose a new feature extraction method for synthetic aperture radar automatic target recognition based on manifold learning theory. By introducing the virtual point in every sample’s neighborhood, we establish the spatial relationships of the neighborhoods. When the samples are embedded into the feature space, each sample moves toward its neighborhood virtual point, whereas the virtual points with the same class label get together, and the virtual points from different classes separate from each other. This can improve the classification and recognition performance effectively. Experiments based on the moving and stationary target acquisition and recognition database are conducted to verify the effectiveness of our method.

A novel technique for anomalous change detection (ACD) in hyperspectral images is presented. The technique embeds a strategy robust to residual misregistration errors that typically affect data collected by airborne platforms. Furthermore, the proposed technique mitigates the negative effects due to random noise, by means of a band selection technique aimed at discarding spectral channels whose useful signal content is low compared to the noise contribution. Band selection is performed on a per-pixel basis by exploiting the estimates of the noise variance accounting also for the presence of the signal-dependent noise component. Real data collected by a new generation airborne hyperspectral camera on a complex urban scenario are considered to test the proposed method. Performance evaluation shows the effectiveness of the proposed approach with respect to a previously proposed ACD algorithm based on the same similarity measure.

Brazing joining is widely used in heat exchangers due to its effectiveness in increasing the efficiency of the heat-exchange process. When there is a defect in the brazing joints of a heat exchanger, damage occurs to the heat exchanger and heat efficiency is decreased. Therefore, to secure the quality of the brazing joints, the development of a highly reliable inspection method that can detect the defects in the brazing joints is required. We utilize an x-ray-using method to inspect the defects in brazing joints. First, x-ray cross-sectional images of the brazing joints are obtained by using computerized tomography (CT) technology. A cross-sectional image obtained from CT is more effective to detect the inner defects than the traditional transmitted x-ray image. Second, the acquired images are processed, and then template-matching-based defect detection algorithms of the brazing joints are proposed. Finally, a series of experiments to detect the brazing defects by using the proposed algorithm are performed concerning two types of brazing joint. The experimental results show that the proposed algorithms are suitable for defect detection of the brazing joint-based heat exchangers.

Detection of the oil palm stem rot disease Ganoderma is a major issue in estate management and production in Malaysia. Conventional diagnostic techniques are difficult and time consuming when using visual inspection, and destructive and expensive when based on the chemical analysis of root or stem tissue. As an alternative, a transportable gamma-ray computed tomography system for the early detection of basal stem rot (BSR) of oil palms due to Ganoderma was developed locally at the Malaysian Nuclear Agency, Kajang, Malaysia. This system produces high quality tomographic images that clearly differentiate between healthy and Ganoderma infected oil palm stems. It has been successfully tested and used to detect the extent of BSR damage in oil palm plantations in Malaysia without the need to cut down the trees. This method offers promise for in situ inspection of oil palm stem diseases compared to the more conventional methods.

A nonparametric method to define a pixel neighborhood in catadioptric images is presented. The method is based on an accurate modeling of the mirror shape by mean of polarization imaging. Unlike most processing methods existing in the literature, this method is nonparametric and enables us to respect the catadioptric image’s anamorphosis. The neighborhood is directly derived from the two polarization parameters: the angle and the degree of polarization. Regardless of the shape of the catadioptric sensor’s mirror (including noncentral configurations), image processing techniques such as image derivation, edge detection, interest point detection, as well as image matching, can be efficiently performed.

Automatic facial expression recognition is an interesting and challenging task. To achieve satisfactory accuracy, deriving a robust facial representation is especially important. A novel appearance-based feature, the multiscale cell local intensity increasing patterns (MC-LIIP), to represent facial images and conduct person-independent facial expression analysis is presented. The LIIP uses a decimal number to encode the texture or intensity distribution around each pixel via pixel-to-pixel intensity comparison. To boost noise resistance, MC-LIIP carries out comparison computation on the average values of scalable cells instead of individual pixels. The facial descriptor fuses region-based histograms of MC-LIIP features from various scales, so as to encode not only textural microstructures but also the macrostructures of facial images. Finally, a support vector machine classifier is applied for expression recognition. Experimental results on the CK+ and Karolinska directed emotional faces databases show the superiority of the proposed method.

For monocular-structured light vision measurement, it is essential to calibrate the structured light plane parameters in addition to the camera intrinsic parameters. A line-feature-based calibration method of structured light plane parameters for a robot hand-eye system is proposed. Structured light stripes are selected as calibrating primitive elements, and the robot moves from one calibrating position to another with constraint in order that two misaligned stripe lines are generated. The images of stripe lines could then be captured by the camera fixed at the robot’s end link. During calibration, the equations of two stripe lines in the camera coordinate system are calculated, and then the structured light plane could be determined. As the robot’s motion may affect the effectiveness of calibration, so the robot’s motion constraints are analyzed. A calibration experiment and two vision measurement experiments are implemented, and the results reveal that the calibration accuracy can meet the precision requirement of robot thick plate welding. Finally, analysis and discussion are provided to illustrate that the method has a high efficiency fit for industrial in-situ calibration.

A full-automatic method for recognizing parking slot markings is proposed. The proposed method recognizes various types of parking slot markings by modeling them as a hierarchical tree structure. This method mainly consists of two processes: bottom-up and top-down. First, the bottom-up process climbs up the hierarchical tree structure to excessively generate parking slot candidates so as not to lose the correct slots. This process includes corner detection, junction and slot generation, and type selection procedures. After that, the top-down process confirms the final parking slots by eliminating falsely generated slots, junctions, and corners based on the properties of the parking slot marking type by climbing down the hierarchical tree structure. The proposed method was evaluated in 608 real-world parking situations encompassing a variety of different parking slot markings. The experimental result reveals that the proposed method outperforms the previous semiautomatic method while requiring a small amount of computational costs even though it is fully automatic.

A novel method for retinal blood vessel detection by using a wavelet-matched filter is proposed to improve the detection performance. Vessel references are generated by using dual Gaussian functions with different widths, separations, and orientations, while a Mexican hat wavelet is used for feature enhancements. The results show that the proposed method has advantages over the conventional matched filter in that the vessels can be easily distinguished from the fluctuating background without the need of a thresholding process, and vessel images can be precisely reconstructed.

Optical flow computation methods are traditionally classified to two categories: local and global. Several previous works have investigated the combination of them by exploiting their complementary effects. Unlike previous works, this paper is motivated by the common weakness of the two schemes and proposes linking local and global computation by subspace regularization. We will show that the subspace regularization can effectively reduce the error caused by ill-conditioned local computation systems, while inhibiting error diffusion suffered by the global regularization. Experimental results on benchmark sequences validate the enhanced performance of the proposed combination scheme.

The H.264/multiview video coding (MVC) standard has been developed to enable efficient coding for three-dimensional and multiple viewpoint video sequences. The inter-view statistical dependencies are utilized and an inter-view prediction is employed to provide more efficient coding; however, this increases the overall encoding complexity. Motion homogeneity is exploited here to selectively enable inter-view prediction, and to reduce complexity in the motion estimation (ME) and the mode selection processes. This has been accomplished by defining situations that relate macro-blocks’ motion characteristics to the mode selection and the inter-view prediction processes. When comparing the proposed algorithm to the H.264/MVC reference software and other recent work, the experimental results demonstrate a significant reduction in ME time while maintaining similar rate-distortion performance.

We propose an efficient image-coding scheme based on vector quantization (VQ). Typically, image qualities of the compressed images by using VQ are restricted by the codebook used. To provide better image qualities of the compressed images while keeping low bit rates, encoding the geometric transformed image block is associated with VQ. To cut down the bit rates, the index table is further processed by the lossless index coding process. According to the results, it is shown that the proposed scheme achieves better image qualities than VQ while keeping low bit rates.

A macroblock-based adaptive loop filter (MBALF) to improve coding gain for all intra-coding was presented. The proposed method adaptively applies the adaptive loop filter for each reconstructed macroblock (MB) in order to reduce the blocking artifact caused by the quantization process. The MBALF can improve coding efficiency of intra-predicted MBs as it is conducted prior to intra-prediction for the subsequent MBs in a slice. We found that the proposed MBALF yields a coding gain of approximately 7.1% compared to the H.264/AVC High profile. In addition, we achieved a coding gain of approximately 8.9%, on average, by combining the conventional in-loop filter, block-based, adaptive filter control.

Military applications that use adaptive optics (AO) often require a point source beacon at the target to measure and correct for wavefront aberrations introduced by atmospheric turbulence. However, turbulence prevents the formation of such a point beacon. The extended beacons that are created instead have finite spatial extents and exhibit varying degrees of spatial coherence. Modeling these extended beacons using a Gaussian Schell-model (GSM) form for the autocorrelation function would be a convenient approach due to the analytical tractability of Gaussian functions. We examine the validity of using such a model by evaluating the field scattered from a rough impedance surface using a full-wave computational technique called the method of moments (MoM). The MoM improves the fidelity of the analysis since it captures all the physics of the laser-target interaction, such as masking, shadowing, multiple reflections, etc. Two rough-surface targets with different roughness statistics are analyzed. The simulation results are verified with experimental bidirectional reflectance distribution function measurements. It is seen that for rough surfaces, in general, the scattered-field autocorrelation function is not of a GSM form. However, under certain conditions, modeling an extended beacon as a GSM source is legitimate. This analysis will aid in understanding the behavior of extended beacons and how they affect the overall performance of an AO system.

We address the methodology and hardware design for detecting defects on a steel surface. The goal of this work is to develop a surface inspection system for defects with three-dimensional (3-D) characteristics on planar steel surface using multispectral photometric stereo technique. First, the reflections of multispectral illuminations from a steel surface are captured by a multi-channel camera system. Then, a 3-D reconstructed surface profile is extracted from estimated gradient fields. The developed system is applied to real steel specimens and the experimental results show that it can reliably detect tiny defects on the surface.

The average normal effective emissivity is widely used for calibration since it depends only on the intrinsic cavity characteristics; thus, it is an important parameter for blackbody designs and evaluations. Nonaxisymmetric cavities are widely used as standard blackbody sources and cryogenic solar absolute radiometers. The finite volume method is modified by adding a black-hole cylindrical extension to extend the integrated effective emissivity computations to the much more complex computations of average normal effective emissivities for nonaxisymmetric cavities. The calculated results using the modified finite volume method have an average relative difference of 0.085% from the Monte Carlo method, which is the only reported method for average normal effective emissivities of nonaxisymmetric cavities. The results show that this method can be used effectively for calculating the average normal effective emissivities of cavities with complex geometries.