This PDF file contains the editorial “SPIE Letters Virtual Journal” for OE Vol. 45 Issue 06

For reconstructing sweep fingerprint sequences, we propose a coarse-to-fine image registration scheme, which first uses the block-matching method as the preregistration and then adopts the curvature-based elastic registration as a fine estimation of nonlinear distortions between two consecutive frames. With respect to two existing state-of-the-art approaches, the new scheme becomes more robust against distortions and therefore the reconstruction accuracy is improved.

We present a novel texture feature persistence metric for automatic-target-recognition (ATR)-directed image compression based on the similarity between shapes. On the basis of spatial fuzzy representation of shapes, a similarity metric between shapes is proposed. Then the impact of lossy image compression on ATR performance is measured by the similarity between shapes, which are obtained by identical segmentation and edge extraction of the source image and degraded image after compression. Experimental results show that this metric effectively measures the extent to which target texture features are preserved after compression.

A new scanning system is presented for the high-accuracy form measurement of flat and slightly curved surface profiles. The system employs a small measuring head with multiple distance sensors that is scanned along the surface. Additionally, an autocollimator is utilized to account for angular scanning stage errors. For this setup, suitable design of experiment allows scanning stage errors as well as systematic distance sensor offset errors to be eliminated. As a consequence, high-accuracy form measurements of flat and slightly curved surfaces with high resolution can be achieved. A demonstrator setup has been realized and tested. The results confirm the high potential of this method.

We describe a fast and accurate method for the measurement of refractive index spectra of absorbing layers from transmittance spectra at two angles of incidence. The method is less sensitive to surface conditions than other photometric techniques.

A kernel-based metric measuring tracking reliability that is based on discriminative components of a kernel target model and kernel mutual information is presented. The discriminative components of the kernel target model are selected by computing the log-likelihood ratios of class-conditional sample densities of these components from a target region and background sampled region. The components selection process is embedded in a metric with kernel mutual information of the target regions of the initial frame and current frame in video infrared target tracking for online evaluation of the tracking reliability. Experimental results have shown that the metric can effectively characterize target tracking results as good or bad.

The main function of a Fresnel lens is to provide light guidance. Since the current LED sources cannot provide enough flux for reading lamps to be designed with a single LED, instead systems must use multiple LEDs. We present an optimal design of a Fresnel lens for a reading light system with multiple light sources of white light LEDs. The groove angles of the Fresnel lens are chosen as design parameters and the design goal is to maximize the illuminance in a specified reading surface while maintaining the distribution uniformity of the light rays. We develop a series of genetic algorithms that are implemented with SCHEME language and macros supported by the commercially available nonimaging optical simulation tool to search for a set of optimal groove angles for the Fresnel lens. From the simulation results we can see that the optimally designed Fresnel lens indeed offers better light-guiding performance than typical Fresnel lenses for a multiple-LED reading light system.

A novel scheme of header extraction for optical packet switched networks is proposed for the first time. The system is based on a modified terahertz optical asymmetric demultiplexer (TOAD) with a differential modulation scheme. Numerical analysis and simulation show that more than 15-dB contrast ratio of the separated header at 2.5 Gbit/s to the suppressed payload at 40 Gbit/s can be achieved. In addition, the semiconductor optical amplifier (SOA) TOAD parameters are discussed and designed to optimize the performance of the proposed scheme.

Most imaging systems today include a mosaic detector array in the focal plane. Optical designers of astronomical telescopes typically produce a design that yields a superb on-axis aerial image in the focal plane, and detector effects are included only in the analysis of the final system performance. Aplanatic optical designs (corrected for spherical aberration and coma) are widely considered to be superior to nonaplanatic designs. However, there is little merit in an aplanatic design for wide-field applications because one needs to optimize some field-weighted-average measure of resolution over the desired operational field of view (OFOV). Furthermore, when used with a mosaic detector array in the focal plane, detector effects eliminate the advantage of the aplanatic design even at small field angles. For wide fields of view, the focal plane is frequently despaced to balance field curvature with defocus thus obtaining better overall performance. We will demonstrate that including detector effects in the optical design process results in a different optimal (nonaplanatic) design for each OFOV that is even superior to an optimally despaced aplanatic design.

This paper describes research on the measurement of the 50% probability of identification cycle criteria (N₅₀,V₅₀) for a set of hand-held objects normally held or used in a single hand. These cycle criteria are used to calibrate the Night Vision Electronic Sensors Directorate (NVESD) target acquisition models. The target set consists of 12 objects, from innocuous to potentially lethal. Objects are imaged in the visible, midwave infrared (MWIR), and long-wave infrared (LWIR) spectrum at 12 different aspects. Two human perception experiments are performed. The first experiment simulates an incremental constriction of the imaging systems modulation transfer function (MTF). The N₅₀, and V₅₀ calibration criteria are measured from this perception experiment. The second experiment not only simulates an incremental constriction of the system MTF but also down samples the imagery to simulate the objects at various ranges. The N₅₀ and V₅₀ values are used in NVTherm 2002 and NVThermIP, respectively, to generate range prediction curves for both the LWIR and MWIR sensors. The range predictions from both NVTherm versions are then compared with the observer results from the second perception experiment. The comparison between the results of the second experiment and the model predictions provides a verification of measured cycle criteria.

This research determines if there is an improvement in human observer performance, identifying potential weapons or threat objects, when imagery is presented in three dimensions instead of two dimensions. The potential improvement in performance is quantified by evaluating the change in the N₅₀ cycle criteria, for this task and target set. The data suggests that as much as a 30% improvement in range capability may result from using 3-D imagery. The advent of affordable, practical, and real-time 3-D displays has led to a desire to evaluate and quantify the performance trade space for this application of the technology. Imagery was collected using a dual-camera stereo imaging system. A series of eight different resolutions were presented to observers in both 2-D and 3-D formats. The set of targets consisted of 12 handheld objects. The objects were a mix of potential threats or weapons and possible confusers. For example, a cellular telephone and a hand grenade are two such objects. This target set is the same target set used in previously reported research that determined the N₅₀ requirements for handheld objects for both visible and infrared imagers.

A mathematical method has been developed to analyze influence functions that are used in a computer-controlled polishing process. The influence function itself is usually generated by some kind of calibration where the exact procedure is dependent on the process used. The method is able to determine asymmetries in an influence function. Application of this method yields a value that may be used to judge the quality of an influence function. That quality is also an indicator of the variance of the evolving surface error profile, since a close relationship between it and the polishing process exists. On the basis of an ideal, theoretical process, a model to handle and quantify the result of a real polishing process is described. Practical application of this model demonstrates the effect of influence-function quality on the polishing result. Based on this model, the predictability of the polishing result is evaluated. This initiative to judge influence functions by their quality is an important contribution to the development of computer-controlled polishing. Due to improved process reliability, the reject rate will decrease, and the result will be more economic manufacture.

An adaptive windowed Fourier transform method in 3-D measurement based on a wavelet transform is proposed, in which, by applying a wavelet ridge, a series of scaling factors are calculated to determine the series of prime windows needed in the windowed Fourier transform method. Because the spectrum of each local fringe is simpler than that of the whole fringe, even though there is frequency aliasing as far as the whole fringe is concerned, the fundamental spectrum may separate into components in each local fringe. It is easy to filter out one of the fundamental frequency components from the local spectra. Adding these local fundamental components, the full fundamental component can be obtained correctly. The advantage of the method is that it not only eliminates the frequency aliasing, but also obtains the modulation distribution function to guide phase unwrapping.

A novel proposal for low-cost photometric testing of automotive headlamps is presented, using a combination of well-known optical metrology principles. Deflectometric measurement techniques and CCD-based photometry permit the precise measurement of the energy distribution and the direction of propagation on a plane close to the headlamp, while simple image-processing techniques permit the far-field photometric distribution on a distant plane to be reconstructed from the near-field data measured. The setup constructed and the main calibrations involved are presented, and results for different headlamp models are shown. The technique may be applied to light sources other than headlamps in order to calculate far-field distributions on any predefined surface of interest from near-field measurements.

Remote sensing of the polarized light emitted or reflected from a scene has the potential to improve object detection, object identification, or to enhance images. The need to accurately measure individual Stokes components depends on the application. In all applications, it is desirable to estimate the uncertainty associated with Stokes images. A process is described that uses an instrument computer simulation to compute expected uncertainties in imaging polarimeter data. The simulation takes measured and/or estimated uncertainties in individual instrument components and propagates them to evaluate their effect on the Stokes measurement. Individual uncertainties are then combined to obtain an overall uncertainty estimate for the given Stokes input. Methods of visualizing the effect of instrument uncertainty on various Stokes input states are also described.

Star trackers based on charge-coupled device (CCD) or complementary metal-oxide semiconductor (CMOS) sensors, use a brightness independent star identification strategy that requires highly accurate measurements of star spot position. Therefore, precise calibration of the measurement model is crucial. Generally, ground-based real night sky observation is a specific and costly approach. In this work, an optical laboratory method for star tracker calibration is proposed. This method is based on ordinary instruments, laser autocollimation adjustment, and image processing techniques. The calibration issues of the star tracker with a brightness independent star identification strategy are analyzed. A new laboratory calibration method is introduced, and its results on an active pixel sensor (APS) star tracker are discussed. This method proves to be practical and adequate in the development of a star tracker with wide field of view.

The rocket Extreme Ultraviolet Grating Spectrograph (EGS) instrument is flown onboard a sounding rocket as an underflight calibration for the Solar Extreme Ultraviolet Experiment (SEE) onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite. The first calibration flight took place from the White Sands Missile Range in New Mexico on February 8, 2002. Both preflight and postflight calibrations are performed in the extreme ultraviolet (EUV) range from 26.5 to 117.2 nm and the far ultraviolet (FUV) range from 120 to 196 nm to determine an accurate quantum throughput (QT) for the EGS instrument. These calibrations are performed using Beam Line 2 at the National Institute of Standards and Technology Synchrotron Ultraviolet Radiation Facility III. This QT determination has an uncertainty of about 10% for the EUV region and around 4.2% for the FUV region. Once the QT for the instrument is found from the calibrations, it is applied to the solar spectrum obtained during the flight in order to get the absolute spectral irradiance with an uncertainty of approximately 12%. The rocket EGS is planned for an annual calibration flight to track the long-term changes of SEE EGS.

The effect of deposition temperature on the properties of 355-nm high-reflectivity (HR) coatings was investigated. A series of 355-nm HR coatings were deposited by electron-beam evaporation using the same deposition process, but different deposition temperatures: 200, 250, 280, and 320 °C. Transmittance and high reflectance of the samples were measured with a Lambda 900 spectrometer, and the highest reflectance, 98.7%, was achieved at a deposition temperature of 280 °C. The laser-induced damage threshold (LIDT) was measured with a 355-nm pulsed laser with a pulse width of 8 ns. It was found that the deposition temperature had a significant effect on the LIDT of coatings. LIDTs up to 18.5 J/cm² were achieved when the deposition temperature was 280 °C. The LIDT of the coating deposited at 280 °C is about three times greater than that of coatings deposited at the other temperatures. Damage morphologies of samples at different deposition temperatures were observed with a Leica-DMRXE microscope. Microstructures of the samples were characterized by x-ray diffraction (XRD). An absorptance-dominated model is proposed, which agrees very well with the damage threshold results.

A video-based spatial optical communication method for a wearable information terminal using a video camera with an infrared LED ring is proposed. By the video image of the wearable terminal that is captured by the camera, the physical location of the terminal and user's messages that are carried by it can be detected simultaneously. Therefore, data communication can be implemented without the private data of users such as an address or ID number; thus the security and privacy of users will be maintained. The effectiveness of this method is demonstrated in a multilanguage communication terminal for a wearable information environment.

Studies on a diode double-end-pumped Nd:YVO₄ laser operating in the fundamental mode with a maximum cw output power of 14.8 W are reported. Measurements were taken with an a-axis-cut crystal in the form of a rectangular bar of size 4×4×10 mm with doping concentration 1.1 at.%, using a diode double-end-pumped resonator configuration operating in the cw TEM₀₀ mode. The pumping arrangement mainly consists of two fiber-coupled diode-laser arrays with a maximum output power of 30 W and output wavelength range of 807 to 810 nm at 25°C set temperature. Since the quality of the pump beam and the actual focused spot size are important parameters for overlap optimization of the pump and cavity modes, these two parameters are calculated for this set up. The fractional thermal loading and effective stimulated emission cross section for ⁴F_3/2→⁴I_11/2 transition of 1.1-at.% doped Nd:YVO₄ crystal are calculated using the planar resonator configuration stabilized by pump-power-induced thermal lensing. The focal length of the effective lens and its variation with the absorbed pump power are determined from the far-field divergence angle of the output beam.

We propose and demonstrate a novel four-wavelength erbium-doped fiber laser using four-wave mixing (FWM). By inserting a length of highly nonlinear photonic crystal fiber (HNPCF) in the laser cavity and using two fiber Bragg gratings as the wavelength-selecting components, four stable wavelengths with equal spacing have been realized at room temperature. The energy-conversion-induced loss caused by the FWM, which happens in the HNPCF among the two oscillating laser lines and the FWM products, is believed to contribute to the stable multiwavelength operation by suppressing the wavelength competition between the two laser lines.

A shape measurement system for Hume pipes (diameter 1200 to 2000 mm) is developed using an omnidirectional sensor and a light sectioning method with laser beam scanning to evaluate degradation of Hume pipes. This system can measure the inner wall shape of Hume pipes at high speeds (about 3000 distance measurement points within 3 s) and high accuracy while moving along the pipe axis, and it can evaluate the corrosion quantity of the pipe wall surface. To measure the 3-D shape, the system is developed using an omnidirectional imaging device combined with a laser beam for slit light projection, and a hyperbolic mirror and high-precision digital camera. Also, an algorithm is developed that calculates position coordinates of the camera optical axis and posture with the distance data from the camera optical axis to the pipe wall surface. Performance test results of the developed system have accuracy in a shape measurement of about 3 mm for distances of 400 to about 1600 mm.

Changes in data marks and groove structures are examined when a high power laser beam (>0.5 W) is focused on compact disk recordable (CD-R) data layers. Observations are recorded as a function of exposure condition and the type of dye used in the recording layer. All samples experience a decrease in the depths of data mark features and the pregroove modulations on exposure. Data marks on cyanine- and azo-dye disks become optically invisible after exposure, while data marks on phthalocyanine-dye disks remain visible, even after high-power exposure. Also, phthalocyanine-dye disks show interesting phenomena, including mixture of the dye and the substrate material during recording and contrast reversal of the marks.

Nonlinear optical microscopy is a relatively new and rapidly growing field of optical engineering, where Ti:sapphire ultrafast laser sources and technologies are finding a wide application. Diagnostic techniques addressed to this kind of application have been widely developed in the last few years. Research efforts have been focused on the evaluation and eventual correction of laser pulse duration widening due to group velocity dispersion of microscope optics, and devices have been specially designed to perform second-order autocorrelation measurements at the objective focal plane. In the present work, innovative, simple setups and procedures are reported that make the best use of all the facilities and characteristics of the microscope itself, so that only a few optical components are needed to temporal characterize the laser pulse at the specimen plane.

A novel fiber Bragg grating (FBG)-based weigh-in-motion (WIM) system is introduced in order to achieve a better performance compared with the existing WIM systems. This novel WIM system uses the fiber-reinforced composite (FRC) as the load-supporting material in combination with the FBG technology. The sensor is designed as a multiply FRC laminate with the FBG embedded inside it. A theoretical model is developed to analyze the mechanism of this WIM system. Both static and dynamic tests are conducted to verify the system performance. With the extraordinary mechanical properties of the FRC, this novel WIM system has achieved larger dynamic range and higher sensitivity than prior works. The simple design of the system also reduces the engineering difficulties and overall costs.

The overlap integral of guided acousto-optic interaction is investigated theoretically. The overlap integral of YZ-LiNbO₃ (Y-cut crystal, Z-propagating surface acoustic wave) is discussed with different penetration depths for TE- and TM-polarized light. Some valuable results are obtained for the design of acousto-optic devices.

A fiber optic variable attenuator using a dichroic polarizer sheet illuminated by a heating beam is described. The light absorbed by the polarizer induces a thermal lens, which allows one to control the amount of light to be coupled into an optical fiber. Some experiments demonstrating the thermal lens action are presented.

We propose a novel optical decoder for a fiber-optic code-division multiple-access communication system. In particular, we discuss a means of reducing the effective multiple-access interference signal by inserting an optical hard limiter (optical thyristor). The optical decoder employs an AND gate logic element (AGLE) composed of a 1×M splitter, optical delay lines, an M×1 combiner, and the optical hard limiter. It is found that the AGLE suppresses the interference signal, so that the autocorrelation sidelobe and the cross-correlation peaks can be fully eliminated for any two users.

We present an analytical model to study the multiclass-traffic-based optical burst switching system. In contrast with the previous on-off burst arrival process model, which is based on a single class of traffic and depends on just one probability of bursts to choose output ports, in our scheme we evaluate the blocking probability for multiclass bursts at the core router, which chooses output ports depending on differential probability, and we give some useful discussion for the design of real optical burst switching networks.

Various dispersion-compensation techniques are compared on the basis of eye opening, eye closure, bit error rate, and Q-factor. The techniques that use dispersion-compensating fiber, fiber Bragg gratings (FBG), optical phase conjugators (OPC), negative dispersion fiber (NDF), and reverse dispersion fiber (RDF) for dispersion compensation are compared. The NDF technique is more attractive for long-distance cable television (CATV) systems as this technique gives better eye opening, eye closure, bit error rate, and Q-factor characteristics than any other technique. The RDF technique is the next-best technique. The FBG technique is attractive only at a 120 km transmission distance in CATV systems. The OPC technique is not recommended for long-distance CATV transmission systems.

This study proposes a novel spectral-amplitude coding optical code-division multiple-access (SAC-OCDMA) scheme with four optical intensity levels by polarization division multiplexing (PDM) to increase the maximum permissible number of simultaneous subscribers using an optical broadband source of finite bandwidth. In the proposed system, each encoder/decoder pair is shared by two subscribers, and the requirement for complex polarization compensator schemes at the receiver is removed. The phase-induced intensity noise (PIIN) induced at high optical intensities significantly degrades the performance of a conventional SAC-OCDMA scheme. Therefore, this study uses two methods to suppress the PIIN effect: 1. two users share the same encoder and transmit signals on mutually orthogonal polarizations, such that some PIIN terms are canceled out; and 2. the receiver structure is equipped with multiple balanced detectors (MBDs) to reduce the PIIN power impinging on each photodiode (PD). The numerical evaluation results demonstrate that under PIIN-limited conditions, the proposed system achieves a higher performance than that of the conventional SAC-OCDMA scheme.

In this work, transmissive spectral characteristics of fiber Bragg gratings (FBGs) are applied to construct a circulator-free scheme of an optical code-division multiple-access (OCDMA) network coder/decoder (codec). The unnecessary spectra would accompany the coding chips to arrive at the photodetectors (PDs) to induce higher phase-induced intensity noise (PIIN) and multiple-access interference (MAI). A residual-spectra eliminator (RSE) between OCDMA encoder and decoder modules is employed to remove the unnecessary spectral parts of data so that the PIIN and MAI can be reduced. A simple experiment performed on the basis of transmissive spectral characteristics of FBGs together with RSE is demonstrated to verify the capability of suppressing residual-spectra noise at the PDs. Performance evaluations indicate that using RSE between network codecs can remarkably lower the PIIN effects in the receiver PDs.

We investigate a semiconductor optical amplifier (SOA) preamplifier model by suitably choosing the material and device parameters for the SOA to reduce the amplified spontaneous emission (ASE) noise at low range of 22.3 µW with 0.1-mW input power for a PIN receiver. Our proposed SOA optical preamplifier is found to be more relaxed from the optical alignment and antireflection coating, eliminates the need for optical filter, and gives large tolerance for an input light wavelength of more than 100 nm. We also investigate the receiver sensitivity for different bit rates. We show that receiver sensitivity is –69.9 dBm at a bit error rate (BER) of 4.6×10^–10 for 10 Gbit/s and for the 40 Gbit/s bit rate the improved receiver sensitivity is –19.2 dBm with a PIN receiver. We also observe a sensitivity of –40.5 dBm at 40 Gbit/s with a differential phase shift keying (DPSK) receiver. Further, the impact of amplified spontaneous emission power, gain variation with input light wavelength, and optical gain for the TE & TM modes with input power for the PIN & DPSK receivers is illustrated. We show that the optical gain of the SOA is polarization independent and remains constant at 30.06 dB up to gain saturation. We also show that the DPSK receiver suffers less from ASE noise. The variation of material loss, length, and bias current for our SOA preamplifier to optimize the receiver sensitivity is further illustrated.

The dispersion relation equation of hybrid modes in hollow optical fiber is derived in the closed form by modeling the fiber in a three-layered structure and by rigorous hybrid mode analysis. The effective refractive indices of hybrid modes as a function of wavelength are accurately calculated. Modal characteristics and transverse field distributions of hollow optical fiber are precisely analyzed by use of the derived hybrid mode dispersion relation equation and the compact 2-D finite difference time domain method. In addition, the effects of the fiber dimension on propagating properties are presented. The number of hybrid modes that can exist in hollow optical fiber is calculated as a function of fiber dimension. We believe that this rigorous analysis is very accurate and provides precise computing methods to design and characterize hollow optical fiber based optical devices.

This paper presents two types of attenuation-controllable 2×2 optical switches utilizing V-shaped 45-deg micromirrors. One type utilizes four single-face mirrors, and the other has a simplified configuration utilizing two double-face mirrors. The designed devices were fabricated on a silicon-on-insulator wafer with a structural layer of 80-µm thickness. Two pairs of lensed fibers with a focal length of 150 µm were aligned for optical characterization. Experiments on the simplified design showed optical insertion losses of less than 1.9 dB and on/off ratios larger than 70 dB. The optical power can be controlled up to a maximum attenuation level of 50 dB within ±0.1 dB tolerance in the other channels. Because the overall optical performance of the two types was verified to be almost the same, the simplified design will be more desirable for practical applications.

The performance of lensless free-space optical interconnects (FSOIs) for chip-to-chip interconnections under different misalignment conditions is analyzed. The signal-to-noise ratio (SNR) is derived as a function of transverse misalignment, longitudinal misalignment, angular misalignment, source and detector pitch, detector size, beam waist, and interconnect distance and used as the performance measure. We show that the fill factor of the detectors and the beam waist of the source can be used as optimization parameters for maximum misalignment tolerance. A FSOI with optimum misalignment tolerance may not have the highest possible SNR, but it can tolerate greater misalignment without a substantial decrease in SNR.

A technology for making multichannel fractional Fourier transform holograms (FRTHs) using a holographic lens array is proposed. With this method, the different-order FRTs can be produced simultaneously for multiple objects. This hologram records the information about both the object wave and the FRT system, including every fractional order, the focal length of every holographic lens, and the distance between the object and the holographic lens array. The FRTH cannot be reconstructed if system parameters are unknown, so this technology can improve the capability of optical anticounterfeiting techniques. Experiments have proved the theoretical analysis correct.

We propose an efficient coding method of digital holograms (or fringe patterns) using standard compression tools for video and image. The fringe pattern is generated by a computer-generated hologram (CGH) algorithm with both an object image and its depth information. The proposed coding consists of preprocessing to separate RGB color space components, localization by segmenting the fringe pattern, frequency transform using M×N (segment size), 2-D discrete cosine transform (DCT) for extracting redundancy, segment scanning the segmented fringe pattern to form a video sequence, classification of coefficients, and hybrid video coding, which uses MPEG-2/4, H.264/AVC, differential pulse code modulation (DPCM), and lossless coding. The proposed algorithm illustrates that it has better properties for reconstruction, from four to eight times higher compression rate than previous research.

Among the methods of spatial detail injection, smoothing-filter-based intensity modulation (SFIM) can quickly merge a huge amount of different spatial resolution imagery with little color distortion. However, the success of spatial-detail injection mainly relies on the designed low-pass filter. For IKONOS-QuickBird image fusion, SFIM requires an elaborate filter to extract adequate spatial details. To ease the filter design and preserve complete spatial information, a modified approach is presented. Experimental results demonstrate that the proposed technique provides significant improvements over the original method.

Advancement in the field of computer graphics has been occurring at an unprecedented pace. It is now possible to generate near-cinematic-quality effects in real time, largely thanks to the programmability of modern graphical processing units (GPUs). However, the spatial fidelity of synthetic imagery relies on anti-aliasing techniques that have not been advanced to the same extent. Custom anti-aliasing techniques are thus required for the generation of synthetic imagery containing high spatial frequencies. In this paper modification of an existing custom anti-aliasing technique to employ the power of modern GPUs is described and applied to infrared scene generation.

All computed-tomography (CT) reconstruction algorithms used today require knowledge of the central ray, which is the projection of the center of rotation (COR) on the detector. The current common practice is to determine it using a wire phantom made of a dense metal material before the CT scan of the object to be inspected. This work presents four methods that can be used for this purpose, the center-of-sinogram, the opposite-angle-interpolation, curve-fitting, and geometrical methods. To our best knowledge, the last two approaches have not been reported before. The performance of the four methods is evaluated under four different situations. The comparison study shows that for all situations, the curve-fitting method and the interpolation method have consistent performance, and that only when the wire-to-COR is small, can all four methods generate close results. When the wire-to-COR distance becomes large, the center-of-sinogram method is generally not reliable. Although in principle the geometrical method is able to provide an exact solution, in practice its accuracy is limited by the finite size of the detector pixel and can be improved if the detector pixel size becomes smaller.

We present a method of using face color in RGB color space for discrimination between real and synthetic human faces. This involves a high-dimensional feature space, so feature dimension reduction is accomplished by the traditional method of median filtering and downsampling, and feature extraction is done with singular-value decomposition. A nonlinear support-vector machine is then used to determine whether the extracted features represent a real human face or a synthetic one. The results from our method are compared with those of traditional face recognition algorithms and are shown to have a higher rate of success even when a only small number of features are is used. The method can achieve a high level of accuracy with little computation time, and is less sensitive to facial expression variations and varying brightness levels than other methods.

We describe some applications of linear and nonlinear projection methods in order to reduce the number of spectral bands in Landsat multispectral images. The nonlinear method is curvilinear component analysis (CCA), and we propose an adapted optimization of it for image processing, based on the use of principal-component analysis (PCA, a linear method). The principle of CCA consists in reproducing the topology of the original space projection points in a reduced subspace, keeping the maximum of information. Our conclusions are: CCA is an improvement for dimension reduction of multispectral images; CCA is really a nonlinear extension of PCA; CCA optimization through PCA (called CCAinitPCA) allows a reduction of the computation burden but provides a result identical to that of CCA.

A new effective algorithm of impulse noise suppression is proposed. Conventional filtering schemes usually utilize a fixed shape for the moving window, such as a rectangle or circle. In contrast, the proposed algorithm exploits a signal-dependent shape for the moving window. We suggest a simple adaptive algorithm of impulse noise detection in monochrome images that takes into account the size of signal gradient neighborhoods and image statistics. Experimental results show superior performance of the proposed algorithm compared to that of conventional algorithms in terms of both subjective and objective criteria.

Motion estimation is a key element of the video coder, which heavily affects the performance of video coding. However, the most significant problem of the discrete wavelet transform is the shift-variant property, which makes the wavelet-domain motion estimation inaccurate. To eliminate the influence of shift variance, an optimal synthesis filtering method is introduced and an efficient motion estimation scheme using the proposed method is presented, which can perform the motion estimation accurately. The experiment results show that the proposed motion estimation scheme outperforms the other wavelet-domain motion estimation schemes by 0.7 dB and has moderate complexity.

Motion detection and tracking are both fundamental steps in video surveillance. This paper describes two improved algorithms for motion detection and tracking, respectively. Firstly, the shadow and ghost detection processing is fused with updating the background subtraction model, after the frame is transformed to HSV color space from RGB color space in order to reduce the effect of illumination changes, shadows, and ghosts. And the result of detection is used as initialization for tracking. Secondly, the gradient field is combined with region information to locate the boundary of the object accurately, instead of the traditional level-set method, which only utilizes the gradient field to propagate a front. Experimental results show that the algorithms decrease the computational complexity and provide accurate location of the object boundary.

The need for accurate and efficient computation of template matching prevails in many applications. However, a challenge in template matching is to obtain high accuracy that involves acceptable computation complexity and is robust to rotation. A new subpixel template matching approach that combines the parametric template method and the ring projection transform process is proposed. It not only achieves subpixel accuracy in location, but also offers rotation invariance in the subpixel template matching. Furthermore, our approach is conceptually simple, easy to implement, and very efficient because no iterative steps are involved. The simulated results show that our approach enjoys very high precision in the presence of image rotations. Experiments with real-world scenes demonstrate that the proposed method can reach subpixel accuracy for finding the distance between two target objects in the presence of rotations and translations. This indicates that our approach is suitable for accurate on-line template matching with scene rotations and translations.

Recent research on neocognitron-like neural feed-forward architectures, which have formerly been successfully applied to the recognition of artificial stimuli such as paperclip objects, now also opens up application to more natural stimuli. Such networks exhibit high-recognition performance with respect to translation, rotation, scaling and cluttered surroundings. In this contribution, we introduce a new type of hierarchical model, which is trained using a non-negative matrix factorization algorithm. In contrast to previous work, our approach cannot only classify objects but is also capable of rapid object detection in natural scenes. Thus, the time-consuming and conceptually unsatisfying split-up into a localization stage (e.g., using segmentation) and a subsequent classification can be avoided. The network consists of alternating layers of simple and complex cell planes and incorporates nonlinear processing schemes that have been proposed in recent literature. Learning of receptive field profiles for the lower layers of the network takes place by unsupervised learning whereas a final classification layer is trained supervised. This final layer is then utilized for detection. We test the classification performance of the network on images of natural objects which are systematically distorted. To test the ability to detect objects, cluttered natural background is used.

We address the robust matching of lines between two views, when camera motion is unknown and dominant planar structures are viewed. The use of viewpoint noninvariant measures gives a lot of nonmatched or wrong matched features. The inclusion of projective transformations gives much better results with short computing overload. We use line features that can usually be extracted more accurately than points, and they can be used in cases where there are partial occlusions. In the first stage, the lines are matched to the weighted nearest neighbor using brightness and geometric-based image parameters. From them, robust homographies can be computed, which allows us to reject wrong matches and to add new good matches. When two or more planes are observed, the corresponding homographies can be computed and they can be used to obtain also the fundamental matrix, which gives constraints for the whole scene. The simultaneous computation of matches and projective transformations is extremely useful in many applications. It can be seen that the proposal works in different situations requiring only a simple and intuitive parameter tuning.

We present the experimental generation and characterization of each one of the four fundamental families of Helmholtz-Gauss beams: cosine-Gauss beams, stationary and helical Mathieu-Gauss beams, stationary and traveling parabolic-Gauss beams, and Bessel-Gauss beams. Both the transverse intensity profile and power spectrum that each one of the beams exhibits upon propagation is observed and compared to the theoretical model with good quantitative agreement. Emphasis is made on the fact that each of the four families of HzG beams is complete and orthogonal, and thus of fundamental relevance.