This PDF file contains the editorial “Visual Expectations” for OE Vol. 47 Issue 04

This letter develops a novel and fast framework called APLPP to tackle the face recognition task by combining locality preserving projections (LPP) with the affinity propagation clustering method. Unlike LPP, which uses all training images to identify a test image, our affinity propagation LPP (APLPP) uses much fewer images, free of noise, for identification. Thus APLPP is more computationally efficient than LPP. Comparative experiments also indicate that APLPP outperforms LPP regarding the recognition rate.

We have explored the use of index-guiding liquid-core (LC) photonic crystal fiber (PCF) as a robust platform for measurements of solutions of trace volume using normal and surface-enhanced Raman scattering (SERS). The LC PCF was fabricated by selectively sealing the cladding air channels at the distal ends of a hollow-core PCF while leaving the center core open, using a fusion splicer. Utilizing a 30-cm-long LC PCF with the entire center core filled with the ~0.1-μL solution of interest, we have obtained normal Raman spectra of water, ethanol, and 1 vol% ethanol in water. Sensitive and reproducible SERS detection of 1.7×10^-7 M thiocyanate anions (≈14 ppb of NaSCN) in water has also been achieved.

A 16- and a 32-element irregular optical phased array based on silicon-on-insulator materials were fabricated. Such a device consists of an array of irregularly spaced single-mode waveguides, each of which has a specific length to give an appropriate phase retardation controllable by the wavelength. The optical beam can be steered continuously in the range of about 0 to 3 deg, corresponding to the wavelength varying from 1550.7 to 1551.9 nm.

A novel ultrawideband (UWB) pulse generation method using hybrid photonic microwave filters is proposed and demonstrated. Both electrical and optical delay are employed to construct microwave filters. The coefficients can be set to be either positive or negative by fiber chromatic dispersion and polarization modulation techniques, respectively. The generated UWB pulse has bandwidth larger than 1.8 GHz and can be used in multiband modulation UWB-over-fiber systems.

Previous studies showed that two- and three-waveband color-mixing methods perform the optical equivalent of two- and three-wavelength band ratio calculations that are typically implemented using multispectral imaging to enhance target classification and detection. This paper presents a prototype two-waveband color-mixing binocular device for enhancing visual target detection and classification, as tested using Ishihara test cards. Target identification for the test cards in this study was improved by using two-waveband color-mixing binoculars fitted with filters centered at wavelength pairs selected according to the criterion of uniform background. The test-card imaging results demonstrate that color-mixing binoculars can be used to greatly enhance target identification and detection.

A method of surface figure measurement is described based on the transmitted wavefront of an optical element obtained from a Mach-Zehnder interferometer. Given known values for the refractive index and center thickness, along with the sample's transmitted wavefront, the unknown surface profile is reconstructed in a deterministic way. The technique relies on knowledge of one of the surfaces of the element, such as an easy-to-measure plano or spherical surface, and is well suited for testing aspheric surfaces. Reverse raytracing is used to bring the transmitted wavefront from the detector to the unknown surface considering the refraction at the surfaces in the system. Reverse raytracing also removes the effects of transmission through a thick lens and the induced aberration associated with the interferometer. In the interferometer, the wavefront transmitted through the sample is tested against a plano reference. This method also has the ability to make measurements on multiplexed surfaces, such as a lenslet array, which traditionally cannot be measured without moving the sample. The surface profile of a plano-convex lens has been produced and verified against other metrology techniques for calibration purposes. Surface measurements on a cylindrical lens and a lenslet array are also presented.

Operations with hidden optoelectronic grid patterns for measuring distances from a camera to an object were described in recent papers. In this paper, the possibility of performing metrological teleoperations with digital moiré patterns processing is discussed. We introduce two new processes: (1) instead of using hidden grids as in previous works, we digitally apply contrasted Ronchi grids to the images by an AND operation; (2) the process is related to the generation of moiré fringes. We perform this operation at two slightly different camera-object distances where the camera displacement ΔL is known. By using this method it is possible to measure both the object dimensions and the distance between the object and camera in the same operation. In a previous paper a relative uncertainty of less than 10% for a distance of 40 m from a photographic analogue camera to an object was reported. In the experimental laboratory demonstration presented in this paper using our method of digital moiré pattern processing, it was possible to reduce the uncertainty to 1.2% for a camera-object distance of 2 m and to 4% for 12 m, using an object dimension of 30 cm. Experimental results for several camera positions are presented along with sources of uncertainties. We also present concluding remarks and prospects for future work.

Wheatstone invented the first stereoscopic display on record in 1834. Numerous approaches to the display of stereo imagery have been demonstrated since; however, all suffer from various drawbacks. Stereoscopic displays typically require the user to wear special headgear. Autostereoscopic displays typically have tight limitations on the position of the viewer's head. We investigate an architecture consisting of two readily available, inexpensive twisted nematic liquid crystal display (TN-LCD) panels sandwiched together to form a compact, rugged stereoscopic display. We describe the theory of operation, the experimental determination of the liquid crystal display modulation characteristics, and modifications to the theory of operation, as a consequence of the experimental results.

A white organic light-emitting diode (WOLED) with an undoped structure based on a novel starburst fluorene derivative of 1,2,3,4,5,6-hexakis(9,9-diethyl-9H-fluoren-2-yl) benzene (HKEthFLYPh) as an energy transfer layer was fabricated by the thermal vacuum deposition method. N,N′-di(naphthalen-2-yl)-N,N′-diphenyl-benzene (NPB) and tris(8-hydroxyquinolinato) aluminum (Alq) were used as the blue and yellow-green emission layers, respectively. The structure of the device was indium-tin-oxide (ITO)/NPB/HKEthFLYPh/Alq/Mg:Ag. The results demonstrated that the triple-layer device had a white light emission with a maximum luminance of 8800 cd/cm² at 15 V and a stable current efficiency from 1.8 to 1.4 cd/A at various bias voltages ranging from 5.5 to 15 V. The electroluminescent (EL) spectra overlaid from 400 to 700 nm with a full width at half maximum (FWHM) of 190 nm, which covered the whole visible wavelength region. The Commission Internationale de l'Eclairage (CIE) chromaticity coordinates showed (x=0.29,y=0.36) at 8 V and changed from (x=0.31,y=0.38) to (x=0.26,y=0.31) under bias voltage from 5 to 12 V.

Optically pumped solid-state lasers with Nd:YAG may have to operate over a wide range of temperatures. We designed and fabricated a diode double end-pumped Nd:YAG laser for free space laser communication. Various laser beam parameters have been characterized for the same application. The temperature dependence of the effective stimulated emission cross section for ⁴F_3/2 → ⁴I_11/2 transition and fractional thermal loading of Nd:YAG are determined using a planar resonator with two collimated and focused pump beams from fiber-array package laser diodes at 808 nm. The pump power-induced thermal lensing is used to stabilize the cavity. The diode double end-pumped Nd:YAG laser possesses an extremely good beam profile that exactly matches the theoretical Gaussian intensity distribution up to a diode current of 30 A. After that the ellipticity slightly increases, indicating deviation from the circular symmetry of beam, which may be due to the thermally induced birefringence of the Nd:YAG crystal offered to the polarized laser beam. The thermal lens focal length decreases with an increase in the absorbed pump power, similar to the case of a lamp pumped Nd:YAG laser and a diode pumped Nd:YVO₄ laser. All the results indicate that the laser beam characteristics are useful for high data rate free space laser communication links.

A new configuration for an erbium-doped fiber laser is reported. It incorporates a linear cavity with fiber loopback and a tunable bandpass filter (TBF). This configuration suppresses the amplified spontaneous emission and achieves a highly stable output power of more than 18 dBm at 1560 nm. A standard spectrum is obtained with TBF adjustment.

A long-period-grating-based fiber optic Michelson modal interferometer with coherence addressing and heterodyne interrogation is studied as a sensing structure for measuring environmental refractive index, temperature, and liquid level. The effects of several system parameters on the measurements are investigated. Experimental results show that the sensitivity to the external refractive index increases with the order of cladding mode and with a reduction of the fiber diameter. The decrease of the fiber diameter from 125 µm down to 70 μm enhances the sensitivity to the external index by a factor of 2.7. It is also shown that the use of a silica-core fiber increases the sensitivity to the external index by a factor of 1.4 and reduces the thermal sensitivity by a factor of 2.5 compared to a standard fiber.

We experimentally investigated the relationship between sensitivity and diaphragm thickness in a glass-based guided-wave optical pressure sensor using intermodal interference between the fundamental TM-like and TE-like modes. The sensor consists of a rectangular diaphragm and a straight single-mode waveguide on the diaphragm. The sensitivity is theoretically known to be inversely proportional to the square of the diaphragm thickness. In this study, to examine this relationship, four sensors with diaphragm thicknesses of 0.30 mm, 0.22 mm, 0.20 mm, and 0.15 mm were fabricated. The area of the diaphragm was 10 mm×10 mm. For the waveguide position nearest to the center of the diaphragm, the measured sensitivities almost agreed with the theoretical ones.

Microring resonators (MRs) are important photonic devices for large-port-count photonic circuits owing to their micrometer-scale device sizes. We describe the implementation of a 4×4 wavelength-reconfigurable photonic switch consisting of eight tunable MRs fabricated on a less expensive material platform: silicon on insulator. Wavelength reconfiguration is achieved through independent thermo-optic tuning of MRs with localized Nichrome microheaters fabricated on the same silicon-on-insulator substrate. A free spectral range of 18 nm and a 3-dB linewidth of 0.1 nm were observed for the fabricated MRs with a diameter of approximately 10 μm. The switch device shows negligible channel crosstalk (<0.01 nm) and moderate switching response time (<1 ms). The switch can potentially be scaled up to benefit the development of large-scale integrated photonics.

This paper presents the results of a successful bidirectional free-space optical link across 16 km to a modulated retroreflector array. The link was implemented at the Naval Research Laboratory's Chesapeake Bay Detachment laser test range. A 6-W cw 1550-nm class 1 M interrogation beam was used to illuminate an array of three modulated cat's-eye retroreflectors located on a tower across the Chesapeake Bay on Tilghman Island. The modulated retroreflectors had a diameter of 16 mm and were arranged in a triangular pattern with a spacing of 30 cm. The interrogating terminal employed a 100-μrad divergence and a high-speed pointing and tracking system to maintain link alignment. Link testing occurred over 12 days in the months of September, October, and November of 2006. Topics presented in this paper include the link scenario for the 16-km free-space optical link, the link budget, and terminal designs, as well as link acquisition and performance. Link performance results presented include data transmission throughput, scintillation data, and pointing and tracking results.

We derive theoretical results on soliton interactions and timing jitter in soliton transmission systems by use of super-Gaussian filters of high order. It is shown that the soliton interactions and timing jitter can be effectively suppressed by filters of various orders. We get that the minimum value of two-soliton separation is maintained almost constant during propagation for different filter orders. The optimal filter for sliding frequency in suppressing soliton interaction is determined. We also show that the higher the filter order is, the better the improvement of the timing jitter is.

We analyze adaptive maximum-likelihood sequence estimation in the presence of chromatic dispersion for optical communication with on-off keying and a direct-detection receiver. The study focuses on two probability density function estimation techniques: parametric and nonparametric. We present a comparison analysis of the performance difference between the two techniques and validate that with experimental results.

We propose and demonstrate a novel method for a radio-frequency photonic arbitrary waveform generator based on a tunable, multiwavelength pulse sequence and wavelength-to-time mapping induced by fiber chromatic dispersion. We simulate and experimentally demonstrate the generation of an arbitrary waveform and obtain burst single-tone, frequency modulation, and phase modulation signals. We also analyze the potential and primary limitations in the proposed architecture.

Growth of conical particles in carbon films deposited on silica glass fibers prepared by thermal chemical vapor deposition is investigated. The results show that the size and number of conical particles on the silica glass fiber increase with the film thickness and deposition temperature, but this effect is reduced when the carbon films are deposited on silica glass plates. The growth of conical particles on the silica glass fiber is mainly due to the small cross-sectional area of the fibers. These conical particles are against the hermetic property of carbon-coated optical fibers. We propose a method to minimize conical particles in carbon films on silica glass fibers.

The implementation of an encoder-decoder over two-dimensional (2-D) optical code-division multiple-access (OCDMA) networks is discussed. This coding uses extended-quadratic-congruence code for wavelength hopping, and optical-orthogonal code for time spreading. Due to the cyclic code pattern of this 2-D code family, one novel compact decoder based on arrayed-waveguide gratings can be used to simplify the OCDMA network architecture.

We present a complete analysis on improving the gain flatness of ultrabroadband tellurite fiber Raman amplifiers (TFRAs) by optimizing the parameters of multiwavelength pumps. Compared to conventional TFRAs, our amplifier has low gain ripple despite the ultrawide amplification bandwidth: well below 3.78% (5.66%, 11.98%) with respect to the average net gain 10 dB over a 120-nm (140-, 160-nm) bandwidth. In addition, we investigate the fractional gain contribution from each pump wavelength for the optimal 140-nm TFRA, and observe that the configuration is effective in equalizing the peculiar dual-peak gain spectra produced by multiple pumps. Finally, we calculate the noise figure for the 140-nm TFRA with a vibration less than 3 dB.

Continuous efforts to develop low-loss flexible waveguides, to transmit mid-IR laser energy for minimally invasive surgical and diagnostic procedures, have been carried out by us and other groups. We have introduced sulfide dielectric films coated over an Ag reflecting layer as another potential solution. The metal sulfides used have high transparency in the IR spectrum, and their thickness can be tailored to minimize the attenuation over a selected wavelength range. The high refractive index contrast of the two metal sulfide materials enables us to produce multilayer hollow waveguides. These waveguide will have low attenuation in both straight and bent conditions, low sensitivity to coupling and to surface roughness, and a broad wavelength range. The lowest loss for a straight guide, measured at 1.55 μm for a 1,000-μm-bore Ag/CdS/PbS/CdS hollow glass waveguide (HGW), was 0.06 dB/m. This loss is three times less than that measured for a single-layer Ag/CdS-coated HGW at 1.55 μm. A theoretical simulation applying the same conditions showed the same pattern with a good potential for improvement.

Holographic two-dimensional beam steering using a pixellated spatial light modulator (SLM) is a flexible and accurate technique to implement advanced space-switching, building-block functions for optical network nodes. We present the design of a specific fiber array for large-capacity holographic switches. We use two-dimensional and irregular array topology to optimize the space-bandwidth product of the SLM and to avoid crosstalk due to the coupling of higher diffraction orders. The fiber-array module is integrated by inserting the fibres through a pair of etched silicon plates aligned and fixed using a steel mount. The device is tested through near-field and fiber-to-fiber free space coupling tests. An average fiber-to-fiber insertion loss of 1 dB is achieved for a prototype containing 64 fibers.

This work points out that a modification of the fringe analysis method proposed by Kreis may serve as a normalization and filtering method for electronic speckle-pattern interferometry (ESPI) fringes. By rotating a half-plane in the frequency space, a fringe pattern may be normalized without being distorted significantly. If a passband filter is used during the rotation, a smoothed fringe pattern is obtained. Experimental verification is presented using images obtained from ESPI.

Link-budget calculations are a common way to assess system parameters, such as the required transmitter power and receiver sensitivity, in free-space optical (FSO) communication systems. One of the biggest challenges for long-range FSO deployment is its signal propagation under turbulent atmospheric conditions, which produce intensity fluctuations. Methods to estimate atmospheric-fading loss in radio-frequency systems cannot be adapted to the FSO channel. Until now no general closed-form methods have been developed to describe the fading loss in such a channel. A method to calculate the losses due to scintillation fading in the threshold approach, based on lognormal statistics of the received power, is presented.

An experimental study has been made on the contribution to the effective scintillation index due to aperture averaging and interference effects when using multiple retroreflectors in free-space optical links. These studies are of relevance to asymmetric data links where modulating retroreflectors are used at the remote end of the free-space optical link. For closely spaced retroreflectors the effect of coherent interference at the receiver is seen to increase the effective variance of the received signal, whereas spatial averaging is apparent for more widely spaced retroreflectors. The scintillation index, probability density functions, and fade rates are all affected by the interference. Experiments were conducted over both a short-range (500 to 800 m) and a long-range (16 km) link. The long-range link used three retroreflectors having a spacing that was large enough that interference effects contributed minimally to the observed variance. However, the variance clearly depended on the number of retroreflectors. In addition to measuring the scintillation index, images of the returned light were recorded using a fast framing camera. These experiments were conducted over land and mixed water-land terrains in the case of the short-range links, and exclusively over water in the case of the 16-km link from Chesapeake Beach to Tilghman Island.

This paper reports on the development of support vector machines for polarimetric radar target classification. Automatic classification of radar signatures of man-made objects has been shown to be improved noticeably by optimum selection of transmitting and receiving states of polarization. However, the optimum polarization states may be target-dependent. Thus the need for an optimum classifier to correctly label radar signatures associated with different targets when sensed at differing pairs of transmitting and receiving polarization states. To generate radar signatures of targets at various transmit-receive pairs of polarization angles from vertical and horizontal states, the technique of polarization synthesis was applied. Then statistical attributes from each radar signature were used for its representation. Finally, support vector machines, using a number of kernels such as linear functions, polynomials, Gaussian radial basis functions, exponential basis functions, linear splines, and basis spline functions, were developed and used on real fully polarimetric radar data. The results indicate that a small subset of polarization angles are sufficient for generating signatures needed for training a classifier for optimal separation of polarimetric-diverse signatures. Moreover, the classification performance in terms of receiver operating characteristic curves shows that Gaussian kernels outperform other kernels that we have used.

Machine vision of specific objects on natural backgrounds in the IR is an extensively studied subject. Characterizing the clutter is essential in order to evaluate a sensor's performance under various conditions. The Ben-Yosef model is the main one used for the characterization and parameterization of rural background IR images in terms of image statistics and texture. However, to the best of our knowledge, no such parameterization of urban images has been established. The aim of this work is a comparison between statistical and spatial characteristics of urban and rural scenes in the IR and their diurnal dynamics. We conclude that the Ben-Yosef model cannot fully describe the urban scene characteristics, mainly due to the model assumptions regarding the uniform spatial structure of the emissivity and of the magnitude of the solar flux over the scene. Experimental results show that, although daytime urban scenes have high variance in the IR, they have a less complex spatial structure than nighttime images, which are characterized by much lower variance.

In the previous article, a comparison between the statistical and the spatial properties of IR images of rural and urban background was presented. Analyzing the characteristics of these two backgrounds yielded noticeable differences in most of the extracted parameters and their diurnal patterns. Furthermore, the experimental data pose a remarkable deviation from those predicted by the most accepted model for desert terrain IR images (Ben-Yosef model). The effect that might be responsible for these discrepancies is the local scene topography, which is clearly enhanced in an urban environment. To investigate this hypothesis, we introduce a simple modification of the Ben-Yosef model that incorporates a simulated urban background. The comparison between the simulation and experiment shows good agreement. We conclude that the scene's topography in an urban background is the most important parameter that governs its statistical and spatial characteristics in the IR band.

Recent developments for long-wave infrared (LWIR) imaging polarimeters include incorporating a microgrid polarizer array onto the focal plane array. Inherent advantages over other classes of polarimeters include rugged packaging, inherent alignment of the optomechanical system, and temporal synchronization that facilitates instantaneous acquisition of both thermal and polarimetric information. On the other hand, the pixel-to-pixel instantaneous field-of-view error that is inherent in the microgrid strategy leads to false polarization signatures. Because of this error, residual pixel-to-pixel variations in the gain-corrected responsivity, the noise-equivalent input, and variations in the pixel-to-pixel micropolarizer performance are extremely important. The degree of linear polarization is highly sensitive to these parameters and is consequently used as a metric to explore instrument sensitivities. We explore the unpolarized calibration issues associated with this class of LWIR polarimeters and discuss the resulting false polarization signature for thermally flat test scenes.

Human automated target recognition (ATR) capability holds important tactical value in military as well as civilian applications. Unmanned systems equipped with real-time human ATR sensors and software will serve to detect potential threats before human forces encounter them. Unattended ground stations may use human ATR in search and rescue applications, to alert rescue teams when help is necessary. The algorithm proposed in this study utilizes infrared imagery to detect people based on the radiance and shape of the human head. The algorithm works in a three-step process of segmentation, feature extraction, and classification. First, the IR image is segmented to reveal only human skin areas (e.g., arms, legs, heads). Next, three morphological features are extracted from each segmented object of interest. Finally, a classifier will use the features to determine whether the object is a head or a nonhead, based on previous algorithmic training. Two types of classifiers were tested in this study: a k-nearest-neighbor classifier and various neural networks. Results show that using a neural network classifier, 97% accuracy in head identification is possible after examining two sequential uncorrelated frames containing the same human head in different views. Tests in a desert environment at nighttime show that the majority of test subjects are detected, with few false positives.

This paper presents the derivation, implementation, and testing of an improved point spread function (PSF) reconstruction technique for the University of Victoria's dual-deformable-mirror (DM) woofer-tweeter (W/T) adaptive optics (AO) system. The methodology has been tested on numerical models and implemented on an experimental dual-DM AO system. The methodology is based on the data saved by the AO system during the science exposure. These data are later used in the postprocessing stage to reconstruct the PSF. Although the results are unique to the present W/T AO bench, the proposed PSF reconstruction methodology will be applicable to other dual-DM systems and to multi-DM AO systems.

For progressive transmission, the limited data streams with high encoding efficiency seem to impose a limit on the sustainable number of significant coefficients to which we can allocate bits with efficiency. But sustained improvement in transmission technology over time can offset the effects of wasting and nonreplenishable data and provide high encoding efficiency for progressive transmission. Here we show necessary and sufficient conditions for steady growth in encoding efficiency.

This paper presents a public-key-based optical image cryptosystem with adaptive steganography for practical secure communications. The optical image cryptosystem employs a hybrid architecture for ciphering and deciphering in which double random-phase encoding and asymmetric encryption algorithms are utilized for images and session keys, respectively. The session key is safely protected and transmitted by using an asymmetric encryption algorithm and an adaptive steganographic scheme, respectively. To perform the adaptive steganographic scheme, a sorting technique is used to find the suitable embedding position in the embedding domain, a least-significant-bit truncation algorithm is presented to find the invariant hiding order, and a quantization-based data-embedding algorithm is utilized to hide message bits. Experimental results show that the proposed scheme is superior to that of a previous one due to Lin et al., no matter what embedding domain, quantization level, and message size are used. Especially, compared with the latter scheme a large improvement (22.56 dB) of image quality is achieved by using the proposed adaptive steganographic scheme.

Fundamental-matrix and key-frame selection constitute one of the most important techniques for full 3-D reconstruction of objects from turntable sequences. This paper proposes the new methods for these selection problems in 3-D reconstruction from uncalibrated sequences taken with a turntable and the Fotonovo camera system. Also, we propose a projection-matrix refinement for accurate full 3-D reconstruction. Our approach utilizes single-axis motion. To evaluate the fundamental matrix, camera calibration and 3-D registration are generally needed. Our main contribution is a method for robustly determining the corresponding points between two images, and for accurately filling gaps in a sparse object so as to make surface reconstruction tractable. We do not need all frames, but only few pairs of images (key frames). The key-frame selection has the advantage in camera pose estimation and 3-D scene reconstruction of reducing the computational costs. Experimental results on real image sequences demonstrate accurate object reconstructions and robustness of the proposed methods.

Although two-photon fluorescence microscopy has quite good optical sectioning ability, it still suffers from image blurring. The Richardson-Lucy deconvolution algorithm has been routinely employed to reduce image blurring because it is well suited to characterizing the Poisson statistics of the photomultiplier. However, noises are amplified in this iterative procedure, so a denoising technique should be introduced before performing the Richardson-Lucy deconvolution. An algorithm that prefilters undesired noise by modifying the robust anisotropic diffusion before performing the regularized Richardson-Lucy deconvolution is proposed. Experiments have shown that noise is almost eliminated, sharp edges are well preserved, and more details of structures are distinguished with this technique. Quantitative data of four evaluation criteria are provided to validate the performance of the proposed scheme. Lastly, we apply the proposed approach to the image restoration of real two-photon microscopic images.

The use of point sets instead of meshes is becoming increasingly more popular. We present a novel meshless approach for point set processing via partial differential equations (PDEs), which introduces the meshless local Petrol–Galerkin (MLPG) method to the field of graphics. The proposed approach neither needs to construct local or global triangular meshes, nor needs global parameterization. It is only based on local tangent spaces and local interpolated surfaces. By constructing the local symmetric weak form (LSWF) for every point, we can easily assemble PDE-specific mass and stiffness matrices. The corresponding sparse linear system can be solved with an iterative solver. The obtained results showed that the proposed approach can smooth noises on point set surfaces while preserving geometric features. Its efficiency is comparable with the traditional finite element method (FEM). The multiscale model of a point set surface can also be constructed using the proposed approach with different iteration times.

We propose a sharing method to progressively reveal a given important image in the recovery phase. In the encoding phase, the distributor utilizes the three frequency bands (low, middle, and high) of the given image to generate shadows according to three prespecified thresholds. In the recovery phase, the secret image cannot be revealed if the number of shadows a team collects is less than the lowest threshold. However, when the number of collected shadows reaches the prespecified low (or middle- or high) threshold, the team can reconstruct a low- (or middle- or high-) quality version of the secret image. In other words, the quality of the reconstructed image depends only on the number of shadows being received, rather than on which of the generated shadows are received. Each noise-like shadow is so small that it can be hidden in an ordinary image that is still several times smaller than the original image.

An algorithm for human-eye localization in images is presented for faces with frontal pose and upright orientation. A given face region is filtered by a highpass wavelet-transform filter. In this way, edges of the region are highlighted, and a caricature-like representation is obtained. Candidate points for each eye are detected after analyzing horizontal projections and profiles of edge regions in the highpass-filtered image. All the candidate points are then classified using a support vector machine. Locations of each eye are estimated according to the most probable ones among the candidate points. It is experimentally observed that our eye localization method provides promising results for image-processing applications.

This study proposes a novel reversible data-hiding method based on an iterative approach for palette-based images. In each iteration, the number of occurrences of palette color in the image is computed in order to identify the most and least frequently occurring colors in a palette for data hiding. Data are hidden by sacrificing the least frequent color and placing the most frequent color in its position in the palette to make a pair. After the most frequent color takes over the palette index of the least frequent color, two palette indices stand for the most frequent color. Therefore, one bit can be hidden in every pixel where the most frequent color occurs in the image. To make the host image reversible, the overhead information caused by sacrificing the least frequent color must be saved for image reconstruction. The performance of the proposed method is demonstrated on test images by showing the capacity and distortion. Several successful similar efforts have also been implemented for comparison. Experimental results indicate that the proposed method has a high embedding capacity and good marked-image quality.

Correspondence is one of the big challenges in machine learning and image processing. To match two high-dimensional data sets with a certain number of aligned training examples, a novel semisupervised method is proposed. It is mainly based on two manifold learning approaches: maximum variance unfolding (MVU) and locally linear embedding (LLE). We have modified MVU to a semi-supervised version to solve the correspondence problem. Additionally, the nonuniform warps and folds caused by employing LLE alone and the computational burden of MVU disappear when they are combined. The proposed algorithm outperforms traditional methods in accuracy and efficiency. Three examples are performed to demonstrate the potential of this method.

A robust and efficient method for overcoming the negative effects of long-time occlusion in the tracking process is presented. The proposed approach is based on the matching of multiple trajectories in time. Trajectories are sets of 2-D points in time and in a joint ground plane of the world coordinate system. In order to avoid mismatches due to possible measurement outliers, we introduce an integral distance between compared trajectories. The proposed method can also be considered as an interpolation algorithm for a disconnected trajectory during the blackout. Thus this technique solves one of the most difficult problems of occlusion handling: the matching of two unconnected parts of the same trajectory.

New adaptive correlation filters for reliable recognition of geometrically distorted objects in blurred and noisy scenes are proposed. The filters are based on modified synthetic discriminant functions. The information about objects to be recognized, false objects, disjoint background, additive noise, and expected degradations of targets and input scenes are utilized in an iterative training algorithm. The algorithm is used to design a correlation filter with a specified discrimination capability. Computer simulation results obtained with the proposed adaptive filters in test scenes are discussed and compared with those of various correlation filters in terms of discrimination capability and location errors.

We propose a novel method using a single catadioptric omnidirectional camera to track 3-D head positions in nonintrusive biometric systems. Existing methods have not been able to deal with cases in which the ground plane is nonorthogonal to the optical axis of the camera. To overcome this problem, our proposed method presents the following three improvements: (i) By using 1-D tracking of the feet and head positions combined with a circular constraint in images instead of conventional 2-D tracking methods, the accuracy and computational efficiency of the tracking process is significantly improved, (ii) based on the detected 2-D head position in images with the precalibration information of the camera, the 3-D head positions can be obtained, and (iii) the 3-D head positions can be obtained without having the optical axis of the camera orthogonal to the ground plane. This makes the proposed method feasible in practical environments that use omnidirectional camera systems. Experimental results showed that the proposed method was able to track 3-D head positions at real-time speed.

Multiview video is obtained by capturing a three-dimensional scene using many cameras simultaneously. Since adjacent view sequences have strong spatial redundancy as well as temporal redundancy, we can achieve additional coding gain by eliminating the spatial redundancy. In this paper, we propose view-temporal prediction structures that can be adjusted to various characteristics of general multiview video by separating them into temporal and view prediction structures. The proposed temporal prediction structure minimizes the average distance between a frame to be coded and its reference frames. The proposed view prediction structure considers the location of the I frame in anchor and the number of B frames to be inserted in anchor. We also propose a quantization parameter selection method for enhancing coding efficiency of views whose anchor frames are coded as B frames. Experimental results show that the proposed algorithms achieved 0.10 to 0.34 dB of peak SNR (PSNR) gain and reduced the variances of PSNR values of views by 28.26% on average against the results by the reference prediction.

Recent statistical methods of video background replacement are robust enough to operate in dynamic environments, but generally require very large computational resources and still have difficulty in clear segmentation of objects. We use a simpler running-average method to model a changing background, and a single global threshold vector, optimized by a genetic algorithm, instead of pixel-by-pixel thresholds. A fitness function is trained to evaluate segmentations by penalizing incorrectly recognized regions. Experimental results on real images show that our new approach outperforms an existing method based on a mixture of Gaussians.

A novel information security system is developed, employing quadrature multiplexing, to be implemented using optoelectronic devices. Two information signals are encrypted using the same code but two orthogonal functions, and then they are multiplexed together in the same domain. With orthogonal functions having zero cross-correlation between them, the encrypted information remains unaffected. Each encryption and multiplexing process can accommodate two information signals for a single code and hence for a single storage cell or transmission channel. The same process can be performed in multiple steps to increase the multiplexing capability of the system. The proposed security system can enhance the storage capacity and/or maximize the utilization of the available transmission bandwidth. For decryption, the composite encoded signal is correlated using the appropriate code and function. Computer simulation results show that the proposed security system is capable of dealing with both binary and gray-level images with the encrypted images remaining secure.

This PDF file contains the errata for “OE Vol. 47 Issue 04 Paper 2904921” for OE Vol. 47 Issue 04