This PDF file contains the editorial “Editorial: Surfin’ Australasia” for OE Vol. 44 Issue 01

We propose and demonstrate an optical watermarking scheme using a digital holographic technique. The holographic watermark is constructed by an off-axis diffuse-type hologram and embedded into a cover image with appropriate weighting. Detection of the hidden mark is optically implemented using a VanderLugt correlator with the watermarked matched filter. Detected correlation is spatially separable and avoids interference from the cover image.

An expert system is developed for the automatic generation of initial layouts for the design of zoom systems with multiple moving lens groups. The Gaussian parameters of the zoom system are optimized using the damped-least-squares method to achieve smooth zoom cam curves, with the f-number of each lens group in the zoom system constrained to a rational value. Then each lens group is selected automatically from a database according to its range of f-number, field of view, and magnification ratio as it is used in the zoom system. The lens group database is established from the results of analyzing thousands of zoom lens patents. Design examples are given, which show that the scheme is a practical approach to generate starting points for zoom lens design.

A new optical architecture of a multiview projection display based on a mirrored light tunnel is presented. The light tunnel is made of two or four parallel plane mirrors, placed between an image projector and a directional screen. An arbitrary number of perspective images are projected by a single image projector being arranged in rows and columns in a certain order. The images appear superimposed on the screen due to the folding of the projection beam by the mirrored tunnel. Working in this way, the mirrored tunnel does not cause any image distortion. The directional screen for autostereoscopic imaging incorporates a slanted directional diffuser. The presented technique allows both autostereoscopic and full parallax image projection. A six-view autostereoscopic display with image resolution of 768×341 has been built in accordance with this new optical concept and tested.

We implement a phase-shifting Talbot interferometric technique to measure step heights of a single-step and channel (dip) objects. Experimentally recorded interferograms include noise due to grating lines and speckles. To make the phase map, four interferograms are recorded with π/2 phase shifts. To remove noise due to grating lines and speckle, interferogram data are first filtered using Fourier filtering. Height variations per profile of the objects is calculated from the phase map made using Fourier-filtered data. Results obtained from this technique are compared with the results acquired from a profile projector having a coordinate measurement facility with a resolution of 1 µm and an accuracy of ±1 µm. The results are in good agreement.

The continuing development of new and fundamentally different classes of imaging spectrometers has increased the complexity of the field of imaging spectrometry. The rapid pace at which new terminology is introduced to describe the new types of imaging spectrometers sometimes leads to confusion, particularly in discussions of the relative merits of the different types. In some cases, multiple different terms are commonly used to describe the same fundamental approach, and it is not always clear when these terms are synonymous. Other terminology in common use is overly broad. When a single term may encompass instruments that operate in fundamentally different ways, important distinctions may be obscured. In the interest of clarifying the terminology used in imaging spectrometry, we present a comprehensive system for classification of imaging spectrometers based on two fundamental properties: the method by which they scan the object spatially, and the method by which they obtain spectral information.

Theoretical principles for computing the refraction influence for precision leveling are considered. In the analysis, the radius ρ of curvature of visible light oscillation is used as a basis. Actually, the curvature radius ρ is a function of the vertical gradient of the light refractive index. The vertical gradient refractive index is expressed by vertical gradients of air temperature, pressure, and humidity. In these procedures, the formulas of Barrel and Sears, and Cauchy-Sellmeier are used, and then, on the basis of the formulas, the group refractive index is expressed. The essential influence on the change of the vertical gradient of refractive index is derived. The vertical temperature gradient has the most influence. Influence on the vertical gradient refractive index of the vertical pressure gradient is approximately 2.5 times less than that of the vertical temperature gradient, and the influence of the vertical air humidity gradient is infinitesimally small. Formulas for determining the precision of the temperature gradient measurement are obtained. Formulas for calculating the refraction correction δ_a for the height difference at a station are also expressed.

We propose a simple confocal system that uses a laser Gaussian beam as a probe to measure microstructure features of curved or turned surfaces. The probe beam is focused by a lens with a low numerical aperture to maintain the beam unclipped throughout the detection process and to limit the vertical resolution to several microns. This resolution is suitable for examining the microstructure of machined surfaces. The size of the pinhole in the plane of detection is characterized for optimal depth discrimination. The analytic description is based on the propagation of Gaussian beams by using the scalar Fresnel diffraction integral.

We describe the design and implementation of a vacuum compatible laser-based absolute distance measurement system with subnanometer resolution. The presented system is compatible with operation in the 10^–8-Torr range, and with some minor modifications it could be used in the 10^–9-Torr range. The system is based on glancing incidence reflection and dual segmented diode detection. The system has been implemented as a focus sensor for extreme ultraviolet interferometry and microlithography experiments at Lawrence Berkeley National Laboratory's Advanced Light Source synchrotron radiation facility. A 3σ operational noise floor of 0.78 nm has been demonstrated.

A white light interferogram can be decomposed into its constituent monochromatic interferograms using a spectrograph. By imaging the white light interferogram on the entrance slit of the spectrograph, the intensities of the monochromatic components can be accessed at its output plane by the pixels of a CCD detector along the direction of dispersion. For a given optical path difference (OPD) in the interferometer, the phases of these constituents are different and linearly related to the wave number of the constituent spectral component. If the phases of all the constituents are determined, the OPD can be obtained as the slope of the phase versus wave number linear fit. Since the OPD is related to the height of the test object at a point, a line profile of the object can be determined if the OPD is measured along the pixels of the CCD parallel to the entrance slit of the spectrograph. To get at the line profile, we must therefore determine the optical phase at all the pixels of the CCD detector. The phase-shifting technique is an obvious choice for this. A piezoelectric transducer (PZT) phase shifter is most common in the application of the phase-shifting technique to monochromatic interferometry. We present the experimental result based on our recent proposal that the conventional PZT phase shifting, although nonachromatic, can be used for this application as well with success.

A dimensional measurement system that also tracks object movements is presented here. The method directly yields the level curves of an object. It is an extension of collimation methods, coupled with the use of structured lighting with features formed from several luminous planes intersecting in a single line. This line defines a set of points of the space at a fixed distance Z₀ from the measuring head. The locus of the points of the object where the lighting is reduced to a single line is the level curve sought. The introduction of an asymmetry into the lighting structure permits one to determine the direction as well as an approximate value of the value of the distance to the level curve from a point on the illuminated object. The experiments performed permit one to evaluate the performance of such a system, and suggest future applications.

An MMI-T/G system composed of a modified four-beam moiré interferometer (MMI) and a Twyman/Green (T/G) interferometer is developed. The MMI-T/G can measure 3-D displacement fringe patterns with a single loading on the specimen. In the MMI-T/G system, one incident laser beam is diffracted into multiple beams by the cross-line grating on the specimen, where the ±1 order diffractive beams are redirected back to the specimen by flat mirrors, then rediffracted by the specimen grating onto the CCD, generating the in-plane displacement fringe pattern; the zero-order diffractive beam interferes with a reference beam of the T/G, generating the out-of-plane displacement fringe pattern. Details of the derivation of the fringe-governing equations are given based on the wavefront interference theory. The fringe-governing equations so obtained are comparable with those derived previously based the Doppler frequency shift theory and conventional moiré interferometry. The in-plane displacement sensitivity of the new system can be shown to be twice of that of a normal moiré interferometer. The optical setup has the advantages of structure novelty, flexibility, and high fringe contrast. Experiments are carried out to validate the derived governing equations, and clear thermodeformation fringe patterns of an electronic package are shown.

We discuss an interference fringe type encoder using a point source LED equipped with a slit; this encoder offers high resolution, a wide temperature range, and high reliability. To optimize the design of this encoder, we develop a simulator for an interference-fringe-type encoder using the Fresnel-Kirchhoff diffraction formula, and we analyze the following elements of the optical system of the encoder: (1) the effect of the LED wavelength band, (2) the effect of the size of the LED radiation area, and (3) the effect of the shape of the diffraction grating surface. The interference fringes of this encoder are generated with 60% greater efficiency than an encoder using an LD featuring a very narrow slit width.

Very large-scale integral imaging (VLSII) systems utilizing multiple micro-optics arrays and display devices can be used for wide viewing angle 3-D displays. We analyze the distortion of 3-D integral images when micro-optics arrays are placed on a spherical surface and are used in direct pickup integral imaging. We show that 3-D orthoscopic real images with non-negligible depth always suffer from image distortion, while orthoscopic virtual images do not. Also, nonplanar (curved) display panels and image sensors are not currently available. We propose a solution to remedy this problem by placing a spherical lens in front of a planar lenslet array.

Enhancement of undersampled imager performance has been demonstrated using superresolution techniques. In these techniques, the optical flow of the scene or the relative subpixel shifts among various snapshots of the scene are calculated, and a high-resolution grid is populated with spatial data using various algorithms. Performance enhancement has been demonstrated for the case of a static image with the undersampled imager compared with a static image that has been acquired through a frame series in a dynamic scene. In this research, the performance is compared for four cases: static image with undersampled imager, static image with superresolution frame sequence, dynamic image with undersampled imager, and dynamic image with superresolution frame sequence.

We report the use of an experimental ferroelectric liquid crystal material called CDRR8 in bistable optically addressed spatial light modulators for both amplitude- and phase-modulating devices. First, the methods used to improve the alignment and obtain truly bistable switching with CDRR8 are described. The diffraction efficiency and switching characteristics of a bistable CDRR8 optically addressed spatial light modulator used as an amplitude-modulating device and then as a phase-modulating device for encoding high-resolution patterns are compared. The CDRR8 devices exhibit bistability when driven by alternating monopolar pulses. The results show that the use of a device as a phase-modulating rather than an amplitude-modulating device, increases the diffraction efficiency by 10 times. Resolution is better than 100 lp/mm, as measured by the fall in diffraction efficiency by 50% compared with the diffraction efficiency at low spatial frequencies.

We develop fast ray-tracing methods for LCD backlight simulation. In general, the LCD backlight uses the light guide plate (LGP) to deliver the lights from the side of backlight to the viewing surface. The printed pattern, which consists of many scattering elements (dots), makes the uniform light distribution on the viewing surface. These dots are distributed in a certain regular array at the bottom of the LGP. Since there are too many dots to be handled, it takes a long time for nonsequential Monte Carlo ray-tracing simulations. To speed up the simulation of the backlight with a printed pattern we use a restricted condition and two fast calculation algorithms for the pattern. From the restricted condition, the ray tracing for pattern is performed only when the ray meets the pattern surface. We use two different fast calculation algorithms to verify whether or not a ray meets the pattern. In the first one, since the probability that a ray meets the pattern is the same as the pattern density at the meeting position, we use the pattern density function as a probability function of meeting. This method makes it possible to speed up the simulation and has another merit that the simulation can be processed without using the pattern data: positions, sizes, and the shape of the pattern elements. In the second one, instead of the great number of dots, we determine four dots that can possibly meet a ray. This method gives faster simulation speed and the same result as that from the calculation with all the dots.

A comprehensive experimental study of the prepumping technology on the passively Q-switched monolithic Cr⁴⁺, Nd:YAG laser is presented. Compared with pulse pumping, the stability of pulse energy and the temporal jitter of laser pulses are improved to a great extent with prepumping modulation. The dependency of output stability performance on the four prepumping parameters is shown. Among them the base current I_b plays an important role. The dynamic of the prepumping is given. The experimental results show that prepumping is a promising method to get stabilized Q-switch pulse in miniature Nd:YAG laser.

A novel spacing-tunable multiwavelength erbium-doped fiber laser source based on a Sagnac loop filter is proposed and experimentally demonstrated. The filter, which is coupled together with the laser cavity, consists of a normal 3-dB fiber coupler, a polarization controller (PC1), and a segment of high-birefringence (Hi-Bi) fiber. The active gain medium, which is a polarization-maintaining erbium-doped fiber (PM-EDF) with an elliptical core, leads to possible multifrequency lasing output at room temperature. In the experiment, by changing the setting of the polarization controller (PC2), multiple-frequency lasing lines with different wavelength spacing are obtained. Experimental results show several stable output lasing wavelengths with high extinction ratios at room temperature.

We develop a simple piece of equipment for measuring methane (CH₄) gas concentration based on IR absorption by sweeping the wavelength of light emitted from a laser diode (LD). The principle of IR absorption enables the selective measurement of CH₄ gas by detecting an absorption line that appears around 1300 nm in the specific absorption spectrum of CH₄. Our method is simpler and more user-friendly than existing measurement methods that involve a measurement system equipped with a cell filled with a known concentration of CH4 gas and a lock-in amplifier. The results of measurements using 220- and 660-mm measurement cells show that CH₄ gas concentration is proportional to absorbance within a concentration range of 5 to 90 vol %. It is also found that our measurement system can selectively measure only the concentration of CH₄ in city gas, which is composed of a mixture of flammable gases. Moreover, a simple technique for removing humidity using silica gel and calcium chloride reduces the influence of relative humidity. These results represent performance superior to other CH₄ measurement methods currently in use.

The feasibility of producing a continuous laser spark (CLS) with low resistance by focusing radiation from a CO₂ laser with a conic mirror is demonstrated. The laser energy input per unit length required for this is experimentally found to be equal to ≈200 J/m. The possibility to efficiently control the trajectory of an electric discharge by means of a CLS is demonstrated. The effect of polarity in the electric breakdown of the air gaps between the CLS plasma channel and a metal rod is discovered and interpreted. The transverse structure of CLS conductivity is investigated. The possibility of producing a long laser spark (LLS) with much higher resistance by focusing radiation from a CO₂ laser with a spherical mirror used to protect objects against lightning is studied. The conditions under which the electric discharges from clouds can be guided reproducibly along a LLS are determined. Experiments reveal that the interaction between the LLS and the discharge from an electrode (lightning rod) leads to a decrease in the lifetime of the streamer corona burst, as well as to an increase in the current of the developing leader and its velocity compared to the case without the LLS.

High-pressure measurement is made by demodulating Bragg grating peak splitting caused by transverse stress differences in the core of a high-birefringence (HB) single-mode fiber, which is bonded on the exterior surface of a free active element bulk modulus. The two orthogonally polarized signals reflected from the HB fiber Bragg grating (FBG) can be independently detected with a simple FBG interrogation system, which is based on the light intensity measurement method. In addition, the cross-sensitivity of the FBG sensor can be self-compensated by this method. The measurement principle is introduced, and preliminary experimental results indicate that the measurement sensitivity is estimated to be ~12 pm/N in a linear measurement range from 0 to 120 N.

The problem of directed waveguide mode scattering in an irregular planar optical waveguide (PWG) is solved using the theory of perturbations. The solution of the inverse waveguide scattering problem consists of restoring the autocovariance function and determining irregularity parameters by the measuring data of a scattering diagram in the far zone. The new complex solution algorithm for the described inverse waveguide scattering problem is a combination of classic regularization and the quasi-optimal filtration (smoothing) of the measured data. The computer simulation enables us to show that our method makes it possible to receive an approximately correct solution of the inverse problem with a root mean square (rms) error in restoring the given autocovariance functions of no more than 35% in the presence of high real noise (SNR≥1). The statistical parameters of the irregularities in this case can be determined with an error less than 15 to 30%. The roughness parameters determined in the experiment are in good agreement with the parameters obtained by a scanning electron microscope (SEM) and by a standard mechanical profilometer.

A math model that can describe the effect of stimulated Raman scattering (SRS) on a pilot-tone detection technique is developed. Through numerical simulation, it is shown that the effect of SRS could produce ghost tones. The power of the ghost tone is larger for the channels separated farther from the real tone. The experiment results show that this model can evaluate the effect accurately. The power ratio between real tone and ghost tone increases linearly with the increase of transmission length when wavelengths transmit longer than 300 km.

The degradation in fiber strength and the change of fiber refractive index during fusion splicing are observed through mechanical optical experiments and microanalysis. A hydrofluoric acid solution effectively enhances some performances after fusion occurs. A novel transmitted-light differential interference contrast (DIC) system is used to nondestructively measure the refractive index profile (RIP) of an optical fiber.

In conventional surface estimation using white light interferometry, data acquisition is followed by a preprocessing step in which the 3-D (space-time) data are reduced to a 2-D surface or height map. Finally, a postprocessing step eliminates the height outliers that arise from the preprocessing under ordinary experimental conditions. We introduce a Bayesian approach that unifies pre- and postprocessing by considering simultaneously both the full 3-D data set and knowledge concerning the surface smoothness. This knowledge is coded into the prior probability of local height configurations. The surface is estimated as the mode of the marginal posterior at each pixel. An adept formulation of the prior allows for the exact computation of the estimate, obviating the need to sample from the posterior using Markov chain Monte Carlo methods. A complete surface can thus be obtained in 3 to 30 s. A quantitative comparison with an (adaptive) median filter shows that all three approaches decimate outliers, but that the Bayesian estimation leads to smaller average absolute errors. For low scanning speeds and good raw data, this is due to a reduced tendency to oversmooth; for poor input data, the enhancement is explained by the more complete exploitation of the observations.

A new method for phase-shifting moiré interferometry is proposed and studied experimentally. A nematic liquid crystal cell is employed as a phase modulator to realize the phase-shifting technique for the conventional moiré interferometry. The phase retardation of the liquid crystal cell is calibrated by measuring transmitted light intensities. By letting one of coherent beams pass through a liquid crystal cell and controlling the phase retardation via suitable voltages across the cell, the phase map that provides quantitative data regarding the in-plane surface displacement can be created. The use of the liquid crystal phase modulator in the moiré optical arrangement has several advantages over alternative methods.

A holographic interferometry system is developed to improve flow field visualization and measurement. The test objects are free-flight models, which have axis-symmetric shape; these models fly at the hypervelocity of M = 2.25 to M = 15 in normal static atmosphere. They are shot into a free-flight ballistic range (FFBR) that is 200 m in length and has 30 observation windows. Finite and infinite holograms of the models are taken and reconstructed. Moreover, the quantitative measuring results of the density distribution and the computation interferogram of the flow field are completed. The separation between the sphere model and the bow shock wave is measured.

The effects of wind on scintillation decorrelation times are well known only for winds transverse to the propagation path. Therefore, we have investigated such effects using laser scintillation and sonic anemometer data obtained at an outdoor test site at DRDC-Valcartier. The data were taken during both day and night periods in May and June 2003. Meteorological data were also taken over these periods. Scintillation decorrelation times were then compared with the times deduced using the sonic anemometer wind data and Clifford's theory, which only uses the wind component transverse to the propagation path of the laser. Substantial differences were observed, because Clifford's theory does not take into account the effects of the wind's longitudinal component. A simple theoretical model has been developed to include the longitudinal wind. The model includes a free parameter that must be fitted to the data. Once this is done, the model allows us to predict, with reasonable accuracy, the scintillation decorrelation time scale given the inner scale and the wind at any angle. Residual discrepancies may be due to the internal evolution of the turbulence, which has not been included in our model and causes a decorrelation independent of the wind.

We develop an optical fiber imaging laser radar based on the focal plane array detection method using a small number of detectors less than the number of the focal plane array resolution. For the development of this kind of the focal array detection method, we produce the optical fiber dissector, the movable aperture, and the small-number parallel multichannel pulse counter receiver. The optical fiber dissector has one vertical cross section of the 35×35 optical fiber square array for the focal plane at one end and 25 vertical cross sections of the 25 optical fiber bundles for the 25-channel parallel multichannel pulse counter receiver at the other end. Each optical fiber bundle has the 49 optical fibers selected from the 35×35 optical fiber square array with no overlap. The movable aperture has a window of a size 5×5 optical fiber cross section to ensure no crosstalk for the detection of the divergent pulse laser beam. The divergent pulse laser beam is focused on some 5×5 area of the 35×35 optical fiber square array related to its scanning direction. The developed optical fiber imaging laser radar shows high range resolution and no-crosstalk angle resolution. The range resolution is under 15 cm. The angle resolution is 1 pixel.

An optical power scale is established at Ulusal Metroloji Enstitüsü (UME) using the helium-cooled primary-level electrical-substitution cryogenic radiometer. The scale is established at discrete laser wavelengths of vertically polarized tuneable Ar⁺, fixed He-Ne, and Nd:YAG (with second harmonic) laser sources. To increase measurement accuracy, laser intensities are stabilized to better than 0.009% using an electro-optical modulator. The spatial profiles of polarized laser beams are cleaned with a spatial filter. The optical power is measured using the static substitution method with an uncertainty of a few parts in 10^–4. Repeatability of optical power measurements in the static substitution method, the measurement of window transmittance, and the measurement of power in a scattered beam are the most significant uncertainty components.

Data association and model selection are important factors for tracking multiple targets in a dense clutter environment without using a priori information about the target dynamic. We propose an interacting multiple model-expectation maximization (IMM-EM) algorithm by incorporating different dynamic models for the target and using Markov random field (MRF) for data association. In this way we are able to track maneuvering and nonmaneuvering targets simultaneously in a single batch mode (sequential). Moreover, it can be used for real-time application. The proposed method overcomes the problem of data association by incorporating all validated measurements together using an EM algorithm and exploiting MRF. It treats the data association problem as an incomplete data problem and measurement association as missing data. In the proposed method, all validated measurements are used to update the target state, and the probability density function (pdf) of observed data, given a target state and measurement association, is treated as a mixture pdf. This allows us to combine the likelihood of a measurement due to each model. The association process now incorporates IMM, and consequently, it is possible to track any arbitrary trajectory. We also consider two different cases for association of measurement to target: association of each measurement to the target is independent of each other; and association of a measurement influences an association of its neighbor measurement.

In radiometers for the x-ray range (E~10 to 100 keV) the use of oxide scintillators based on gadolinium oxyorthosilicate (GSO) has many advantages over alkali halide scintillators, e.g., NaI(Tl). The shape of spectra obtained with GSO and cadmium tungstate (CWO) scintillators has certain features that substantially increase the sensitivity of radiometers that use the energy windows algorithm and allowed us to design a detector for simultaneous detection of low-energy γ radiation of ²⁴¹Am (59.6 keV) and ¹³⁷Cs (≈33 keV). These features of oxide scintillators have allowed a substantial increase in sensitivity of the selective radiometer RK-AG-02M, which is designed for measurements of ²⁴¹Am activity in soil samples against the background of ¹³⁷Cs. The results obtained in this work show that the use of GSO and (in several cases) CWO scintillators in instruments involving x-ray range of radiation (e.g., thickness meters, radiometers) is a very promising field for their application. To ensure efficient use of GSO, sufficiently high optical luminescence, scintillation, and other functional characteristics of this scintillator are required, which can be improved by thermal treatment. In this connection, results are presented on thermal treatment of GSO:Ce crystals. In RK-AG-02M we are using a scintillation unit based on a GSO scintillator. To increase the measurement accuracy in the bulk density range of 0.6 to 2.5 g/cm³, a correcting function has been obtained for the radiometer sensitivity.

Vibration distortions cause the major problems faced by various imaging sensors placed on automated platforms. The nature of those vibrations is expressed in distortion of high spatial frequencies existing in the captured image. Such distortions are caused by the movements of the camera (or the object) during the integration time of the detector. We suggest a temporally masked time integrating readout process that results in enhancement of the captured spatial frequencies. The enhancement requires some digital processing operations. The suggested temporally blocked readout process is expressed by blocking the integration at predetermined times. Since the integration block periods are very short, the suggested technique is energetically efficient.

Intuitively, the point spread function (PSF) of a computed tomographic (CT) system can be determined by the reconstruction of a microphantom (diam<1 mm), such as a microbead for 3-D PSF or a thin wire for 2-D PSF (or line spread function). In fact, this direct method has its own limitations and drawbacks. First, the microphantom (not necessarily infinitesimal) is difficult to be precisely manufactured. Second, the reconstructed volume (containing the micron phantom image) is prone to the uncertainty in digital representation due to the aperture effect associated with grid cells (pixels for 2-D grid or voxels for 3-D grid). Third, the reconstructed digital volume of a microphantom is both material dependent and size dependent, and so is the PSF; this is not convenient for CT system evaluation. We reveal the pitfalls associated with the microphantom-based cone-beam CT PSF measurement by theoretical explanation and experimental demonstration. To avoid the pitfalls, we are in favor of the edge-based techniques for PSF measurement through the use of a macroedge phantom (diam>1 mm). In conclusion, the CT PSF can be efficiently determined by an edge-based technique, such as the iterative edge-blurring algorithm.

A new image hiding scheme is proposed that can embed color secret images into color host images. The secret image to be embedded is first color quantized using a palette previously sorted by the principal component analysis technique to generate the indexed color image. Then the concept of pixel difference is employed to process both the host image and the indexed color image. Then the difference image of the indexed color image is embedded into the difference image of the color host image. According to our experimental results, the image quality of the stegoimage is quite good when our new method is used to embed a color secret image into the color host image.

A new joint region-merging criterion for watershed-based image segmentation is proposed. The proposed method combines, in a weighted fashion, criteria based on region homogeneity and edge integrity, which have each been applied separately in image and video segmentation with some success. However, each criterion has shown some significant drawbacks when applied independently. The new criterion takes joint advantage of these two methods, giving a final segmentation that is more visually appropriate. Additionally, a nonlinear pre- and postfiltering procedure is proposed for reducing oversegmentation in the watershed algorithm. This procedure preserves the location of the watershed boundaries and yields a merging procedure that requires fewer steps to produce a final segmentation. Experimental results are presented showing the advantages of the new merging criterion and the pre- and postfiltering method.

For the problem of restoration of turbulence-degraded images, it is of utmost importance to make a correct estimation of the turbulence' s stochastic point spread function (PSF). A new method is presented for estimating the discrete values of overall PSFs of turbulence-degraded images. For this method, two short-exposure turbulence-degraded images are used as the inputs, for which the Fourier transforms are made and a series of equations for calculating the discrete values of the turbulence PSFs are developed. Some effective rules for selecting equations have been worked out to ensure a reliable solution for the PSFs. To overcome the interference of noise, two optimization algorithms for estimating the turbulence PSF values, based on quadratic and nonquadratic regularization that can be incorporated into the estimation process, are proposed, in which the constraints of the PSF values are non-negative and smooth [quadratic regularization non-negative and smooth (QRNNS) and nonquadratic regularization non-negative and smooth (NQRNNS)]. A series of experiments are performed to test the algorithms proposed, which show that the NQRNNS algorithm is both rational and highly effective.

We analyze an algorithm for the misregistered trade-off heterocorrelation filter (HCF) using nonlinear transformation methods. This HCF consists of a matched filter modified by a transmittance function that has been optimized for the metric peak-to-mismatched energy. We find that this algorithm employs a new form of the nonlinear synthetic discriminant function algorithm that generates multiple correlation peaks for both autocorrelation and heterocorrelation when the filter function is made up of functions misregistered (i.e., shifted) with respect to each other. By means of computer simulations we study the effect that the trade-off factor (β), weighting the Fourier spectrum difference, has on the autocorrelation, heterocorrelation, and cross-correlations for centered inputs when the matched filter is used as the basic filter. We find that as β increases, the difference between the autocorrelation and heterocorrelation peak intensities diminishes and reaches a minimum value when β approaches 1. Furthermore, we find that for exactly registered (i.e., unshifted) images used to make up the HCF, there is only one order of autocorrelation peak and only one order of heterocorrelation peak; however, as the amount of misregistration increases, both the autocorrelation and heterocorrelation peaks split into many orders and their positions are displaced relative to each other. The amount of shift between successive autocorrelation and heterocorrelation peaks is equal to the amount of shift in the misregistered images used to make up the filter.

We continue our study of the misregistered trade-off heterocorrelation filter (HCF), introduced in Part 1. Instead of using the matched filter, we use only the phases of the Fourier transforms of the functions constituting the filter, with our basic filter being the phase-only filter. We show that by adjusting the value of the trade-off factor it is possible to make the correlation pattern and intensities of the heterocorrelation peaks equal to those of the autocorrelation peaks; in effect, making the HCF a homogeneous filter. This means that it can equally recognize totally different objects that one designs it to recognize. These results (1) turn out to be independent of the amount of misregistration (i.e., shift) between the centers of the impulse responses of the functions making up the filter and (2) can also support the claim that a HCF is a totally new approach to generating synthetic discriminant filter functions. We also produce plots showing how the intensities, peak-to-noise ratios, and peak-to-secondary ratios of both autocorrelation and heterocorrelation peaks behave as a function of trade-off factor.

We summarize some design tips and design procedures of nanoapertures with strong field enhancement, based on the theoretical calculations and analyses of near-field distributions of unconventional C apertures and bow-tie apertures by a finite-difference time-domain method. A novel L-shaped aperture is proposed and further validates the proposed design rule. As a result, a 15×15-nm full width half maximum spot forms in the light exit plane of the L aperture. Its intensity maximum enhancement reaches a factor of about 568 and the power throughput is bigger than unity. The mechanisms of electromagnetic field enhancement are preliminarily analyzed. This unconventional nanoaperture is likely to be directly used as an exit aperture of very small aperture lasers, or as an unattached shield, to produce a subwavelength light source with high transmission.

A method to detect production faults in plastic packages using terahertz (THz) radiation is presented. Relying on the large difference between the absorption coefficients of plastic and water (for water-filled defects), and on the refraction index difference between plastic and air (for air-filled defects), our technique consists of focusing and scanning a terahertz beam on the sealed area of the package, followed by the detection of the transmitted signal. Compared to previous methods such as visual and ultrasound inspection, our technique can be applied for optically opaque packages and does not require immersion in a matching liquid. We tested our terahertz system on defects simulated by water-filled and air-filled round channels imbedded in polyethylene films, with diameters ranging from 10 to 100 µm. The results show that detection is possible down to 30 µm for water-filled and 40 µm for air-filled channels. The results are the same for both transparent and opaque packages.