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August 2007

Volume 46, Issue 8, Articles (08xxxx)

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Editorial

Select this Article OPEN ACCESS		Papers Donald C. O’Shea, Editor Opt. Eng. 46, 080101 (Aug 21, 2007); http://dx.doi.org/10.1117/1.2770466 Online Publication Date: Aug 21, 2007 Full Text: Read Online (HTML) \| Download PDF
		Abstract Unavailable

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OE Letters

Select this Article OPEN ACCESS		Automatic power control with electronic amplified spontaneous emission compensation W. Craig Michie, Stephen Conner, Anthony E. Kelly, and Ivan Andonovic Opt. Eng. 46, 080501 (Aug 03, 2007); http://dx.doi.org/10.1117/1.2766946 \| Cited 1 time Online Publication Date: Aug 03, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Semiconductor-based optical amplifiers (SOAs) offer solutions to a variety of amplification needs covering wavelengths ranging from of 0.6 to 1.6 μm. Gain adjustment, through the bias current, enables automatic power control to be implemented. However, this requires knowledge of the signal strength. The amplified spontaneous emission power, particularly in high gain SOAs, can be significant with respect to the signal strength, and therefore additional components may be required to derive an accurate measure of the signal strength. This increases both the complexity and cost of implementing automatic power control (APC). We report on a method for estimating the signal strength based on measurement of the total output power and the SOA drive current. The method is extendable to other methods of optical amplification, e.g., erbium-doped fiber amplifiers.

Select this Article OPEN ACCESS		All-optical nonreturn-to-zero to return-to-zero format conversion with wavelength conversion using an electroabsorption modulator Zhixin Chen, Jian Wu, Kun Xu, and Jintong Lin Opt. Eng. 46, 080502 (Aug 03, 2007); http://dx.doi.org/10.1117/1.2766938 \| Cited 1 time Online Publication Date: Aug 03, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Simultaneous all-optical nonreturn-to-zero (NRZ) to return-to-zero (RZ) format conversion and wavelength conversion in an electroabsorption modulator (EAM) based on cross-absorption modulation (XAM) at 10 Gbit/s is demonstrated. The impact of the bias voltage of EAM and the input NRZ data signal power on the performance of converted RZ signals is studied. The maximum extinction ratio (ER) of converted RZ signals is about 12.08 dB. By tuning the wavelength of input NRZ signals from 1550 to 1570 nm, negative power penalty with a range of −0.9 to −0.2 dB is observed for converted RZ signals. Thus, error-free all-optical simultaneous format and wavelength conversion using EAM is reported, in a setup that has not been demonstrated in the past.

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Optical System Design

Select this Article		Optical design and salient features of an objective for a firefighting camera Ranabir Mandal and Ikbal Singh Opt. Eng. 46, 083001 (Aug 27, 2007); http://dx.doi.org/10.1117/1.2768080 Online Publication Date: Aug 27, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Thermal imagers based on an uncooled microbolometer detector are finding many applications in short-range devices because of cost effectiveness. A typical application for such a system is firefighting, by providing visibility through smoke and absolute darkness. The design of an objective lens for an infrared (IR) camera to be utilized in firefighting is described. Because of the relatively poor responsivity of the thermal detector, the objective lens is to be operated at fast f-numbers (typically f/1 or faster). The proposed camera lens is simple and lightweight, able to operate under harsh ambient conditions, gives acceptable image quality for various object distances as well as operating temperatures without any focus adjustment, and has a wide field of view and an auto-iris facility. The design constraints of such lenses are also discussed. The performance evaluation curves of the lens of the camera and a few photographs taken with the camera in a fire situation are presented. Experimental results are in accordance with the predicted values.

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Imaging Systems

Select this Article		Two-step triangular-pattern phase-shifting method for three-dimensional object-shape measurement Peirong Jia, Jonathan Kofman, member spie, and Chad English Opt. Eng. 46, 083201 (Aug 13, 2007); http://dx.doi.org/10.1117/1.2768616 \| Cited 5 times Online Publication Date: Aug 13, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Existing phase-shifting measurement methods involve processing of three acquired images or computation of functions that require more complex processing than linear functions. This paper presents a novel two-step triangular-pattern phase-shifting method of 3-D object-shape measurement that combines advantages of earlier techniques. The method requires only two image-acquisition steps to capture two images, and involves projecting linear grayscale-intensity triangular patterns that require simpler computation of the intensity ratio than methods that use sinusoidal patterns. A triangular intensity-ratio distribution is computed from two captured phase-shifted triangular-pattern images. An intensity ratio-to-height conversion algorithm, based on traditional phase-to-height conversion in the sinusoidal-pattern phase-shifting method, is used to reconstruct the object 3-D surface geometry. A smaller pitch of the triangular pattern resulted in higher measurement accuracy; however, an optimal pitch was found, below which intensity-ratio unwrapping failure may occur. Measurement error varied cyclically with depth and may partly be due to projector gamma nonlinearity and image defocus. The use of only two linear triangular patterns in the proposed method has the advantage of less processing than current methods that process three images, or methods that process more complex functions than the intensity ratio. This would be useful for high speed or real-time 3-D object-shape measurement.

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Instrumentation, Measurement, and Metrology

Select this Article		Analysis of structured highlight stereo imaging for shape measurement of specular objects Kynan Graves, Romesh Nagarajah, and Paul R. Stoddart Opt. Eng. 46, 083601 (Aug 30, 2007); http://dx.doi.org/10.1117/1.2769607 \| Cited 1 time Online Publication Date: Aug 30, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Structured highlight stereo (SHS) is a technique for the measurement of specular objects, and is based on viewing the reflection of a structured highlight pattern from multiple directions. This paper reports the results of a simulation and experimental analysis of the approach in order to further understand the accuracy and limitations of SHS. In particular, this paper describes two important findings related to this technique. Firstly, it is shown that the search region containing a consistent set of candidate highlights may be minimized using epipolar constraints. Secondly, an analysis is presented to quantify the accuracy of the SHS approach for different surface curvatures. The results indicate that, although it is possible to accurately measure the surface height of planar specular objects, the accuracy is reduced for objects with curved surface profiles. The measurement error occurs because in general it is not possible to measure the same surface location with both cameras, which then leads to an inconsistency between the surface normal estimates for each camera. The measurement error increases in relation to both the distance between measurement locations on the surface and the surface curvature.

Select this Article		Polarimetric measurements of fabric surfaces Michel Tourlonias, Laurent Bigué, member spie, and Marie-Ange Bueno Opt. Eng. 46, 083602 (Aug 20, 2007); http://dx.doi.org/10.1117/1.2771122 Online Publication Date: Aug 20, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We describe an optoelectronic setup designed to evaluate the surface parameters of fabrics that influence their tactile feel. The developed texturometer uses the periodic structure of a textile material and its ability to reflect light to evaluate its surface properties through its polarimetric properties. The device scans the surface with a laser line and performs a temporal Fourier analysis of the reflected light, which allows us to consider the periodical structure of the material’s surface. Instead of using the overall reflected energy, the analysis is performed on the degree of polarization of light. Results obtained with this new texturometer are compared to those obtained with a nonpolarimetric device that uses overall reflected energy. Emerized and nonemerized twill fabrics are tested, as well as spun-bonded nonwovens. We show that discrimination between samples is enhanced with this polarimetric texturometer. For emerized fabrics, the results exhibit a decrease in depolarization as emerizing intensity increases. For nonwovens, a complementary study in polarimetric imaging has been performed to better understand the phenomena. Nonwoven thermobonded points exhibit lower depolarization of the lightwave than the rest of the structure. Moreover, their depolarization differentiates the tested nonwovens.

Select this Article		Spatially modulated illumination microscopy using one objective lens Hans Mathée, David Baddeley, Christoph Wotzlaw, Christoph Cremer, and Udo Birk Opt. Eng. 46, 083603 (Aug 03, 2007); http://dx.doi.org/10.1117/1.2768085 Online Publication Date: Aug 03, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract The spatially modulated illumination (SMI) microscope is a wide-field fluorescence microscope featuring axially structured illumination, through which access to information about subresolution object structures is obtained. We present a simplified setup where the interference pattern is generated by reflecting the laser beam with a mirror. We characterize our setup by presenting measurements on fluorescent microspheres with diameters ranging from 44 to 200 nm. The results agree well with the sizes provided by the manufacturer. Furthermore, the spheres are analyzed with 458-, 514-, 488-, and 568-nm excitation wavelengths, giving good agreement of the sizes determined at the respective wavelengths. A measurement of the same objects using different excitation wavelengths leads to a size difference of a few nanometers only. The potential of SMI microscopy for the fast analysis of many fluorescent objects is also addressed. In addition, the applicability to biological specimens is shown on fluorescently labeled, specific chromatin domains. The results obtained using the presented mirror geometry agree well with data obtained using a standard SMI microscope setup.

Select this Article		Assessment of sampling errors of laser beam analyzers Anton Dandarov, member spie and Ivelin Bakalski Opt. Eng. 46, 083604 (Aug 21, 2007); http://dx.doi.org/10.1117/1.2771648 Online Publication Date: Aug 21, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We offer an approach to the analysis of measurements performed by the laser beam analyzers. The proposed criterion for accuracy of the laser power distribution measuring apparatus can be used for assessing the potential ability of laser beam analyzers for high accuracy evaluation of linear dimensions. The criterion takes into account the quality of the optics and scanning system, detector performance, and the method of measurement. The test setup allows testing of errors in the full power assessment and diameter measurement. These errors are connected to real physical values and therefore can be used to compare the performance of arbitrary laser beam analyzers. The key point is that the process of measurement is considered totally in the spatial frequency domain. This allows us to put the method specifics of the measurement in comparable terms, extract some important features of the measurement crosses, and create a base for comparing instrument accuracy.

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Optical Components, Detectors, and Displays

Select this Article		New retroreflector technology for light-collecting systems Yong-Jing Wang, Kenneth Li, and Seiji Inatsugu, member spie Opt. Eng. 46, 084001 (Aug 07, 2007); http://dx.doi.org/10.1117/1.2769594 \| Cited 1 time Online Publication Date: Aug 07, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A novel retroreflector design using a pseudo-phase-conjugation mirror, viz., a corner cube mirror array (CMA), is proposed for light-collecting systems to increase the apparent brightness of the light source and thus increase the light collection efficiency. Measurement data for a dual paraboloid reflector system using a CMA retroreflector are presented. Design issues for the CMA are discussed. The advantages of the CMA retroreflector are: (1) it is a self-aligning technique, so it works regardless of its shape and position; (2) it is self-compensated for image distortion. Therefore a highly efficient low-cost light collection system with bigger manufacture tolerances is possible.

Select this Article		Generation of hollow conic beams using a metal axicon mirror Satya Ram Mishra, Sanjiv K. Tiwari, Surjya P. Ram, and Shrikant C. Mehendale Opt. Eng. 46, 084002 (Aug 13, 2007); http://dx.doi.org/10.1117/1.2771155 \| Cited 9 times Online Publication Date: Aug 13, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We propose and demonstrate generation of hollow conic beams using a new element—a metal axicon mirror. A good-quality hollow conic beam was generated from a Gaussian laser beam with high conversion efficiency. We also show that by focusing the hollow conic beam with suitable lenses, it is possible to obtain a weakly converging hollow beam for which the diameter remains between 1 and 3 mm over a propagation distance of about 10 cm, which should be of interest for atom-guiding applications. In the focal region, a nearly nondiffracting central spot of size ≈ 13 μm (FWHM) was observed for a propagation distance of ≈ 8 mm.

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Laser Applications

Select this Article		Application of extended tuning range for external cavity diode lasers to water vapor differential absorption measurements Michael D. Obland, member spie, Amin R. Nehrir, member spie, Kevin S. Repasky, John L. Carlsten, and Joseph A. Shaw, member spie Opt. Eng. 46, 084301 (Aug 20, 2007); http://dx.doi.org/10.1117/1.2771654 \| Cited 2 times Online Publication Date: Aug 20, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Recent advances using electronic feedback to control the optical cavity length of external cavity diode lasers (ECDLs) have led to extended continuous tuning ranges. Mode-hop-free tuning over more than 65 GHz has been demonstrated. The ability to tune ECDLs asross a wide range is particularly useful to differential absorption lidar (DIAL) systems that use ECDLs as seed laser sources. Experiments using a multiple-pass gas absorption cell are performed to test a widely tunable, amplified ECDL DIAL transmitter with this extended tuning range system. Experimental results show that the system can be tuned to and maintained at a user-defined wavelength for one hour, then tuned to and maintained at a second user-defined wavelength for one hour without mode hopping. This tuning is successfully accomplished between wavelengths separated by approximately 44 GHz. A computer-controlled feedback loop in the tuning system tunes and holds the laser system to the on- and off-line wavelengths to within ±88 MHz. The laser power transmitted through the gas absorption cell is monitored and used to perform a differential absorption calculation to find the number density of water vapor molecules within the cell. The measured value is in agreement with a HiTRAN prediction of the expected value.

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Integrated Optics

Select this Article		Binary-phase micrograting and polarization beamsplitter for free-space micro-optical pickups Chi-Hung Lee, Yi Chiu, and Han-Ping D. Shieh Opt. Eng. 46, 084601 (Aug 13, 2007); http://dx.doi.org/10.1117/1.2769362 Online Publication Date: Aug 13, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A pop-up binary-phase micrograting and a pop-up micro polarization beamsplitter, for potential use in micro-optical pickups, have been realized on a single silicon chip using a two-layer polysilicon and one-layer silicon nitride micromachining process. In the case of the micrograting, a diffraction efficiency ratio between 4 and 10 can be achieved provided that the duty cycle is between 0.4 and 0.6 and the depth between 455 and 485 nm, respectively. For a grating designed for a diffraction ratio of 7, the measured ratio is 8.31. The polarization beamsplitter is a silicon nitride thin film placed at the Brewster angle. The transmittance of the TM mode was measured to be more than 98.5%, while the reflectance of the TE mode was 21.4%.

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Fiber Optics and Optical Communication

Select this Article		Analysis and modeling of a nonlinear radio-over-fiber system Xianwei Zhou, Jianping Wang, and Xiao Liu Opt. Eng. 46, 085001 (Aug 13, 2007); http://dx.doi.org/10.1117/1.2769616 Online Publication Date: Aug 13, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A radio-over-fiber (ROF) system that combines a wireless link and an optical fiber link is studied. After introducing the configuration and analyzing the nonlinear distortion of the system, the Volterra series is proposed and used to model the system. The adaptive least mean square (LMS) and recursive least squares (RLS) algorithms for identifying the Volterra kernel are studied. A simulation is given, which uses both Volterra LMS and Volterra RLS to model a nonlinear ROF system, and indicates that the method is efficient.

Select this Article		Illumination design of a white-light-emitting diode wireless transmission system Damon W. K. Wong and George Chen, member spie Opt. Eng. 46, 085002 (Sep 05, 2007); http://dx.doi.org/10.1117/1.2769650 Online Publication Date: Sep 05, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Conventional wireless communications make use of radio frequency. However, congestion and regulation of the spectrum have led to a search for alternatives. White-light-emitting diodes (WLEDs) can be modulated similarly to communications-wavelength infrared-light-emitting diodes. For WLEDs to be used for both wireless communication or an illumination, they have to be arranged in a manner that achieves a minimum signal power. To achieve this, an optimization routine has been created that optimizes the angular arrangement of the WLEDs to meet a predetermined illumination level. The irradiation profiles of the WLEDs are modeled for arbitrary tilt angles using a combination of theoretical expressions and experimental data. Lamps were created with 120 WLEDs each and implemented using the optimized angles. To demonstrate the use of the WLED wireless system in the transmission of audio signals, driving circuits were designed and implemented. The complete system was tested, and it is shown that the illumination levels meet the minimum required level. Characterization of the received signals shows a maximum ratio of bit energy to noise power density of 11.8 dB, corresponding to a bit error rate of 10⁻⁴.

Select this Article		Waveform distortion of wavelength conversion based on a periodically poled lithium niobate waveguide at a pulsed pump Chuanhong Luo, Junqiang Sun, Jing Liu, and Jun Chen Opt. Eng. 46, 085003 (Aug 13, 2007); http://dx.doi.org/10.1117/1.2771124 Online Publication Date: Aug 13, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract The wavelength conversion based on cascaded second-order nonlinearity by using pulsed pump waves is theoretically analyzed in a periodically poled lithium niobate waveguide. By numerical simulation, the evolution of pulses and the walk-off between pulses is discussed, and a distorted waveform of converted pulse is illustrated. A tunable and single-to-dual-channel wavelength converter is realized by pumping with picosecond pulses at a repetition rate of 40 GHz, and the waveform distortion of a converted pulse is demonstrated in our experiments.

Select this Article		Impact of Internet protocol traffic on differential phase-shift keying wavelength division multiplexing systems Xuetian Huang, Xiaojie Xu, Gang Chen, Min Zhang, and Peida Ye Opt. Eng. 46, 085004 (Aug 07, 2007); http://dx.doi.org/10.1117/1.2768036 Online Publication Date: Aug 07, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Based on analytical methods, we show that when Internet protocol (IP) traffic is loaded directly over differential phase-shift keying (DPSK) wavelength division multiplexing (WDM) systems with perfect dispersion compensation, the burstiness of IP packets has significant effects on the cross-phase modulation (XPM)-induced nonlinear phase noise, and therefore exerts an influence on the packet-error probability performance of the systems. It is demonstrated that the packet-error probability is dependent on the traffic source models. Moreover, we can shorten the packet and diminish the burstiness of the IP traffic to get a small packet-error probability. The results given are helpful for the design of DPSK WDM systems.

Select this Article		Performance investigation of all-optical clock recovery circuit based on Fabry-Pérot filter and semiconductor optical amplifier assisted Sagnac switch John S. Vardakas and Kyriakos E. Zoiros Opt. Eng. 46, 085005 (Aug 13, 2007); http://dx.doi.org/10.1117/1.2768956 \| Cited 3 times Online Publication Date: Aug 13, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A theoretical model is developed and exploited for characterizing the behavior of an all-optical circuit that deploys a Fabry-Pérot filter (FPF) and a semiconductor optical amplifier (SOA)-assisted Sagnac switch driven by an intense continuous wave (cw) holding beam to extract the clock signal from a received ultra-fast data stream. The role of each unit is thoroughly studied, and its understanding allows us to identify the critical operational parameters, which include the cw power, the energy of the data pulses, the SOA small signal gain, carrier lifetime and linewidth enhancement factor, the Sagnac loop asymmetry, and the finesse of the FPF. By means of numerical simulation, an extensive set of diagrams is derived, and from their interpretation the impact of these key factors on the amplitude modulation of the extracted clock pulses is investigated and evaluated. This process enables us to appropriately select and combine them to ensure enhanced performance concerning the defined quality metric, first at 10 Gb/s and then at 40 Gb/s. The final outcome demonstrates the technological feasibility and effectiveness of the proposed clock recovery scheme. The obtained results may be useful for theoretically addressing various all-optical signal processing tasks, whose proper execution relies decisively on clock recovery.

Select this Article		Effect of second-order polarization mode dispersion on the performance of polarization mode dispersion emulators Deepak Gupta, Arun Kumar, and K. Thyagarajan Opt. Eng. 46, 085006 (Aug 30, 2007); http://dx.doi.org/10.1117/1.2772246 \| Cited 1 time Online Publication Date: Aug 30, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We analyze the performance of multisection fiber polarization mode dispersion (PMD) emulators based on random fiber sectioning and ordered sectioning, with the inclusion of second-order PMD in individual sections. Numerical simulations show that this inclusion leads to (1) an asymmetry in the autocorrelation function (ACF) that increases with the magnitude of second-order PMD and whose form depends on the sign of the second-order term, and (2) a shift in the probability distribution functions of the differential group delay (DGD), and hence the mean DGD, with frequency that are undesirable. This behavior is found to be similar for both types of sectioning and has negligible effect on their corresponding background autocorrelation. This analysis leads to the requirement of suitable design parameters of fibers for which the second-order PMD in individual sections is minimized so that the desired ACF of the fabricated PMD emulator is symmetric and the mean DGD is the same at all frequencies.

Select this Article		Multiwavelength optical sender/receiver mounted on a PC connected to a passive optical network Hironari Matsuda, member spie, Takuya Kaminogou, and Tadahiko Yasui Opt. Eng. 46, 085007 (Aug 17, 2007); http://dx.doi.org/10.1117/1.2771645 Online Publication Date: Aug 17, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract The authors have developed a multiwavelength Internet protocol (IP) packet sender/receiver to be inserted into a peripheral component interconnect (PCI)-bus slot of a personal computer (PC) or a workstation. When the PCs or workstations with the sender/receiver are connected to an Internet access network configured on a passive optical network (PON) as client terminals, a peer-to-peer connection-oriented communication path can be set up between them. The PCs can afford a real-time interactive communication with quality of service (QoS) fully guaranteed.

Select this Article		Enhancing mobile ad hoc networks with free-space optics Peng Yan, James J. Sluss, Jr., member spie, Hazem H. Refai, and Peter G. LoPresti Opt. Eng. 46, 085008 (Aug 07, 2007); http://dx.doi.org/10.1117/1.2768973 Online Publication Date: Aug 07, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A mobile ad hoc network (MANET) offers a cost-effective solution for communications in areas where infrastructure is unavailable, e.g., emergency response, disaster recovery, and battlefield scenarios. Traditional MANETs operate in the radio frequency (RF) spectrum, where the available bandwidth faces the challenge of rapidly increasing demands. Free-space optics (FSO) provides an attractive complement to RF wireless MANETs because of its high bandwidth and interference-free operation. We have made an effort to combine the main advantages of MANET and FSO technologies by equipping the network nodes with hybrid communications capabilities. Computer models of such a network were created using the network simulator OPNET Modeler. Various indicators of network performance, including packet loss ratio, end-to-end delay, throughput, etc., were obtained through simulation and examined. The analysis will be of significant assistance in the design and implementation of such next-generation MANETs.

Select this Article		Efficient wavelength assignment strategy for wavelength-division multiplexing optical networks Paramjeet Singh, Shaveta Rani, and Ajay K Sharma Opt. Eng. 46, 085009 (Aug 21, 2007); http://dx.doi.org/10.1117/1.2771580 Online Publication Date: Aug 21, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract When a physical network and its required connections are given, the routing and wavelength assignment (RWA) is a problem. A suitable path and wavelength must be selected from among the many possible choices for each connection such that no two paths using the same wavelength pass through the same link. In the absence of wavelength conversion, a lightpath must use the same wavelength on all fiber links that it spans. In wavelength-division multiplexing (WDM) optical networks, there is a need to maximize the number of connections accepted and to minimize the number of connections rejected, i.e., the blocking probability. We propose a new strategy to assign the wavelength. Then we compare the performance of the proposed strategy with commonly used wavelength assignment strategies in terms of the number of attempts required to establish the given connection. The comparison shows that fewer attempts are required for the proposed strategy, leading to a reduced connection establishment time.

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Optical Interconnects

Select this Article		Digital micromirror device for optical scanning applications Hakki H. Refai, member spie, James J. Sluss, Jr., member spie, and Monte P. Tull Opt. Eng. 46, 085401 (Aug 13, 2007); http://dx.doi.org/10.1117/1.2768978 \| Cited 1 time Online Publication Date: Aug 13, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Recent mechanical and nonmechanical optical scanning devices do not meet the fast scanning requirements for contemporary and emerging applications and can only steer optical beams over relatively narrow angles. A variety of important applications require fast optical scanning devices that can steer laser beams rapidly to an arbitrary location and with no moving parts. We introduce a new optical scanning technique that can be used to collimate and steer optical beams for precision alignment in either 2-D free-space optical (FSO) communications links or image scanners. This nonmechanical technique is capable of rapidly redirecting the optical beams to arbitrary locations without greatly sacrificing other parameters such as aperture size, efficiency, and scanning range. A digital micromirror device (DMD) beam-steering system was successfully demonstrated and exhibited better performance results when compared with other available systems.

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Interferometry

Select this Article		Robust unwrapping algorithm for three-dimensional phase volumes of arbitrary shape containing knotted phase singularity loops Olov Marklund, Jonathan M. Huntley, and Rhodri Cusack Opt. Eng. 46, 085601 (Sep 07, 2007); http://dx.doi.org/10.1117/1.2771652 \| Cited 2 times Online Publication Date: Sep 07, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract The extension of path-independent 2-D phase unwrapping algorithms, based on placement of branch cut lines between phase singularities of opposite sign, was recently proposed for phase volumes in a paper by Huntley. In 3-D, the singularities were shown to form closed loops, and path independence was achieved by placing branch cut surfaces across the loops. In the current work, we describe in detail an optimized and extended version of Huntley’s algorithm. It deals in particular with two aspects that are essential for practical phase volumes: 1. how to close partial loops that pass through arbitrary boundaries separating valid and invalid phase data, and 2. how to select the set of loops having the shortest length. The second algorithm is necessary to deal with ambiguous cases that can arise when the singularities form knots, i.e., two loops pass through a single phase volume element. The performance of the algorithm is demonstrated on 3-D phase maps from two types of medical imaging data: medical resonance imaging (MRI) and x-ray interferometry.

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Holography

Select this Article		Watermarking by encrypted Fourier holography Liujie Sun and Songlin Zhuang, member spie Opt. Eng. 46, 085801 (Aug 07, 2007); http://dx.doi.org/10.1117/1.2769366 \| Cited 1 time Online Publication Date: Aug 07, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We propose and demonstrate a new encrypted Fourier holographic watermarking scheme based on double random phase encoding, digital holography, digital watermarking, and printing techniques. A digital watermark image to be hidden is encrypted by double random phase encoding with uniformly distributed random phase in both the input and Fourier planes. Using interference with a reference wave, an encrypted Fourier hologram is recorded digitally. The encrypted Fourier hologram can be hidden in a host image to protect the copyright. The watermark can be recovered by holographic reconstruction without the information of the host image (blind detection). Theoretical analysis and computer simulations prove that the new technique is valid and secure. The experimental results on the printing and scanning processes are presented to demonstrate that the proposed watermarked image can be used to prevent forgery of printed products.

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Atmospheric and Ocean Optics

Select this Article		Infrared phototransistor validation for atmospheric remote sensing application using the Raman-shifted eye-safe aerosol lidar Tamer F. Refaat, Syed Ismail, Terry L. Mack, M. Nurul Abedin, Shane D. Mayor, Scott M. Spuler, and Upendra N. Singh Opt. Eng. 46, 086001 (Aug 17, 2007); http://dx.doi.org/10.1117/1.2772280 \| Cited 2 times Online Publication Date: Aug 17, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract An InGaAsSb/AlGaAsSb phototransistor has been validated for lidar atmospheric remote sensing. The validation was performed using the Raman-shifted eye-safe aerosol lidar (REAL) at the National Center for Atmospheric Research. Although the device is optimized for detection around the 2-μm wavelength, the validation was performed at 1.543 μm, where mature commercial detectors are available. Simultaneous measurement of the atmospheric backscatter signals using the custom-built phototransistor and commercial InGaAs avalanche photodiode indicated good agreement between both devices. The validation included detecting 11-km-range hard targets, 5-km atmospheric structure consisting of cirrus clouds, and a near-field boundary layer. Far-field low intensity and spatially narrow atmospheric features were also detectable with the new phototransistor. Preliminary results related to systematic effects are discussed in the first attempt of incorporating a phototransistor in a lidar system.

Select this Article		Analysis of beam wander effects for a horizontal-path propagating Gaussian-beam wave: focused beam case Jaume Recolons, Larry C. Andrews, fellow spie, and Ronald L. Phillips, fellow spie Opt. Eng. 46, 086002 (Aug 24, 2007); http://dx.doi.org/10.1117/1.2772263 \| Cited 12 times Online Publication Date: Aug 24, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Failure of the first-order Rytov approximation to properly predict the scintillation index of a large-aperture focused beam, or an uplink collimated (or focused) beam, has been discussed in several recent publications, which cite beam wander effects as the main reason for this failure. We use computer simulations to examine several aspects of beam wander phenomena on a propagating convergent beam in the weak-fluctuation regime over a horizontal path at high altitude for which the refractive index structure parameter is on the order of Cn2 = 1.39×10⁻¹⁶ m^−2/3. Simulation results are presented at various ranges up to 10 km for (1) the beam wander centroid displacement, (2) the kurtosis excess of the irradiance profile, (3) the irradiance profile, (4) the mean-square hot spot displacement from the boresight and from the centroid, and (5) the scintillation index at the optical axis of the beam. In addition, simulation results are compared with theoretical models.

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Remote Sensing

Select this Article		Calibration, data processing, and maintenance of the United States Department of Agriculture high-resolution ultraviolet spectroradiometers Peter Kiedron, Mark Beauharnois, Jerry Berndt, Patrick Disterhoft, Lee Harrison, Joseph Michalsky, Gwen Scott, Jim Schlemmer, and James Slusser Opt. Eng. 46, 086201 (Aug 13, 2007); http://dx.doi.org/10.1117/1.2769599 \| Cited 1 time Online Publication Date: Aug 13, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract The USDA ultraviolet radiation network currently includes four high-resolution spectroradiometers, located at Table Mountain, Colorado (deployed November 1998); the Atmospheric Radiation Measurement Climate Research Facility in Oklahoma (October 1999); Beltsville, Maryland (November 1999); and Fort Collins, Colorado (October 2002). These spectroradiometers contain Jobin Yvon’s 1-m Czerny-Turner double additive spectrometers. The instruments measure total horizontal radiation in the 290- to 371-nm range, once every 30 min, with a nominal FWHM of 0.1 nm. We describe data quality control techniques as well as the data processing required to convert the raw data into calibrated irradiances. The radiometric calibration strategies using Central UV Calibration Facility FEL lamps that are directly NIST-traceable, portable field calibrators, and vicarious calibrations using data from UV multifilter rotating shadowband radiometers (MFRSRs) are discussed. Using direct-to-diffuse ratios from UV MFRSRs, we derive direct and diffuse high-resolution horizontal spectra from the collocated UV spectroradiometers of the USDA network. The direct-beam spectra can be used in a Langley regression that leads to spectroradiometric in situ calibration and to ozone column and aerosol optical depth retrievals. The high-resolution direct spectra are used to obtain the ozone column and aerosol optical depth in the 290- to 360-nm range at 0.1-nm resolution. A statistical summary of network performance is presented.

Select this Article		Change detection in synthetic aperture radar images using a spatially chaotic model Yu-Chang Tzeng and Kun-Shan Chen Opt. Eng. 46, 086202 (Aug 13, 2007); http://dx.doi.org/10.1117/1.2771146 Online Publication Date: Aug 13, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A new synthetic aperture radar (SAR) image change detection algorithm was developed using a spatially chaotic model for coherent SAR images. This algorithm is tolerant of misregistration even when the signal-to-noise ratio is low. Despeckling is unnecessary, making the method especially attractive wherever the radiometric changes are subtle. To demonstrate the algorithm’s performance, a varied set of multitemporal polarimetric SAR images was used for testing. As a reference, the simple image difference (DI) technique and the principal-component analysis (PCA) were used for comparison. The proposed method performs very well and can detect minute changes despite the presence of speckle, for which both DI and PCA fail.

Select this Article		Resonance lidar system for mesospheric sodium measurements Y. Bhavani Kumar, D. Narayana Rao, M. Sundara Murthy, and M. Krishnaiah Opt. Eng. 46, 086203 (Aug 13, 2007); http://dx.doi.org/10.1117/1.2767271 \| Cited 2 times Online Publication Date: Aug 13, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract This paper describes a newly developed resonance lidar system at Gadanki (13.5°N, 79.2°E), India. The lidar system is set up to probe the natural layer of neutral sodium atoms existing between 80 and 110 km. The lidar employs a YAG pumped dye laser as a transmitter. The laser is tuned to the sodium D₂ line at 589.0 nm. The lidar achieved first light on 10 January 2005 and made the first mesospheric sodium measurements from India. The lidar-measured vertical profiles of resonant backscatter are found to have sufficient signal strength for deriving the mesospheric sodium concentration profiles. Using the system, sodium concentration profiles are obtained with a vertical resolution of 300 m and a time integration of 120 s. These features allow the system to detect the time and space variability of Na concentration profiles. During the initial six nights of observation, the average nocturnal columnar abundances were in the range (2 to 8.3)×10⁹ cm⁻². The nightly mean centroid heights range between 92.7 and 95.1 km, and the rms widths vary between 4.3 and 4.9 km. The preliminary analysis of Na layer dynamics on 10 January 2005 shows the presence of wavelike structures with characteristics similar to those of propagating gravity waves. The preliminary analyses of data show a considerable variability in Na concentration distribution in the mesopause region during a sporadic Na event.

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Radiometry, Infrared Systems, Tracking

Select this Article		New two-stage correlation-based approach for target detection and tracking in forward-looking infrared imagery using filters based on extended maximum average correlation height and polynomial distance classifier correlation Sharif M. A. Bhuiyan, Mohammad S. Alam, fellow spie, and Mohamed Alkanhal Opt. Eng. 46, 086401 (Aug 17, 2007); http://dx.doi.org/10.1117/1.2769648 \| Cited 4 times Online Publication Date: Aug 17, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A novel approach is proposed to recognize and track multiple identical and/or dissimilar targets in forward-looking infrared (FLIR) image sequences using a combination of an extended maximum average correlation height (EMACH) filter and polynomial distance classifier correlation filter (PDCCF). The EMACH filter and PDCCF are trained a priori using representative training images of targets with expected size and orientation variations. In the first step, the input scene is correlated with all EMACH filters (one for each desired or expected target class). Based on the regions with higher correlation peak values in the combined correlation output, a sufficient number of regions of interest (ROIs) are selected from the input scene. In the second step, a PDCCF is applied to these ROIs to identify target types and reject clutter and background. Moving-target detection and tracking is accomplished by applying this technique independently to all incoming image frames. Independent tracking of target(s) from one frame to the other allows the system to handle complicated situations such as a target disappearing in a few frames and then reappearing in later frames. This method yields robust performance for challenging FLIR imagery in terms of accurate detection and classification as well as tracking of the targets.

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Ultraviolet and X-ray Applications

Select this Article		Multilayer coatings for x-ray mirrors: extraction of stack parameters from x-ray reflectivity scans and comparison with transmission electron microscopy results Daniele Spiga, Giovanni Pareschi, Vincenzo Cotroneo, Rodolfo Canestrari, Dervis Vernani, Alessandro Mirone, Claudio Ferrero, Claudio Ferrari, and Laura Lazzarini Opt. Eng. 46, 086501 (Aug 07, 2007); http://dx.doi.org/10.1117/1.2769325 \| Cited 4 times Online Publication Date: Aug 07, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract The reflectance effectiveness of a multilayer depends strongly on the stack properties (thickness, roughness, and density of each layer) and can be directly tested by means of x-ray reflectivity scans at definite photon energies. The reflectivity curves are also a powerful tool for the in-depth, nondestructive characterization of the stack structure: The complex task of extracting the stack parameters from reflectivity curves can be achieved via a suitable best-fitting computer code based on a global automatic optimization procedure. We present the computer-assisted layer-by-layer analysis of the characteristics of Ni/C, Pt/C, and W/Si multilayers, based on x-ray reflectivity scans performed at 8.05 and 17.45 keV. In order to verify the correctness of the code predictions, we present also a comparison of the computer model with the transmission electron microscope profiles of the same multilayer samples.

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Adaptive Optics

Select this Article		Characterizing static aberrations in liquid crystal spatial light modulators using phase retrieval Nathaniel W. Hart, Michael C. Roggemann, fellow spie, Alex Sergeyev, member spie, and Timothy J. Schulz, member spie Opt. Eng. 46, 086601 (Aug 07, 2007); http://dx.doi.org/10.1117/1.2767258 \| Cited 4 times Online Publication Date: Aug 07, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract There is a significant fixed aberration in some commercial off-the-shelf liquid crystal spatial light modulators (SLMs). In a recent experiment we conducted to simulate the effects of atmospheric turbulence and correction schemes in a laboratory setting using such an SLM, this aberration was too strong to neglect. We then tried to characterize and correct the observed aberration. Our method of characterizing the device uses a measurement of the far-field intensity pattern caused by the aberration and processing based on a parameterized version of the phase retrieval algorithm. This approach uses simple and widely available hardware and does not require expensive aberration sensing equipment. The phase aberrations were characterized and compared with the manufacturer’s published measurements for a similar device, with excellent agreement. To test the quality of our aberration estimate, a correction phase was computed and applied to the SLM, and the resulting far-field patterns were measured and compared to the theoretical patterns with excellent results. Experiments show that when the correction is applied to the SLM, nearly diffraction-limited far-field intensity patterns are observed.

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Image Processing

Select this Article		All-optical wavelet transform realization and use for imaging, image processing, and increased depth of focus Zeev Zalevsky, Eran Rossmann, and David Mendlovic Opt. Eng. 46, 087001 (Aug 13, 2007); http://dx.doi.org/10.1117/1.2769614 Online Publication Date: Aug 13, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We realize optical wavelet transforms by two methods. In the first, we image an object through an array of lenses having various diameters. This results in images of the object at different resolutions (according to the imaging lens). We show that a weighted combination of these images may realize the wavelet transform coefficients. In the second method we use the fact that defocus aberrations affect the resolution of the image. Imaging an object in high resolution (with a large-diameter lens) while focusing on different planes enables us to perform a wavelet transformation when the object is two-dimensional. After realizing the wavelet transform optically, we show how the suggested optical configurations can be used for image processing, for compression, and for extending the depth of focus of the imaged object. All required processing operations have very low computational complexity.

Select this Article		Color textile image segmentation based on multiscale probabilistic reasoning Xiqun Lu Opt. Eng. 46, 087002 (Aug 07, 2007); http://dx.doi.org/10.1117/1.2768319 \| Cited 1 time Online Publication Date: Aug 07, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Color textile images usually show a few dominant colors, and the inherent fabric thread structure makes it a difficult job for automatic clustering-based techniques to extract dominant colors from textile images. Based on the two distinctive features of textile images, a probabilistic reasoning segmentation algorithm for color textile images is proposed. Due to the uniform texture of the fabric appearing in textile images, dominant colors are extracted interactively. Then a hierarchic probabilistic reasoning model is applied to capture not only the statistical dependences of color information across adjacent scales, but also those among intrascale neighbor blocks. The multiscale approach is used to avoid the conflict between boundary localization and high-resolution segmentation by deducing the maximum posterior probability for each block recursively from coarse to fine scale. No special prior distribution assumption is made about the size and shape of regions in this algorithm. That there is no need to train the multiscale contextual model prior to the segmentation is one of the big advantages of this approach. Experimental results show that the proposed algorithm can produce better segmentation results and smoother edge maps for color textile images than some state-of-the-art segmentation techniques, both supervised and nonsupervised.

Select this Article		Color stereoscopic images requiring only one color image Yael Termin, Gal A. Kaminka, Sarit Semo, and Ari Z. Zivotofsky Opt. Eng. 46, 087003 (Aug 21, 2007); http://dx.doi.org/10.1117/1.2772235 \| Cited 2 times Online Publication Date: Aug 21, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Utilizing remote color stereoscopic scenes typically requires the acquisition, transmission, and processing of two color images. However, the amount of information transmitted and processed is large, compared to either monocular images or monochrome stereo images. Existing approaches to this challenge focus on compression and optimization. This paper introduces an innovative complementary approach to the presentation of a color stereoscopic scene, specialized for human perception. It relies on the hypothesis that a stereo pair consisting of one monochromatic image and one color image (a MIX stereo pair) will be perceived by a human observer as a 3-D color scene. Taking advantage of color redundancy, this presentation of a monochromatic-color pair allows for a drastic reduction in the required bandwidth, even before any compression method is employed. Herein we describe controlled psychophysical experiments on up to 15 subjects. These experiments tested both color and depth perception using various combinations of color and monochromatic images. The results show that subjects perceived 3-D color images even when they were presented with only one color image in a stereoscopic pair, with no depth perception degradation and only limited color degradation. This confirms the hypothesis and validates the new approach.

Select this Article		Error concealment method for the low-frequency subband in motion JPEG 2000 coding Jun Hou, Xiangzhong Fang, Jiliang Li, and Haibin Yin Opt. Eng. 46, 087004 (Aug 17, 2007); http://dx.doi.org/10.1117/1.2771135 Online Publication Date: Aug 17, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract An error concealment algorithm for motion JPEG 2000 (Joint Picture Expert Group 2000) is proposed. It reconstructs the totally corrupted low-frequency subband. First, the edge map of the image is achieved according to a well-defined procedure. Based on the features of the human visual system, motion compensation or replacement is then applied to recover the lost information. Simulation results indicate that the recovered frame can yield high subjective quality.

Select this Article		Integrated fingerprint verification method using a composite signature-based watermarking technique Farid Ahmed, member spie Opt. Eng. 46, 087005 (Aug 13, 2007); http://dx.doi.org/10.1117/1.2771232 \| Cited 1 time Online Publication Date: Aug 13, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We propose a composite signature-based digital watermarking technique for fingerprint verification and identity extraction applications. In a two-step process, our scheme attempts to integrate three modalities of authentication—“what you know,” “what you have,” and “what you are.” Using a signature extracted from the Fourier phase of an original image, we hide an encoded signature back into the original image using a frequency domain bit-plane embedding technique. Additionally, other identity information is embedded in the spatial domain using a spread-spectrum method. The detection process computes the Fourier transform of the watermarked image, then extracts the embedded signature and correlates it with a calculated signature. The embedding of a composite signature ensures robustness against any chosen form of distortion. Simulation results for the signature and identity embedding and detection are provided for the Fingerprint Verification Competition (FVC) fingerprint image database.

Select this Article		Cone-beam filtered backprojection image reconstruction using a factorized weighting function Guang-Hong Chen, Ting-Liang Zhuang, member spie, Shuai Leng, member spie, and Brian E. Nett, member spie Opt. Eng. 46, 087006 (Aug 17, 2007); http://dx.doi.org/10.1117/1.2771643 \| Cited 2 times Online Publication Date: Aug 17, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We present several new families of mathematically exact cone-beam image reconstruction algorithms for a general source trajectory that fulfills Tuy’s data sufficiency condition. The basic structure of the new algorithms is to reconstruct images via filtered backprojection (FBP) with a 1-D shift-invariant filter. Specifically, the general weighting function w(x,;t) for redundant data was decomposed into three components w₁(x,), w₂(x,t), and sgn[∙y′(t)], viz. w(x,;t) = [w₁(x,)w₂(x,t)sgn(∙y(t))]. Based upon the normalization condition of the weighting function, the first component w₁(x,) may be calculated using the second component w₂(x,t) Thus, the design of the weighting function was reduced to the selection of the second component w₂(x,t). Using this scheme, it has been demonstrated that, for a given scanning configuration, one may develop infinitely many different, exact cone-beam FBP image reconstruction algorithms. To demonstrate how this general procedure may be used to develop FBP image reconstruction algorithms, a two-concentric-circle scanning configuration is discussed in detail. Numerical simulations have been conducted to validate several of the derived image reconstruction algorithms. Several possible scan strategies are presented, and the possibility of performing multiple reconstructions with different scan configurations to reduce image noise is described. Noise properties also have been numerically studied for the implemented image reconstruction algorithms, then compared with two other shift-invariant FBP reconstruction algorithms.

Select this Article		Compression rates comparison of entropy coding for three-bit chain codes of bilevel images Luis Echávarri Aguinaga, Ricardo A. Neri-Calderón, and Ramón M. Rodríguez-Dagnino, member spie Opt. Eng. 46, 087007 (Aug 13, 2007); http://dx.doi.org/10.1117/1.2771241 \| Cited 3 times Online Publication Date: Aug 13, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We carried out a comparative study between different entropy coding schemes applied to bilevel images. The study was centered on their application to reduce existing redundancies in the three-bit chain code used to compress bilevel images. We propose a variant of the run-length codes using joint runs of two symbols at the same time. According to our results, the number of bits needed to store chain codes is reduced more than 50% over the case that is not compressed, and a 45% improvement is achieved over the results obtained with classical Huffman coding.

Select this Article		Design of a fast vector quantization image encoder Yung-Gi Wu Opt. Eng. 46, 087008 (Aug 13, 2007); http://dx.doi.org/10.1117/1.2768066 \| Cited 1 time Online Publication Date: Aug 13, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Vector quantization (VQ) is an efficient technique for signal compression. However, it requires much encoding time to find the closest codeword for every input vector. We propose a fast encoding method to speed up the encoding. With the help of a table that is created off-line and can be used by all the images, the encoder searches only part of the entire codebook. The proposed method is implemented to encode Lena and other images to test its performance. Compared to full-searching VQ (FS-VQ), although the encoder searches only about 20 codewords in the codebook for every input vector, more than 95% of the codewords searched by the proposed method are the same as the results searched by FS-VQ on average. In addition, we also adopt partial distortion searching (PDS) and lookup table (LUT) to decrease the mathematic computation. This saves 98.44% of the encoding time and 98.07% of the mathematic operation while encoding Lena. The proposed method is superior to all the existing fast VQ encoding methods. While encoding 100 nature images for testing, it can save more than 97% of the encoding time and mathematic operations, but the PSNR decays at most only 0.19 dB, which is invisible to human eyes.

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Machine Vision, Pattern Recognition

Select this Article		Uncooled infrared-imaging face recognition using kernel-based generalized discriminant analysis Dimitrios I. Domboulas, Monique P. Fargues, and Gamani Karunasiri Opt. Eng. 46, 087201 (Aug 27, 2007); http://dx.doi.org/10.1117/1.2769638 Online Publication Date: Aug 27, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We investigate the application of the kernel-based generalized discriminant analysis (GDA) approach to the recognition of infrared face images collected using a low-resolution uncooled IR camera. Results show that a low-cost, low-resolution IR camera combined with an efficient classifier is a usable tool in uncooled IR face recognition applications, and that best GDA-based recognition performance improves over that obtained with the fisherface approach by 3.96 percentage points, from 94.59% to 98.55%, on the data considered. This study also investigates the effects the number of projection vectors used in the GDA step, the kernel expression, and the specific distance type have on recognition performance. Results show the Mahalanobis angular distance to be the best choice, and that the recognizer computational load may be reduced by decreasing the number of eigenvectors selected in the GDA projection step without significant impact on recognition performance.

Select this Article		Efficient hybrid appearance model for object tracking with occlusion handling Bo Zhang, Weifeng Tian, and Zhihua Jin Opt. Eng. 46, 087202 (Aug 17, 2007); http://dx.doi.org/10.1117/1.2771656 \| Cited 1 time Online Publication Date: Aug 17, 2007 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract During object tracking, the appearance of the object being tracked often suffers from complex variations due to large illumination, pose changes, and frequent occlusions. Modeling a robust appearance model for accommodating those variations becomes a crux for appearance-based tracking algorithms. We present a tracking algorithm based on the hybrid appearance models that include a fixed appearance model, a fast-change appearance model, and an eigenspace-based model. The hybrid appearance models reveal three factors of appearance changes: stable, transient, and gradual. A particle filter is invoked to perform state inference and simultaneously be responsible for intermodel switching. In addition, robust statistics is utilized to deal with occlusion events. Numerous experiments on many difficult sequences demonstrate that our algorithm can effectively track the object undergoing large pose, lighting, and viewpoint changes. More importantly, our algorithm shows powerful ability of addressing severe occlusions.

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