This PDF file contains the editorial “Correcting the Record I: Plagiarism” for OE Vol. 46 Issue 10

We propose a new system of quantum key distribution via optical wireless communication links, where the required information, especially telephone conversation, can be secured by using a quantum code/decode (CODEC) technique incorporated in the networks. The entangled photons can be encoded into the classical information and then the decoded signal can also be retrieved. The proposed system consists of quantum key generation and uplink and downlink parts that can be implemented in the mobile telephone handset and networks. Such a system and technique show the feasibility of use for a perfectly security telephone networks.

A relief diffraction grating is holographically recorded in azo-polymer. The polymer layer under the grating serves as a waveguide for the light coupled by the grating. When a guiding condition is met, sharp minima appear in the transmitted spectrum and sharp maxima appear in the reflected spectrum. Since the resonance conditions for transverse electric (TE) and transverse magnetic (TM) polarized waves occur at different wavelengths, the effect can be used for fast wavelength encoding of a binary signal. The speed of such a device would be limited only by the speed of the encoding part, which changes the azimuth of the input linearly polarized light.

A continuous variable modulation frequency optical single sideband (OSSB) can be generated by a Sagnac interferometer and a continuous variable differential group delay (DGD) element of photonic crystal fibers (PCFs). Furthermore, the OSSB signals with different modulation frequencies can be generated simultaneously.

The concept of the simplest possible reflecting anastigmat is discussed, and anastigmats consisting of four spherical mirrors are introduced in this context as being the last remaining family for which the solution set has not been thoroughly explored. Burch's "plate diagram" method is introduced and used to derive a closed-form analytical solution for four-spherical-mirror anastigmatic telescope systems. This solution is then applied to mapping the solution space for four-spherical-mirror anastigmats. Two novel systems are revealed that represent the first published instances of axially symmetrical, all-spherical anastigmatic reflecting telescope designs with concave primary mirrors. Due to the completeness of the analytic description of the solution set, it also can be stated that there are no other design variants for this class of system.

Use of the capsule endoscope to inspect the digestive system, and in particular the intestine, for pathological change has recently been a great breakthrough in medical engineering. Some problems, however, need to be overcome. The field of view is not wide enough, and the image quality is not good enough. These drawbacks cause unclear and ambiguous digestive disease examinations by medical professionals. In order to solve these problems, the paper proposes a novel design for miniature lenses with a wide-angle field of view and good imaging quality. The lenses employed in the capsule endoscope would consist of a plastic aspheric lens and a glass lens, in a capsule 9.8 mm (W)×9.8 mm (L)×10.7 mm (H), associated with white LED light sources and a 256×256 CMOS array sensor of 10-µm pixel size. Experimental results prove that the lens field of view can be made as large as 86 deg, and the modulation transfer function for field of view 0 deg can be made 78.2% at 50-lp/mm spatial frequency and 53.3% at 100 lp/mm. Tolerance analysis shows that our design is feasible for manufacture, and consistent with the finished prototype.

Optical sparse-aperture systems can be designed to obtain a high resolution when imaging an astronomical object. These systems are the arrays synthesized by several small filled imaging systems. A principal experiment is set up for an optical sparse-aperture system by which imaging of an extended complex object is achieved. Image restoration of the direct output by the sparse-aperture system is performed by measuring the point-spread functions (PSF) and by using a Weiner filter. The correlation coefficient is proposed as a criterion to determine the optimal parameter and to evaluate the performance of the algorithms. The results show that among the three kinds of configuration models, the Tri-Arm array configuration can produce the highest resolution and largest correlation coefficient value after the restoration. Accordingly, the experimental data, demonstrate that an optical sparse-aperture system can achieve almost the same resolution and image quality as an equivalent filled system.

The 3-D reconstruction of an environment with high accuracy and real textures represents an important challenge for applications related to multimedia and cinematography. The complete development, from electronic design to algorithmic restitution of the environment, of a multispectral omnidirectional stereoscopic sensor that tackles this problem is presented. Although panoramic sensors exist, the vision system presented here has four channels of acquisition coupled to a projector of structured light emitting in the infrared. This original process separates the acquisition of color images from 3-D reconstruction. The panoramic color images are corrected using the International Color Consortium profile applied to images coming from the two cameras. The reconstruction of the environment uses only the information available in the infrared channel. An active calibration technique is also presented. Experimental results demonstrate the feasibility of this new class of multispectral omnidirectional sensors.

An ordinary digital camcorder was converted to a three-dimensional (3-D) camcorder by means of an attachment. The 3-D image can be viewed with the built-in monitor, or on a laptop computer display, or on a TV screen. The principle of operation is based on the manipulation of polarized light. Playback of the 3-D image is simple, and the camcorder attachment is small, rugged, and lightweight.

Imaging system performance can be described in the spatial domain, where the optical blur diameter is compared to the detector size, or in the frequency domain [modular transfer function (MTF) approach], where the optics cutoff is compared to the detector cutoff. Both comparisons provide a metric that is a function of Fλ/d, where F is the focal ratio, λ is the wavelength, and d is the detector size. Fλ/d is applied to three models: Schade's equivalent resolution (visible systems), Snyder's MTFA (MTF area; visible systems), and target acquisition (NVThermIP—an infrared system model). All models produced curves that exhibit a transition in the region 0.41<Fλ/d<1.0, representing a change from detector-limited to optics-limited performance. NVThermIP's contrast equations are simplified to easily calculate resolution and acquisition range. Trade-off analyses include range versus detector size, versus focal ratio, and versus field of view (FOV). When Fλ/d<2, no aliasing occurs. This may be important for medical imaging, where sampling artifacts may be interpreted as a medical abnormality, or for space probes, where it is impossible to obtain ground truth.

A two-dimensional light-emitting diode array is used to replace the viewing-zone-forming optics in-multiview full-parallax three-dimensional image display systems. Since the array is not working merely as the viewing-zone-forming optics but also as the backlight panel for the liquid-crystal display (LCD) panel, it allows constructing three-dimensional imaging systems having the same structure as the current LCD display. The designed system displays images with good depth sense.

Thermally induced errors were identified as a large error source during diamond turning of micrometer-size optical structures. We investigate the effects of spindle growth, application of cutting fluid mist, and temperature variation errors (TVEs), or thermal drifts, on the ability to hold tool position tolerances. It is shown how certain process variables, such as opening and closing of doors around the machine, affect the TVE. A first-order temperature model was derived to predict the TVE of the manufacturing process. The model uses the ambient temperature inside the machine enclosure because the part temperature could not be measured directly during machining. Documented long-term drift errors over 23 h were as large as 1.7 μm. Short-term drift errors from pass to pass were as large as 0.3 μm. Transient effects caused displacement shifts as large as 0.9 μm.

A novel scheme for an object's surface area measurement is proposed that is suitable for area computation of a planar object with smooth and irregular edges. This scheme consists of four steps. First, a photoelectric image collimation system is devised to obtain a target image of a detected object. Second, a multiscale active contour is applied in the defocusing and focusing image sequence so that it gradually converges to the target's contour edge from coarse to fine scales. Third, for the convergent active contour, two formulas for the area and centroid computation of a closed B-spline curve are applied to compute the image target's area and centroid exactly. Finally, a novel centroid-self-calibration technology is applied, which measures the pixel's size equivalence with the computed centroid and uses a dual-frequency laser to measure the object's true surface area exactly. An experiment on a circular aperture area measurement indicates that this scheme's repetition error decreases to 0.11%, when the control point number of the B-spline active contour is 25.

We present the measurement and graphical representation of spatial differential values of the surface roughness factor for various steel samples. The measurements were made by a newly developed optoelectronic sensor system comprising a light emitting diode (LED) and two phototransistors. The light beam from the LED illuminated an area of 1 mm² on the metallic surface. The reflected light and scattered light were captured by two different photo detectors. The sample surface was scanned using a computer numerical control (CNC) machine. The photocurrent signals acquired at each point on the surface were digitized, and a parameter was calculated to correspond to the degree of roughness of the surface at the given point. The measured roughness factor is compared with the readings of a standard instrument, and the instrument was calibrated to display the measurements in micrometers. The measured values processed by a personal computer provided a three-dimensional (3-D) mapping of the surface texture.

Modulating retroreflectors (MRRs) couple passive optical retroreflectors with electro-optic modulators to allow free-space optical communication with a laser and pointing-acquisition-tracking system required on only one end of the link. Recently, MRR using multiple quantum well (MQW) modulators have been demonstrated using a large-area MQW placed in front of the aperture of a corner cube. For a MQW modulator, the maximum modulation rate can range into the gigahertz, limited only by the RC time constant of the device. Most MRR systems have used corner-cube retroreflectors with apertures of about 1 cm, which require large, and hence high-capacitance, modulators. Thus data rates exceeding a few megabits per second are not possible. We describe a new kind of MQW MRR that uses a cat's-eye retroreflector with the MQW in the focal plane of the cat's-eye. This system decouples the size of the modulator from the size of the optical aperture and allows much higher data rates. A 45-Mbit/s free space link over a range of 7 km is demonstrated.

Interorbit links, intersatellite links, and deep space missions are certain key applications of free-space optical communication links. For efficient and better signal propagation ensuring minimum possible bit error rate (BER) and maximize signal-to-noise ratio (SNR), the laser source used for carrying information should be one in which the laser power and beam quality do not degrade due to vibrations, shock, and thermal cycling. As part of our attempt to design an efficient and suitable laser source for optical free-space communication, a diode double-end pumped and Q-switched Nd:YVO₄ laser is designed and fabricated. The thermally induced lens in the laser crystal brings the flat-convex cavity into geometric stability. A slope efficiency of 58.38% is observed in continuous wave (CW) multimode and 40.49% is observed in CW TEM₀₀ mode operation, which is sufficiently high for free-space optical communication. A minimum pulse width of 7.3 ns is observed corresponding to a peak power of 63.01 kW at 20 kHz. It can be seen that at lower Q-switch frequencies, the pulse width is short and the energy per pulse is high, whereas at higher Q-switch frequencies, the energy per pulse is low and the pulse width is long but the average power is high. The peak power increases with the absorbed pump power, similar to a lamp-pumped Nd:YAG laser. The maximum pulse energy observed is 430 μJ at 10 kHz. Below 20 kHz, no further increase in pulse energy is observed due to the lower lifetime of the upper laser level (~90 to 100 μs) of Nd:YVO₄ crystal. Changes in the laser beam profile with pump power have been studied. The major advantage of the Nd:YVO₄ crystal is the ability to retain short pulse width even at higher Q-switch frequencies like 100 kHz, which makes this laser suitable for ultrahard material processing at higher Q-switch frequencies.At full pump power, the pulse width varies from 7.3 ns at 20 kHz to 19.5 ns at 100 kHz.(partial abstract)

Optical array technology is an attractive method of achieving high power output using diode bars, which is different from using traditional diode stacks. Reflectors are the main optical elements in optical array diode lasers, and their influences of alignment errors on the output beam are analyzed using the matrix method. Analytical expressions of the beam size and deviation influenced by the misalignment of the reflectors are deduced, and the misalignment tolerances are also given. Based on the results, it is helpful to adjust the reflectors to achieve an output beam of good beam quality from the optical array diode lasers.

Optical access to combustion chambers via windows is desirable for combustion diagnostics as well as for laser ignition. By nature, combustion deposits can form on the inner surface of the light-transmitting window, leading to malfunction. We investigated whether a Nd:YAG ignition laser could cope with combustion-chamber deposits by means of ablation. In a 1.8-kW four-stroke internal combustion engine an optical window was installed to couple in the laser light. Ignition was carried out by a spark plug. Due to inherent high fuel and oil consumption, a deposit layer would form on the substrate within some tens of minutes. Elementary analysis showed carbonaceous as well as inorganic compounds gradually reducing light transmission. With cyclic 5-ns laser shots through the window, the pass-through stayed essentially free of deposits provided the energy fluence was around 10 mJ/mm2. Microanalysis showed evidence of the soundness of the principle. In addition, even single shots with a higher flux were enough to remove a relatively thick layer of deposits at once. Thus an optical window in an internal combustion engine can in principle be kept transmissive by the action of a compact solid-state laser.

In a typical optic fiber Bragg grating (FBG) strain measurement, unless made in an ideal static laboratory environment, the presence of vibration or often disturbance always exists, which often creates spurious multiple peaks in the reflected spectrum, resulting in a nonunique determination of strain value. We attempt to investigate the origin of this phenomenon by physical arguments and simple numerical simulation. We postulate that the fiber gratings execute small-amplitude transverse, vibrations changing the optical path in which the reflected light traverses slightly and nonuniformly. Ultimately, this causes the multipeak reflected spectrum.

Strain sensor calibration is investigated using extrinsic Fabry-Pérot interferometric (EFPI) fiber optic sensors. The approach is based on the Bessel harmonic components from the nonlinear EFPI output signal under sinusoidal excitation. For known sensor parameters of optical wavelength and gauge length, the local maxima and minima of each Bessel harmonic profile occur for specific strain levels. The theoretical Bessel harmonic profiles are shown and a calibration approach is proposed using local maxima and minima in selected Bessel harmonics. The signal from a colocated companion strain sensor can be calibrated by comparison to salient EFPI reference strains. An experimental implementation is demonstrated for a polyvinylidene fluoride (PVDF) piezoelectric strain sensor that is colocated with an EFPI reference sensor on a cantilever beam apparatus. The experimental strains at the local maxima and minima closely match the strains determined theoretically.

We describe the design of a waveguide Fabry-Pérot optical sensor with high sensitivity to surface refractive index change. The optical thickness and field can be accommodated in a high-refractive-index waveguide, leading to a high sensitivity. Incorporating the resonance structure further enhances the sensitivity.

Group-index birefringence in silicon-on-insulator photonic wire waveguides is determined through a polarization beating technique and a Fabry-Pérot resonance method. A large group-index birefringence, up to 0.67, is obtained as a result of the structural asymmetry and high field confinement of our waveguides. The group index and linear propagation loss are also determined. In particular, the group index is found to be as large as 4.45 due to the significant change in the effective mode index of the waveguide as a function of the wavelength. The effects of structure size on the measured losses and group indices are analyzed. Our experimental results are in good agreement with our simulations, and the method employed is found to be effective in analyzing the linear properties of submicrometer optical waveguide structures.

The attenuation properties of Tm³+ -doped fluorozirconate optical fibers at 632.8 nm induced by a signal at 1175 nm are investigated for the first time. We believe this approach has potential applications in Q-switching of fiber lasers. A red-guided signal is gradually attenuated up to 14.7 dB by increasingly applying a copropagating 1175-nm signal. This value is obtained in 12.5-cm samples. Fibers with different concentrations (1000, 2000, and 20,000 ppm wt) are characterized. For example, the most efficient, the 20,000-ppm wt fiber, requires ~120 mW to exhibit complete attenuation, although 30 mW would be sufficient for a smaller core. In general, low concentration is related to fast response and high concentration to high efficiency. In the fiber with the best performance, the 2000 ppm wt, a red signal is 13.5% modulated up to 130 Hz with a theoretical limit of 266 Hz.

We present a cost-effective double-pass erbium-doped fiber amplifier (EDFA) configuration with an embedded chromatic dispersion compensation fiber and optical gain control function. The amplifier was characterized and tested over a 100-km 10 Gb/s×C-band 16-channel wavelength division multiplexing system and demonstrated excellent performance.

A novel method to reduce the probability of error in the presence of inter-symbol interference (ISI) and additive Gaussian noise is introduced. The proposed technique is based on modifying the characteristic function of the ISI variable used in the Beaulieu series method to evaluate the probability of error for binary symmetric channels, such that some pulses are omitted to reduce the effect of ISI. This is accomplished by mapping words of certain bit lengths to prescribed series of pulses where some of the pulses are omitted (zeros). The probability of error for the proposed method is evaluated for different word lengths using Gaussian pulses. Test results show that certain pulse series of lengths 12 or greater, with free distances of two or more and consisting of 30% zeros or more, would achieve lower probability of error in the presence of ISI and Gaussian noise.

Two types of all-optical non-return-to-zero to return-to-zero (NRZ-to-RZ) format conversion schemes are presented by exploiting semiconductor optical amplifier (SOA) nonlinearities, including nonlinear polarization rotation (NPR) assisted with blue-shifted filtering (NPR-BF) and cross-phase modulation (XPM) assisted with blue-shifted filtering (XPM-BF). Experimental results show that the power penalties of the NPR-BF and XPM-BF schemes are about -0.5 dB and 1 dB, respectively. Furthermore, experimental results also show that the converted output extinction ratio (ER) of the NPR-BF scheme is higher than that of the XPM-BF scheme under the same conditions.

An optical spectral compensation scheme is proposed to flatten the chips spectra over an arrayed-waveguide grating (AWG), router-based code-division multiplexing (CDM) network. Spectral coding chips are attained by slicing the spectrum from a broadband light source (BLS) and then coded with an AWG router to form a stream of spectral chips. The chips spectra sliced from the contemporary BLS are usually not flat and will induce coding chips with unequal power levels. The resulting unequal chips power will cause multiple-access interference (MAI) at the receiver. Chips spectra compensation is therefore examined with backward-pumped fiber Raman amplifiers (FRAs). The study adopts a genetic algorithm (GA) and linear matrix to flatten the power spectra of coded wavelength-division multiplexing (coded-WDM) chips by identifying the optimal pump wavelengths and pump power of backward-pumped FRAs. The signal-to-interference ratio (SIR) is evaluated with spectral compensation, and the performance improvement is found to be in the range of ~20 dB.

An original experimental setup for shearography with metrological applications is presented. The simplicity and the efficiency of the setup are provided by a shearing device, a prism that separates the TE and TM polarization modes with a coating and a thin glass plate placed on its face. The use of this shearing device enables an in-line and almost-common path configuration for the shearing interferometer, a path that leads to high stability and a low sensitivity to external disturbances. Moreover, the sensitivity of the interferometer can be easily adjusted for different applications by varying the shearing amount with glass plates of different thicknesses or by moving the shearing device between two lenses along the optical axis. The temporal phase-shifting method is applied through the use of a liquid crystal variable retarder.

The phase-generated carrier (PGC) is the best-known signal-processing method for an optical fiber interferometer, and has been widely adopted for experimental systems such as hydrophones and optical fiber current sensors. It has many advantages, such as high resolution and passive sensor structure, and has been used for more than 20 years. In this paper, the signal dependence of the PGC is reported for the first time. Our results imply, in view of the highpass filter that is needed to suppress the temperature fluctuation of the interferometer, that the application of the PGC method is inappropriate for the measurement of low-frequency but sharp-rising-edge signals, such as seismic signals, whose frequency extends down to ~1 Hz and whose rising edge is very sharp. In such a case, the signal dependence will cause fatal errors. Experimental and simulation results are provided to describe the defects of this method. An analysis of the restrictions on the use of the PGC method is also provided.

We propose a technique for dynamic full-range Fourier-domain optical coherence tomography by using sinusoidal phase-modulating interferometry, where both the full-range structural information and depth-resolved dynamic information are obtained. A novel frequency-domain filtering algorithm is proposed to reconstruct a time-dependent complex spectral interferogram from the sinusoidally phase-modulated interferogram detected with a high-rate CCD camera. By taking the amplitude and phase of the inverse Fourier transform of the complex spectral interferogram, a time-dependent full-range cross-sectional image and depth-resolved displacement are obtained. Displacement of a sinusoidally vibrating glass cover slip behind a fixed glass cover slip is measured with subwavelength sensitivity to demonstrate the depth-resolved dynamic imaging capability of our system.

In object/target reconstruction and recognition based on laser radar data, the range value's accuracy is important. The range data accuracy depends on the accuracy in the laser radar's detector, especially the algorithm used for time-of-flight estimation. In this paper, a general direct-detection laser radar system applicable for hard-target measurements is modeled. The time- and range-dependent laser radar cross sections are derived for some simple geometric shapes (plane, cone, sphere, and paraboloid). The cross-section models are used, in simulations, to find the proper statistical distribution of uncertainties in time-of-flight range estimations. Three time-of-flight estimation algorithms are analyzed: peak detection, constant-fraction detection, and matched filter. The detection performance for various shape conditions and signal-to-noise ratios is analyzed. Two simple shape reconstruction examples are shown, and the detectors' performance is compared with the Cramér-Rao lower bound. The performance of the peak detection and the constant-fraction detection is more dependent on the shape and noise level than that of the matched filter. For line fitting the matched filter performs close to the Cramér-Rao lower bound.

To detect and track moving dim targets against the complex cluttered background in IR image sequences is still a difficult problem because the nonstationary structured background clutter usually results in low target detectability and a high probability of false alarm. A new adaptive anisotropic filter based on a modified partial differential equation (AFMPDE) is proposed to detect a small target in such a strong cluttered background. A regularizing operator is employed to adaptively eliminate structured background and simultaneously enhance the target signal. The proposed algorithm's performance is illustrated and compared with the two-dimensional least mean square (TDLMS) adaptive filter on real IR image data. Experimental results demonstrate that the proposed novel method is fast and effective.

This paper describes a study that measured the performance of human image analysts in the surveillance context, using images from synthetic-aperture radar, in terms of the analyst's receiver operating characteristic (ROC) and an ancillary analysis of variance (ANOVA). The experiment was designed to correspond as closely as possible to an operational one for analysts using similar imagery. In particular, the effects of target contrast and background clutter on human analysts' target detection performance were quantified. Our ROC and ANOVA studies show that the clutter and contrast metrics used account for most of the variation in human performance as measured by probability of detection.

We derive a modified version of the cubic convolution scaler to enlarge or reduce the size of digital images with arbitrary ratio. To enhance the edge information of the scaled image and to obtain a high-quality scaled image, the proposed scaler is applied along the direction of an edge. Since interpolation along the direction of an edge has to process nonuniformly sampled data, the kernel of the cubic convolution scalar is modified to interpolate the data. The proposed scaling scheme can be used to resize pictures in various formats in a transcoding system that transforms a bit stream compressed at one bit rate into one compressed at another bit rate. In many applications, such as transcoders, the resolution conversion is very important for changing the image size while maintaining high quality of the scaled image. We show experimental results that demonstrate the effectiveness of the proposed interpolation method. The proposed scheme provides clearer edges, without artifacts, in the resized image than do conventional schemes. The algorithm exhibits significant improvement in the minimization of information loss when compared with the conventional interpolation algorithms.

This paper describes an efficient approach to the fusion of spatially registered images and image sequences. The fusion method uses an improved wavelet representation, which has low redundancy as well as near-shift-invariance. Specifically, this representation is derived from an extended discrete wavelet frame with variable resampling strategies, and it corresponds to an optimal strategy. The proposed method lends itself well to rapid fusion for image sequences. Experimental results tested on different types of imagery show that the proposed method, as a shift-invariant scheme, provides better results than conventional wavelet methods and it is much more efficient than existing shift-invariant methods (the undecimated wavelet and the dual-tree complex wavelet methods).

Intensity diffraction tomography (IDT) is an imaging method for reconstructing the complex refractive index distribution of a weakly scattering three-dimensional object. Unlike classic diffraction tomography, which requires measurement of the transmitted wave-field phase, IDT accomplished this reconstruction from knowledge of wave-field intensity measurements on parallel detector planes at each tomographic view angle. In this work, novel scanning protocols and reconstruction algorithms for IDT are proposed that require two intensity measurements on a single detector plane positioned at a fixed distance from the object. Each measurement corresponds to a probing spherical wave field that possesses a distinct curvature. Accordingly, the form of the incident wavefield, rather than the detector position, represents the degree of freedom in the imaging system that is varied for acquisition of the necessary measurement data. Computer simulation studies are conducted to investigate the developed data acquisition and image reconstruction algorithms.

We propose a new algorithm to calculate the sum square difference (SSD) metric for estimating translational motion. Using some substitutions and complex arithmetics, computation of the SSD is derived to be a correlation function of two substituting functions. The former can be computed using the fast Fourier transform (FFT) approach, which is less computationally expensive than the direct computation of the SSD. Zero padding of the block is useful both to avoid the circular character of the FFT and to computes the SSD function at once. We prove the existence of a simple and optimal correlation method for noncircular SSD matching.

An algorithm for pose estimation of vehicles in synthetic aperture radar imagery is presented. The algorithm utilizes robust features and a structured decision process to achieve high precision for pose angle estimation. It is shown that the pose angle could theoretically be recovered from two simple features: the fill ratio and aspect ratio of the segmented target; and this analysis leads to useful nonlinear feature transformations. Four neural networks are used to make estimates conditional on angular region, and then a general neural network makes the best estimate with the feature set including the regional estimates. The algorithm is demonstrated for MSTAR (Moving and Stationary Target Acquisition and Recognition) data. It is relatively robust to scale variations, and significantly more precise than previously published results.

We develop a framework of construction strategies for traceability codes on the subject of multimedia fingerprinting, which constructs traceability codes in a concatenated way. In fingerprinting systems, there are tradeoffs among the size of the customer base, the collusion resilience, and the codeword length. Our goal is to find a strategy to construct, traceability codes that reach an equilibrium among these tradeoffs. Instead of investigating a "high-performance" code, which has proven challenging in existing researches, we introduce a concatenated construction methodology to provide a flexible approach for producing more applicable traceability codes by composing several existing "low-performance" collusion-secure codes. Instead of just giving an example constructed by specific codes, we describe a general code construction strategy and give a detailed analysis on it. Moreover, we propose two concatenated construction schemes based on group fingerprinting to show the feasibility of the concatenated construction strategy. Experimental results show good performances on the code length, detection time, and tracing ability.

The calibration of a camera is an essential step for the metric reconstruction of the world. Intrinsic and extrinsic parameters of the camera are computed using a one-to-one correspondence between 3-D and 2-D coordinates of control points on the calibration target. Three-dimensional coordinates of control points are given in advance, and 2-D coordinates are detected on the image. The calibration target uses cross lines, circles, and a chessboard pattern to improve detection of the control points on the image. We propose an algorithm to automatically detect the control points on an image, especially for a chessboard pattern. Two symmetric properties of a chessboard pattern related to geometric and brightness distribution are used, and two concentric circles are used as probes for the effective use of the two properties. The two symmetric properties of the chessboard generate the candidates of control points. Finally, a cross-ratio of four points on a line is used for verification. The experimental results using images that vary in scale, pose, and illumination demonstrate the robustness of the proposed algorithm.

By using a combination of the Mellin radial harmonic function and the Mexican-hat wavelet transform, scale- and shift-invariant pattern recognition is reported. Without preprocessing of the input object, this filter is capable of identifying over a wide allowable scale range of 0.25 to 1. The correlation peaks are sharp, and the peak intensity is fairly uniform, with a variance below 30%. Computer simulation is adopted to investigate the performance of the filter. Experimental results implemented using a photorefractive joint-transform correlator, including those obtained under white noise, are also presented.

Feature detectors have long been one of the touchstones of image processing. Most vision tasks are entirely dependent on the accurate determination of fiducial marks on images, which ultimately led to a quest for methods able to detect feature locations with high resolution. We report the development of an intensity-based subpixel corner detector based on the two-dimensional (2-D) Hilbert transform. Extensive testing of both accuracy and precision with live images finds the method adequate for subpixel detection at better than 10^-1 pixel accuracy. The subpixel corner detectors and the evaluation proposals to date are briefly reviewed, and the proposed method is described. The results are shown and discussed.

The peak signal-to-noise ratio (PSNR) is one of the most popular video quality metrics. This ratio is computed using both original and processed images. We propose a new method to estimate the PSNR from an encoded bit stream without using original video sequences. In the proposed method, the transform coefficients of images or video frames are modeled by a generalized Gaussian distribution. By utilizing the model parameters of this distribution, the PSNR can be estimated. We also propose a fast method that can be used to estimate the model parameters of the original transform coefficient distribution using quantized transform coefficients as well as quantization information extracted from encoded bit streams. Experimental results with H.264 bit streams show that the proposed generalized Gaussian modeling method delivers better performance compared to the standard Laplacian modeling method when estimating the PSNR. The proposed method can be applied to image or video streams compressed with standard coding algorithms, such as MPEG-1, 2, 4, H.264, and JPEG. The proposed method can also be used for image or video quality monitoring systems on the receiver's side.

Current video encoding methods base their decisions (which sequence of bits must be sent at each instant t) on a single knowledge base throughout all transmission times (in most cases, the knowledge is based on energy values, so coefficients with higher energy are prioritized over to those with lower energy). This way, there are no mechanisms working simultaneously with, or in parallel with, the transmission process and imposing the need to modify the knowledge base in accordance with the requirements of the transmission process (sending the information that will produce the best possible quality per bit transmitted). Since the knowledge base is conceived statically (it does not change over time), there will come a time when all information to be transmitted is of equal relevance, even though there may still be differences in that information. Based on this reasoning, we propose a video compression method with automatic internal mechanisms that make it possible to specify a knowledge base (containing the optimal sequences to be sent for each quantizer) at each instant of the transmission process. The methodology is based on a hierarchical quantizer decomposition. In the first level we have quantizers with an high linear velocity, and in the second level, quantizers with high energy. We automatically select the best decomposition by minimizing the cost of coding the information. Comparisons with the state of the art in video coding show the advantages of the approach.

A CO₂ laser with a hollow cone-shaped resonator (HCR) for producing a hollow laser beam (HLB) is proposed. The HCR consists of a totally reflective mirror and a partially reflective mirror at the two ends of a hollow cone-shaped discharge tube. In a longitudinal section of the HCR along its axis of symmetry it can be regarded as a folded cavity. Employing an standard optical system, the HLBs can be focused to meet the requirements of various applications. Analysis shows that not only can an HLB be obtained, but also the radius of the dark region of the focused HLB is easy to adjust. The hollow cone-shaped CO₂ laser may be used as a new type of optical tweezers.

The work presented deals with the possibilities of synthesizing white color, which is of great interest for diffractive image devices. The method of additive mixing is utilized for synthesizing arbitrary nonspectral colors using diffracted light. The suggested solution is based on employing only two complementary colors as primaries for additive mixing, which is simpler and offers better energy efficiency than color-mixing models using three or more primaries. For comparison, two different two-component mixing models are considered together with a three-component RGB model. First, the theory of additive color mixing is modified for the case of diffracted light, and equations for relative areas of primary gratings are derived. Using colorimetry, a method of measurement and determination of diffracted light color is proposed and practically tested. Finally, a set of available primary gratings was used for experimental preparation of white color, and results of the two approaches to color mixing models are compared.

An optical method for synthesizing a binary matrix representing all feasible solutions of a bounded (input length restricted) NP-complete combinatorial problem is presented. After the preparation of this matrix, an optical matrix-vector multiplier can be used in order to multiply the synthesized binary matrix and a grayscale vector representing the weights of the problem. This yields the required solution vector. The synthesis of the binary matrix is based on an efficient algorithm that utilizes a small number of long-vector duplications. These duplications are performed optically by using an optical correlator. Simulations and experimental results are given.

Filtered backprojection (FBP) is the basic operation of image reconstruction algorithms in tomography. It is widely used but very time-consuming. We propose a new implementation, based on an optoelectronic architecture, providing a speedup of about two orders of magnitude over a classical digital implementation. The realization of the optical core, based on a rotated Dove prism, requires careful attention in order to ensure good image quality. This aspect has been studied in simulation with a suitable model of the architecture, and in practice with an experimental setup. Results are very encouraging.