Showing papers on "Optical transfer function published in 2009"

Quantitation and mapping of tissue optical properties using modulated imaging

Abstract: We describe the development of a rapid, noncontact imag- ing method, modulated imaging MI, for quantitative, wide-field characterization of optical absorption and scattering properties of tur- bid media. MI utilizes principles of frequency-domain sampling and model-based analysis of the spatial modulation transfer function s-MTF. We present and compare analytic diffusion and probabilistic Monte Carlo models of diffuse reflectance in the spatial frequency domain. Next, we perform MI measurements on tissue-simulating phantoms exhibiting a wide range of l* values 0.5 mm to 3 mm and s /a ratios 8t o 500, reporting an overall accuracy of approxi- mately 6% and 3% in absorption and reduced scattering parameters, respectively. Sampling of only two spatial frequencies, achieved with only three camera images, is found to be sufficient for accurate deter- mination of the optical properties. We then perform MI measurements in an in vivo tissue system, demonstrating spatial mapping of the ab- sorption and scattering optical contrast in a human forearm and dy- namic measurements of a forearm during venous occlusion. Last, met- rics of spatial resolution are assessed through both simulations and measurements of spatially heterogeneous phantoms. © 2009 Society of

Impact of Nonlinear LED Transfer Function on Discrete Multitone Modulation: Analytical Approach

Abstract: Light-emitting diodes constitute a low-cost choice for optical transmitters in medium-bit-rate optical links. An example for the latter is local-area networks. However, one of the disadvantageous properties of light-emitting diodes is their nonlinear characteristic, which may limit the data transmission performance of the system, especially in the case of multiple subcarrier modulation, which is starting to attract attention in various applications, such as visible-light communications and data transmission over polymer optical fibers. In this paper, the influence of the nonlinear transfer function of the light-emitting diodes on discrete multitone modulation is studied. The transfer function describes the dependence of the emitted optical power on the driving current. Analytical expressions for an idealized link were derived, and these equations allow the estimation of the power of the noise-like, nonlinear crosstalk between the orthogonal subcarriers. The crosstalk components of the quadrature and in-phase subcarrier components were found to be independent and approximately normally distributed. Using these results, the influence of light-emitting-diode nonlinearity on the performance of the system was investigated. The main finding was that systems using a small number of subcarriers and/or high QAM level exhibit a large signal-to-noise-ratio penalty due to the nonlinear crosstalk. The model was applied to systems with white and resonant-cavity light-emitting diodes. It is shown that the nonlinearity may severely limit the performance of the system, particularly in the case of resonant-cavity light-emitting diodes, which exhibit a strong nonlinear behavior.

Relative Transfer Function Identification Using Convolutive Transfer Function Approximation

Abstract: In this paper, we present a relative transfer function (RTF) identification method for speech sources in reverberant environments. The proposed method is based on the convolutive transfer function (CTF) approximation, which enables to represent a linear convolution in the time domain as a linear convolution in the short-time Fourier transform (STFT) domain. Unlike the restrictive and commonly used multiplicative transfer function (MTF) approximation, which becomes more accurate when the length of a time frame increases relative to the length of the impulse response, the CTF approximation enables representation of long impulse responses using short time frames. We develop an unbiased RTF estimator that exploits the nonstationarity and presence probability of the speech signal and derive an analytic expression for the estimator variance. Experimental results show that the proposed method is advantageous compared to common RTF identification methods in various acoustic environments, especially when identifying long RTFs typical to real rooms.

A fast, direct x-ray detection charge-coupled device

Abstract: A charge-coupled device (CCD) capable of 200 Mpixels/s readout has been designed and fabricated on thick, high-resistivity silicon. The CCDs, up to 600 μm thick, are fully depleted, ensuring good infrared to x-ray detection efficiency, together with a small point spread function. High readout speed, with good analog performance, is obtained by the use of a large number of parallel output ports. A set of companion 16-channel custom readout integrated circuits, capable of 15 bits of dynamic range, is used to read out the CCD. A gate array-controlled back end data acquisition system frames and transfers images, as well as provides the CCD clocks.

Convolutive Transfer Function Generalized Sidelobe Canceler

Abstract: In this paper, we propose a convolutive transfer function generalized sidelobe canceler (CTF-GSC), which is an adaptive beamformer designed for multichannel speech enhancement in reverberant environments. Using a complete system representation in the short-time Fourier transform (STFT) domain, we formulate a constrained minimization problem of total output noise power subject to the constraint that the signal component of the output is the desired signal, up to some prespecified filter. Then, we employ the general sidelobe canceler (GSC) structure to transform the problem into an equivalent unconstrained form by decoupling the constraint and the minimization. The CTF-GSC is obtained by applying a convolutive transfer function (CTF) approximation on the GSC scheme, which is a more accurate and a less restrictive than a multiplicative transfer function (MTF) approximation. Experimental results demonstrate that the proposed beamformer outperforms the transfer function GSC (TF-GSC) in reverberant environments and achieves both improved noise reduction and reduced speech distortion.

Optimal single image capture for motion deblurring

Abstract: Deblurring images of moving objects captured from a traditional camera is an ill-posed problem due to the loss of high spatial frequencies in the captured images. Techniques have attempted to engineer the motion point spread function (PSF) by either making it invertible using coded exposure, or invariant to motion by moving the camera in a specific fashion. We address the problem of optimal single image capture strategy for best deblurring performance. We formulate the problem of optimal capture as maximizing the signal to noise ratio (SNR) of the deconvolved image given a scene light level. As the exposure time increases, the sensor integrates more light, thereby increasing the SNR of the captured signal. However, for moving objects, larger exposure time also results in more blur and hence more deconvolution noise. We compare the following three single image capture strategies: (a) traditional camera, (b) coded exposure camera, and (c) motion invariant photography, as well as the best exposure time for capture by analyzing the rate of increase of deconvolution noise with exposure time. We analyze which strategy is optimal for known/unknown motion direction and speed and investigate how the performance degrades for other cases. We present real experimental results by simulating the above capture strategies using a high speed video camera.

Three-dimensional localization with nanometer accuracy using a detector-limited double-helix point spread function system

Abstract: Accurate estimation of the three-dimensional (3D) position of particles is critical in applications like biological imaging, atom/particle-trapping, and nanomanufacturing. While it is well-known that localization accuracy better than the Rayleigh resolution limit is possible, it was recently shown that, for photon-limited cases, 3D point spread functions (PSFs) can be shaped to increase accuracies over a 3D volume [Pavani and Piestun, Opt. Express 16, 22048 (2008)]. Here, we show that in the detector-limited regime, the gain in accuracy occurs in all three dimensions throughout the axial range of interest. The PSF is shaped as a double helix, resulting in a system with fundamentally better 3D localization accuracies than standard PSF systems, capable of achieving single-image subnanometer accuracies.

Increase in depth of field taking into account deconvolution by optimization of pupil mask.

Abstract: We consider optimization of hybrid imaging systems including a phase mask for enhancing the depth of field and a digital deconvolution step. We propose an image quality criterion that takes into account the variability of the system's point-spread function along the expected defocus range and the noise enhancement induced by deconvolution. Considering the classical cubic phase mask as an example, we show that the optimization of this criterion may lead to filter parameters that are significantly different from those usually proposed to ensure the strict invariance of the PSF.

Noise aliasing and the 3D NEQ of flat-panel cone-beam CT: effect of 2D/3D apertures and sampling.

Abstract: The ability to tune an imaging system to be optimal for a specific task is an essential component of image quality. This article discusses the ability to tune the noise-equivalent quanta (NEQ) of cone-beam computed tomography (CBCT) by managing noise aliasing through binning of data at different points in the reconstruction cascade. The noise power spectrum, modulation transfer function, and NEQ for CBCT are calculated using cascaded systems analysis. Binning is treated as a modular process, insertable between any two stages (in both the 2D projection domain and in the 3D reconstruction domain), consisting of the application of an aperture, followed by the resampling of data (which introduces noise aliasing). Several conditions were examined to demonstrate the validity of the model and to describe the effect on the image quality of some common reconstruction and visualization techniques. It was found that when downsampling data for increased reconstruction speed, binning in 2D results in a superior low-frequency NEQ, while binning in 3D results in a superior high-frequency NEQ. Furthermore, visualization procedures such as slice averaging were found not to degrade the NEQ provided the sampling interval is unchanged. Finally methods for reducing noise aliasing by oversampling are examined, and a method to eliminate noise aliasing without increasing reconstruction time is proposed. These results demonstrate the ease with which the NEQ of CBCT can be modified and thus optimized for specific tasks and show how such analysis can be used to improve image quality.

Deriving the modulation transfer function of CT from extremely noisy edge profiles.

Abstract: The point spread function (PSF) method is currently the one predominantly used to determine the modulation transfer function (MTF) of an X-ray CT system. However, the image examined with the PSF method must have a very high contrast-to-noise ratio (CNR); it must also be reconstructed with a fine pixel pitch using a zooming reconstruction. Therefore, the PSF method is often inappropriate for describing the MTF of clinical operating conditions when image linearity is not guaranteed. The edge spread function (ESF) method requires no zooming reconstruction, but its susceptibility to image noise is no better than that of the PSF method. We describe a technique for rendering the ESF method robust to image noise. We smooth out the noisy ESF through multiple stages of filtering. Invariably, the line spread function (LSF) obtained from the smoothed ESF is blurred, and the MTF obtained from the LSF is incorrect. However, because the filtering that has been applied is known, much of the LSF blurring can be corrected. An estimate of the true LSF is obtainable from the blurred LSF, assuming that the true LSF is not very different from either a Gaussian or a composite of multiple Gaussians. For an image reconstructed with a kernel for soft-tissue imaging, the MTF obtained by our method is sufficiently consistent with the theoretical MTF, even when the CNR is as low as 2.

Fast ultrasound imaging simulation in K-space

Abstract: Most available ultrasound imaging simulation methods are based on the spatial impulse response approach. The execution speed of such a simulation is of the order of days for one heart-sized frame using desktop computers. For some applications, the accuracy of such rigorous simulation approaches is not necessary. This work outlines a much faster 3-D ultrasound imaging simulation approach that can be applied to tasks like simulating 3-D ultrasound images for speckle-tracking. The increased speed of the proposed simulation method is based primarily on the approximation that the point spread function is set to be spatially invariant, which is a reasonably good approximation when using polar coordinates for simulating images from phased arrays with constant aperture. Ultrasound images are found as the convolution of the PSF and an object of sparsely distributed scatterers. The scatterers are passed through an anti-aliasing filter before insertion into a regular beam-space grid to reduce the bandwidth and significantly reduce the amount of data. A comparison with the well-established simulation software package field II has been made. A simulation of a cyst image using the same input object was found to be in the order of 7000 times slower than the presented method. Following these considerations, the proposed simulation method can be a rapid and valuable tool for working with 3-D ultrasound imaging and in particular 3-D speckle-tracking.

Optical design and multiobjective optimization of miniature zoom optics with liquid lens element

Abstract: We propose an optical design for miniature 2.5× zoom fold optics with liquid elements. First, we reduce the volumetric size of the system. Second, this newly developed design significantly reduces the number of moving groups for this 2.5× miniature zoom optics (with only two moving groups compared with the four or five groups of the traditional zoom lens system), thanks to the assistance of liquid lens elements in particular. With regard to the extended optimization of this zoom optics, relative illuminance (RI) and the modulation transfer function (MTF) are considered because the more rays passing through the edge of the image, the lower will be the MTF, at high spatial frequencies in particular. Extended optimization employs the integration of the Taguchi method and the robust multiple criterion optimization (RMCO) approach. In this approach, a Pareto optimal robust design solution is set with the aid of a certain design of the experimental set, which uses analysis of variance results to quantify the relative dominance and significance of the design factors. It is concluded that the Taguchi method and RMCO approach is successful in optimizing the RI and MTF values of the fold 2.5× zoom lens system and yields better and more balanced performance, which is very difficult for the traditional least damping square method to achieve.

Comparison of different analytical edge spread function models for MTF calculation using curve-fitting

Abstract: The measurement of the modulation transfer function (MTF) is one of the key steps in characterizing the signal transfer characteristics of an imaging system as a function of spatial frequency in terms of linear response theory. Various methods have been proposed to determine the MTF of an imaging system which are based on point, slit or edge images. The slanted-edge method is the ISO 12233 standard for the MTF measurement of electronic still-picture cameras. In this paper, the method is modified to avoid amplifying the noise during the derivative computation by performing curve-fitting. In the experiments, we compare several different analytical function models for the ESF fitting and find that Logistic (Fermi) function gives the best result.

Physical and psychophysical characterization of a novel clinical system for digital mammography.

Abstract: Purpose: In recent years, many approaches have been investigated on the development of full-field digital mammography detectors and implemented in practical clinical systems. Some of the most promising techniques are based on flat panel detectors, which, depending on the mechanism involved in the x-ray detection, can be grouped into direct and indirect flat panels. Direct detectors display a better spatial resolution due to the direct conversion of x rays into electron-hole pairs, which do not need an intermediate production of visible light. In these detectors the readout is usually achieved through arrays of thin film transistors (TFTs). However, TFT readout tends to display noise characteristics worse than those from indirect detectors. To address this problem, a novel clinical system for digital mammography has been recently marketed based on direct-conversion detector and optical readout. This unit, named AMULET and manufactured by FUJIFILM, is based on a dual layer of amorphous selenium that acts both as a converter of x rays (first layer) and as an optical switch for the readout of signals (second layer) powered by a line light source. The optical readout is expected to improve the noise characteristics of the detector. The aim is to obtain images with high resolution and low noise, thanks to the combination of optical switching technology and direct conversion with amorphous selenium. In this article, the authors present a characterization of an AMULET system. Methods: The characterization was achieved in terms of physical figures as modulation transfer function(MTF),noise power spectra (NPS), detective quantum efficiency (DQE), and contrast-detail analysis. The clinical unit was tested by exposing it to two different beams: 28 kV Mo/Mo (namely, RQA-M2) and 28 kV W/Rh (namely, W/Rh). Results: MTF values of the system are slightly worse than those recorded from other direct-conversion flat panels but still within the range of those from indirect flat panels: The MTF values of the AMULET system are about 45% and 15% at 5 and 8 lp/mm, respectively. On the other hand, however, AMULET NNPS results are consistently better than those from direct-conversion flat panels (up to two to three times lower) and flat panels based on scintillation phosphors. DQE results lie around 70% when RQA-M2 beams are used and approaches 80% in the case of W/Rh beams. Contrast-detail analysis, when performed by human observers on the AMULET system, results in values better than those published for other full-field digital mammography systems. Conclusions: The novel clinical unit based on direct-conversion detector and optical reading presents great results in terms of both physical and psychophysical characterizations. The good spatial resolution, combined with excellent noise properties, allows the achievement of very good DQE, better than those published for clinical FFDM systems. The psychophysical analysis confirms the excellent behavior of the AMULET unit.

Optimized circularly symmetric phase mask to extend the depth of focus

Abstract: We propose a novel design method for a circularly symmetric phase mask to extend the depth of focus. Using the free-form rational function as the solution space, we optimize the profile of the phase mask by analysis of the axial intensity distribution, which can be calculated efficiently by employing the fast Fourier transform algorithm. Numerical comparisons prove the resulting rational phase mask's superiority to the existing quartic phase mask in intensity distribution and imaging performance.

Combined optical and single photon emission imaging: preliminary results

Abstract: In vivo optical imaging instruments are generally devoted to the acquisition of light coming from fluorescence or bioluminescence processes. Recently, an instrument was conceived with radioisotopic detection capabilities (Kodak in Vivo Multispectral System F) based on the conversion of x-rays from the phosphorus screen. The goal of this work is to demonstrate that an optical imager (IVIS 200, Xenogen Corp., Alameda, USA), designed for in vivo acquisitions of small animals in bioluminescent and fluorescent modalities, can even be employed to detect signals due to radioactive tracers. Our system is based on scintillator crystals for the conversion of high-energy rays and a collimator. No hardware modifications are required. Crystals alone permit the acquisition of photons coming from an in vivo 20 g nude mouse injected with a solution of methyl diphosphonate technetium 99 metastable (Tc99m-MDP). With scintillator crystals and collimators, a set of measurements aimed to fully characterize the system resolution was carried out. More precisely, system point spread function and modulation transfer function were measured at different source depths. Results show that system resolution is always better than 1.3 mm when the source depth is less than 10 mm. The resolution of the images obtained with radioactive tracers is comparable with the resolution achievable with dedicated techniques. Moreover, it is possible to detect both optical and nuclear tracers or bi-modal tracers with only one instrument.

Design and characterization of thin multiple aperture infrared cameras

Abstract: We describe a multiple-aperture long-wave infrared camera built on an uncooled microbolometer array with the objective of decreasing camera thickness. The 5 mm thick optical system is an f/1.2 design with a 6.15 mm effective focal length. An integrated image is formed from the subapertures using correlation-based registration and a least gradient reconstruction algorithm. We measure a 131 mK NETD. The system's spatial frequency is analyzed with 4 bar targets. With proper calibration, our multichannel interpolation results recover contrast for targets at frequencies beyond the aliasing limit of the individual subimages.

Fourier deconvolution reveals the role of the Lorentz function as the convolution kernel of narrow photon beams

Abstract: The two-dimensional lateral dose profiles D(x, y) of narrow photon beams, typically used for beamlet-based IMRT, stereotactic radiosurgery and tomotherapy, can be regarded as resulting from the convolution of a two-dimensional rectangular function R(x, y), which represents the photon fluence profile within the field borders, with a rotation-symmetric convolution kernel K(r). This kernel accounts not only for the lateral transport of secondary electrons and small-angle scattered photons in the absorber, but also for the 'geometrical spread' of each pencil beam due to the phase-space distribution of the photon source. The present investigation of the convolution kernel was based on an experimental study of the associated line-spread function K(x). Systematic cross-plane scans of rectangular and quadratic fields of variable side lengths were made by utilizing the linear current versus dose rate relationship and small energy dependence of the unshielded Si diode PTW 60012 as well as its narrow spatial resolution function. By application of the Fourier convolution theorem, it was observed that the values of the Fourier transform of K(x) could be closely fitted by an exponential function exp(−2πλνx) of the spatial frequency νx. Thereby, the line-spread function K(x) was identified as the Lorentz function K(x) = (λ/π)[1/(x2 + λ2)], a single-parameter, bell-shaped but non-Gaussian function with a narrow core, wide curve tail, full half-width 2λ and convenient convolution properties. The variation of the 'kernel width parameter' λ with the photon energy, field size and thickness of a water-equivalent absorber was systematically studied. The convolution of a rectangular fluence profile with K(x) in the local space results in a simple equation accurately reproducing the measured lateral dose profiles. The underlying 2D convolution kernel (point-spread function) was identified as K(r) = (λ/2π)[1/(r2 + λ2)]3/2, fitting experimental results as well. These results are discussed in terms of their use for narrow-beam treatment planning.

Rational phase mask to extend the depth of field in optical-digital hybrid imaging systems

Abstract: We propose a novel phase mask called the rational phase mask (RPM) to extend the depth of field in optical-digital hybrid imaging systems. Using the invariance to defocus of the modulation transfer function as the merit function, we adopt the simulated annealing algorithm to optimize the RPM together with the other three existing phase masks. Numerical comparisons prove the RPM's superiority.

Optimized Design of Integrated Optical Angular Velocity Sensors Based on a Passive Ring Resonator

Abstract: In this paper, we report, for the first time, on the effects of two counterpropagating laser beams in a passive ring resonator to be used as a key element of an integrated optical angular velocity sensor, in order to optimize the design of the whole sensor. The ring resonator is modeled and the analytical expressions of the power transfer function for both drop- and through-port configurations are derived. At both drop and through ports, the two counterpropagating beams provide an increase of the amplitude of the transfer function, while at the through port, we observed also a mode suppression due to a physical effect similar to the Vernier effect. A parametric analysis has been carried out to optimize the sensor design. A minimum angular velocity as low as a few degrees per hour has been achieved, which is suitable for aerospace applications.

Image Pickup Apparatus and Method for Manufacturing the Same

Abstract: An image pickup apparatus and manufacturing method is disclosed. The image pickup apparatus comprises an optical system, an optical wavefront modulator that modulates an optical transfer function, an aperture adjacent to the optical wavefront modulator, and an image pickup device for detecting an object image passing through the optical system and the optical wavefront modulator. A product of a diameter of the aperture at a stop position multiplied by a distance between the aperture and the optical wavefront modulator is less than 2.

The Monte Carlo evaluation of noise and resolution properties of granular phosphor screens

Abstract: The imaging performance of phosphor screens, used as x-ray detectors in diagnostic medical imaging systems, is affected by their both noise and resolution properties. Amplification and blurring processes are due to a sequence of conversion stages within the screen which contribute to fluctuations in the number and spatial distribution of the optical quanta recorded by the optical detector (e.g. film, television camera, CCD, etc). The purpose of this paper is to investigate the stochastic noise arising from granularity as well as the variation of spatial resolution of granular fluorescent screens in terms of the detector's structure. Using a custom-validated Monte Carlo model, the parameters of interest were evaluated for the widely used Gd2O2S:Tb phosphor material. We have studied the variations of (i) the modulation transfer function, (ii) the Swank factor and (iii) the zero-frequency detective quantum efficiency (DQE), under several conditions employed in conventional and digital mammography and radiology. Several evaluations are provided for the imaging metrics as a function of the x-ray energy (18 keV, 49 keV and 51 keV), phosphor coating weight (20 mg cm−2, 34 mg cm−2 and 60 mg cm−2), grain size (from 4 µm up to 13 µm) and packing density (from 50% up to 85%). It was found that screens of high packing density can combine high zero-frequency DQE with improved resolution properties. For a digital mammographic imaging system (34 mg cm−2, 18 keV), a packing density of 85% can improve the spatial resolution of the screen by 1.6 cycles mm−1 in comparison to that of 50% packing density. Similarly, for radiographic cases (60 mg cm−2, 49 keV), the spatial resolution can be improved by 1.7 cycles mm−1. The aforementioned findings provide the resolution benefits of using high packing density screens.

Wide-field optical nanoprofilometry using structured illumination.

Abstract: We combine the differential height measurement concept with structured illumination microscopy to develop wide-field optical nanoprofilometry. Sub-diffraction-limit lateral resolution and axially sectioning imaging are achieved with structured illumination using a liquid-crystal spatial light modulator. As the sample surface is placed into the linear region of the sectioning axial response curve, the signal change owing to topographic variations provides nanometer depth sensitivity. The lateral resolution and the depth profiling accuracy are about 0.3 wavelengths and 6 nm, respectively. Depth profiling on solid-state specimens and label-free superresolution imaging of living cells are demonstrated.

Image processing method and apparatus, image capturing apparatus, and image processing program

Abstract: PROBLEM TO BE SOLVED: To reduce asymmetrical aberration such as coma aberration and chromatic aberration of magnification and improve sharpness while preventing amplification of noise in a restored image. SOLUTION: An image processing method includes: a step of obtaining an image generated by imaging systems 101, 102 and a step of performing correction processing of the image by using an image restoration filter generated or selected based on an optical transfer function of the imaging systems. The image restoration filter is a filter to reduce a phase degradation component of the image. COPYRIGHT: (C)2011,JPO&INPIT

On the Design of Efficient and Accurate Arbitrary-Order Temporal Optical Integrators Using Fiber Bragg Gratings

Abstract: In this paper, we propose and numerically investigate a simple and practical all-fiber design for implementing first-order and higher order all-optical passive temporal integrators with optimized energetic efficiencies. The proposed solution is based on a high-reflectivity fiber Bragg grating (FBG) providing a reflection spectral response that approaches the frequency transfer function of a time-limited Nth-order optical integrator (N = 1, 2, 3 ...). A closed-form analytical expression has been derived for the frequency response to be targeted for implementing an optical integrator of any given integration order operating over a prescribed limited time window. The required grating profile can then be designed using a layer-peeling FBG synthesis algorithm. Our simulations show that for a sufficiently long FBG, a relatively smooth amplitude-only apodization profile is required for any desired integration order even when an FBG peak reflectivity > 99% is targeted. The resulting FBG integrators can provide at least a sixfold increase in energetic efficiency as compared with previously proposed FBG designs while offering a similar or superior performance in terms of processing accuracy. We estimate that ultrafast highly efficient arbitrary-order all-optical temporal integrators capable of accurate operation over nanosecond time windows could be implemented using readily feasible, centimeters-long FBGs.

Impulse attack-free four random phase mask encryption based on a 4-f optical system.

Abstract: Optical encryption methods based on double random phase encryption (DRPE) have been shown to be vulnerable to different types of attacks. The Fourier plane random phase mask (RPM), which is the most important key, can be cracked with a single impulse function attack. Such an attack is viable because the Fourier transform of a delta function is a unity function. Formation of a unity function can be avoided if RPMs are placed in front of both lenses in a 4-f optical setup, thereby protecting the DRPE from an impulse attack. We have performed numerical simulations to verify the proposed scheme. Resistance of this scheme is checked against the brute force and the impulse function attacks. The experimental results validate the feasibility of the scheme.

High-resolution surface-plasmon resonance real-time imaging

Abstract: We use surface-plasmon resonance in a silver film to obtain high-resolution real-time images of a transparent dielectric sample in contact with it. A new aspect of the work was the use of radially polarized illumination from a LED at 530 nm to obtain speckle-free images with high spatial resolution along all orientations. The sensitivity to refractive index changes in the sample is estimated to be better than 10−3, and the modulation transfer function out to spatial frequency 1 μm−1 was measured.

Image capturing apparatus, image-capturing method, and program

Abstract: PROBLEM TO BE SOLVED: To provide an image-capturing apparatus capable of providing a desired subject image, regardless of the distance. SOLUTION: The image-capturing apparatus is provided for capturing an image of a subject and includes an optical system, causing a light-receiving section of the image capturing apparatus to receive, in substantially the same spread, light from positions within a range of positional relation predetermined with the image capturing apparatus, and having different optical transfer functions for light from different positions lying within the range of positional relation predetermined with the image capturing apparatus; a process parameter storage for storing each process parameter for correcting the effect of an optical transfer function on the captured image, in association with a condition, regarding the positional relation between a subject and the optical system to be satisfied in performing correction using the process parameter; a positional information obtaining section for obtaining positional information indicating a positional relation between the subject and the optical system; and a process parameter selecting section for selecting a process parameter stored in the process parameter storage, in association with the condition that the positional relation indicated by the positional information obtained by the positional information obtaining section be satisfied. COPYRIGHT: (C)2009,JPO&INPIT