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We propose a novel optical asymmetric cryptosystem based on a phase-truncated Fourier transform. Two decryption keys independent of each other are generated. They are referred to as universal key and special key, respectively. Each of them can be used for decryption independently in absence of the other. The universal key is applicable to decrypt any ciphertext encoded by the same encryption key, but with poor legibility. On the contrary, the special key is adequate for legible decryption, but only valid for one ciphertext corresponding to the specified plaintext. A set of simulation results show the interesting performance of two types of decryption keys.

In this letter, we propose a novel method to quantitatively recover a complex-valued object from diffraction intensity maps. A wavefront modulation is introduced in the optical path, and several diffraction intensity maps are recorded through position shift of a phase mask. A phase retrieval algorithm is further developed, and advantages of the proposed method are discussed.

In this letter, we present a new design for a light-emitting diode- based bike headlamp. The optical design contains two horizontal reflectors and a light pipe with two horizontal parallel mirrors. The designed illumination pattern in our simulations performs a contrast of 250 in the K-mark regulation, and it was measured to be 21 in the experiment with a not well-finished prototype, which was operated at 1 W. The contrast is higher than 5 as requested in the regulation.

A texture video-assisted motion vector predictor for depth map coding is proposed in this letter. Based on the analyses of motion similarity between texture videos and their corresponding depth maps, the proposed approach uses the motion vectors of texture videos and the median predictor jointly to determine the optimal predicted motion vector for depth map coding by employing a rate-distortion (R-D) criterion. Experimental results demonstrate that compared with the median predictor utilized in H.264/AVC, the proposed method can save the maximum and average bit rate as high as 4.89% and 3.68%, respectively, while guaranteeing the quality of synthesized virtual views.

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Liquid crystals are nowadays widely used in all types of display applications. However their unique electro-optic properties also make them a suitable material for nondisplay applications. We will focus on the use of liquid crystals in different photonic components: optical filters and switches, beam-steering devices, spatial light modulators, integrated devices based on optical waveguiding, lasers, and optical nonlinear components. Both the basic operating principles as well as the recent state-of-the art are discussed.

A liquid crystal optically variable device (LCOVD) was fabricated by linearly polarized photoalignment technique. The device is composed of a nematic liquid crystal layer on the polyethylene terephthalate (PET) substrate and two parallel polarizers. By continuously changing the polarization direction during photoalignment, the optical axes of the liquid crystal can be variably aligned. We measured the colors and transmission spectra of the LCOVD at different observing angles. The results indicate that the colors of the device distribute continuously. The colors shift to others with the changing of the observing positions, and such color shift phenomenon depends not only on the observing inclination angle but also the azimuth angle. Furthermore, a calculation method based on the Jones matrix for simulating the performance of the LCOVD was established. The theoretical results show good agreement with the experiment. Because of the distinctive optical features, one highly significant application of the LCOVD may be its use for improving document security.

A finite element modesolver and beam propagation (BPM) algorithm are applied to the optical analysis of liquid crystal waveguides. Both approaches are used in combination with advanced liquid crystal calculations and include a full dielectric tensor in solving the Helmholtz equation to model the liquid crystal behavior properly. Simulation of the beam propagation in a waveguide with tunable liquid crystal cladding layer illustrates the coupling of a Gaussian beam to the fundamental waveguide mode obtained with the modesolver. Excellent quantitative agreement between both approaches illustrates the potential of these methods for the design of advanced devices. The high accuracy of the BPM algorithm for wide angle propagation, essential in the analysis of high index contrast waveguides, is illustrated for angles up to 40 deg.

Ferroelectric liquid crystals (FLCs) and antiferroelectric liquid crystals (AFLCs) have several interesting properties; such as low switching times, high contrast, and wide viewing angle. Such properties suggest that those materials can be appropriate for high end electro-optical applications. Upon manufacturing, the alignment conditioning of the cell plates where the liquid crystal is placed has a strong influence on the eventual electro-optical behavior of the device. If the alignment conditioning of either cell surface is different, asymmetric electro-optical responses can be obtained. Asymmetric devices having fluorinated block copolymers on one side and a conventional alignment layer on the other side seem to be promising for developing grayscale in FLCs and improving dynamic switching of AFLCs. This work explores the performance of FLC and AFLC materials in asymmetric cells showing some interesting effects such as video rate multiplexed analog grayscale.

A new electrical equivalent circuit (EEC) has been proposed to model antiferroelectric liquid crystal devices. This circuit includes a constant phase element to take into account the ferroelectric part of the dielectric response in these devices. Electrical characterization of samples has been carried out using a specific experimental protocol based on impedance spectroscopy. The parameters of waveforms used in impedance measurements have been optimized. The procedure to obtain the components of the EEC has also been explained. Finally, the EEC has been validated by comparing experimental and simulated impedance results. A reasonable agreement between both of them has been obtained in a wide frequency range for all selection voltages.

Liquid crystal tunable filters (LCTFs) are a technology that can act as both a spectral and linear polarization filter for an imaging device. Paired with the appropriate hardware, a LCTF can be configured to collect hyperspectral Stokes imagery which contains both spectral as well as polarimetric information on a per-pixel level basis. This data is used to investigate the utility of spectro-polarimetric data with standard spectral analysis algorithms, in this case anomaly detection. A method to simulate different ground sample distances (GSDs) is used to illustrate the effect on algorithm performance. In this paper, a spectro-polarimetric imager is presented that can collect spectro-polarimetric image cubes in units of calibrated sensor reaching radiance. The system is used to collect imagery of two scenes, each containing die-cast scale vehicles and different background types. An anomaly detector is applied to the intensity and polarized image cubes to find those pixels that are different from the background spectrally and/or polarimetrically. The effect of changing the apparent GSD on the anomaly detection performance is explored. This shows that applying anomaly detection to spectro-polarimetric data can improve the false alarm rate over standard spectral data for finding certain types of man-made objects in complex backgrounds.

We present results on how the dielectric anisotropy in the low frequency region up to 1 GHz and the birefringence of the nematic liquid crystal (LC) phase at optical wavelength (589 nm) influences the performance of LC mixtures at microwave frequencies. For this, we prepared a wide range of mixtures being nematic at room temperature and containing different classes of promising compounds. Their quasistatic and frequency depended dielectric properties, their birefringence and the impact of those properties on their microwave behavior were investigated. The measurements were done using the cavity perturbation method at 30 and 38 GHz, respectively, in the temperature interval of -20°C and 135°C.

This paper reports the design and the implementation of a Stokes imaging polarimeter able to provide full polarimetric information at 200 fps. This portable implementation is based on a division-of-time architecture and uses a single ferroelectric liquid crystal device as the polarization modulating element. Our system is designed to work at 532 nm with natural light or with controlled illumination, without temperature control. We propose an optimized driving scheme of the modulator such that the liquid crystal device can produce four polarization states which makes it possible to retrieve the full polarimetric information. The modulator characterization is reported and experimental results are provided.

We present infrared spectrometer design options offered through a wave propagation analysis throughout the optical system that would not be known otherwise. A recent inclusion of wave propagation into the atmospheric infrared sounder (AIRS) design model to account for an unanticipated measured spectral line narrowing with wavelength has shown that a wider slit option could have been used on the spectrometer to improve energy throughput. The underlying slit image width that narrowed could have been traded for a wider entrance slit increasing the instrument light sensitivity up to 15%, restoring the original un-narrowed slit width baseline, and recovering the spectral sampling requirement of two detectors per line profile. Of the 11 slits on the AIRS spectrometer, each slit width could have been spectrally tailored to become wider as the dispersed wavelength band increased, leading to a more optimal sounder configuration. We will show the newer suggested AIRS slit array below for future sounder design consideration after first reviewing past results that substantiate the wave propagation model being used.

A motion compensated fiber-optic confocal microscope system is demonstrated by utilizing a Fourier domain common-path optical coherence tomography (FD-CP-OCT) distance sensor and a high-speed linear motor at the distal end of a fiber-optic confocal microscope imaging probe. The fiber-optic confocal microscope is based on a 460 μm diameter imaging bundle with 10 K cores. The fiber bundle was terminated with a gradient index lens system. Using one-dimensional A-scan data of CP-OCT, the distance deviation of the target from the focal plane of the probe was monitored and motion compensated at the rate of 840 Hz, for a confocal microscopic imaging frame rate of 1fps and was 200 × 200 pixels in size, with a distance error less than 5 μm.

This paper describes a novel idea for reduction of speckle contrast in laser display projectors using the rotation of a diffraction pattern whose zeroth order has been canceled out without loosing power. The feasibility of the proposed method was investigated by illuminating gratings with a sinusoidal phase on two spatial light modulators (SLMs) in series for minimal intensity modulation, where the phase grating pattern was rotated with respect to the previous one on both SLMs. Two series of measurements were done with different periods of the sinusoidal grating. For each series, an image of the speckle pattern was recorded at discrete rotation angles of the phase grating, and then an average image was calculated. Experimental results were compared with a new theoretical model for speckle contrast of N partially correlated speckle patterns. The experimental measurement results compare well with the theoretical predictions resulting in a minimum speckle contrast of 0.36, with further reduction possible. Parameters necessary to achieve target contrast (0.08 or less) are discussed.

Raman spectroscopy has provided a powerful means of chemical identification in a variety of fields, partly because of its noncontact nature and the speed at which measurements can be taken. Given a library of known Raman spectra, a common detection approach is to first estimate the relative amount of each chemical present, and then compare the estimated mixing coefficients to a threshold. We present a more rigorous detection scheme by formulating the problem as one of multiple hypothesis detection and using the maximum a posteriori decision rule to minimize the probability of classification error. The probability that a specific target chemical is present is estimated by summing the estimated probabilities of all the hypotheses containing it. Alternatively, since we do not typically have reasonable priors for the hypotheses, it may be preferable to interpret the result as an abstract score corresponding to the minimum description length approach. The resulting detection performance of this approach is compared to that of several other classification algorithms.

The direct replication of a periodic W/Si multilayer was investigated systematically. The W/Si multilayer was deposited by a high vacuum dc magnetron sputtering system. After deposition, the multilayer was transferred from the supersmooth mandrel onto a commercially available float glass substrate by the epoxy replication technique. The multilayer was characterized by the grazing incident x-ray reflectance (GIXR) measurement, atomic force microscope (AFM), and Zygo GPI interferometer before and after replication. The measured results showed that the multilayer structure and reflectivity were almost the same, and the surface roughness was 0.22 and 0.23 nm before and after replication, respectively. It was demonstrated that the W/Si multilayer was successfully replicated without modification of the structure, a significant increase of surface roughness, or apparent change of reflectivity. The optical figure of the substrate after replication experienced significant changes of many waves but was actually improved for this specific test. Future studies will focus on learning how to control the resulting optical figure of our replication process on a thin substrate.

Second harmonic generation (SHG) of femtosecond pulses in layered photonic crystal with combined nonlinearity is analyzed. Within the approximation of plane wave, the problem under consideration is solved analytically. One shows the possibility of a multistable mode of frequency conversion that occurs due to self-action of laser pulses because of cubic susceptibility. Dependence of the number of solutions on parameters of the problem is discussed and demonstrated. On the basis of the obtained analytical solution, the possible modes of frequency conversion are found out. To verify and prove the realization of obtained analytical results, a computer simulation on the basis of Schrödinger equations is made. This comparison demonstrates good agreement between the analytical solution and computer simulation during a definite time interval, depending on thickness of layers of the photonic crystal and wavelength of laser radiation.

This paper presents a comparative study on thermal lensing characteristics of a low temperature copper vapor laser (CVL) (LT-CVL as Copper-HBr laser) and a high temperature CVL (HT-CVL as elemental CVL). Interferometric techniques were used to study the combined thermal lens power of active gaseous medium and discharge sealing optical windows as well as that of the optical windows separately at different electrical input powers. As the input power varied from 2.7 to 4.6 kW, the combined thermal lens power varied from −1.4 to +0.94 km⁻¹ for LT-CVL and from +1.4 to +13 km−1 for HT-CVL. The thermal lens power of the windows varied from +3 to +15 km⁻¹ for HT-CVL. On the other hand, for LT-CVL, the thermal lens due to windows was very weak and could not be measured. It was observed that the origin of net thermal lensing mostly resides in the discharge tube windows owing to its higher temperature variation of refractive index as compared to that of gaseous active medium. The weaker thermal lens characteristics of an LT-CVL was attributed to its much lower working temperature and relatively flatter radial gas temperature profile than that of an HT-CVL.

The unpredictability properties of an optical microring resonator with modulation are investigated quantitatively, by adopting a recently introduced quantifier, the permutation entropy (PE). We can obtain rich nonlinear dynamics, such as period, bifurcation, and chaos by changing the modulation coefficients and the input power. The effect of the nonlinear refractive index is also considered. Moreover, we adopt the permutation entropy to quantify the unpredictability of the resonator's output. The results not only qualitatively agree with the dynamical changes, but also indicate the unpredictability of the chaotic regimes. The chaotic carrier with high PE values would contribute to the unpredictability-enhanced optical microring resonator-based chaotic communication.

In this paper laser ablation of a polyethersulfone (PES) film using a XeCl laser was investigated. It was found that the dominant mechanism in the laser ablation of PES is photothermal. An effective absorption coefficient of 6.5 × 10⁴ cm−1 was obtained from fitting the Arrhenius curve with experimental data.

This paper presents a new computer interface system based on laser spot detection and moving pattern analysis of the detected laser spots in real-time processing. We propose a systematic method that uses either the frame difference of successive input images or an autoassociative multilayer perceptron (AAMLP) to detect laser spots. The AAMLP is applied only to areas of the input images where the frame difference of the successive images is not effective for detecting laser spots. In order to enhance the detection performance, the AAMLP is trained by a new training algorithm that increases the sensitivity of the input-to-output mapping of the AAMLP allowing a small variation in the input feature of the laser spot image to be successfully indicated. The proposed interface system is also able to keep track of the laser spot and recognize gesture commands. The moving pattern of the laser spot is recognized by using a multilayer perception. It is experimentally shown that the proposed computer interface system is fast enough for real-time operation with reliable accuracy.

The conventional planar grating (CPG) system has a complicated optical structure, which causes complexities in various aspects, e.g., a variety of processes such as fabrication, assembly, and alignment. The size of the CPG cannot be further reduced due to the minimum optical path length requirement imposed by the spectral resolution. This paper proposes an ultracompact grating system that is turned into a reality by a shorter optical path length through a specified grating profile. Our proposed microphotolithographic inductive coupled plasma - reactive ion etching process demonstrates that an arbitrary grating profile with high aspect ratio and small surface roughness can be achieved. The aberrations of different wavelengths are greatly reduced or eliminated. An etching depth of 30 to 60 μm is achieved. The surface roughness meets the requirement of λ/10 (50 nm). The size of the grating system is 30 × 30 × 2 mm. The resolving power R reaches 600 to 700 in the visible region.

A waveguide-based wide free-spectral-range (FSR) triple ring resonator (TRR) as an optical filter has been investigated in this article. The transmittance of the TRR is presented in Z-domain. The delay line signal processing approach and Mason's gain formula have been used to develop the transmittance of the TRR. The TRR in the article is capable of providing an FSR up to 605 GHz with lower crosstalk limited within -10 dB. Another efficacious scheme of TRR with much wider FSR of 1029 GHz and with reduced unit delay length is presented in the article. Here also crosstalk, as well as resonance loss, remains within reasonable limits. The FSRs obtained using the present TRR architectures in this work are until now reported as maximum for a corresponding class of optical ring resonators. The issues of group delay and dispersion, two important parameters associated with high frequency optical communication have been addressed in this article.

A photonic analog-to-digital converter (ADC) preprocessing architecture based on the robust symmetrical number system (RSNS) is presented. The RSNS preprocessing architecture is a modular scheme in which a modulus number of comparators are used at the output of each Mach-Zehnder modulator channel. The number of comparators with a logic 1 in each channel represents the integer values within each RSNS modulus sequence. When considered together, the integers within each sequence change one at a time at the next code position, resulting in an integer Gray code property. The RSNS ADC has the feature that the maximum nonlinearity is less than a least significant bit (LSB). Although the observed dynamic range (greatest length of combined sequences that contain no ambiguities) of the RSNS ADC is less than the optimum symmetrical number system ADC, the integer Gray code properties make it attractive for error control. A prototype is presented to demonstrate the feasibility of the concept and to show the important RSNS property that the largest nonlinearity is always less than a LSB. Also discussed are practical considerations related to multi-gigahertz implementations.

The modulation instability and the phase-matching condition around the zero dispersion wavelength of the high nonlinear photonic crystal fiber (PCF) is numerically analyzed and simulated. The ultrawide tunable range can be obtained from the fiber optical parametric oscillator and the ultrashort pulse can be generated through choosing the parameters of dispersion coefficient, nonlinear coefficient, and pump power appropriately. The numerical simulation results show that a tunable range as wide as 318 nm has been obtained from the femtosecond PCF optical parametric oscillator, around 1.5 μm.

Transparent optical network (TON) is now rapidly booming to be popular, and a threat of an all-optical crosstalk attack with high power will emerge. In this paper, the penalty of crosstalk attack propagation, including intrachannel crosstalk inside the optical cross-connects, as well as direct and indirect interchannel crosstalk within fibers, is evaluated. Our work has proved that these crosstalk attacks do propagate in the TON but with limited propagation stages, which will be useful for the planning, management, and design of TON.

Throughout this paper, a closed form expression of the multiple access interference (MAI) limited bit error rate (BER) is provided for the multiwavelength optical code-division multiple-access system when the system is working above the nominal transmission rate limit imposed by the passive encoding-decoding operation. This system is known in literature as the optical overlapped code division multiple access (OV-CDMA) system. A unified analytical framework is presented emphasizing the impact of optical hard limiter (OHL) on the BER performance of such a system. Results show that the performance of the OV-CDMA system may be highly improved when using OHL preprocessing at the receiver side.

A complete complementary/prime/shifted prime (CPS) code family for the optical code-division multiple-access (OCDMA) system is proposed. Based on the ability of complete complementary (CC) code, the multiple-access interference (MAI) can be suppressed and eliminated via spectral amplitude coding (SAC) OCDMA system under asynchronous/synchronous transmission. By utilizing the shifted prime (SP) code in the SAC scheme, the hardware implementation of encoder/decoder can be simplified with a reduced number of optical components, such as arrayed waveguide grating (AWG) and fiber Bragg grating (FBG). This system has a superior performance as compared to previous bipolar-bipolar coding OCDMA systems.

The generation of high energy, wavelength-tuned supercontinuum sources has been investigated numerically. A stable wavelength-tunable soliton source was first obtained by compressing a pulse with a parabolic shape in a dispersion decreasing fiber. Subsequently, a widely tunable supercontinuum was generated by propagating the resulting soliton in a highly nonlinear silica fiber. In this paper, we have also investigated the influence of the width, the initial chirps, and the pulse shape of the compressed pulse on the generation of the supercontinuum.

In this paper we study the possibility and the potentiality of using metal semiconductor-metal photodetector (MSM-PD) in three-dimensional parallel free space optical interconnect (FSOI) systems. The signal-to-noise ratio (SNR) and time response are used as performance measures to optimize the geometry of MSM-PD used in FSOI systems. Both SNR and time response are evaluated, analyzed, and their dependence on feature parameters of the MSM-PD, including finger size, spacing, and number of fingers, are considered. Based on the results obtained, we show that the use of MSM-PD in FSOI improves the interconnect speed at a given acceptable SNR.

A type of computer-generated hologram (CGH) with 4-step microstructure is designed based on diffraction theory. Results show that this CGH has almost the same diffraction efficiency at zeroth diffractive order and positive first diffractive order, which are 38.51% and 38.04%, respectively, and the intensity of these two beams is 76.55% of incident beam. This type of 4-step CGH can be used in an off-axis convex aspherical mirror interferometric system with double CGHs, while the signal-to-noise ratio (SNR) of the interferogram is high enough.

Delta modulation (DM) is a classical technique that is generally applied to compress audio signals with a negligible amount of computation. Recently, it has been demonstrated that a similar approach can be applied to provide a moderate degree of compression, and at the same time maintain favorable coding fidelity, in compressing digital Fresnel holograms. The downside of this method is that it is necessary to determine an optimal step size for each of the source holograms through a trial and error process. In this paper we attempt to overcome this problem with adaptive delta modulation (ADM). Being different from the classical DM, the step size in ADM is automatically adjusted according to the intensity variation of the hologram. Experimental evaluation reveals that our proposed method is capable of attaining a compression ratio of 32 times without the need of determining the step size for each hologram. Hence, the proposed technique is useful for any holographic video system where holograms are needed to refresh at video rate. In addition, the proposed technique maintains favorable fidelity on the reconstructed images, and the complexity of both the encoding and decoding process is so small that they can be regarded as near computation-free operations.

Experimental studies of holographic thermal stability in phenanthrenequinone (PQ)-doped poly(methyl methacrylate-co-methacrylic acid) [P(MMA-co-MAA)] photopolymers are presented. A possibility to improve the thermal stability of holograms is demonstrated by doping methacrylic acid (MAA) into the poly(methyl methacrylate) (PMMA) polymer matrix. MAA as a copolymerization monomer can form a more stable polymer matrix with methyl methacrylate (MMA) monomer and increase average molecular weight of photoproducts, which finally depress the diffusion of photoproduct. The optimized MAA concentration copolymerized into P(MMA-co-MAA) polymer matrix can bring nearly a month's lifetime of gratings, which is obviously an improvement over the usual PQ-PMMA material under thermal treatment.

The problem of registering point sets with outliers including noises and missing data is discussed in this paper. To solve this problem, a novel objective function is proposed by introducing an overlapping percentage for partial registration. Moreover, a novel robust iterative closest point (ICP) algorithm is proposed which can compute rigid transformation, correspondence, and overlapping percentage automatically at each iterative step. This new algorithm uses as many point pairs as possible to yield a more reliable and accurate registration result between two m-D point sets with outliers. Experimental results demonstrate that our algorithm is more robust than the traditional ICP and the state-of-the-art algorithms.

Although discriminative locality alignment (DLA), which is based on the idea of part optimization and whole alignment, has better performance than classical methods in feature extraction, DLA is too overly sensitive to the values of the parameters and falls short of exploiting the full supervision information. We propose a novel supervised feature extraction method, named enhanced discriminative locality alignment (EDLA), for robust feature extraction. EDLA is not sensitive on the choice of the parameters, and both the local structure and class label information are taken into consideration in EDLA algorithm. Moreover, a kernel version of EDLA, named kernel EDLA, is developed through applying the kernel trick to EDLA to increase its performance on nonlinear feature extraction. Experiments on the face databases demonstrate the effectiveness of our methods.

We propose a simple skeletonization method for gray-scale fringe patterns. The proposed method is based on the gradient vector field (GVF) of a given image. We establish an appropriate complex-valued cost function using a second-order oriented partial differential equation for calculating the GVF, in which the fringe orientation can act as a powerful aid to perfect the process. We test the proposed method on numerically simulated and experimentally obtained fringe patterns, respectively. The experimental results show that the proposed method performs effectively.

The Hough transform is a well-known method for detecting lines. The standard Hough transform (SHT) uses a straight line equation parameterized by an angle and a distance, so the axes of the Hough space are continuous and it is difficult to determine their optimal resolutions for digitization. To resolve this difficulty, we propose a discrete Hough transform (DHT) using line segment representation for line detection. The end points of line segments are used as parameters, so the resolutions of the axes can be easily determined and accumulated bins can be easily smoothed for noise suppression. Therefore, the proposed DHT is more appropriate for detecting isolated lines than the SHT.

In dice recognition, there are several situations that may cause dice image identification problems, including the color of background being the same as the dice, the shape of the dice being round, or the dice touching each other. Especially when the camera zooms in or out, the pip sizes become irregular. We analyze the dice structure features to develop an intelligent memorized least-distance search method (IMLDSM) that can achieve accurate dice detection. Compared to other schemes, our method has two major advantages: (i) Unlike other schemes using complicated classification methods to segment the dice, we adopt a novel, simple, and effective method to analyze dice structure features to achieve more accurate recognition results and (ii) the IMLDSM solves the problems of image zooming in and out, which other methods cannot. After over 250 test images that include different shapes, styles, sizes, and colors used in simulations, this scheme is proven to achieve 100% dice image identification.

In scene-based nonuniformity correction (NUC) methods for infrared focal plane array cameras, the statistical approaches have been well studied because of their lower computational complexity. However, when the assumptions imposed by statistical algorithms are violated, their performance is poor. Moreover, many of these techniques, like the global constant statistics method, usually need tens of thousands of image frames to obtain a good NUC result. In this paper, we introduce a new statistical NUC method called the multiscale constant statistics (MSCS). The MSCS statically considers that the spatial scale of the temporal constant distribution expands over time. Under the assumption that the nonuniformity is distributed in a higher spatial frequency domain, the spatial range for gain and offset estimates gradually expands to guarantee fast compensation for nonuniformity. Furthermore, an exponential window and a tolerance interval for the acquired data are introduced to capture the drift in nonuniformity and eliminate the ghosting artifacts. The strength of the proposed method lies in its simplicity, low computational complexity, and its good trade-off between convergence rate and correction precision. The NUC ability of the proposed method is demonstrated by using infrared video sequences with both synthetic and real nonuniformity.

Bone age assessment is a common radiological examination used in pediatrics to diagnose the discrepancy between the skeletal and chronological age of a child; therefore, it is beneficial to develop a computer-based bone age assessment to help junior pediatricians estimate bone age easily. Unfortunately, the phalanx on radiograms is not easily separated from the background and soft tissue. Therefore, we proposed a new method, called the grayscale-histogram morphology algorithm, to segment the phalanges fast and precisely. The algorithm includes three parts: a tri-stage sieve algorithm used to eliminate the background of hand radiograms, a centroid-edge dual scanning algorithm to frame the phalanx region, and finally a segmentation algorithm based on disk traverse-subtraction filter to segment the phalanx. Moreover, two more segmentation methods: adaptive two-mean and adaptive two-mean clustering were performed, and their results were compared with the segmentation algorithm based on disk traverse-subtraction filter using five indices comprising misclassification error, relative foreground area error, modified Hausdorff distances, edge mismatch, and region nonuniformity. In addition, the CPU time of the three segmentation methods was discussed. The result showed that our method had a better performance than the other two methods. Furthermore, satisfactory segmentation results were obtained with a low standard error.

Edges characterize the boundaries of objects in images and are informative structural cues for computer vision and target/object detection and recognition systems. The Canny edge detector is widely regarded as the edge detection standard. It is fairly adaptable to different environments, as its parametric nature attempts to tailor the detection of edges based on image-dependent characteristics or the particular requirements of a given implementation. Though it has been used in a myriad of image processing tasks, the Canny edge detector is still vulnerable to edge losses, localization errors, and noise sensitivity. These issues are largely due to the key tradeoff made in the scale and size of the edge detection filters used by the algorithm. Small-scaled filters are sensitive to edges but also to noise, whereas large-scaled filters are robust to noise but could filter out fine details. In this paper, novel edge detection kernel generalizations and a shape-dependent edge detector are introduced to alleviate these shortcomings. While most standard edge detection algorithms are based on convolving the input image with fixed size square kernels, this paper will illustrate the benefits of different filter sizes, and more importantly, different kernel shapes for edge detection. Moreover, new edge fusion methods are introduced to more effectively combine the individual edge responses. Existing edge detectors, including the Canny edge detector, can be obtained from the generalized edge detector by specifying corresponding parameters and kernel shapes. The proposed representations and edge detector have been qualitatively and quantitatively evaluated on several different types of image data. Computer simulations demonstrate that nonsquare kernel approaches can outperform square kernel approaches such as Canny, Sobel, Prewitt, Roberts, and others, providing better tradeoffs between noise rejection, accurate edge localization, and resolution.

Biometric identification is an emerging technology that can solve security problems in our networked society. A reliable and robust personal verification approach using dorsal hand vein patterns is proposed in this paper. The characteristic of the approach needs less computational and memory requirements and has a higher recognition accuracy. In our work, the near-infrared charge-coupled device (CCD) camera is adopted as an input device for capturing dorsal hand vein images, it has the advantages of the low-cost and noncontact imaging. In the proposed approach, two finger-peaks are automatically selected as the datum points to define the region of interest (ROI) in the dorsal hand vein images. The modified two-directional two-dimensional principal component analysis, which performs an alternate two-dimensional PCA (2DPCA) in the column direction of images in the 2DPCA subspace, is proposed to exploit the correlation of vein features inside the ROI between images. The major advantage of the proposed method is that it requires fewer coefficients for efficient dorsal hand vein image representation and recognition. The experimental results on our large dorsal hand vein database show that the presented schema achieves promising performance (false reject rate: 0.97% and false acceptance rate: 0.05%) and is feasible for dorsal hand vein recognition.

The support vector machine (SVM) has become a popular classifier in pattern recognition, computer vision, and other fields. Traditional SVM may result in a nonrobust solution for classifying complex data because its separating hyperplane only reflects the marginal distance information of isolated support vectors, while discarding some useful class structural information. In this paper a new support vector classifier with neighborhood preserving constraint is proposed to enhance the support vectors by preserving the local geometric structure on the manifold of within-class samples. This structure can be represented as a weighted graph matrix and regulated by adding a preprocessing transform in standard SVM. Experimental results validate its effectiveness with comparison to related methods on several synthetic and real-world data sets and show its competence, especially for classifying high dimensional data in a small sample size case.

As video data from a variety of different domains (e.g., news, documentaries, entertainment) have distinctive data distributions, cross-domain video concept detection becomes an important task, in which one can reuse the labeled data of one domain to benefit the learning task in another domain with insufficient labeled data. In this paper, we approach this problem by proposing a cross-domain active learning method which iteratively queries labels of the most informative samples in the target domain. Traditional active learning assumes that the training (source domain) and test data (target domain) are from the same distribution. However, it may fail when the two domains have different distributions because querying informative samples according to a base learner that initially learned from source domain may no longer be helpful for the target domain. In our paper, we use the Gaussian random field model as the base learner which has the advantage of exploring the distributions in both domains, and adopt uncertainty sampling as the query strategy. Additionally, we present an instance weighting trick to accelerate the adaptability of the base learner, and develop an efficient model updating method which can significantly speed up the active learning process. Experimental results on TRECVID collections highlight the effectiveness.

In this paper, we propose an eye tracking system using a variable parallax barrier capable of providing the utmost natural stereo images. The variable parallax barrier consists of four sub-barriers, and a new cross connector composed of 640 lines flexible-printed-circuit is designed to create a sub-barrier. A depth camera based on the time-of-flight theory is utilized to implement an eye tracking system for an observer. The variable parallax barrier located in front of a monitor will be operated and controlled electrically through serial communication according to the values of coordinates gained by the camera. We compared the performance of the variable parallax barrier with that of other general systems via computer simulation.

This research analyzed key technologies, including object tracking and image matching, for realizing a television guidance system and proposed multiple kernels matching for precise television guidance. A semiphysical simulation system was designed to test the effectiveness of the proposed method. The experimental results showed that this method performed well in a television guidance system and did better than a template matching method.

A simple but effective phase analysis method for the fringe pattern that occurs in two superposed grating marks applied in the previously designed dual-grating-based alignment scheme for lithography is proposed. First, the fringe pattern is processed and analyzed using a frequency domain method based on two-dimensional (2D) Fourier transform, and the 2D notch filter is appropriately designed to select the useful spectrum to obtain the target phase information. Further, phase difference of two sets of fringes is computed to acquire the alignment offset. Numerical simulation and experiment are both performed to verify this method. Finally, certain analysis about the error of phase difference extraction in the fringe pattern and precision of alignment are also presented. The results indicate that the background and noise of the fringe pattern can be efficiently filtered and target phase information can be extracted with high accuracy through this method.

Changes have been made to this article. See the full text for a description of the changes.

Changes have been made to this article. See the full text for a description of the changes.

Changes have been made to this article. See the full text for a description of the changes.