Modulation Transfer Function Research Papers (original) (raw)

The light does not penetrate deeply into the skin tissue because of tissue turbidity. Light penetration depth in skin tissue can be increased by using optical clearing agents such as glycerol, glucose and dimethyl sulfoxide(DMSO). The stratum corneum prevents most optical skin clearing agent from diffusing into the tissue. Previous studies demonstrated the optical tissue clearing effect using optical clearing agents and presented several physical methods to improve transdermal delivery of optical clearing agents. In previous study, we introduced a micro-needling method to enhance optical clearing efficacy against skin barrier and suggested quantitative analysis method to evaluate the optical tissue clearing efficacy. In this study, we present a new physical micro-needling method combined with sonophoresis to further enhance the optical tissue clearing efficacy. The optical tissue clearing effect was quantitatively evaluated with a modulation transfer function target placed under ex-vivo porcine skin samples. To improve transdermal delivery of glycerol, 70% glycerol solution as optimal concentration was topically applied. In conclusion, the samples treated with micro-needling method and sonophoresis resulted in noticeable optical tissue clearing effect.

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- Ultrasound, Quantitative analysis, Skin, Modulation Transfer Function

an important figure of merit in focal pllyle array sensors, especially for accurate target positions such as star trackers. In-situ evaluation by MTF in different stages of imager system developments is necessary for an ideal design of different sensors and their signal processing. Understanding the tradeoff between different figures of merit will enable designers to achieve the most efficient design in specific missions. Advanced active pixel test sensors have been designed and fabricated where different pixel shapes were placed. Research on analyzing the "I?? for the proper pixel shape is currently in progress for a centroidal configuration of a star. Explicit formulas for the modulation transfer function have been studied for the rectangular shaped pixel array. MTF will give us a more complete understanding of the tradeoffs opposed by the different pixel designs and by the signa4 processing conditions. In this paper, preliminary results of two different active pixel sensor ( A P S ) focal plane arrays are presented in terms of crosstalk using a laser. MTF measurements of the A P S arrays are achieved by applying only a single image. A rising or falling edge rather than the conventional bar target of slit scanning is needed to perform the measurement in each direction for the evaluation of the design efficiency.

- by Bedabrata Pain
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- Signal Processing, Imaging, Image Quality, Sensors

The RASTI-method is a simplified version of the speech transmission index. that has heen evaluated in several languages. In this paper. a comparative study of' the scores of speech intelligibility obtained by the traditional speaker-listener tests in the Spanish language and the RASTI-method has been carried out in classrooms. The list of monosyllabic words used are phonetically bulanced and representutive of' the Spanish language. The percentage qf monosyllables giving a poor and bud RASTI-inde.\decreased more slowly when the words were pronounced without u prerecorded voice.

- by Cesar Diaz
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- Mechanical Engineering, Architecture, Classical Physics, Speech Intelligibility

A technique is presented for determining the frequency modulation transfer function of a laser. The method is based on a Mach-Zehnder interferometer, with a significant difference in the optical path lengths of the two arms. A frequency-modulated laser beam incident on the interferometer produces a phase-modulated photocurrent signal with an effective modulation index that is related to the amplitude of the optical frequency modulation. Techniques for determining both the amplitude and the phase of the optical frequency modulation from the photocurrent signal are described. PACS 42.60.Fc; 42.55.Px; 07.60.Ly

- by Terry Mcrae
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- Mechanical Engineering, Semiconductor Lasers, Transfer Function, Optical physics

We are developing large-area, thick, structured CsI(Tl) imaging sensors for a wide variety of X-ray imaging applications. Recently we have fabricated structured CsI(Tl) scintillators ranging from 30 µm (16 mg/cm 2 ) to 2000 µm (900 mg/cm 2 ) in thickness and up to 15 x 15 cm 2 in area. Even 2000-µm-thick film showed well-controlled columnar growth throughout the film.

- by Vivek Nagarkar
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- Biomedical Engineering, X-ray imaging, Material Characterization, Nuclear science

A brief review is given of the advances in solid-state imaging during the last ten years. The issues of surface channel versus buried channel, aliasing versus prefiltering, frame transfer (FT) versus interline transfer (IT) versus charge-injection device (CID), and direct view versus EBIC imaging are discussed. Timedelay-and-integration (TDI) and infrared imaging are discussed. Finally applications are considered.

- by David Barbe
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- Optical Imaging, Frequency, Photosensitivity, Lithography

A regression-based model was developed relating aerial image quality, expressed in terms of the National Imagery Interpretability Rating Scale ͑NIIRS͒, to fundamental image attributes. The General Image-Quality Equation ͑GIQE͒ treats three main attributes: scale, expressed as the ground-sampled distance; sharpness, measured from the system modulation transfer function; and the signal-to-noise ratio. The GIQE can be applied to any visible sensor and predicts NIIRS ratings with a standard error of 0.3 NIIRS. The image attributes treated by the GIQE are influenced by system design and operation parameters. The GIQE allows system designers and operators to perform trade-offs for the optimization of image quality.

- by John Irvine
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- Mechanical Engineering, Optics, Medical Imaging, Fiber Optics

This paper presents a method for calculating the
Zernike aberrations in a lens design using transformation optics
in FDTD. Currently there is no literature on calculating image
aberrations in FDTD. In this paper I divulge the methods to
calculate the Zernike aberration using a polynomial fitting for
a wavefront. The results are shown to match very well with the
Zernike aberrations in an equivalent lens in ZEMAX.

- by saul wiggin
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- Optics, Metamaterials, Transformation Optics, Modulation Transfer Function

PURPOSE: To study in a standard eye model the changes in modulation transfer function (MTF) of a monofocal intraocular lens (IOL) when a phakic IOL (pIOL) is placed in the anterior chamber, compare the MTFs of the rigid Artisan pIOL and foldable Artiflex pIOL, and evaluate the temporal evolution of the MTF of the foldable pIOL after the mechanical stress the pIOL undergoes when injected.

- by Norberto López-gil and +1
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- Myopia, Clinical Sciences, Optometry and Ophthalmology, Modulation Transfer Function
- by Sophie Triantaphillidou
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- Modulation Transfer Function

In accordance with the present international standard for intraocular lenses (IOLs), their imaging performance should be measured in a model eye having an aberration-free cornea. This was an acceptable setup when IOLs had all surfaces spherical and hence the measured result reflected the spherical aberration of the IOL. With newer IOLs designed to compensate for the spherical aberration of the cornea there is a need for a model eye with a physiological level of spherical aberration in the cornea. A literature review of recent studies indicated a fairly high amount of spherical aberration in human corneas. Two model eyes are proposed. One is a modification of the present ISO standard, replacing the current achromat doublet with an aspheric singlet cut in poly(methyl methacrylate) (PMMA). The other also has an aspheric singlet cut in PMMA, but the dimensions of it and the entire model eye are close to the physiological dimensions of the eye. They give equivalent results when the object is at infinity, but for finite object distances only the latter is correct. The two models are analyzed by calculation assuming IOLs with different degrees of asphericity to elucidate their sensitivity to variation and propose tolerances. Measured results in a variant of the modified ISO model eye are presented.

- by Marrie Van Der Mooren
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- Mechanical Engineering, Visual perception, Cornea, Visual acuity

- by John Irvine
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- Mechanical Engineering, Optics, Medical Imaging, Fiber Optics

A digital camera is a complex system including a 4 lens, a sensor (physics and circuits), and a digital image processor, 5 where each component is a sophisticated system on its own. Since 6 prototyping a digital camera is very expensive, it is highly desir-7 able to have the capability to explore the system design tradeoffs 8 and preview the system output ahead of time. An empirical digital 9 imaging system simulation that aims to achieve such a goal is 10 presented. It traces the photons reflected by the objects in a scene 11 through the optics and color filter array, converts photons into 12 electrons with consideration of noise introduced by the system, 13 quantizes the accumulated voltage to digital counts by an analog-14 to-digital converter, and generates a Bayer raw image just as a 15 real camera does. The simulated images are validated against 16 real system outputs and show a close resemblance to the images 17 captured under similar condition at all illumination levels.

- by Dmitry Bakin
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- System Design, Complex System, System Simulation, Modulation Transfer Function

The simulation of remote sensing images is a useful tool for a variety of tasks, such as the definition of future Earth Observation systems, the optimization of instrument specifications, and the development and validation of data processing algorithms. A scene simulator for optical hyperspectral and multispectral data has been implemented in the frame of the Environmental Mapping and Analysis Program (EnMAP) mission. EnMAP is a German built hyperspectral space sensor scheduled for launch in 2012. EnMAP will measure in the 420-2450 nm spectral range at a varying spectral sampling of 6.5-10 nm. Images will cover 30 km×30 km areas at an approximate ground sampling distance of 30 m. The EnMAP scene simulator presented in this paper is able to generate realistic EnMAP-like data in an automatic way under a set of user-driven instrumental and scene parameters. Radiance and digital numbers data are generated by 5 sequential processing modules which are able to produce data over a range of natural environments, acquisition and illumination geometries, cloud covers and instrument configurations. The latter include the simulation of data non-uniformity in the spatial and spectral domains, spatially coherent and non-coherent instrumental noise and instrument's modulation transfer function. Realistic surface patterns for the simulated data are provided by existing remote sensing data in different environments, from dry geological sites to green vegetation areas. A flexible radiative transfer simulation scheme enables the generation of different illumination, observation and atmospheric conditions. The methodology applied to the complete scene simulation and some sample results are presented and analyzed in this paper.

- by Karl Segl
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- Geophysics, Imaging spectroscopy, Geomatic Engineering, Natural Environment

This study investigated the effect of lens induced defocus on the contrast sensitivity function in myopes and non-myopes. Contrast sensitivity for up to 20 spatial frequencies ranging from 1 to 20 c/deg was measured with vertical sine wave gratings under cycloplegia at different levels of positive and negative defocus in myopes and non-myopes. In non-myopes the reduction in contrast sensitivity increased in a systematic fashion as the amount of defocus increased. This reduction was similar for positive and negative lenses of the same power (p ¼ 0:474). Myopes showed a contrast sensitivity loss that was significantly greater with positive defocus compared to negative defocus (p ¼ 0:001). The magnitude of the contrast sensitivity loss was also dependent on the spatial frequency tested for both positive and negative defocus. There was significantly greater contrast sensitivity loss in non-myopes than in myopes at low-medium spatial frequencies (1-8 c/deg) with negative defocus. Latent accommodation was ruled out as a contributor to this difference in myopes and non-myopes. In another experiment, ocular aberrations were measured under cycloplegia using a Shack-Hartmann aberrometer. Modulation transfer functions were calculated using the second order term for defocus as well as the fourth order Zernike term for spherical aberration. The theoretical maximal contrast sensitivity based on aberration data predicted the measured asymmetry in contrast sensitivity to positive and negative defocus that was observed in myopic subjects. The observed asymmetry in contrast sensitivity with positive and negative defocus in myopes may be linked to the altered accommodative response observed in this group.

- by Richard Calver
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- Myopia, Visual acuity, Accommodation, Vision

To assess the performance and optical limitations of standard, aspheric, and wavefront-customized intraocular lenses (IOLs) using clinically verified pseudophakic eye models. White light pseudophakic eye models were constructed from physical measurements performed on 46 individual cataract patients and subsequently verified using the clinically measured contrast sensitivity function (CSF) and wavefront aberration of pseudophakic patients implanted with two different types of IOLs. These models are then used to design IOLs that correct the astigmatism and higher order aberrations of each individual eye model's cornea and to investigate how this correction would affect visual benefit, subjective tolerance to lens misalignment (tilt, decentration, and rotation), and depth of field. Physiological eye models and clinical outcomes show similar levels of higher order aberration and contrast improvement. Customized correction of ocular wavefront aberrations with an IOL results in contra...

- by Pablo Artal
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- Refractive Surgery, Higher Order Thinking, Contrast sensitivity, Clinical Sciences

It is shown theoretically and verified experimentally that by writing a low spatial frequency Ronchi grating by a computer and printing two copies of it on two transparencies by a printer, the modulation transfer function (MTF) of the printed image can be evaluated by measuring the transmittance of the superimposed gratings in a moire´fringe spacing. Application of the technique is quite simple and the results are reasonably reproducible. The technique does not require a high sensitive intensity detector and a very narrow slit for transmission scanning. Also, the presented technique can be applied to other imaging systems. r (K. Madanipour), tavasoli@iasbs.ac.ir (M. Taghi Tavassoly).

- by Saifollah Rasouli
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- Quantum Physics, Low Frequency, Atmospheric Turbulence, Refractive Index

BiLSAT, launched to its sun-synchronous orbit on 27.09.2003, is a 129 Kg small satellite carrying a panchromatic camera and a 4band multispectral camera with Ground Sampling Distances (GSD) 12.6 m and 28 m, respectively. The multispectral camera is composed of 4 totally independent cameras. All five refractive optic cameras have 2048 by 2048 frame CCDs as sensors. The overall Modulation Transfer Functions (MTF) of the imaging systems are very important for characterization of imagers. In this study, the MTF of BiLSAT imagers are calculated using two different methods. The first method for image-based MTF determination uses sharp linear edges for estimating the Edge Spread Function (ESF), from which Point Spread Function (PSF) is obtained by differentiation. A man-made high-contrast almost linear structure is used as imaging target. For precise detection of the edges, a 2D edge model is fitted to manually picked linear edge and the root-meansquare (RMS) difference between the image and the model is minimized by gradient search. Then, a parametric curve fitting is performed using a new parametric model. The PSF and MTF are obtained after differentiation and Fourier transformation, respectively. Second method is based on comparing BiLSAT images to high-resolution IKONOS images whose PSF is already known. The blur function that minimizes the RMS difference between the registered images is estimated. Image registration, blur estimation and radiometric correction parameter estimation are performed simultaneously. The fact that the images are taken with 3 months time difference and from slightly different angles cause difficulties. Small and almost planar areas are chosen to avoid parallax effects. Finally, the results obtained by two different methods are compared and the results are discussed.

- by Ugur Murat Leloglu
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- Modulation Transfer Function, Satellite Imaging

Automatic focusing is very important to high-quality image acquisition for digital still camera system. This paper will propose a new automatic focusing method using skincolor face detection to automatically determine focusing area. In order to overcome the influence of color temperature on the face detection method, this paper proposes a new automatic white balance method by learning color temperature curve with a statistical method. The method compensates color shifts of images by locating a set of compensation gains from the trained color temperature regression curve. A comparative setup of experiments is built to verify the effectiveness of the proposed method. Controlled experimental factors include light source, object distance and initial lens position. Modulation transfer function of images is applied to objectively evaluate the image quality before and after the new automatic focusing method. Experimental results show our method has high success rate of face localization, and effectively achieves automatic focusing.

- by Yuan-Kai Wang
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- Image Quality, Color Constancy, Face Detection, Gaussian Mixture Model

One of the most challenging problems in medical imaging is the development of reconstruction algorithms for nonstandard geometries. The standard geometry is the parallel ray geometry of the conventional Radon transform. This work focuses on the resampling of a nonstandard geometry to obtain a data set in standard geometry. The approach is guided by the application of Fourier analysis to resampling. Fourier Transform Resampling (FI'RS) offers potential improvement because the Modulation Transfer Function (MTF) of the process behaves like an ideal low pass filter. Simulated MTF's were obtained by projecting point sources at different transverse positions in the flat fan beam detector gfxxnetry. These MTF's were compared to the closed form expression for FTFG. Excellent agreement was obtained for frequencies at or below the estimated cutoff frequency. The resulting FTRS algorithm is applied to simulations with symmetric fan beam geometry, an elliptical orbit and uniform attenuation, with a normalized root mean square error (NRME) of 0.036.. FTRS is also compared to sinc interpolation, and it is shown empirically that the two methods are not equivalent. General expressions are obtained for the transfer function, the MTF, the frequency map, and the resampled autocovariance function. A closed form expression is found for the ftequency map associated with the circular arc fan beam geometry.

- by William Hawkins
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- Physics, Biomedical Engineering, Medical Imaging, PET

Measurements of various image quality parameters were carried out with two different detector systems in an otherwise unchanged medical computed tomography (CT) scanner. As all other components of the scanner and the image reconstruction system remained identical, we were able to quantify the difference in performance between a Xenon gas ionization detector and a new solid-state scintillation detector in an isolated fashion. We determined noise, spatial resolution, and artifact behavior and assessed the potential for dose reduction.

- by Theobald Fuchs
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- Engineering, Computed Tomography, Comparative Study, Instrumentation

Five individual projects characterized the spatial performance of the IKONOS commercial imaging sensor. The result was determination of the spatial image quality of IKONOS data products in terms of the National Imagery Interpretability Rating Scale (NIIRS), the system Modulation Transfer Function (MTF), the system stability over its first year of operation, the characteristics of the Space Imaging MTF Compensation (MTFC) procedure, and the application-specific capabilities of IKONOS imagery. Both panchromatic and multispectral imagery were evaluated. Major conclusions of this work are that the system was stable in imaging performance during the first year of operation, that its MTF meets the specification for the NASA Scientific Data Purchase program, that the initial MTFC processing appears to be transposed in the in-track and the cross-track directions, that the MTFC results in a noise amplification of 2 Â to 4 Â in addition to sharpening the imagery, and that IKONOS panchromatic imagery achieves an average NIIRS rating of 4.5. D

- by Slawomir Blonski
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- Image Quality, Image Interpretation, Geomatic Engineering, Rating Scale

In high-resolution ultranarrow field-of-view thermal imagers, image quality over relatively long path lengths is typically limited by atmospheric degradation, especially atmospheric blur. We report our results and analyses of infrared images from two sites, Fort A. P. Hill and Aberdeen Proving Ground. The images are influenced by the various atmospheric phenomena: scattering, absorption, and turbulence. A series of experiments with high-resolution equipment in both the 3-5-and 8 -13-m regions at the two locations indicate that, as in the visible, image quality is limited much more by atmosphere than by the instrumentation for ranges even of the order of only a few kilometers. For paths close to the ground, turbulence is more dominant, whereas for paths involving higher average elevation, aerosol modulation transfer function ͑MTF͒ is dominant. As wavelength increases, turbulence MTF also increases, thus permitting aerosol MTF to become more dominant. A critical role in aerosol MTF in the thermal infrared is attributed to absorption, which noticeably decreases atmospheric transmission much more than in the visible, thereby reducing high-spatial-frequency aerosol MTF. These measurements indicate that atmospheric MTF should be a basic component in imaging system design and analysis even in the infrared, especially as higher-resolution hardware becomes available.

- by Natan Kopeika
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- Mechanical Engineering, Image Quality, Optical Imaging, Applied

Second in a two-part series comparing measurement techniques for the assessment of basic image quality metrics in digital radiography, in this paper we focus on the measurement of the image noise power spectrum ͑NPS͒. Three methods were considered: ͑1͒ a method published by Dobbins et al. ͓Med. Phys. 22, 1581-1593 ͑1995͔͒, ͑2͒ a method published by Samei et al. ͓Med.

- by James Dobbins
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- Algorithms, Biomedical Engineering, Medical Physics, Image Quality

A modulation transfer function (MTF) measurement technique suitable for large-format, small-pixel detector characterization has been investigated. A volume interference grating is used as a test image instead of the bar or sine wave target images normally used. This technique permits a high-contrast, large-area, sinusoidal intensity distribution to illuminate the device being tested, avoiding the need to deconvolve raw data with imaging system characteristics. A high-confidence MTF result at spatial frequencies near 200 cycles/mm is obtained. We present results at several visible light wavelengths with a 6.8-.pm-pixel CCD. Pixel response functions are derived from the MTF results.

- by mike marchywka
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- Mechanical Engineering, Physics, Medicine, Spatial Frequency

Background and purpose: While the optical performance of monofocal refractive lenses can be measured quite easily, more efforts are required to assess the performance of multifocal lenses, due to imaging to several foci. The purpose of this study was to develop a rugged test setup for evaluation of the optical properties of intraocular lenses (IOLs) in conformity to the International Standard ISO 11979. Methods: We built a test setup in order to measure the point spread function and to determine the modulation transfer function (MTF) of IOLs. We measured three multifocal IOLs with (1) a diffraction limited model cornea and an individualized aspheric model cornea which shows a significant amount of spherical aberration. Results: All the three IOL samples tested showed a different impact of spherical aberration on the MTF. The bispheric lenses (Alcon and Dr Schmidt) showed a degradation of the MTF and Strehl ratio with model (2) compared to model (1). In contrast, the MTF of the Tecnis lens, which has a prolate aspheric front surface, improved dramatically in combination with model (2). Conclusion: We demonstrated the functional capability of our measurement system by presentation of a set of working examples. Two different model corneas were used to study the influence of spherical aberration on the MTF of our working examples. An aspheric model cornea, which had already been shown to be suitable for testing monofocal aspherics, was shown to be well suited for testing aspheric multifocal lenses.

- by Timo Eppig
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- Algorithms, Cornea, Computer Simulation, Retina
- by Dov Wulich
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- Optical Engineering, Computer Vision, Image Processing, Random Vibration

At present, system design usually assumes the Kolmogorov model of refractive index fluctuation spectra in the atmosphere. However, experimental data indicates that in the atmospheric boundary layer and at higher altitudes the turbulence can be different from Kolmogorov's type. In optical communications, analytical models of mean irradiance and scintillation index have been developed for a traditional Kolmogorov spectrum and must be revised for non-Kolmogorov turbulence. The image quality (resolution, MTF, etc.) is essentially dependent on the properties of turbulent media. Turbulence MTF must be generalized to include non-Kolmogorov statistics. The change in fluctuation correlations of the refractive index can lead to a considerable change in both the MTF form and the resolution value. In this work, on the basis of measurements and model calculations, the influence of non-Kolmogorov turbulence on imaging and communications through the atmosphere is estimated for different scenarios of vertical and slant-path propagation. The atmospheric model of an arbitrary (non-Kolmogorov) spectrum is applied to estimate the statistical quantities associated with optical communication links (e.g., scintillation and fading statistics) and imaging system. Implications can be significant for optical communication, imaging through the atmosphere, and remote sensing.

- by Arkadi Zilberman
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- Remote Sensing, Turbulence, Atmospheric Modeling, Optical Communication

The temporal resolution of cochlear-nerve fibres in the European starling was determined with sinusoidaily amplitude-modulated noise stimuli similar to those previously used in a psychoacoustic study in this species . Temporal modulation transfer curves (TMTFs) were constructed for cochlear afferents allowing a direct comparison with the starling's behavioural performance. On average, the neuron's detection of modulation was less sensitive than that obtained in the behavioural experiments, although the most sensitive cells approached the values determined psychophysically. The shapes of the neural TMTFs generally resembled low-pass or band-pass filter functions, and the shapes of the averaged neural functions were very similar to those obtained in the behavioural study for two different types of stimuli (gated and continuous carrier). Minimum integration times calculated from the upper cut-off frequency of the neural TMTFs had a median of 0.97 ms with a range of 0.25 to 15.9 ms. The relations between the minimum integration times and the tuning characteristics of the cells (tuning curve bandwidth, Q10 dB-value, high-and low-frequency slopes of the tuning curves) are discussed. Finally, we compare the TMTF data recorded in the starling auditory nerve with data from neurophysiological and behavioural observations on temporal resolution using other experimental paradigms in this and other vertebrate species.

- by Otto Gleich
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- Electrophysiology, Psychoacoustics, Temporal Resolution, Low Frequency

In order to predict and optimize the response of phosphor screens, it is important to understand the role played by the different physical processes inside the scintillator layer. Monte Carlo simulations were carried out to determine the Modulation Transfer Function (MTF) of phosphor screens for energies used in X-ray medical imaging and nondestructive testing applications. The visualization of the dose distribution inside the phosphor layer gives an insight into how the MTF is progressively degraded by X-ray and electron transport. The simulation model allows to study the influence of physical and technological parameters on the detector performances, as well as to design and optimize new detector configurations. Preliminary MTF measurements have been carried out and agreement with experimental data has been found in the case of a commercial screen (Kodak Lanex Fine), at an X-ray tube potential voltage of 100 kV. Further validation with other screens (transparent or granular) at different energies is under way.

- by Gerard Montarou
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- Monte Carlo Simulation, Monte Carlo, X-ray imaging, Nondestructive testing
- by Ulrich Neitzel
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- Algorithms, Biomedical Engineering, Medical Physics, Calibration

A description of a Hartmann-Shack sensor to measure the aberrations of the human eye is presented. We performed an analysis of the accuracy and limitations of the sensor using experimental results and computer simulations. We compared the ocular modulation transfer function obtained from simultaneously recorded double-pass and Hartmann-Shack images. The following factors affecting the sensor performance were evaluated: the statistical accuracy, the number of modes used to reconstruct the wave front, the size of the microlenses, and the exposure time.

In X-and gamma ray based medical systems, detector performance is a key driver for diagnostic quality. Over the last years and decades, indirect conversion scintillator detectors have become the standard for many medical applications including X-ray Radiography, Computed Tomography and SPECT. Recently, direct conversion semiconductor detectors based on CdTe and CdZnTe (CZT) have come into focus, as they might offer improved or additional performance for specific applications. In this paper we use generic physical models to compare the spatial and spectral resolution of both detector types. The spatial resolution is quantified by the Modulation Transfer Function (MTF). We find that the direct conversion of quanta leads to an approximately sinc-like MTF. In comparison, the MTF of a pixelized scintillator detector shows a mid-frequency drop due to optical signal cross-talk.

- by Debora Henseler
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- Computed Tomography, X Rays, Modulation Transfer Function, Spatial resolution

In general, analysing cameras is a difficult problem and solutions are often found only for geometric approach. In this paper, the image capturing capability of a camera is presented from optical perspective. Since most compact cameras can acquire only visible light, the description and propagation method of the visible part of the electromagnetic spectrum reflected by a scene object is made based on Maxwell’s
equations. We then seek to use this understanding in the modelling of the image formation process of the
camera. The dependency of camera sensor field distribution on aperture dimension is emphasized. This modelling leads to an important camera and image quality parameter called Modulation Transfer Function. The model presented is based on a wave optics in which the wavefront is modified by the lens
after diffraction has taken place at the camera rectangular aperture positioned at the front focal point of the lens. Simulation results are presented to validate the approach.

Optical Metrology tools, especially for short wavelength (EUV and X-Ray), must cover a wide range of spatial frequencies from the very low, which affects figure, to the important mid-spatial frequencies and the high spatial frequency range, which produces undesirable scattering. A major difficulty in using surface profilometers arises due to the unknown Point-Spread Function (PSF) of the instruments [1] that is responsible for distortion of the measured surface profile. Generally, the distortion due to the PSF is difficult to account because the PSF is a complex function that comes to the measurement via the convolution operation, while the measured profile is described with a real function. Accounting for instrumental PSF becomes significantly simpler if the result of measurement of a profile is presented in a spatial frequency domain as a Power Spectral Density (PSD) distribution [2]. For example, the measured PSD distributions provide a closed set of data necessary for three-dimensional calculations of scattering of light by the optical surfaces [3], [4]. The distortion of the surface PSD distribution due to the PSF can be modeled with the Modulation Transfer Function (MTF), which is defined over the spatial frequency bandwidth of the instrument [1], [2]. The measured PSD distribution can be presented as a product of the squared MTF and the ideal PSD distribution inherent for the System Under Test (SUT). Therefore, the instrumental MTF can be evaluated by comparing a measured PSD distribution of a known test surface with the corresponding

- by Rossana Cambie
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- Materials Engineering, Aerospace Engineering, Physics, Gamma Ray Astronomy

A theoretical treatment of the effect of quantization upon the determination of modulation transfer functions (MTF) of digital acquisition devices is initially developed for an noiseless system, when using sinusoidal targets. The analytical work shows that a component due to quantization exists in the measured MTF which increases as the bitdepth of the quantization and the amplitude of the input signal decreases. An expression to estimate this component from parameters describing the input signal and quantizer is derived. Modifications are made to account for quantization and input signal noise, yielding new estimates of the compone for single measurements. The estimates w re experimentally tested using an analogue to digital converter (ADC).

- by John Jarvis
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- Computer Science, Physics, Modulation Transfer Function

In this work, we have applied the fractional Fourier transform to obtain the Fresnel di raction patterns in a theoretical eye. The FRT approach to Fresnel di raction is easily implemented in a Gullstrand±Emsley theoretical eye, and it allows us to obtain the retinal image and then to derive the modulation transfer function of the eye, which can be used in the determination of optical performance of the eye.

- by Álvaro M Pons
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- Quantum Physics, Nanotechnology, Optical physics, Modern Optics

In this paper we derive an approximate analytical representation for the modulation transfer function (MTF) of an imaging system possessing a defocused cubic-phase pupil function. This expression is based on an approximation using the Arctan function and significantly reduces the computational time required to calculate the resulting MTF. We derive rigorous bounds on the minimum and average accuracy of our approximation. Using this approximate representation of the MTF, the analytical solution of the problem of calculating the extension of the depth of field for a circular aperture with a cubic phase mask becomes possible. We also comment on how one can modify our method to construct a lower-bound or an upper-bound approximate analytical expression for the MTF.

The design of a dual-field-of-view telescope for an 8 -12-m imaging waveband is described. Preliminary calculations are made to determine the first-order parameters of the narrow-and the wide-field modes. To achieve a switchable dual-field-of-view system, one uses an optical configuration based on the axial motion of a single lens group along the optical axis. The same lens is also used for focusing at near objects and for athermalization by small axial movement. A total of six lenses with one conic surface are used in the design, making the telescope cost effective and lightweight. The final optical design is presented, along with the aberrations curves and modulation transfer function plots, showing excellent performance in both fields of view.

- by Muhammad Akram
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- Mechanical Engineering, Optical Design, Applied Optics, Optical physics

Modulation transfer functions (MTF's) of 26 low-vision aids (LVA's) were measured by using the EROS solid-state system. The object and image distances of the LVA's were as in normal usage by a patient. The contrast thresholds of patients who use LVA's were also measured. All LVA's measured have more than adequate contrast transmission at the low frequencies that are important for these subjects, but many have wasted transmission at medium and high frequencies. LVA's with poorer high-frequency MTF can be used successfully by low-vision patients. It is suggested that in future design high resolution should be sacrificed for a greater lens diameter while maintaining a high MTF at low spatial frequencies.

- by Susan Leat
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- Mechanical Engineering, Low vision, Spatial Frequency, Applied Optics

The operator description of Fourier optics is extended and applied to holography. The existing' lens models for ideal holographic processes appear as a self-evident intermediate result; generalization to include apertures, recording-material modulation transfer function, and extended source effects is straightforward. The extended source effect is generally shown to be equivalent to a modification of the actual holographic apertures. The final result is a compact expression for the description of the holographically reconstructed field distribution at an arbitrary plane. A useful, comprehensive list of operator relations is given in two appendixes.

- by Moshe Nazarathy
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- Algebra, Image Reconstruction, Holography, Transfer Function

A GE Revolution 41RT flat-panel detector (GE 41RT) from GE Healthcare (GE) has been in operation at the Advanced Photon Source (APS) for over two years. The detector has an active area of 41 cm x 41 cm with 200 μm x 200 μm pixel size. The nominal working photon energy is around 80 keV. The physical setup and utility software of the detector system are discussed in this article. The linearity of the detector response was measured at 80.7 keV. The memory effect of the detector element, called lag, was also measured at different exposure times and gain settings. The modulation transfer function (MTF) was measured in terms of line-spread function (LSF) using a 25 μm x 1cm tungsten slit. The background (dark) signal, the signal that the detector will carry without exposure to x-rays, was measured at three different gain settings and with exposure times of 1 ms to 15 s. The radial geometric flatness of the sensor panel was measured using the diffraction pattern from a CeO 2 powder standard. The large active area and fast data-capturing rate -8 fps in radiography mode, 30 fps in fluoroscopy mode -make the GE 41RT one of a kind and very versatile in synchrotron diffraction. The loading behavior of a Cu/Nb multilayer material is used to demonstrate the use of the detector in a strain-stress experiment. Data from the measurement of various samples, amorphous SiO 2 in particular, are presented to show the detector effectiveness in pair distribution function (PDF) measurements.

- by Jon Almer
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- Synchrotron Radiation, X Rays, Pair Distribution Function, Transfer Function

We present and evaluate two corrections applicable in determining the modulation transfer function (MTF) of a charge-coupled device (CCD) by the speckle method that minimize its uncertainty: one for the low frequency region and another for the high frequency region. The correction at the low-spatial-frequency region enables attenuation of the high power-spectral-density values that arise from the field and CCD response non-uniformities. In the high-spatial-frequency region the results show that the distance between the CCD and the aperture is critical and significantly influences the MTF; a variation of 1 mm in the distance can cause a root-mean-square error in the MTF higher than 10%. We propose a simple correction that minimizes the experimental error committed in positioning the CCD and that diminishes the error to 0.43%.

- by Joaquin Campos
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- Low Frequency, High Frequency, Root-Mean Square Error, Optical physics

The modulation response of quantum-dot (QD) lasers is studied. Based on a set of four rate equations, a new analytical modulation transfer function is developed via a small-signal analysis. The transfer function can clearly describe the impacts of the wetting layer and the excited states: finite carrier capture and carrier relaxation times as well as the Pauli blocking limits the modulation bandwidth. The definitions of the resonance frequency and the damping factor of QD lasers are also improved. From the analysis, it is demonstrated that carrier escape from the ground state to the excited states leads to a nonzero resonance frequency at low bias powers associated to a strong damping factor.

- by jacky even
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- Signal Analysis, Wetting, Transfer Function, Optical physics

Optical quality in barn owl eyes is presented in terms of measuring the ocular wavefront aberrations with a standard Tscherning-type wavefront aberrometer under natural viewing conditions. While accommodative state was uncontrolled, all eyes were focused within 0.4 D with respect to the plane of the aberrometer. Total RMS wavefront error was between 0.06 and 0.15 lm (mean: 0.10 lm, STD: 0.03 lm, defocus cancelled) for a 6 mm pupil. The results suggest that image quality in barn owl eyes is excellent.

- by Hermann Wagner
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- Binocular vision, Image Quality, Vision, Astigmatism

As a new three-dimensional imaging technique, digital breast tomosynthesis allows the reconstruction of an arbitrary set of planes in the breast from a limited-angle series of projection images. Though several tomosynthesis algorithms have been proposed, no complete optimization and comparison of different tomosynthesis acquisition techniques for available methods has been conducted as of yet. This paper represents a methodology of noise-equivalent quanta NEQ (f) analysis to optimize and compare the efficacy of tomosynthesis algorithms and imaging acquisition techniques for digital breast tomosynthesis. It combines the modulation transfer function (MTF) of system signal performance and the noise power spectrum (NPS) of noise characteristics. It enables one to evaluate the performance of different acquisition parameters and algorithms for comparison and optimization purposes. An example of this methodology was evaluated on a selenium-based direct-conversion flat-panel Siemens Mammomat Novation prototype system. An edge method was used to measure the presampled MTF of the detector. The MTF associated with the reconstruction algorithm and specific acquisition technique was investigated by calculating the Fourier Transform of simulated impulse responses. Flat field tomosynthesis projection sequences were acquired and then reconstructed. A mean-subtracted NPS on the reconstructed plane was studied to remove fixed pattern noise. An example of the application of this methodology was illustrated in this paper using a point-by-point Back Projection correction (BP) reconstruction algorithm and an acquisition technique of 25 projections with 25 degrees total angular tube movement.

In this work, a unified model, based on a thorough analysis of experimental data, is developed for the overall Modulation Transfer Function (MTF) estimation for CMOS image sensors. The model covers the physical diffusion effect together with the influence of the pixel active area geometrical shape. Comparison of both, our predicted results and the MTF calculated from the Point Spread Function (PSF) measurements of an actual pixel array gives excellent agreement. This confirms the hypothesis that the active area shape together with the photocarrier diffusion effect are the determining factors of the overall CMOS Active Pixel Sensor (APS) MTF behavior, and allows us to extract the minority-carrier diffusion length. The results indicate that for any potential active area shape, a reliable estimate of image performance is possible, so the trade off between the conflicting requirements, such as signal-to-noise ratio (SNR) and MTF could be compared per each pixel design.

- by Orly Yadid-Pecht
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- Engineering, Physics, Data Analysis, Image Analysis

MTF measurement methods for imaging devices usually require the use of an optical system to project the image of the object onto the detector. So, MTF results quality strongly depends on the accuracy of the optical adjustments (alignments, focusing…). Dedicated edge patterns have been implemented at the chip level on a CMOS imager. One of them emulates the target used in the ISO 12233 slanted-edge technique and the others one are inspired by the knife-edge method. This allows to get the MTF data without optical focusing. In order to validate the results, comparisons have been made between MTF measurements using these patterns and results obtained through direct measurements with the transmissive slanted-edge target and sine target.

- by Pierre Magnan
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- Sensors, Chip, Cmos Image Sensor, Modulation Transfer Function

We report the design of binary-amplitude masks that in conjunction with digital restoration enable mitigation of optical aberrations. Essentially, the design process aims to reduce destructive interference of optical transfer function... more

- by Tom Vettenburg
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- Modulation, Design process, Modulation Transfer Function, Destructive Interference

We present a biologically motivated method for assessing the intelligibility of speech recorded or transmitted under various types of distortions. The method employs an auditory model to analyze the effects of noise, reverberations, and other distortions on the joint spectro-temporal modulations present in speech, and on the ability of a channel to transmit these modulations. The effects are summarized by a spectro-temporal modulation index (STMI). The index is validated by comparing its predictions to those of the classical STI and to error rates reported by human subjects listening to speech contaminated with combined noise and reverberation. We further demonstrate that the STMI can handle difficult and nonlinear distortions such as phase-jitter and shifts, to which the STI is not sensitive. Ó 2002 Published by Elsevier B.V.

- by Mounya Elhilali
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- Cognitive Science, Linguistics, Speech Communication, Speech Intelligibility