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A novel 10-Gbps bidirectional optical subassembly (BOSA) comprised of a 1577 nm electroabsorptive modulated laser (EML) transmitter optical subassembly (TOSA) and 1270 nm avalanche photodiode (APD) receiver optical subassembly (ROSA) was developed. Here, a 10-Gbps microdevice compatible two-window flat package was proposed to simplify the EML BOSA structure, considering both the mechanical reliability and cooling performance. As a result, an optical output power of 8 dBm was obtained due to a high optical coupling efficiency of 60%, an extinction ratio of 7 dB, and a dispersion penalty at 20 km transmission of less than 1.5 dB for the EML TOSA. The APD ROSA sensitivity was -21.5 dBm at a bit error rate (BER) of 10−12 and -27 dBm at a BER of 10−3 without forward error correction. In addition, the sensitivity penalty of the APD ROSA due to signal crosstalk was less than 1.2 dB.

In this letter, a novel optimized view synthesis distortion model is proposed for bit allocation in three-dimensional video coding. The proposed model separates the view synthesis distortion into two independent terms, and the two terms are modeled respectively by quadratic distortion models. Finally, the optimal quantization parameters for texture and depth can be determined by minimizing the view synthesis distortion under the total bitrate constraint. Experimental results show that compared with a fixed 5:1 method, the proposed method can obtain higher view synthesis rate-distortion performance.

An introduction to the special section by the guest editors.

Rudolf Kingslake (1903 to 2003) is perhaps the most widely-known name in lens design and is arguably recognized as the father of lens design in the United States. Although his contributions in optical design, engineering, and education after he moved to the United States in 1929 are generally well-known, little has been written about his technical activities beforehand. In the early summer of 1929, the president of the University of Rochester, Rush Rhees, visited England to recruit faculty members for the new Institute of (Applied) Optics and hired 26-year-old Rudolf Kingslake as its first faculty member, and appointed him as assistant professor of geometrical optics and optical design. The following review of Kingslake's nine published papers while at the Imperial College illustrates his early and already remarkable talents in the field of optical engineering and justifies Dr. Rhees' insightful decision. Kingslake made significant contributions in the area of optical testing. In particular, he expanded the utility of the Hartmann test to measure oblique aberrations and improved the metrology for large optics, and was the first to mathematically analyze interferograms to obtain the primary aberration coefficients.

This paper describes a process for designing a faceted freeform Fresnel lens. Where a traditional Fresnel lens uses a profile revolved around a central axis, a freeform Fresnel lens uses individual triangular or trapezoidal facets that comprise a freeform surface. This type of lens combines the capability of a freeform surface with the benefits of a Fresnel lens, in particular: thin profile, low cost, small size, and relatively simple geometry calculations. An algorithm is presented to design such a lens that generates an output intensity distribution without depending on symmetry in the light source, the lens aperture, or the output intensity distribution. Two example systems are presented, demonstrating how a freeform Fresnel lens can reshape a beam of light without relying on symmetry.

Our acquaintance with rays and refraction is based on previous work carried out by scientists, practitioners, artisans, and optics users. Here a selection of illustrations from ancient books and documents is presented, testifying to the substantive development that took place at the turn of 1600. Achievements at the roots of our continuing advances in optical sciences are acknowledged.

To meet today's demanding requirements for increased performance, reduced size, lower mass, and cost, simple lenses containing multiple aspheric surfaces are required. It is now common for the number of aspheric surfaces used in an infrared lens to exceed the actual number of lens elements. Multiple aspheric and diffractive surfaces provide additional degrees of freedom in the lens design. This is required to achieve increased levels of imaging performance demanded by reduced pitch detectors. Aspheric surfaces also enable a greater diversity of materials to be used such that athermal solutions can be realized without the need for additional lens elements. More recent advances in detector technology will demand multispectral operation, but the requirements for simple, inexpensive optics will remain. Innovative use of aspheric components can also create very simple multispectral optics to fulfil this emerging need. This paper will review the range of applications that can be satisfied using no more than two optical components, highlighting the specific benefits that aspheric and diffractive surfaces provide. Consideration will also be given to future developments where enhanced functionality can be achieved using computational imaging techniques. Examples will be given for several military applications including weapon sights, driver's vision enhancement and remote weapon stations.

Specific developments in optical technology over the past 30 years including refractive materials, thin film coatings, and surface profiles will be discussed. A large variety of optical designs which depend on some of these developments will be described. The optical design examples presented will cover the infrared, visible, ultraviolet, and combinations of these wavebands. A novel multiwaveband optical system that utilizes many of these developments will be illustrated in several possible configurations to meet different application requirements. A summary of the technologies employed in all of the optical design examples will indicate whether or not there may be trends in optical technology development. The optical design examples will be taken from issued Patents or published Patent applications, and hence their optical prescriptions will be available for detailed analysis.

This paper presents a novel colony analysis system including an adjustable image acquisition subsystem and a wavelet-watershed-based image segmentation algorithm. An illumination box was constructed-both front lightning and back lightning illuminations can be chosen by users based on the properties of Petri dishes. In the illumination box, the lightning is uniform, which makes image processing easy. A digital camera at the top of the box is connected to a PC computer; all the camera functions are controlled by the developed computer software in this study. As usual, in the image processing part, the hardest task is image segmentation which is carried out by the four different algorithms: 1. recursive image segmentation on gray similarity; 2. canny edge detection-based segmentation; 3. the combination of 1 and 2, and 4. colony delineation on wavelet and watershed. The first three algorithms can obtain good results for ordinary colony images, and for the images including a lot of small (tiny) colonies and dark colonies and overlapping (or touching) colonies, the algorithm 4 can obtain better results than the others. The algorithms are tested by using a large number of different colony images, and the testing results are satisfactory.

Modern computed tomography (CT) equipment allowing fast 3-D imaging also makes it possible to monitor dynamic processes by 4-D imaging. Because the acquisition time of various 3-D-CT systems is still in the range of at least milliseconds or even hours, depending on the detector system and the source, the balance of the desired temporal and spatial resolution must be adjusted. Furthermore, motion artifacts will occur, especially at high spatial resolution and longer measuring times. We propose two approaches based on nonsequential projection angle sequences allowing a convenient postacquisition balance of temporal and spatial resolution. Both strategies are compatible with existing instruments, needing only a simple reprograming of the angle list used for projection acquisition and care with the projection order list. Both approaches will reduce the impact of artifacts due to motion. The strategies are applied and validated with cold neutron imaging of water desorption from originally saturated particles during natural air-drying experiments and with x-ray tomography of a polymer blend heated during imaging.

When the emitted light from a small object illuminates a rough interface, the image of the object is formed in reflection if the incident angle of the light is larger than a threshold angle. The threshold angle is the angle beyond which the specularly scattered light acquires a coherent component. The threshold angle depends on interface roughness and light wavelength. In transmission mode, the incident angle on the rough interface has an upper limit for image formation. The latter angle depends also on the refractive indices of the media surrounding the rough interface. We have determined the threshold angles and corresponding roughness for three different wavelengths using rough sheet-glass surfaces that were prepared by grinding sheet-glass surfaces by powders of different grain size. The roughnesses obtained by this method are in good agreement with those obtained by other methods. Our experimental studies also show that the threshold angle is practically independent of the illumination intensity. The presented method has the potential to be used in process measurement due to simplicity of the required optical system.

Three-dimensional (3-D) tracking and trajectory measurement of group translating and rotating particles may greatly help applications in collective behavior study, motion measurement, etc. Binocular stereo methods are commonly used to track and measure 3-D trajectories of drifting particles. Nevertheless, binocular methods usually suffer from severe stereo-matching ambiguity facing these situations even if motion constraint is adopted to disambiguate stereo matching. We try to help the disambiguating by optimizing viewpoint placement. We model the stereo-matching ambiguity and test different viewpoint placements upon our geometrical analysis to show the influence on the disambiguation that utilizes motion constraint. When the targets undergo group translation and rotation which are highly ambiguous, we find the optimal viewpoint placement such that stereo-matching ambiguity decreases as fast as possible over time. The optimal viewpoint placement can greatly improve the performance of existing methods.

Automatically adapting the camera exposure time is crucial for industrial applications where minimum human intervention is usually desirable. However, it is very challenging to realize such a capability for a conventional fringe projection system where only a finite increment of the exposure time is allowed due to its digital fringe generation nature. We study the generation of sinusoidal fringe patterns by properly defocusing binary ones, which permits the use of an arbitrary exposure time. This provides the potential to adapt the exposure time automatically. We present the principle of an automatic exposure technique and show some experimental results.

An electroactive polymer (EAP)-based MOEMS spatial light modulator (SLM), which shows high reliability and fast response speed, is reported in this work. The reliability is achieved by designing the SLM without direct contact between electrodes and deformable EAP surface; while the fast response speed is obtained by optimizing the microstructure of the EAP material. The concept of SLM, material optimization approach, fabrication processes, as well as characterization methods, are described. The SLM is driven by relatively low voltage, which is 200 V dc and 60 V ac and the response time is 35 μs. The manufactured SLM shows no degradation or breakdown after millions of actuation cycles, indicating a good reliability of the device.

In this paper, the influence of the operating parameters on the performance of a waveguide-CO₂ laser was investigated. The output power versus discharge current, gas pressure, and gas mixture ratio were measured using a different tube design. Also, it is observed that the laser output wavelengths vary as the discharge current changes. The obtained maximum powers are ∼14.5 W in a tube of diameter 3 mm and length 70 cm at the pressure 50 mbar, using the active medium with two discharge regions.

As novel sensors, rotational symmetric triangulation sensors (RSTSs) have broad application potential because of their robustness and accuracy. However, existing RSTSs have the disadvantages of complicated structure and high cost. The current paper presents a novel RSTS based on an object space mirror. The proposed sensor uses a cone mirror and a commercial camera, which significantly simplifies the structure and reduces its cost. Mathematical models are discussed to reveal the measurement range of the sensor and the relation between the displacement of the spot and the radius of the ring in the image. An improved image processing method is also introduced for a more efficient processing. Finally, two experimental systems with mirror angles at π/6 and π/4 are set up. Experimental results showed that the proposed sensor can achieve a comparable accuracy of 1.6 μm compared with that of existing methods, as well as a higher efficiency of image processing, while remaining at a low cost.

A colonoscopy's near-blind navigation process frequently causes disorientation for the scope operator, leading to harm for the patient. Navigation can be improved if real-time colonoscope shape, location, and orientation information is provided by a shape-tracking aid, such as a fiber optic bend sensor. Fiber optic bend sensors provide advantages over conventional electromechanical shape-trackers, including low cost and ease of integration. However, current fiber optic bend sensors lack either the ability to detect both bending direction and curvature, or the ability to detect multiple localized bends. An inexpensive multifiber bend sensor was developed to aid users in navigation during colonoscopy. The bend sensor employs active-cladding optical fibers modified with fluorescent quantum dots, bandpass filters, and a complementary metal-oxide-semiconductor imager as key components. Results from three-fiber sensors demonstrate the bend sensor's ability to measure curvature (error of 0.01 mm), direction (100% accuracy), and location (predetermined distance) of a bend in the fiber bundle. Comparison with spectroscopy data further confirmed the accuracy of the bending direction measurement for a three-fiber sensor. Future work includes improvements in fiber manufacturing to increase sensor sensitivity and consistency. An expanded 31 fiber bundle would be needed to track the full length of a colonoscope.

The overall procedure toward the implementation of a compact tunable athermal filter mounted on a piezoelectric actuator and based on a π-shift chirped fiber Bragg grating is presented. This package ensures an active tunablility over 2 nm with a cross thermal induced Bragg wavelength shift below 100 pm over a temperature range from −20°C to +80°C. The proposed filter makes use of the overall response of a π-shift chirped fiber Bragg grating and a bulk broadband microfilter that enables a sharp optical transmission spectrum response having a FWHM below 20 pm within a 2 nm region and 20 dB rejection band to be obtained.

We present the results of a real fire test using optical fiber sensors embedded in concrete samples. The temperature curve used in this experiment is described in the Spanish/European standard UNE-EN 1363-1 temperature profile for normalized concrete resistance to real fire tests, reaching temperatures of more than 1000°C inside the fire chamber and up to 600°C inside the concrete samples. Three types of optical sensors have been embedded in concrete: 1. standard fiber Bragg gratings inscribed in photosensitive germanium-boron co-doped fiber, 2. regenerated fiber Bragg grating (RFGB) inscribed in germanium doped fiber, and 3. RFBG inscribed in germanium-boron co-doped fiber.

A fiber-optic localized surface plasmon (FO LSPR) sensor was fabricated by gold nanoparticles (Au NPs) immobilized on the end-face of an optical fiber. When Au NPs were formed on the end-face of an optical fiber by chemical reaction, Au NPs aggregation occurred and the Au NPs were immobilized in various forms such as monomers, dimers, trimers, etc. The component ratio of the Au NPs on the end-face of the fabricated FO LSPR sensor was slightly changed whenever the sensors were fabricated in the same condition. Including this phenomenon, the FO LSPR sensor was fabricated with high sensitivity by controlling the density of Au NPs. Also, the fabricated sensors were measured for the resonance intensity for the different optical systems and analyzed for the effect on sensitivity. Finally, for application as a biosensor, the sensor was used for detecting the antibody-antigen reaction of interferon-gamma.

Integrated waveguide microwave photonic filters (MPFs) have the potential to bring down volume, weight, and power consumption of signal processing equipment besides the common advantages of discrete-component-based MPFs. A polysiloxane-liquid polymer-based optical wave-guide microring resonator was designed and fabricated by a simple ultraviolet-based soft-imprint technology, with which the quasi-single-sideband filtering for the 10 to 22 GHz microwave signal was realized and 20 Mbps quadrature phase shift keying signal carried by 14.35 GHz microwave transmission over a 25 km single mode fiber was demonstrated.

Realization of two-bit all-optical analog-to-digital conversion for an analog signal sampled by a femtosecond soliton sequence is investigated. Two approaches are suggested. The first one is based on filtering the broadened soliton spectrum after evolution over half of the soliton period in a standard single-mode fiber. In the second approach, the pulse is temporally sampled at the specified times after propagating through one soliton period. The sampled soliton sequence must be amplified to achieve an initial peak power of between 0 and 75 kW for the first method and between 0 and 66 kW for the second method. The soliton pulse-width is 50 fs. Based on the resulted peak power, the "0" or "1" bit is generated with reference to the threshold values. Subsequently, the digital gray code is produced at the outputs. The effect of inaccuracy in filter frequency and fiber length are also studied in this paper. The first method is sensitive to variations in the filter frequency, whereas the second method is affected by the fiber length inaccuracy.

Due to the number of wavelengths in fibers increasing, the transmission ports consumed in optical cross-connect (OXC) are greatly enhanced. To reduce the complexity and the cost of OXC, waveband switching technology is proposed. At the same time, since an optical channel carries a lot of traffic, its failure may lead to a huge data loss. Therefore, survivability in waveband switching (WBS) optical networks is important. Previous work for survivable WBS optical networks did not consider the holding time of connection request. However, in a practical network, the different connection requests generally have different holding times. This fact affects the network performances. In this paper, we propose a new method, holding time aware differentiated protection (HTADP), to provide the survivability for single-link failure in WBS optical networks. In HTADP, if the holding time of a connection request is smaller than the preset threshold, the protection path will not be assigned for saving network resources. In addition, we design a waveband integrated auxiliary graph for HTADP to well support the routing and waveband assignment. Simulation results demonstrate that HTADP not only saves more transmission ports but also is able to obtain lower blocking probability compared with previous method.

A novel hexagonal lattice photonic crystal fiber (PCF) design with two triangular arrays of semiminor-axis-decreasing elliptical air holes is proposed in this paper. The PCF characteristics based on the full-vector finite element method with perfect matched layer boundary conditions show that a wider bandwidth and dispersion-flattened profile for single-polarization single-mode (SPSM) operation is achieved. The SPSM operation can be realized in a spectral region ranging from the wavelength of 1.4 to 2 μm. The profile with convex and dispersion-flattened dispersion is obtained from the wavelength of 1.391 to 1.624 μm.

In order to achieve multisignal power equalization in a quasidistributed fiber Bragg grating (FBG) sensing system, an erbium-doped fiber (EDF) superfluorescent source with high flatness and broadband spectrum is presented using a three-stage double-pump configuration. The spectral protrusions in the vicinity of 1532 and 1570 nm are flattened, which is achieved by designing a gain flattening filter with a long-period grating. The result shows that the flatness of the output spectrum covering the C and L band, from 1526.52 to 1607.87 nm, is less than 0.76 dBm. The 3 dB bandwidth is 75.68 nm, and the output power of 13.11 mW is achieved in the C and L band. By using the fiber amplified spontaneous emission (ASE) source in FBG sensing system for decreasing multisignals peak power variation, the standard deviation of multisignals peak power is decreased to 1.00 dBm. In a multiplexed FBG sensing system, the high flattening fiber ASE source is beneficial to long-distance transmission, amplification, recognition, and demodulation of FBG sensing signals.

In this study a new design of terahertz frequency carrier generation for radio frequency identification (RFID) application is proposed. The dense wavelength-division multiplexing can be generated and obtained by using a Gaussian or soliton pulse propagating within a modified add-drop filter known as a PANDA ring resonator. The broad bandwidth of terahertz signals can be obtained and are available for useful applications, in which the use of the generated terahertz pulses for RFID application, for instance Ad-Hoc network, uses RFID. Results obtained have shown that the increase in channel capacity can be obtained and useful for the large demand of RFID applications.

In this work, we propose and experimentally demonstrate a novel distributed-controlled protection architecture for automatic and fast network restoration in wavelength division multiplexing-passive optical network (WDM-PON). The proposed scheme can support both C and L bands. Besides, duplication of network equipments, such as optical networking unit (ONU) or optical line terminal, is not required. In this distributed-controlled system, each ONU can always keep track of the network status. Hence, this can facilitate the network manage by removing the work loads from the central office. Besides, the proposed scheme can tolerate simultaneous fiber cuts in the feeder and distributed fibers.

An optical Miller coding scheme is proposed with the help of high speed electrical logic gates. With both Miller and Manchester being from the same family of code, i.e., 1B/2B, the former has less electrical spectrum compared with that of Manchester coding and thereby demonstrates a relatively higher tolerance against fiber dispersion within a certain range of distance. The applicability of this code in optical communication has not been explored adequately by the researchers until now, despite its advantages. Here we have investigated the dispersion tolerance of this code and found it to be nearly 1.2 times that of Manchester coding. The dispersion tolerance of Miller code obtained is from −306.4 to +263.9 ps/nm at 1 dB power penalty.

In this demonstration, we propose and investigate a long reach passive optical network (PON) using four wavelength-multiplexed signals with both on-off keying modulations for 40 Gb/s downlink traffic in 100 km fiber transmission without dispersion compensation. In the exchange node, we can use four channels with video services broadcasting to each optical network unit (ONU) for the uplink signal remodulation. Hence, four wavelength-multiplexed video signals also can be used to inject into the corresponding reflective semiconductor optical amplifiers in each ONU for uplink signal remodulation to achieve a 4 × 2.5 Gb/s data rate. In addition, under the 32 split ratio PON system, the power penalties of nearly 6.7 and 1 dB could be measured at the bit error rate of 10−9 for the downlink and uplink traffic, respectively.

An autoregressive method to analyze the fringe pattern observed in holographic interferometry is reported. Considering the impact of a 30 dB signal-to-noise ratio, we have shown that the reconstruction of the simulated symmetric profiles with 3, 4, and 5 fringes produces a maximum error of 0.300, 0.520, and 1.015 rad, respectively. The reconstruction of an asymmetric profile gives a larger error. The method was also applied to a recent fringe pattern. Our results are in qualitative agreement with those obtained using other methods.

This article reports a study done on eosin-doped poly(vinyl alcohol)/acrylamide films for holographic recording using 488 nm Ar⁺ laser. Films were fabricated using gravity settling method at room temperature and were stored under normal laboratory conditions. Ar⁺ laser (488 nm) was used for fringe recording. Characterization was done by real time transmittance measurement, optical absorption studies, and diffraction efficiency measurements. Various holographic parameters such as exposure energy, recording power, spatial frequency, etc., were optimized so as to ensure maximum performance. More than 85% diffraction efficiency was obtained at an exposure energy of 50 mJ/cm² in the optimized film. Efforts were taken to study the environmental stability of this self-developing polymeric material by looking at its shelf life and storage life. Compatibility for recording transmission hologram was also checked.

Strong experimental data supporting the theoretical relationship between linear and circular depolarizations for randomly oriented particles are presented. The analysis of the data leads to the first experimental validation of the theoretical representation of the scattering Mueller matrix as having indeed only one free parameter for randomly oriented particles, which is the depolarization parameter, d. Consequently, there is no added information on the nature of the aerosols when the four Stokes parameters are measured for randomly oriented aerosols, as opposed to measuring only the linear polarization or only the circular polarization related parameters. This conclusion has a direct impact on the analysis of the level of complexity of the systems that are required to analyze aerosols based on their depolarization signatures.

NASA Langley Research Center is working on a continuous wave (cw) laser-based remote sensing scheme for the detection of CO₂ and O₂ from space-based platforms suitable for an active sensing of CO2 emissions over nights, days, and seasons (ASCENDS) mission. ASCENDS is a future space-based mission to determine the global distribution of sources and sinks of atmospheric carbon dioxide (CO₂). A unique, multifrequency, intensity modulated cw laser absorption spectrometer operating at 1.57 μm for CO₂ sensing has been developed. Effective aerosol and cloud discrimination techniques are being investigated in order to determine concentration values with accuracies less than 0.3%. In this paper, we discuss the demonstration of a pseudonoise code-based technique for cloud and aerosol discrimination applications. The possibility of using maximum length sequences for range and absorption measurements is investigated. A simple model for accomplishing this objective is formulated. Proof-of-concept experiments carried out using a sonar-based LIDAR simulator that was built using simple audio hardware provided promising results for extension into optical wavelengths.

Hyperspectral imagery contains a large number of mixed pixels, which limits its utility. Super-resolution mapping is a potential solution to this problem, designed to use the proportion of land covers to obtain a sharpened thematic map with higher resolution. Endmember is a fundamental variable in the process, which is a critical issue for decomposing the mixed pixels and sharpening the subpixel level images. In most cases, the forms of the endmember combination in diverse pixels are very distinct. However, traditional soft classification methods neglect this point and model endmembers as fixed composition entities. Due to the reliance on this flawed spectral mixture model, the super-resolution mapping is unable to represent detail in the following result image precisely and effectively. In this work, therefore, endmember variability is considered, focusing on identifying the most suitable form of the endmember combination. This issue is addressed by applying a new selective endmember spectral mixture (SESM) model, which allows the endmember number and type to vary at a per pixel level, and then super-resolution mapping can be subsequently performed according to the produced spectral abundances. Two different types of hyperspectral data are used in our experiments. First, the SESM model is tested individually for validation of its applicability. Then the complete algorithm integrating SESM and super-resolution mapping based on a back-propagation neural network is evaluated. It showed that a more accurate endmember combination in the parent pixel results in a finer representation image. The experimental results prove that the proposed algorithm can effectively improve the accuracy of the super-resolution mapping results compared to the traditional method.

Man-portable air-defense (MANPAD) systems have developed sophisticated counter-countermeasures (CCM) to try and defeat any expendable countermeasure that is deployed by an aircraft. One of these is a seeker that is able to detect in two different parts of the electromagnetic spectrum. Termed two-color, the seeker can compare the emissions from the target and a countermeasure in different wavebands and reject the countermeasure. In this paper we describe the modeling process of a two-color infrared seeker using COUNTERSIM, a missile engagement and countermeasure software simulation tool. First, the simulations model a MANPAD with a two-color CCM which is fired against a fast jet model and a transport aircraft model releasing reactive countermeasures. This is then compared to when the aircraft releases countermeasures throughout an engagement up to the hit point to investigate the optimum flare firing time. The results show that the release time of expendable decoys as a countermeasure against a MANPAD with a two-color CCM is critical.

A new theory for describing the ultraviolet (UV) laser generation mechanism by frequency doubling of focused Gaussian beam in nonlinear crystal was presented. The nonlinear crystal used for UV laser generation, such as β-barium borate (BBO), has dramatically small phase matching acceptance angles Δθx and large walk-off angle ρ. Numerical simulation shows the variation of the waist of input Gaussian beam brings change in conversion efficiency and far-field transverse intensity distribution. For validating the theory, we investigated the single-pass conversion efficiency in BBO crystal by using acoustic-optic Q switched 532 nm laser; and took a photograph of fringe structure far-field intensity distribution of the UV beam. Comparison between the numerical simulation and experimental results support our theory and analysis. Our theory provides a useful tool for estimating ultraviolet laser generation processes for low power nanosecond pulsed laser and cw laser.

Removing shadows from single color images is an important problem in computer vision. In this paper, we propose a novel shadow removal approach, which could effectively remove shadows from textured surfaces, yielding high quality shadow-free images. Our approach aims at calculating scale factors to cancel the effect of shadows. Based on the regional gray edge hypothesis, which assumes the average of the reflectance differences in a region is achromatic, the scale factors can be computed without the restrictions that former algorithms need. The experimental results show that the proposed algorithm is effective.

The problem of low and nonuniform resolution has long been a topic of research in omnidirectional imaging. A novel fusion method based on nonsubsampled contourlet transform is proposed in this paper to fuse the pair of complementary panoramic images unwrapped from the inner and outer of the omni-image. This work can be considered as a continuation research of the complementary-structure catadioptric imaging technique based on multiple mirrors. Specifically, the high-frequency details are extracted by nonsubsampled directional filters only in the horizontal and vertical directions, since the complementarity mostly exists in two orthogonal directions. The horizontal and vertical high-frequency coefficients of the fused image are selected from the panoramic image which has the advantage in the corresponding direction. The fusion rule for the low-frequency coefficients is an improved "selecting" scheme with considering the high-frequency directional vector. Simulation experiments based on decimation and interpolation are implemented using the proposed fusion method, which outperforms other existing fusion methods in terms of both visual quality and objective evaluation. The proposed fusion method has demonstrated on experiments that both indoor and outdoor of real-scene imaging can gain better performance by using our prototype omnidirectional sensor.

A novel switching-based filter is proposed in this work to remove the impulse noise from the corrupted image. First, samples in 5×5 filter window are fully considered to detect whether the center is corrupted by impulse noise or not. Then, the detected noise free samples in the 5×5 filter window, aligned in the main direction, are weighted more heavily than those that are not on the main direction when using the median operation to suppress the impulse noise. At last, simulation results demonstrated that this algorithm outperforms many other methods in terms of both quantitative and qualitative aspects.

In this paper, we present an approach to learn latent semantic analysis models from loosely annotated images for automatic image annotation and indexing. The given annotation in training images is loose due to: 1. ambiguous correspondences between visual features and annotated keywords; 2. incomplete lists of annotated keywords. The second reason motivates us to enrich the incomplete annotation in a simple way before learning a topic model. In particular, some "imagined" keywords are poured into the incomplete annotation through measuring similarity between keywords in terms of their co-occurrence. Then, both given and imagined annotations are employed to learn probabilistic topic models for automatically annotating new images. We conduct experiments on two image databases (i.e., Corel and ESP) coupled with their loose annotations, and compare the proposed method with state-of-the-art discrete annotation methods. The proposed method improves word-driven probability latent semantic analysis (PLSA-words) up to a comparable performance with the best discrete annotation method, while a merit of PLSA-words is still kept, i.e., a wider semantic range.

Lensless thermal-light ghost imaging of moving objects is investigated. The second-order correlation function of thermal-light ghost imaging of moving objects is obtained by quasistatic approximation. The relationship between the visibility of the ghost imaging and the transverse coherent length l_c is demonstrated, and the smallest distinguishable distance (or resolution) of the ghost imaging system equals l_c. We provide a method to decide a proper sampling number for ghost imaging of a moving object.

We propose a novel image-importance model for content-aware image resizing. In contrast to the previous gradient magnitude-based approaches, we focus on the excellence of gradient domain statistics. The proposed scheme originates from a well-known property of the human visual system that the human visual perception is highly adaptive and sensitive to structural information in images rather than nonstructural information. We do not model the image structure explicitly, because there are diverse aspects of image structure and they cannot be easily modeled from cluttered natural images. Instead, our method obtains the structural information in an image by exploiting the gradient domain statistics in an implicit manner. Extensive tests on a variety of cluttered natural images show that the proposed method is more effective than the previous content-aware image-resizing methods and it is very robust to images with a cluttered background, unlike the previous schemes.

We denoised computed tomography (CT) imagery using a novel framework. This approach allows methods optimized for white noise to be used for signal-dependent noise present in low-dose CT imagery. Lowering the dose of x-rays results in an increase in quantum noise. We denoised an image independently several times using different parameters, then we selected pixels from those denoised images to form a final composite image. We compared results using a block-matching collaborative approach and a nonlocal means algorithm, but in principle other methods could work within this framework as well. The proposed framework improved denoising results in CT imagery when compared to not using the framework.

Most driver-monitoring systems have attempted to detect either driver drowsiness or distraction, although both factors should be considered for accident prevention. Therefore, we propose a new driver-monitoring method considering both factors. We make the following contributions. First, if the driver is looking ahead, drowsiness detection is performed; otherwise, distraction detection is performed. Thus, the computational cost and eye-detection error can be reduced. Second, we propose a new eye-detection algorithm that combines adaptive boosting, adaptive template matching, and blob detection with eye validation, thereby reducing the eye-detection error and processing time significantly, which is hardly achievable using a single method. Third, to enhance eye-detection accuracy, eye validation is applied after initial eye detection, using a support vector machine based on appearance features obtained by principal component analysis (PCA) and linear discriminant analysis (LDA). Fourth, we propose a novel eye state-detection algorithm that combines appearance features obtained using PCA and LDA, with statistical features such as the sparseness and kurtosis of the histogram from the horizontal edge image of the eye. Experimental results showed that the detection accuracies of the eye region and eye states were 99 and 97%, respectively. Both driver drowsiness and distraction were detected with a success rate of 98%.

Cascaded object detectors have demonstrated great success in fast object detection, where image regions can quickly be rejected using a cascade of increasingly complex rejectors/detectors. Although such cascaded detectors typically are fast and require minimal computation, they usually require iterative training, where classifiers are retrained to optimize rejection thresholds after testing on a validation set. We propose a cascaded object detector that uses probabilistic resampling for boosting reweighting, which has the advantage that only a single training step is required. Decision thresholds can be tuned on a validation set without the need for classifier retraining. Empirical results on a pedestrian detection task demonstrate that this reweighting results in a strong classifier that quickly rejects image regions and offers higher accuracy than other competing approaches.

This paper presents a novel vision system for people detection using an omnidirectional camera mounted on a mobile robot. In order to determine regions of interest (ROI), we compute a dense optical flow map using graphics processing units, which enable us to examine compliance with the ego-motion of the robot in a dynamic environment. Shape-based classification algorithms are employed to sort ROIs into human beings and nonhumans. The experimental results show that the proposed system detects people more precisely than previous methods.

In this paper, a feature extraction model for face recognition is proposed. This model is constructed by implementing three biologically inspired strategies, namely a hierarchical network, a learning mechanism of the V1 simple cells, and a data-driven attention mechanism. The hierarchical network emulates the functions of the V1 cortex to progressively extract facial features invariant to illumination, expression, slight pose change, and variations caused by local transformation of facial parts. In the network, filters that account for the local structures of the face are derived through the learning mechanism and used for the invariant feature extraction. The attention mechanism computes a saliency map for the face, and enhances the salient regions of the invariant features to further improve the performance. Experiments on the FERET and AR face databases show that the proposed model boosts the recognition accuracy effectively.

We present an adaptive and efficient background modeling strategy for real-time object detection in multicamera systems. The proposed approach is an innovative multiparameter adaptation strategy of the mixture of Gaussian (MoG) background modeling algorithm. This approach is able to efficiently adjust the computational requirements of the tasks to the available processing power and to the activity of the scene. The innovative approach allows one to adapt the MoG without a significant loss in the detection accuracy while contemporarily adhering to the real-time constraints. The adaptation strategy works at the local level by modifying, independently, the MoG parameters of each task, and then, whenever the results of the local strategy are not satisfactory, a global adaptation strategy starts that aims at balancing the workload among the tasks. Our approach has been tested on three different data sets, including several image sizes, heterogeneous environments (indoor and outdoor scenarios), and different real-time constraints. The results show that the proposed adaptive system is well suited for multicamera applications thanks to this efficiency and adaptability; it guarantees real-time highly accurate detections.

Pavement crack detection plays an important role in the pavement maintaining and management. Recently, the laser scanning technique for pavement crack detection becomes more and more popular due to its ability of discriminating dark areas, which are not caused by pavement distress such as tire marks, oil spills, and shadows. However, this technique still bears some errors for pavement crack recognition errors, thus in the present work, the factors contributed to these errors in laser scanning system are first analyzed, and then a decision model for the laser scanning pavement crack detection system based on the hypothesis test is proposed. Experimental analyses and results show that this model not only allows us to build the relationship between the contribution factors and crack detection accuracy and to provide the criteria to compare the detection accuracy for the different roads, but also can be used to judge whether the crack exists with a reasonable number of deformed light stripes. Therefore, the proposed decision model can provide guidance on the pavement crack detection and has a practical value.

We propose a three-phase spectral matching imager (3PSMI) to realize a novel spectral matching method called quadrature spectral matching (QSM) in real time. The 3PSMI is comprised of the correlation image sensor (CIS) and wavelength-swept monochromatic illumination (WSMI) to perform QSM at each pixel on the CIS at a video frame rate. QSM consists of spectral correlation between an ac component of an object spectrum and an orthonormal pair of reference spectra, being equivalent to projecting the ac object spectrum onto a two-dimensional subspace spanned by the reference spectra. Similarity of the ac object spectrum to the reference spectra is evaluated in terms of the azimuth angle of the projection, independently of the norm of the ac object spectrum as well as spatial intensity distribution of the WSMI. A programable spectral light source is employed to implement the WSMI so that the spectral characteristics of the WSMI and CIS cancel each other and thus do not affect QSM on the 3PSMI. Experimental results confirm that the developed 3PSMI system can distinguish objects with smaller difference in spectral reflectance in real time than RGB imaging with off-the-shelf cameras.

In daily life, language is an important tool of communication between people. Besides language, facial action can also provide a great amount of information. Therefore, facial action recognition has become a popular research topic in the field of human-computer interaction (HCI). However, facial action recognition is quite a challenging task due to its complexity. In a literal sense, there are thousands of facial muscular movements, many of which have very subtle differences. Moreover, muscular movements always occur simultaneously when the pose is changed. To address this problem, we first build a fully automatic facial points detection system based on a local Gabor filter bank and principal component analysis. Then, novel dynamic Bayesian networks are proposed to perform facial action recognition using the junction tree algorithm over a limited number of feature points. In order to evaluate the proposed method, we have used the Korean face database for model training. For testing, we used the CUbiC FacePix, facial expressions and emotion database, Japanese female facial expression database, and our own database. Our experimental results clearly demonstrate the feasibility of the proposed approach.

In this study, we cast hand posture recognition as a sparse representation problem, and propose a novel approach called joint feature sparse representation classifier for efficient and accurate sparse representation based on multiple features. By integrating different features for sparse representation, including gray-level, texture, and shape feature, the proposed method can fuse benefits of each feature and hence is robust to partial occlusion and varying illumination. Additionally, a new database optimization method is introduced to improve computational speed. Experimental results, based on public and self-build databases, show that our method performs well compared to the state-of-the-art methods for hand posture recognition.

Dynamic range reduction and detail enhancement are two important issues for effectively displaying high-dynamic-range images acquired by thermal camera systems. They must be performed in such a way that the high dynamic range image signal output from sensors is compressed in a pleasing manner for display on lower dynamic range monitors without reducing the perceptibility of small details. In this paper, a new method of display and detail enhancement for high dynamic range infrared images is presented. This method effectively maps the raw acquired infrared image to 8-bit domain based on the same architecture of bilateral filter and dynamic range partitioning approach. It includes three main steps: First, a bilateral filter is applied to separate the input image into the base component and detail component. Second, refine the base and detail layer using an adaptive Gaussian filter to avoid unwanted artifacts. Then the base layer is projected to the display range and the detail layer is enhanced using an adaptive gain control approach. Finally, the two parts are recombined and quantized to 8-bit domain. The strength of the proposed method lies in its ability to avoid unwanted artifacts and adaptability in different scenarios. Its great performance is validated by the experimental results tested with two real infrared imagers.

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