A message from the editor-in-chief.Today (June 19, 2012), the Chicago Tribune reported that Romanian Prime Minister Victor Ponta said he would not resign over accusations of plagiarism against him. The Tribune explained that “Nature said it had seen documents indicating that more than half of Ponta’s 432-page, 2003 Romanian-language thesis on the International Criminal Court for his doctorate at the University of Bucharest consisted of duplicated text.”

In this letter, we propose parallel-pass architecture for Embedded block coding with optimal truncation (EBCOT) entropy encoding in JPEG 2000. In the proposed method the time consuming sequential pass architecture is replaced with the parallel-pass approach. The experimental results show that the proposed method reduces the processing time by 22.6% as compared with the Taubman's Kakadu architecture of EBCOT.

With the rapid development of information technology, natural disaster prevention is growing as a new research field dealing with surveillance systems. To forecast and prevent the damage caused by natural disasters, the development of systems to analyze natural disasters using remote sensing geographic information systems (GIS), and vision sensors has been receiving widespread interest over the last decade. This paper provides an up-to-date review of five different types of natural disasters and their corresponding warning systems using computer vision and pattern recognition techniques such as wildfire smoke and flame detection, water level detection for flood prevention, coastal zone monitoring, and landslide detection. Finally, we conclude with some thoughts about future research directions.

An introduction to the special section by the guest editors.

Compressed sensing can recover a signal that is sparse in some way from a small number of samples. For computed tomography (CT) imaging, this has the potential to obtain good reconstruction from a smaller number of projections or views, thereby reducing the amount of radiation that a patient is exposed to In this work, we applied compressed sensing to fan beam CT image reconstruction, which is a special case of an important 3-D CT problem (cone beam CT). We compared the performance of two compressed sensing algorithms, denoted as the LP and the QP, in simulation. Our results indicate that the LP generally provides smaller reconstruction error and converges faster; therefore, it is preferable.

We describe the design and performance of a coded aperture spectral imager with a wide spectral range of 320 to 700 nm over 87 channels and 1988-by-1988 pixels of spatial resolution. A custom-designed relay lens was designed and built for the system, including a dispersive prism element in the collimated space of the relay lens. The optical design process, prescription, and performance are reported for the entire system, including calibration and alignment. Simulations of high-resolution spectral images are conducted to verify the reconstruction algorithm and relative resolution of the instrument compared to ground truth data. Measured data were taken with the instrument using both a random coded aperture and standard slit for spatial resolution comparisons. Finally, reconstructed spectral images from the instrument are presented of a sunlight-illuminated flower from 360 to 700 nm.

High dynamic range (HDR) imaging is an important and challenging research topic in computational photography. A simple but effective image fusion method is proposed to accomplish the multi-exposure image composition in both static and dynamic scenes. The foundation of the proposed method is an experiential criterion that optimizes the exposure that occurs at a dramatic alteration point in the low dynamic range image sequence (LDRI). To extract these well-exposed pixel vectors, each pixel curve formed by the pixel vectors at same position along all frames in the LDRIs is first preprocessed by the chord length parameterization. Then a single high-quality pseudo-HDR image can be extracted directly and efficiently from the LDRIs using a pixel-level fusion index matrix derived from the first- and second-order difference quotients of the preprocessed pixel curves. The main advantage of the proposed method is its use of a single independent pixel in computing. It is highly parallel, allowing a graphic processing unit-based, real-time implementation. The experiments on various scenes discussed here indicate that the proposed exposure fusion method can combine a large image sequence with 10 megapixels into a visually compelling pseudo-HDR image at a rate of 30  frames/s on a consumer hardware.

Millimeter wave (MMW) readily penetrates fabrics, thus it can be used to detect objects concealed under clothing. A passive MMW imaging system can operate as a stand-off type sensor that scans people both indoors and outdoors. However, because of the diffraction limit and low signal level, the imaging system often suffers from low image quality. Therefore, suitable computational processing would be required for automatic analysis of the images. The authors present statistical and computational algorithms and their implementations for real-time concealed object detection. The histogram of the image is modeled as a Gaussian mixture distribution, and hidden object areas are segmented by a multilevel scheme involving the expectation-maximization algorithm. The complete algorithm has been implemented in both MATLAB and C++. Experimental and simulation results confirm that the implemented system can achieve real-time detection of concealed objects.

For the first time, a high-resolution hyperspectral single-pixel imaging system based on compressive sensing is presented and demonstrated. The system integrates a digital micro-mirror device array to optically compress the image to be acquired and an optical spectrum analyzer to enable high spectral resolution. The system's ability to successfully reconstruct images with 10 pm spectral resolution is proven.

Some scenes and objects have a wide range of brightness that cannot be captured with a conventional camera. This limitation, which degrades the dynamic range of an imaged scene or object, is addressed by use of high dynamic range (HDR) imaging techniques. With HDR imaging techniques, images of a very broad range of intensity can be obtained with conventional cameras. Another limitation of conventional cameras is the range of wavelength that they can capture. Outside the visible wavelengths, the responsivity of conventional cameras drops; therefore, a conventional camera cannot capture images in nonvisible wavelengths. Compressive imaging is a solution for this problem. Compressive imaging reduces the number of pixels of a camera to one, so a camera can be replaced by a detector with one pixel. The range of wavelengths to which such detectors are responsive is much wider than that of a conventional camera. A combination of HDR imaging and compressive imaging is introduced and is benefitted from the advantages of both techniques. An algorithm that combines these two techniques is proposed, and results are presented.

A new approach of optimization and optical design for a miniature projector with two liquid lenses is proposed. To get the satisfactory performance of the optics, we achieve the optimization via integrating damped least square with the modified ant colony algorithm. The results show that we achieve a successful optical design and the optimization of the miniature projector with liquid lenses, whose clear image ranges from 120 to 2500 mm.

We report the design and implementation of a high-speed, automated laser radar (ladar) system with sensitivity enhanced by a polarimetric imaging technique. This ladar is able to analyze the Stokes vector of the reflected light from a target at video-rate. With a polarization state generator and a polarization state analyzer, the system is capable of performing a complete Mueller matrix imaging of the scene under observation. This polarization-sensitive ladar (pladar) is applied to various scenes and found to yield the ability to detect information that is indiscernible to a conventional, intensity-based ladar.

The art of stereoscopic cinematography has been held back because of the lack of a convenient way to reduce the stereo camera lenses' interaxial to less than the distance between the eyes. This article describes a unified stereoscopic camera and lens design that allows for varying the interaxial separation to small values using a unique electro-optical polarizing aperture design for imaging left and right perspective views onto a large single digital sensor, the size of the standard 35 mm frame, with the means to select left and right image information. Even with the added stereoscopic capability, the appearance of existing camera bodies will be unaltered.

Variations in the spectral shape and the amplitude of the optical coherence tomography (OCT) signal and reference cause fixed-pattern noise and light reflected from a highly specular surface might cause saturation artifacts. In real-time video-rate OCT imaging, these effects make the OCT video image appear unstable and difficult to view. To eliminate these problems, we implemented real-time reference A-line subtraction and saturation detection and correction on standard Fourier-domain optical coherence tomography (FD-OCT) video imaging frame-by-frame. This real-time OCT data processing method eliminates the need for the physical reference measurement procedure and automatically detects and corrects saturated A-scans if there is any within one frame. This technique is also robust to the reference and signal amplitude variations, and provides higher signal-to-noise ratio compared to the normal fixed-reference subtraction method. To implement an effective interventional OCT imaging system, the technique was integrated along with other graphics processing unit-based OCT processing techniques [resampling, dispersion compensation, fast Fourier transform, log-scaling, and soft-thresholding]. The real-time fixed-pattern artifact-free FD-OCT imaging was achieved at 70  frames/s for a frame size of 1000 (lateral) by 1024 (axial) pixels. The theoretical maximum processing and rendering rate was measured to be 266,000  A-scans/s.

Precision glass molding is the technology of choice for the production of complex-shaped optical components. Protective coatings can significantly extend the lifetime of the molding tools, but the coating properties have to be exactly customized for individual application conditions. The current biggest challenge is to ensure the reliability of newly developed coatings without resorting to extensive and expensive practical testing. However, the usual coating qualification methods either cannot be used or don't provide meaningful results. In this work a new three-tier, application-specific methodology for the qualification such coatings is presented. First, the basic characterization of coating properties is discussed, taking into account the specific characteristics of the coatings used for precision glass molding tools. In the second step, application-specific testing methods are devised, based on the analysis of the loads during glass molding. Finally, a new machine for testing the lifetime of the coated molding tools is proposed. Three case studies are presented where nanoscratch, nanoimpact and glass contact tests are performed with Pt-Ir, TiAlN, and CrAlN-coated samples in combination with various glass types, showcasing the usefulness of the proposed three-tier methodology.

We have investigated femtosecond-laser-induced microstructures (on the surface and within the bulk), gratings, and craters in four different polymers: polymethyl methacrylate, polydimethylsiloxane, polystyrene, and polyvinyl alcohol. The structures were achieved using a Ti:sapphire laser delivering 100-fs pulses at 800 nm with a repetition rate of 1 kHz and a maximum pulse energy of 1 mJ. Local chemical modifications leading to the formation of optical centers and peroxide radicals were studied using ultraviolet-visible absorption and emission, confocal micro-Raman and electron spin resonance spectroscopic techniques. Potential applications of these structures in microfluidics, waveguides, and memory-based devices are demonstrated.

A simple, new, self-referenced technique for the internal measurement of a right angle is presented. A polarization cyclic path optical configuration (CPOC) receives as the input beam a pair of laterally separated plane wave components, having angular separation of ψw = (π±4nδ), produced due to internal reflection of a linearly polarized plane wave on the surfaces enclosing the 90-deg (±δ) angle of a right-angled prism (where δ is the error in 90-deg angle and n is the index of refraction of the material of the prism). The CPOC is used to superpose the mutually inclined plane wave components by duplicating the input pair of plane wave fronts and introducing appropriate lateral shear between the identical pairs. The superposed inclined plane wave components interfere to produce two beam Fizeau fringes (FF), when brought to the same state of polarization. The error in the right angle can be calculated simply from the spacing of the resulting FFs or, more accurately, from the slope of the optical path difference variation obtained by applying polarization phase-shifting interferometry. Results obtained for a right-angled prism are presented.

High-resolution measurement and contouring of objects with micro-scale sizes have been two of the research challenges in many areas, such as nondestructive testing and imaging, imaging of artifacts in MEMS, and lab-on-chip devices, as well as in biomedical imaging. In this context, we use a transillumination incorporated fiber probe imaging system to enable imaging of the targeted object in a single shot. It also enables positioning of the probe system to the region of interest for further fine analysis, thereby reducing the long scanning time faced by conventional approaches. The capability of the developed probe is illustrated using standard USAF resolution chart and fluorescent microspheres as test targets. The probe system has axial and lateral resolutions of about 16 μm and 144  lp/mm, respectively. This proposed probe scheme can potentially be employed as a viable diagnostic imaging methodology.

The swing arm optical coordinate-measuring machine (SOC), a profilometer with a distance measuring interferometric sensor for in situ measurement of the topography of aspheric surfaces, has shown a precision rivaling the full aperture interferometric test. To further increase optical manufacturing efficiency, we enhance the SOC with an optical laser triangulation sensor for measuring test surfaces in their ground state before polishing. The calibrated sensor has good linearity and is insensitive to the angular variations of the surfaces under testing. Sensor working parameters such as sensor tip location, projection beam angle, and measurement direction are calibrated and incorporated in the SOC data reduction software to relate the sensor readout with the test surface sag. Experimental results show that the SOC with the triangulation sensor can measure aspheric ground surfaces with an accuracy of 100 nm rms or better.

Analytical expressions, based on single and multiple incoherent beams at slab interfaces, are revised. It is applied for determining spectral refractive indices of plane parallel slab material. These expressions were introduced by Pankove and have been widely used in optical measurements. However, some researchers misuse these expressions by using the total slab reflectance instead of the interface reflectance. Refractive indices of four glassy slabs with different thicknesses and composition are experimentally measured and compared with that given by the glasses manufacturer. These expressions give precise results with experimental error of about 0.022 across broad spectral range of 0.2 to 2.5 um. Comparisons between the correct use and misused expressions in case of single and multiple beams are presented. The misuse of expressions produces percentage deviation from the reference values of about 17.6% to 24.4% depending on the slab refractive index.

Optical singularities are localized regions in a light field where one or more of the field parameters, such as phase or polarization, become singular with associated zero intensity. Focused on a small spot, the electromagnetic field around the singularity has interesting characteristics, especially when it interacts with matter. The light scattered by a material object within the strongly varying optical field around the singularity is extremely sensitive to changes and can be exploited for metrology with high sensitivity and the study of physical processes on a nanometer scale. Several earlier application examples are briefly described and a more detailed presentation is provided of a novel approach to particle sizing down into the nanometer region.

A low-cost image orthorectification tool based on the utilization of compact cameras and scale bars is developed to obtain the main geometric parameters of masonry bridges for inventory and routine inspection purposes. The technique is validated in three different bridges by comparison with laser scanning data. The surveying process is very delicate and must make a balance between working distance and angle. Three different cameras are used in the study to establish the relationship between the error and the camera model. Results depict nondependence in error between the length of the bridge element, the type of bridge, and the type of element. Error values for all the cameras are below 4 percent (95 percent of the data). A compact Canon camera, the model with the best technical specifications, shows an error level ranging from 0.5 to 1.5 percent.

This paper describes a method based on bi-objective evolutionary algorithms to obtain the profile of a convex aspherical surface, which is defined by a set of synthetic points placed on an xyz coordinate system. The set of points to be analyzed is constructed considering the sources of measurement error in a coordinate measuring machine (CMM), such as machine, probe, and positioning errors. The proposed method is applied to solve a bi-objective optimization problem by minimizing two objective functions. By minimizing the first objective function the positioning error is removed from the coordinates of each affected point. Once the first goal is achieved, the second objective function is minimized to determine from the resulting data all parameters related to the test surface, such as paraxial radius of curvature, the conic constant and the deformation constants. Hence, this method can obtain the correct surface profile even when the positioning error tends to increase the CMM measurement error in the set of analyzed points. The bi-objective evolutionary algorithm (BEA) was tested against a single-objective evolutionary algorithm, and illustrative numerical examples demonstrate that the BEA performs better.

Pulsed operations can be used to improve the efficiency of light-emitting diodes (LEDs) on human perception. We conducted an experiment asking 46 observers to compare the brightness of a viewing area that was separated into two similar parts and illuminated by both pulse-modulated LEDs and DC-driven LEDs. Using filters, we eliminated the influence of color shift on human perception. The results show that the efficiency improves more when the duty ratio decreases. In addition, the perception enhancement has a linear relationship with duty ratios ranging between 20% and 80%. When the duty ratio is close to 100%, there is almost no effective enhancement.

We discuss an optical model which describes silicon thin-film solar cells with rough interfaces in a fast and easy way. In order to simulate thin layer stacks with rough interfaces diffuse scattering as well as interference effects have to be taken into account. Algorithms like the finite-difference time-domain method (FDTD) solve the Maxwell Equations, and therefore fulfil these demands; yet, they take a considerable amount of simulation time and computation capacity. To overcome these drawbacks, an optical model was developed which combines the transfer-matrix method (TMM) and the raytracer algorithm. The fraction of TMM and raytracer in the model is determined by a separating function which can be interpreted as the integral haze. In order to verify the combined optical model, a series of amorphous silicon single cells with varying intrinsic layer thicknesses was produced on two different kinds of textured substrates. The results of the combined optical model are compared to measured data and the simulation results of the FDTD method. We show that the combined optical model yields good results at low simulation time.

A backlight unit is constructed by laying out an optical fiber on a two-dimensional plane and letting the light leak out in a controlled manner. In experiment, we formed multiple grooves on the surface of a plastic optical fiber by pressing a heated knife edge. The depth of the groove determined the percentage of the optical power leaking out. The optical fiber with multiple grooves was embedded in an acrylic plate with a spiral trench, and a diffuser sheet was placed over it. When we injected laser light into the end of the optical fiber, this configuration successfully worked as an area illuminator. However, the coherent nature of the laser light caused severe speckle noise. We evaluated the speckle contrast under darkness, and it varied from 80% to 23%, depending on the lens aperture used to capture the images of the illuminator. We glued an ultrasound generator to the optical fiber to introduce phase modulation for the light propagating inside the optical fiber. In this way, the speckle contrast was reduced by a factor of seven to four. Under room lighting, the speckle noise was made barely noticeable by turning on the ultrasound generator.

We propose a new design method for the photonic crystal (PhC) wideband passive optical filters. For this, we join the PhC spectral analysis with investigation of guiding properties of the PhC-waveguides and filters. The method allows improvement of the characteristics of the demultiplexers presented in earlier works, which has been designed by means of photonic band gap maps analysis.

Vanadium oxide uncooled bolometer with gold black absorber of high long-wave-infrared-rays absorption has been fabricated and optimized. The fabrication processes for mirobolometer were developed with surface micromachining below 350°C. We evaluated gold black film reflectance by Fourier transform infrared spectroscopy. Low reflectance shows that gold black has good absorption at 8 to 14 μm infrared window. Detector tests show that a bolometer with gold black absorber, compared with the one without gold black, had better performance, with maximum responsivity and detectivity of 8.4×10⁴  V/W and 6.16×10⁸  cm Hz^{1/</sup<2/W, respectively, at 13 Hz chopper frequency and bias current 67 μA.}

In this work, three strategies for shortening the output pulse of a silicon photomultiplier (SiPM) are reported. The first strategy is passive filtering, where band-pass filtering removes the lowest frequency components in the signal, getting a noticeable reduction in pulse width (a compression ratio of 10∶1 was obtained). In the second place, a reflectometric scheme is proposed where the amplified signal coming from the SiPM is injected into a signal splitter with one of its stubs connected to a short-circuited stub. In the last strategy, the reflectometric part is replaced by an analog subtractor circuit. In this approach, a signal splitter with stubs of different lengths is used. All solutions provide good compression ratios, up to 10∶1. Best pulses obtained are single narrow peaks, with width below 10 ns, preserving the photonic modulation and with good pseudo-Gaussian shape, single polarity and low ringing. The potential of pulse shortening for improving the capability of the detector to resolve single photons is demonstrated by mean of single photon counting patterns. The detection error probability is reduced in one order of magnitude when shortening is used for conditioning the output photosignal.

We report the object-distance effect on the focusing properties of a two-dimensional (2-D), photonic quasicrystal (PQC) flat lens by numerical simulation. For the image power and image quality, the half-thickness of the flat lens is no longer the optimal object distance. The object-image distance is not always double the flat lens thickness, which is apparently different from a 2-D, periodic photonic crystal (PPC) flat lens and left-handed material (LHM) flat lens. With the point-light source located near half-thickness of the lens object distance, a 2-D PQC flat lens can achieve a perfect image in a certain range. With an appropriate object distance, a 2-D PQC flat lens is much better than a 2-D PPC flat lens in the aspect of imaging resolution. The results are beneficial to understand the focusing and imaging of a 2-D PQC flat lens.

Modeling and detailed performance analysis is carried out to realize a multimode interferometer optical switch by inserting an appropriate image-modulated (IM) region. The concept of self-imaging characteristics of multimode waveguides has been utilized in order to drive the designed device as a photonic switch. Transition losses in the waveguides of the structure are maintained at low levels by selecting appropriate dimensions to increase overall performance of the switch. It has been observed that by inserting an additional IM region, switching losses and corresponding crosstalk levels can be reduced significantly. The device performance is checked for a wider range of index variation in the IM region with respect to other regions for a test wavelengh of 1.55 µm. With rigorous and repetitive simulation, a crosstalk level better than -22.2 dB for either case of polarization state (transverse electric and transverse magnetic) of input has been achieved. The design also possesses a design tolerance in the range of ±0.25 to ±0.5 μm, within which variation in the imaging length and its subsequent adverse effects on device performance remains less than 1.5%.

There is a need to develop miniature optical tunable filters for small hyperspectral imagers. We plan to develop a number of miniature Fabry-Perot tunable filters (FPTFs) using microelectromechanical systems (MEMS) technology, each operating over a different wavelength region, to cover spectral regions from the visible to the longwave infrared (IR). Use of a MEMS-based FPTF as a dispersive element will reduce the size, weight, and power requirements of hyperspectral imagers and make them less expensive. A key requirement for such a filter is a large optical aperture. Recently, we succeeded in fabricating FPTFs with a 6 mm optical aperture operating in the visible to near IR spectral region (400 to 800 nm) using commercially available thin quartz wafers as the substrate. The FPTF design contains one fixed silver (Ag) mirror and one electrostatically movable Ag mirror, each grown on a quartz substrate with a low total thickness variation. Gold (Au) bumps are used to control the initial air gap distance between the two mirrors, and Au-Au bonding is used to bond the device. We describe material selection, device design, modeling, fabrication, interferometric, and spectral characterizations.

We investigate on a multi-wavelength operation erbium-doped fiber laser Q-switched by a graphene-based saturable absorber. Stable pulses were generated with the widths from 6.9 to 1.5 μs, energies from 40.4 to 130.2 nJ and repetition rates from 68.32 to 132.9 kHz, when the pump power increased from 142.32 to 441.86 mW. A fiber Bragg grating with five reflective peaks was inserted into the fiber ring through an optical circulator, resulting in a stable output of five-lasing-wavelength output. The laser can perform as a low-cost and easy-built all fiber light source, and has potential applications in the fields where pulses at multi-wavelength operation are needed, i.e., temperature or strain fiber sensors.

We investigate the characteristics of vector solitons with and without locked phase velocities of orthogonal polarization components in a specially-designed laser cavity which is formed by a bidirectional fiber loop together with a semiconductor saturable absorber mirror. The characteristics of the two states are compared in the temporal and spectrum domain, respectively. Both of the two states exhibit the characteristic of mode locking while the two orthogonal polarization components are not resolved. However, for the vector soliton with unlocked phase velocities, identical intensity varies after passing through a polarization beam splitter (PBS) outside the laser cavity. Contrary to the polarization rotation locked vector soliton, the intensity does not change periodically. For the polarization-locked vector soliton (PLVS), the identical pulse intensity is still obtained after passing through the PBS and can be observed on the oscilloscope screen after photodetection. A coupler instead of a circulator is integrated in the laser cavity and strong interaction on the polarization resolved spectra of the PLVS is observed. By comparing the two states, we conclude that interaction between the two orthogonal components contributes to the locked phase velocities.

The temperature sensitivity of a tapered Yb-doped fiber laser is numerically investigated. The laser rate equations are modified to analyze the output characteristics of the tapered fiber laser in the continuous wave regime under different temperature conditions. Numerical analysis shows that for different pump schemes, high sensitivity can be achieved when the pump power is reduced to close to the threshold value. Our results are reproducible and contribute new information to the development and optimization of tapered Yb-doped fiber lasers and temperature fiber laser sensors.

We present a method of designing a grating outcoupler to obtain the desired two dimensional-intensity profile and improved field distribution of the optical beam emitted by a grating coupled surface-emitting laser. The method is based on variation of the periodicity, the duty cycle, and the groove tilt angle of the grating. Grating design involves numerical analysis of the optical field propagated through the grating by applying the rigorous coupled wave approach method. Experimental evaluation of the designed grating components was done by fabrication and testing the broad area semiconductor lasers with the monolithically integrated grating outcouplers. We present a grating design that provides the spreading of a single optical output into multibeams at different outcoupling angles in the emitting plane. We also present an approach to provide uniform optical intensity profile from the grating outcoupler based on varying duty cycle.

An adaptive-weight fast-Fourier-transform-based iterative algorithm is proposed for far-field flat-top beam shaping. This algorithm inherits the projection optimization idea from the Gerchberg-Saxton algorithm, but the far-field amplitude for inverse fast Fourier transform is adaptively modified by using a novel optimized adaptive-weight strategy. First, the application of this method to square flat-top intensity-profile beam shaping is discussed as an example. The pure-phase distribution simulated by 100 iterations of this method concentrates 93.89% of the incident laser energy into the desired region and the root mean square error (RMSE) of the tailored flat-top intensity profile is 0.0094. Less than 20 iterations of this method concentrate more than 90% of the incident laser energy into the desired region and the RMSE of the tailored flat-top intensity profile is under 0.05. Then, the applicability of the method to designing the phase distributions for variable-shape or variable-diameter flat-top beam shaping is demonstrated.

Self-organization of optical waveguides that connect two optical devices automatically through a reflective self-organized lightwave network (R-SOLNET) using a phosphor was simulated by the finite difference time domain method. The simulation showed that a R-SOLNET is constructed between a waveguide with a core width of 1.2 μm and a phosphor target, which is located a distance of 6.4 μm from the waveguide edge and guides the probe beam to the phosphor target. The optical coupling efficiency was 95% when the waveguide and phosphor target were fully aligned. Even when the misalignment was 800 nm, a coupling efficiency of 60% was obtained. The coupling efficiency for the SOLNET without the phosphor target was 16%. In addition, experiments to confirm the principle of a R-SOLNET using a phosphor were performed with an optical fiber and tris(8-hydroxyquinolinato) aluminum (Alq₃) phosphor target. The experiments revealed that the write beam is propagated toward the Alq3 target, and consequently, a R-SOLNET connecting the fiber edge and Alq₃ target is formed to guide probe beams to the target. The R-SOLNET expanded from the diameter of the fiber core to the width of the Alq₃ target.

The efficiency of integrated acousto-optic (AO) modulators with different optical penetration depths fabricated on 128-deg-rotated Y-cut X-propagation lithium niobate (128-deg YX-LiNbO₃) is analyzed theoretically for the first time by determining the overlap integral between the optical and acoustic field distribution. The results show that the smaller the optical penetration depth is, the higher the optimum surface-acoustic-wave (SAW) frequency and diffraction efficiency and the larger the bandwidth will be. Compared with TM-polarized light, TE-polarized light offers better performance for modulation. However, for a well-concentrated optical waveguide, TM-polarized light is attractive for AO modulators, which employ a single SAW.

A novel kind of wavelength-insensitive wide-spectrum polymer electro-optic (EO) switch is proposed by employing two symmetric active Mach-Zehnder interferometers (MZIs), a passive middle directional coupler and a pair of passive phase-generating couplers. Extinction ratio compensation condition under off-state and insertion loss compensation condition under on-state are derived to expand wavelength spectrum. With sufficient consideration of the wavelength dispersion of material and waveguide, optimization, and simulation were performed. The switch exhibits a switching voltage of 4.96 V with each MZI EO region length of 5000 μm. An S-C-L band (1460 to 1625 nm) covering a wide-spectrum more than 165 nm was obtained, and within this range, an extremely high extinction ratio more than 40 dB and an insertion loss within 1.8 to 11.9 dB were reached. This spectrum was more than 8 times of that of the traditional MZI EO switch (only 20 nm).The proposed device can function normally at any wavelength, and is an ideal candidate for a broadband photonic switching element in next-generation nonwavelength selective optical networks-on-chip.

Using beam propagation method, we investigated the switching behavior of a nonlinear Mach-Zehnder interferometer (NMZI). The focus of the present investigation was exponentially saturable type nonlinearity of the NMZI. The results were compared with the results of NMZIs with saturable type nonlinearity. NMZIs with both types of nonlinearity offer stable on and off states; however, exponentially saturable nonlinearity proves to be much better, as NMZIs with this type of nonlinearity offer a stable on state with higher transmission coefficient (i.e., with lower device loss) compared to those with saturable nonlinearity. Moreover, the stable on state could be achieved at much lower power levels.

We propose a broadband light-tapping technique, where an input fiber excites the cladding modes of an output fiber through a gap between the two fibers, and the cladding modes of the output fiber are transferred to a parallel tapping fiber through evanescent-field coupling between the two fibers. The tapping efficiency and the excess loss of the fiber tap depend on the fiber type and the gap distance between the input fiber and the output fiber. We demonstrate the technique with standard single-mode fibers and photonic crystal fibers and discuss its performance. The proposed tap configuration is applicable to practically any fibers and could be further developed into useful light-tapping devices or sensors.

We present the development procedure as well as preliminary fabrication results for a CO₂ laser-based tapering rig allowing one stage tapering of optical fibers. Our aim is to develop in-fiber devices constructed from fibers filled with various materials, which can be drawn from thick preforms using the presented procedure. The constructed tapering rig consists of a CO₂ laser as the heating source, ellipsoid-based mirror optics, and computer-controlled high-precision motors.

Nonlinear phase noise (NLPN) induced by the interaction between the amplified spontaneous emission noise (ASE) and the information signal in polarization-multiplexed quadrature phase-shift keying (PM-QPSK) systems at 42.8(112) Gbit/s over dispersion-managed (DM) link is investigated by numerical simulations. Both symbol-aligned non-return-to-zero (NRZ) PM-QPSK and symbol-interleaved return-to-zero (RZ) PM-QPSK formats are considered and compared. We find that for aligned NRZ-PM-QPSK systems, the impact of NLPN on system performance seems rather weak due to the strong interchannel cross-polarization modulation (XPolM). However, when the interleaved RZ-PM-QPSK format is used, in which the XPolM is suppressed significantly, the system performance is seriously degraded by NLPN, especially at low bit rates. Results of 1000-km transmission employing standard single-mode fiber (SSMF) over DM link show that for 42.8 Gbit/s coherent RZ-PM-QPSK systems, the nonlinear threshold (NLT) will decrease from 6 to 2 dBm due to nonlinear phase noise when symbol-interleaved format is used.

We configure the input pump pulse energy of semiconductor optical amplifiers (SOAs) to maximize the four-wave mixing (FWM) conversion efficiency. We simulate the propagation of optical waves in the SOA using the nonlinear propagation equation, taking into account the gain spectrum dynamics, gain saturation, which depends on carrier depletion, carrier heating, spectral hole-burning, group velocity dispersion, self-phase modulation, and two photon absorption. Our simulation results confirm that corresponding to each input probe pulse, there is an input pump pulse with optimum energy that maximizes the FWM conversion efficiency in the SOA. We introduce a pattern for tuning the input pump pulse energy of SOA, which leads to saving the energy in practical applications. We show that the FWM conversion efficiency will decrease when the input pump pulse energy increases from its optimum point. Moreover, for further input pump pulse energies, the width of the generated FWM pulse increases, and its energy will remain constant.

The performance of metallic-hollow-core-waveguides (MHCWs) and multimode polymer waveguides (MMPWs) are numerically evaluated using ray-tracing method for complex board level optical interconnects systems such as optical bus. Based on an ideal model neglecting the waveguide surface roughness, we find that MHCWs will provide lower optical loss for small curvature bending waveguides, 45 deg micro-mirror couplers and optical beam splitters, while MMPWs shows a better optical transmission for straight waveguides. The conclusion is that MHCWs will be a better choice than MMPWs for complex optical bus architectures in terms of performance, cost and stability.

We describe an ultra-thin and low-power optical interconnect module for mobile electronic devices such as mobile phones and notebooks. The module was fabricated by directly packaging optic and electronic components onto a thin and flexible optical printed circuit board having a size of 70×8×0.25  mm. The completed active module has features of thinness (0.5 mm), small size (7×5  mm), very low total power consumption (15.88 mW), and high data rate transmissions (2.5 Gbps).

Testing with a single holographic lens or grating in a collimated beam is normally not possible because of the inherent tilt caused in the wavefront. The tilt between the two beams in shearing creates a large number of linear fringes which overshadow the information about the wavefront. However, here, we show that we can use this tilt to make quantitative measurements which was otherwise not possible. In the novel method, we obtain shear in a relatively simple way, and at the same time we extract phase information using spatial Fourier transform technique. This technique is suitable for making quantitative measurement of wavefront and disturbances in turbulent conditions. Here, we demonstrated the real-time phase measurement capacity of the interferometer, a result of one such application is shown.

We propose a three-dimensional (3-D) holographic display system which consists of a phase-only spatial light modulator (SLM) and a modified 4-f system. The 3-D scene is generated from OpenGL, and the point source algorithm with anti-aliasing technique is used to generate the Fresnel hologram. A modified 4-f system is proposed to produce distortion-free magnification of the 3-D image and eliminate the zero-order interruption of the 3-D holographic imaging system. This method can make efficient utilization of the space-bandwidth product of the SLM, which promises the image quality and keeps the 3-D imaging zone unchanged. Numerical simulations and optical experiments are performed, and the results show that our proposed method can reconstruct enlarged 3-D optical image with correct magnification factor and low image noise.

A computer-generated hologram (CGH) is well-known to reconstruct 3-D images faithfully, and several CGH printers are reported. Since those printers can only output a transmission hologram, the large-scale optical system is necessary to reconstruct the full-parallax, full-color image. As a method of a simple reconstruction, it is only necessary to use a volume reflection hologram. However, the making of a volume hologram needs to transfer the CGH by means of an optical system. On the other hand, there are printers that output volume type holographic stereograms with the full-parallax, full-color image. However, the reconstructed image whose depth is large gets blurred due to the insufficient sampling rays of a 3-D object. The authors propose the volume hologram printer to record the wavefront of a 3-D object. By transferring the CGH that is displayed on a liquid crystal on silicon, the proposed printer can output the volume hologram. In addition, the large volume hologram can be printed by transferring plural CGH that recorded the partial 3-D object in turn. As a result, the printed volume hologram has been able to reconstruct a monochrome 3-D image by white light illumination, and realized the full-parallax image.

Light detection and ranging (LiDAR) has demonstrated its capabilities as a prominent technique for the direct acquisition of high density and accurate topographic information. To achieve the potential accuracy of such systems, a rigorous system calibration should be performed. We introduce a novel rigorous LiDAR system calibration procedure where the system parameters are determined by minimizing the discrepancies among conjugate surface elements in overlapping strips and control data, if available. The method is automated and does not require specific features (e.g., planes or lines) in the covered area or preclassification of the point cloud. Suitable primitives, which do not involve preprocessing of the data, are implemented. The correspondence between conjugate primitives is determined using a robust matching procedure. A modification to the Gauss Markov model is introduced to keep the implementation of the calibration procedure simple while utilizing higher order primitives. Experimental results have demonstrated the effectiveness of the proposed method over different types of terrain coverage.

Spectral image analysis problems often begin by applying a transformation that generates an alternative representation of the spectral data with the intention of exposing hidden features not discernable in the original space. We introduce and demonstrate a transformation based on a Markov-chain model of a random walk on a graph via application to spectral image clustering. The random walk is quantified by a measure known as the average commute time distance (CTD), which is the average length that a random walker takes, when starting at one node, to transition to another and return to the starting node. This distance metric has the important characteristic of increasing when the number of paths between two nodes decreases and/or the lengths of those paths increase. Once a similarity graph is built on the spectral data, a transformation based on an eigendecomposition of the graph Laplacian matrix is applied that embeds the nodes of the graph into a Euclidean space with the separation between nodes equal to the square-root of the average commute time distance. This is referred to as the Commute Time Distance transformation. As an example of the utility of this data transformation, results are shown for standard clustering algorithms applied to hyperspectral data sets.

Detectors of infrared focal plane arrays are, in the nature of their photoresponse, nonuniform. Response curves are nonlinear. In view of this, a novel nonuniformity correction algorithm based on the S-curve nonlinear response model and its simplified correction algorithm is proposed. The algorithm is an essential calibration and interpolation correction based on an analytical formula. It requires calibrating in advance, but possesses higher correction precision and wider applicative response range, which is particularly applicable to uncooled infrared focal plane arrays. Borrowing ideas from look-up tables, a real-time hardware correction system, which provides an experimental platform for contrasting different algorithms, is expounded. Experimental results validate that the proposed S-curve model-based algorithm does much better than the two-point correction algorithm and the simplified S-curve model-based correction algorithm.

A light probe is commonly used for measuring the illumination of a real scene. Instead of equipping a man-made light probe such as a mirror ball, we propose to use a face in images as a natural light probe. To that end, we construct a statistical reflectance model for faces and use this model to extract the lighting and the reflectance field of an input face. With an iterative procedure, we can obtain the lighting condition from an unknown face image. As a byproduct of this procedure, we also estimate the reflectance field of the same face. By identifying the lighting condition of scene, we can provide an effective solution for various practical applications. First, we can insert a virtual object seamlessly into a real scene by illuminating the virtual object under the lighting present in the real scene. Second, we can relight a face under an arbitrary lighting condition using the estimated reflectance fields. Third, we can swap two unknown faces using the estimates of both lighting and reflectance fields. Based on various experiments, we show that the proposed algorithm is an effective tool for many practical applications: inserting a virtual object into a real scene, face relighting, and face swapping.

The modified one-bit transform (M1BT) motion-estimation method efficiently combines the low-complexity 1BT algorithm and the high-accuracy full search algorithm. As a result, it provides a good tradeoff between performance and computational complexity. The search range scheme in the M1BT method, however, is somewhat inefficient. A proposal was made for a new search range scheme that efficiently increases the search range without increasing the computational complexity. The proposed method also makes use of statistical data to reduce the number of search points. By using both the new search range scheme and the new search strategy, the proposed method not only reduces the complexity, but also improves the performance. The proposed method can be easily extended to similar methods, such as the modified two-bit transform (M2BT) and modified constrained 1BT (MC1BT) methods.

A new digital speckle correlation method (DSCM) based on phase vortices is proposed in this paper. The complex signal is reconstructed by a Laguerre-Gauss filter applied to the original speckle pattern. Moreover, the pseudophase distribution is obtained. Each phase vortex position is then located, and its topology charge of +1 or −1 is used to replace the values of the original elements in the pseudophase matrix, in which other elements occupy with zeros. Finally, two sparse matrices representing the speckle field before and after displacement are constructed, respectively. Using these two sparse matrices, correlated calculation is conducted. The results show that this method has the same precision as the traditional subpixel DSCM, while its resumption time is only one-tenth of that of the latter. It is also strongly robust to immune noise.

A novel method to correct texture variations resulting from scale magnification, narrowing caused by cropping into the original size, or spatial rotation is discussed. The variations usually occur in images captured by a camera using different focal lengths. A representative region-matched algorithm is developed to improve texture classification after magnification, narrowing, and spatial rotation. By using a minimum ellipse, a representative region-matched algorithm encloses a specific region extracted by the J-image segmentation algorithm. After translating the coordinates, the equation of an ellipse in the rotated texture can be formulated as that of an ellipse in the original texture. The rotated invariant property of ellipse provides an efficient method to identify the rotated texture. Additionally, the scale-variant representative region can be classified by adopting scale-invariant parameters. Moreover, a hybrid texture filter is developed. In the hybrid texture filter, the scheme of texture feature extraction includes the Gabor wavelet and the representative region-matched algorithm. Support vector machines are introduced as the classifier. The proposed hybrid texture filter performs excellently with respect to classifying both the stochastic and structural textures. Furthermore, experimental results demonstrate that the proposed algorithm outperforms conventional design algorithms.

Total variation minimizing methods have known great success in image denoizing. Although edge sharpness is well preserved by these methods, important information like textures or small details is often removed in the process of denoizing. We propose a novel denoizing model which better preserves fine scale features. In our model, a set of local constraints are imposed to keep local variance of the noise at certain scale within its proper bounds. Each constraint corresponds to a certain scale of dyadic region of image and therefore the Lagrange multiplier in the model is space and scale adaptive, which can control the extent of denoizing over dyadic image regions. We characterize the local constraints by wavelet coefficients in order to transform the model into wavelet domain, and then give the solution and algorithm of the proposed model. Finally, we display some numerical experiments to demonstrate that the proposed model can preserve fine scale features effectively in the process of denoizing and the algorithm is quite practical.

We propose an image fusion method robust to misaligned source images based on their multiscale edge representations. Significant long edge curves at the second scale are selected to decide edge locations at each scale for the multiscale edge representations of source images. Then, processes are only executed on the representations that contain the main spatial structures of the images and also help suppress noise interference. A registration process is embedded in our fusion method. Edge correlation, calculated at the second scale, is involved as a match measure determining the fusion rules and also as a similarity measure quantifying the matching extent between source images, which makes the registration and fusion processes share the same data and hence lessens the computation of our method. Experimental results prove that, no matter whether in a noiseless or noisy condition, the proposed method provides satisfying treatment to misregistered source images and behaves well in terms of visual and objective evaluations on the fusion results, which further verifies the robustness of our edge-based method to misregistration and noise.

Fast and precise iris localization is a vital technique for face recognition, eye tracking, and gaze estimation. Low-resolution images bring about great difficulties for locating the iris precisely by traditional methods. In this paper, a fast and robust method to precisely detect the position and contour of the irises in low-resolution facial images is presented. A three-step coarse-to-fine strategy is employed. First, a gradient integral projection function is proposed to roughly detect the eye region, and the vertical integral projection function is adopted to select several possible vertical boundaries of the irises. Second, we have proposed a novel rectangular integro-variance operator to precisely locate both of the irises. Finally, the localization results are verified by two simple heuristic rules. A novel and more rigorous criterion is also proposed to evaluate the performance of the algorithm. Comparison experiments on images from the FERET and the Extended YaleB databases demonstrate that our method is more robust than traditional methods to scale variation, illumination changes, part occlusion, and limited changes of head poses in low-resolution facial images.

Classification of images in many categorized datasets has rapidly improved in recent years. However, methods that perform well on particular datasets typically have one or more limitations, such as insufficient image-transformation invariance or significant performance degradation as the number of classes is increased. We attempt to overcome these challenges by extracting and matching visual features only at the focuses of visual saliency instead of the entire scene. First, we propose a visual-saliency detection method that combines the respective merits of color-saliency boosting and global-region-based contrast schemes to achieve more accurate saliency maps. Using a single feature type, we then obtain good performance on three public datasets when compared to other state-of-the-art approaches. Overall, our results prove that robust and efficient fixation-based classification, in terms of reducing the complexity of feature extraction, is possible.

An improved tree-ring dating method able to detect and count tree-ring boundaries from images of wood cross sections is introduced. It can also be developed to analyze tree-ring features in future research. This proposed method first uses hue saturation intensity (HSI) color to get rid of the blue background to obtain the region of interest, the wood section. Then, using the watershed method and the window method, sapwood and heartwood regions are segmented, and the segmented image is dichotomized by the method, followed by cross calibrated miss detection correction to add missed rings. In order to reduce the fallout ratio, a method based on distance limitations is also utilized. In this way, the total number of the tree-rings are finally counted. A pilot study was conducted using seven images from an online library and five scanned images of Pinus massoniana wood discs provided by Zhejiang A&F University. Experimental results show that this method can be used to count ring numbers even when the color difference of sapwood and heartwood is distinct, and is able to correct the miss and fallout detection errors, increasing the accuracy of tree-ring dating.

The sparse representation can deal with the lack of sample problem due to utilizing of all the training samples. However, the discrimination ability will degrade when more training samples are used for representation. We propose a novel appearance-based palmprint recognition method. We aim to find a compromise between the discrimination ability and the lack of sample problem so as to obtain a proper representation scheme. Under the assumption that the test sample can be well represented by a linear combination of a certain number of training samples, we first select the representative training samples according to the contributions of the samples. Then we further refine the training samples by an iteration procedure, excluding the training sample with the least contribution to the test sample for each time. Experiments on PolyU multispectral palmprint database and two-dimensional and three-dimensional palmprint database show that the proposed method outperforms the conventional appearance-based palmprint recognition methods. Moreover, we also explore and find out the principle of the usage for the key parameters in the proposed algorithm, which facilitates to obtain high-recognition accuracy.

Abnormal event identification in crowded scenes is a fundamental task for video surveillance. However, it is still challenging for most current approaches because of the general insufficiency of labeled data for training, particularly for abnormal data. We propose a novel active-supervised joint topic model for learning activity and training sample collection. First, a multi-class topic model is constructed based on the initial training data. Then the remaining unlabeled data stream is surveyed. The system actively decides whether it can label a new sample by itself or if it has to ask a human annotator. After each query, the current model is incrementally updated. To alleviate class imbalance, causality-weighted method is applied to both likelihood and uncertainty sampling for active learning. Furthermore, a combination of a new measure termed query entropy and the overall classification accuracy is used for assessing the model performance. Experimental results on two real-world traffic videos for abnormal event identification tasks demonstrate the effectiveness of the proposed method.

We present an approach for human face recognition using eye region extraction/replacement method under low illumination and varying expression conditions. For conducting experiments, two different sets of face images, namely visual and corresponding thermal, are used from Imaging, Robotics, and Intelligent Systems (IRIS) thermal/visual face data. A decomposition and reconstruction technique of Daubechies wavelet co-efficient (db4) is used to generate the fused image by replacing the eye region in the visual image with the same region from the corresponding thermal image. After that, independent component analysis over the natural logarithm domain (Log-ICA) is used for feature extraction/dimensionality reduction, and finally, a classifier is used to classify the fused face images. Two different image sets, i.e., training and test image sets, are mainly prepared using the IRIS thermal/visual face database for finding the accuracy of the proposed system. Experimental results show the proposed method is more efficient than other image fusion techniques which have used region extraction techniques for dark faces.

High-performance pedestrian detection with good accuracy and fast speed is an important yet challenging task in computer vision. We design a novel feature named pair normalized channel feature (PNCF), which simultaneously combines and normalizes two channel features in image channels, achieving a highly discriminative power and computational efficiency. PNCF applies to both gradient channels and color channels so that shape and appearance information are described and integrated in the same feature. To efficiently explore the formidably large PNCF feature space, we propose a statistics-based feature learning method to select a small number of potentially discriminative candidate features, which are fed into the boosting algorithm. In addition, channel compression and a hybrid pyramid are employed to speed up the multiscale detection. Experiments illustrate the effectiveness of PNCF and its learning method. Our proposed detector outperforms the state-of-the-art on several benchmark datasets in both detection accuracy and efficiency.

We propose a robust calibration method for central omnidirectional cameras. It makes use of two mutually orthogonal sets of parallel lines. Based on the unified sphere model, the intrinsic parameters are initialized by two pairs of vanishing points in the image plane. Furthermore, the extrinsic parameters are estimated based on two geometric preservations of the two line sets on the viewing sphere. We test the method on both simulated and real data. The simulated experiments show the effectiveness of the proposed method. Experiments with respect to calibration results and validation of extrinsic parameters for real images prove that the proposed method has higher accuracy compared with Mei's toolbox.

Based on the local patch concept, we proposed locally reconstructive patch alignment (LRPA) for dimensionality reduction. For each patch, LRPA aims to find the low-dimensional subspace in which the reconstruction error of the within-class nearest neighbors is minimized and the reconstruction error of the between-class nearest neighbors is maximized. LRPA preserves the local structure hidden in the high-dimensional space. More importantly, LRPA has natural connections with linear regression classification (LRC). While LRC uses reconstruction errors as the classification rule, a sample can be classified correctly when the within-class reconstruction error is minimal. The goal of LRPA makes it cooperate well with LRC. The experimental results on the extended Yale B (YALE-B), AR, PolyU finger knuckle print, and the palm print databases demonstrate LRPA plus LRC is an effective and robust pattern-recognition system.

Distributed video coding (DVC) reduces the complexity at the encoder by using source statistics at the decoder. However, a performance gap still exists between DVC and hybrid video coders due to the inaccuracy of correlation noise (CN) modeling and inefficient exploitation of side information. We propose improvements to the performance of DVC using the two following aspects. Firstly, a progressive refinement method is proposed to improve the accuracy of CN modeling for transform domain Wyner-Ziv video coding, in which previously decoded bitplanes are exploited to progressively refine estimated CN as bitplane decoding proceeds. Secondly, a maximum likelihood pre-decoding method is also proposed to obtain a further reduction in bitrate. In our method, bitplanes are pre-decoded first using the conditional bit probability without syndrome bits. The bitrate is reduced by avoiding requests for syndrome bits for the bitplanes having strong temporal correlation. The experimental results show that our proposed methods could provide bitrate savings up to 8.26% and PSNR gains up to 0.2 dB without a significant increase in decoding complexity.

A new technology is presented that enables liquid crystal displays (LCDs) to have temperature-independent characteristics. This work shows how severely the color image quality of LCDs is affected by the ambient temperature change in addition to showing how the ambient temperature considerably affects the motion image quality of overdriven LCDs. Transmittance-voltage curve-shifting technology is proposed to compensate for the color change owing to temperature change. This new technology reduces a half-maximum luminance error from 24% to 6% over the temperature range from 0°C to 50°C. The linear overdrive (OD) technology over the wide temperature is presented to overcome the temperature-dependent characteristics of LCDs. With this technique, the distribution of the OD error is reduced by 65%. The color and motion image quality of LCDs can be kept the same with these techniques, regardless of temperature.

We address video data-hiding on the context-adaptive variable-length coding domain of the H.264/AVC standard. It is challenging to maintain a minimum variation of rate-distortion performance when hiding data in compressed videos by slightly modifying one or more transform coefficients of prediction residual data. The fluctuant variation of rate-distortion performance is especially serious in the case of hiding data in H.264/AVC compressed videos due to the thorough use of various prediction modes. Most current video data-hiding schemes concentrate on hiding messages in video intra (I)-frames to mitigate performance degradation at the expense of limited hiding capacity and applicability. Unlike most previous video data-hiding schemes, this paper considers data-hiding schemes on both I- and predicted (P)-frames of videos. We first investigate the possible ways used to suppress the significant degradation of the rate-distortion performance for hiding data in H.264/AVC videos. Based on the investigation, a hybrid video data-hiding scheme is designed to perform the classification of 4×4 residual blocks according to the characteristics of each block and to hide message data differently in each classified block in order to reduce the performance degradation caused by the data-hiding process. The block classification is based on the magnitude of the last non-zero coefficient and the coefficient difference energy of each block to select suitable blocks that are capable of contributing less degradation of coding performance for hiding additional messages. Moreover, the proposed data-hiding algorithm is incorporated with the rate-distortion optimization loop of the H.264/AVC encoder to provide further degradation suppression on the output bit-rate and decoded quality. From experiments on several well-known test videos, it can be seen that the proposed data-hiding scheme demonstrates improved efficiency on video quality and output bit-rate compared to other similar methods.

Ocular aberrations can be corrected with wavefront correctors created in a photoresist layer. The simplest type of the mask used in optical lithography is a binary amplitude mask. It is known that such a mask has a periodic hole pattern. The purpose of this research was to assess applicability of a binary amplitude mask for creating ocular wavefront correctors. The photoresist was applied to the substrate by using the dip-coating method. The photoresist layer was illuminated through a mask printed on a transparent film by using a laser printer. The surface of the wavefront correctors was evaluated by aberrometry, scanning electron microscopy and profilometry method. The dip-coating method can be used to apply an uniform photoresist layer on the substrate. Despite rapid variations in the surface depth the required shape of the wavefronts can still be obtained. Because of strong light scattering the wavefront correctors manufactured by using a binary amplitude mask aren't suited for studying visual functions. However, the wavefront correctors manufactured by such a type of the mask may be used for calibration of aberrometers.