Average Modulation Transfer Function Research Articles

Long-term assessment and analysis of the radiometric quality of standard data products for Chinese Gaofen-1/2/6/7 optical remote sensing satellites

The first Chinese Gaofen (GF) remote sensing satellite was launched in August 2013 and has been in orbit for more than 10 years, providing a rich variety of image product data for remote sensing applications in various industries, with other remote sensing satellites of the GF series. To ensure the reliability of the information generated via remote sensing applications, all remote sensing images must undergo systematic quality evaluation. The quality of GF satellites is evaluated almost comprehensively during in-orbit testing at the early stage after launch; however, the remaining evaluations of product quality including geometric or radiometric calibrations are performed only annually. Thus, long-term systematic image quality evaluations are lacking, and the quality level and long-term change trends of the image products are unknown. These deficits have introduced uncertainty in the application of these products. This study aimed to establish a radiometric quality evaluation index framework for GF satellites to comprehensively measure the radiometric quality of GF image products. Multiple types of sample data, such as uniform field, knife-edge target, and radiometric calibration field data with different reflectance features, were acquired globally. Four core indexes, namely, the relative radiometric correction accuracy (RRCA), absolute radiometric correction accuracy (ARCA), modulation transfer function (MTF), and signal-to-noise ratio (SNR), were used to analyze and evaluate the long-term radiometric quality of the images from four GF optical remote sensing satellites: GF1, GF2, GF6, and GF7. The four GF satellites had high SNR and RRCA but low dynamic MTF and variable ARCA for different reflectance features. For example, the average SNRs for the four satellites reached 42.66, 43.91, 44.33, and 47.46 dB; the average RRCA (@root-mean-square errors) values reached 1.6%, 1.0%, 1.6%, and 0.1%; the average MTF values (at Nyquist frequency) of the panchromatic bands were only 0.15, 0.12, 0.07 and 0.04; and the difference in ARCA for different reflectance targets was approximately 10%. In the long time series, the SNRs for each sensor of the four GF satellites were high and stable for high-reflectance features, whereas the RCA and SNR values for low-reflectance features and the MTF of the sensors fluctuated in a cyclic manner. Meanwhile, large dynamic fluctuations and episodic image quality problems occurred at certain local time points, which must be considered during practical applications. The findings presented here will lay a foundation for the in-depth application of GF images.

Modulation transfer function formula for different age ranges.

The modulation transfer function (MTF) is one of the most complete tools to study the optical performance of the eye. We present the average radial MTF profiles measured in 68 subjects grouped in six age ranges (from 20 to 80years) and a general formula to estimate the radial profile of human MTF as a function of pupil size and age. The mean MTF for each age group was fitted to an analytical expression to compute two parameters related to aging. The proposed formula fitted reasonably well to experimental data available in previous works and predicted the average changes with aging of different optical quality parameters obtained from MTF.

Reduction and reconstruction strategy of active thermal control system based on unsupervised learning and thermo-optics for spaceborne high-resolution remote sensor

The development of small Earth observation satellites with high performance optical remote sensors has received much attention in recent years due to its responsiveness and immediacy. As one of the most resource-intensive subsystems of spacecrafts, the active thermal control system (ATCS) should be optimized; however, manual thermal design does not guarantee an optimal solution and requires months. For this purpose, we presented a ATCS’s reduction and reconstruction strategy based on an unsupervised learning framework, in which factor loadings are applied to combine kernel-based principal component analysis and Gaussian mixture model clustering. This strategy was implemented on a spaceborne high-resolution remote sensor (HRS) with 0.5 m ground sample distance. As a result, with the cumulative variance contribution rate > 90 % and 10 Gaussian distributions, the reconstructed ATCS of HRS had a 78.6 % reduction rate and took only 3 h, which suggests the high efficiency and low computational cost of the proposed strategy. Finally, the performed orbital thermal and thermo-optical integrated analyses indicated that temperature fluctuations were within ± 0.02–0.6 °C and optical surface errors were within the tolerance. The average modulation transfer function in the tangential and sagittal directions decreased by only 2 % and 2.5 %, respectively, and the radius of the spot root mean square was considerably smaller than the size of one pixel (8.75 μm). These results prove the feasibility and validity of the proposed strategy. This study solved the problem of identifying the optimal ATCS for optical remote sensors and significantly reducing the ATCS’s resource occupancy, which provided a reliable research basis for the development of high-performance small Earth observation satellites. Additionally, the proposed strategy is versatile and can be used in thermal engineering applications of various complex spacecrafts and payloads.

Study of the performance change in digital mammography systems depending on the total number of examinations

Digital mammography equipment should operate at a high-performance level for detecting breast cancer over the lifetime of the systems. This study investigates the performance of the Fujifilm Amulet Innovality full-field digital mammography system in relation to the number of exposures. The performance of twelve systems, from new and up to 17 000 examinations, was compared. The x-ray output, half-value layer (HVL), contrast-detail (C-D) detectability, contrast-to-noise ratio (CNR), mean glandular dose (MGD), signal transfer property (STP), pre-sampled modulation transfer function (MTF), normalized noise power spectra (NNPS), detective quantum efficiency (DQE) tests were performed to determine the performance change. The noise sources were also analyzed in the spatial domain. The x-ray output and HVL values at 28 kV with tungsten anode and rhodium filter were 15 μGy/mAs ± 1.0 (coefficient of variation (cov) = 7.0%) and 0.54 mmAl ± 0.008 (cov = 1.5%), respectively. The average MGDs for 60 mm equivalent breast to reach the achievable image quality level for 0.1 mm and 0.25 mm detail diameters of circular discs on the CDMAM 3.4 phantom image were 1.17 mGy ± 0.13 (cov = 11%) and 1.40 mGy ± 0.09 (cov = 6%), respectively. The average MGD for 53 mm equivalent breast was 1.08 mGy ± 0.14 (cov = 13%) at dose setting Normal in automatic exposure control (AEC) mode. All tested devices demonstrated good linearity with R2 ≥ 0.999 in the STP curves. The average MTF at 5.0 mm−1 spatial frequency was 0.66 ± 0.007 (cov = 1.0%). The average NNPS was 2.38 × 10−6 mm2 ± 2.13 × 10−7 (cov = 9.0%) at 5.0 mm−1. The average DQE value at 5.0 mm−1 was 0.33 ± 0.02 (cov = 5.0%), and the mean peak DQE was 0.66 ± 0.03 (cov = 5.0%). The mean power coefficient (b), determined from the power relationship between linearised standard deviation and detector dose while analyzing noise sources, was 0.49 ± 0.007 (cov = 1.4%). There was no gradual change in the x-ray tube and detector performance by the number of exposures, and taking up to 68 000 images did not decrease the quality of the systems.

Freeform wide-angle camera lens enabling mitigable distortion.

Allowing natural scenes as well as maximizing field of view (FoV) can benefit from the minimization of distortion for the wide-angle camera. The wide-angle camera utilizing freeform surfaces for mitigating distortions, either barrel distortion or pincushion distortion, is therefore of interest. In this paper, the designs of using all-aspherical surfaces and aspherical surfaces combined with freeform surfaces are investigated. To minimize the deviation before and after converting from aspherical surfaces to freeform surfaces, a mathematical conversion scheme is derived. By applying it to the design example, the methodology is shown to be effective in the case of an optical system with a large number of aspherical/freeform surfaces. Additionally, custom freeform analysis tools are developed for quantitative analysis and visualization of the critical characteristics of optical performance, namely, a 2D lateral color field map, 2D relative illumination field map, 2D spot radius field map, and 2D average modulation transfer function (MTF) field map. Compared to classical all-aspherical design, simulation results show that freeform design has the capability to reduce distortion, and other performances such as relative illumination, spot size, and MTF can also be improved, even though there are some compromises on the peripheral FoV. The design approach will have potential important research and application values for lens systems utilized in miniature camera lenses, especially the wide FoV capability.

Comprehensive design analysis and verification of space-based short-wave infrared coded spectrometer via curved prism dispersion.

The spaceborne dispersive spectrometer is widely used in environmental, resource, and ocean observations. The coded spectrometer has higher energy advantages than the dispersion spectrometer, so it has great application prospects. In the current study, we developed an off-axis short-wave infrared coded optical system (SICOS) based on curved prism dispersion, and we further explored the design and optimization of the SICOS structure. Finite element analyses of a space-based short-wave infrared coded spectrometer based on curved prism dispersion (SSICS-CPD), including static simulation, modal analysis, sinusoidal vibration mechanical analysis, and random vibration mechanical analysis, were carried out. Simulation results showed that the SICOS support structure had excellent mechanical and thermal stability. As off-axis optical systems cannot meet the requirements of optical position accuracy through centering processing, a point source microscope and three-coordinate measuring machines were employed to complete the high-precision and rapid assembly of the SSICS-CPD. In addition, verification tests of surface shape error, stress relief, random vibration, and optical design parameters were carried out to validate the high stability and imaging performance of the SSICS-CPD. Results showed that the average modulation transfer function in the full field was 0.43 at 16.67 lp/mm, the spectral smile was <0.2 pixels, and the spectral keystone was <0.1 pixels. The design, analysis, assembly, and verification of the SSICS-CPD provide a useful reference for the development of other spaceborne prism dispersion spectrometers.

Research on thermal design and thermal optical performance of space telescope based on multidisciplinary integration

This paper first analyzes the external heat flow of a low-orbit space telescope in different flight attitudes, and determines the position of the heat dissipation surface and the thermal analysis cases. Then, the detailed thermal design of each component of the telescope is completed to reduce the influence of thermal deformation of optical elements and supporting structures caused by temperature changes on the imaging quality of telescope. Especially for the thermal control difficulties of CCD detectors such as large heat generation in a short time and one-dimensional movement in a narrow space, a segmented proprietary cold chain with flexible section is designed to transfer the heat to the radiant cold plate. Finally, the thermal/structure/optical integrated simulation analysis under extreme cases is carried out. It is concluded that the average modulation transfer function (MTF) of the optical system at the cutoff frequency satisfies the design requirement greater than 0.3. The analysis results show that the thermal control system designed in this paper can ensure the optical performance of the telescope, which has important reference significance for the thermal design of other space telescopes.

Optical design of an integrated imaging system of optical camera and synthetic aperture radar.

This paper presents an integrated imaging system of optical camera and synthetic aperture radar (SAR). The system can realize 400 nm-900 nm visible and near infrared band and 35 GHz microwave Ka band dual-band imaging. Compared with the single band imaging system, the observation ability and environmental adaptability of the integrated imaging system have been significantly improved. The optical camera shares a common front system with the synthetic aperture radar. After simulation, the average modulation transfer function (MTF) of 50 line pairs per millimeter (lp/mm) of the optical subsystem is 0.47. In addition, a principle prototype with a pupil diameter of 210 mm was developed to verify the performance of synthetic aperture radar antennas. After the experimental test, the SAR radiation pattern simulation results are in good conformity with the measured results, which are in line with the expected results.

Design of a Dual-Band Compact Integrated Remote Sensing System for Visible Light and Long-Wave Infrared

This paper presents a design of a dual-band integrated space telescope system for visible light and long-wave infrared. The system can simultaneously image the visible light band of 450–900 nm and the long-wave infrared band of 7700–10,500 nm. The dual-band integrated imaging system can freely switch the observation band to adapt to different scenes and environmental changes. The camera can also further expand its capabilities in the fields of multi-spectral observation and low-light observation by collocation with different detectors. This design is based on a coaxial reflection system, the two bands share the camera’s primary and secondary mirrors, and the separation of the two bands is achieved through a separate field of view design. After simulation, the average Modulation Transfer Function (MTF) value of the visible light band of the system at 50 lp/mm (line pairs per millimeter) reaches 0.45, and the average MTF value of the long-wave infrared band at 50 lp/mm reaches 0.36. In addition, tolerance analysis, ambient temperature analysis and transmittance analysis of the integrated system are carried out in this paper to further improve the integrated system scheme, and the feasibility of the system is further verified.

Comparison of visual quality in cataract patients with low astigmatism after ART2 or ReSTOR intraocular lens implantation.

To compare visual quality in cataract patients with low corneal astigmatism who underwent intraocular lens (IOL) implantation, and evaluate effects of low levels of astigmatism on visual outcomes in multifocal pseudophakic eyes. This retrospective review of clinical records comprised patients with preoperative regular corneal astigmatism of 0.75-1.0 diopters (D) with-the-rule or 0.5-0.75 D against-the-rule who had uneventful cataract surgery and AcrySof IQ ReSTOR Toric-2 IOL (ART2) or AcrySof IQ ReSTOR IOL (ReSTOR) implantation. Retrospective data collection included postoperative ART2 axis rotation, uncorrected astigmatism, uncorrected entire visual acuities, distance corrected entire visual acuities, average modulation transfer function (aMTF), Strehl ratio (SR), spectacle independence, and patient satisfaction between groups. Mean ART2 axis rotation was 3.12°±0.70°. No secondary surgery was required to realign IOL axis. Residual astigmatism values were -0.18±0.07 D and -0.91±0.25 D in groups ART2 and ReSTOR (P<0.05). Three months postoperatively, the mean uncorrected distant, intermediate, and near visual acuities of group A were 0.01±0.05, 0.05±0.07, 0.02±0.07 logMAR, respectively; these were better than those of group R, which were 0.08±0.06, 0.15±0.12, and 0.09±0.08 logMAR, respectively (P<0.05). aMTF, SR, and spectacle independence rates were not significantly different. All patients were satisfied with postoperative results. ART2 is more suitable than ReSTOR for cataract patients with regular corneal astigmatism 0.75-1.0 D with-the-rule or 0.5-0.75 D against-the-rule.

SU‐E‐T‐22: A Novel Sub‐Pixel MTF Calculation Algorithm for Arbitrarily Shaped QA Phantoms

Purpose:Measurement of MV, kV, and CBCT imager resolution is recommended by AAPM Task Group 142 for commissioning and quality assurance. A sub‐pixel modulation transfer function (MTF) calculation algorithm was formulated for use with arbitrary shaped phantoms such as circular, ring, or rectangular shapes. This allows resolution to be measured on many commonly available phantoms such as the MV Las Vegas (square), kV Leeds (ring), and CBCT Catphan (circular).Methods:The algorithm was implemented in Python and takes the Laplacian of a phantom edge profile. The zero crossing of the Laplacian corresponds to the location of the edge. A 6th degree polynomial spline fitted to the Laplacian was used to interpolate the sub‐pixel position corresponding to the zero crossing of the Laplacian. Testing of the algorithm was performed on a square Las Vegas EPID phantom image with a pixel resolution of .784 mm. A linear fit was performed to the sub‐pixel localizations for each of the 4 edges of the Las Vegas phantom. This linear fit was taken to be the true location of the edges. This sub‐pixel localization allowed construction of a sub‐pixel ESF, which is then differentiated to obtain an LSF. The fast Fourier transform of the LSF is taken to obtain the MTF. A Hann window is also applied to the LSF. The MTF was normalized to its zero frequency.Results:The standard deviation from the linear fit for all sub‐pixel localizations was 0.12 pixels or .09 mm. An average MTF was produced corresponding to crossings of the 4 edges of our Las Vegas phantom.Conclusion:Our sub‐pixel edge localization allows computation of the MTF for an arbitrarily rotated Las Vegas phantom. Simple modifications to this algorithm would allow subpixel MTF calculation for arbitrarily rotated circular phantoms, ring phantoms, or any other potential phantom shape.Research was partially funded by NIH Grant T32 EB002103‐21 from NIBIB. Contents are solely the responsibility of the authors and do not necessarily represent the official views of the NIBIB or NIH.

长焦距大口径连续变焦距光学系统

To accomplish the real-time track and measurement of remote distance objects, a continuous zoom optical system with an aperture of 650 mm and the long focuses of 5000-2000 mm was designed. The combinatorial design method of a Newton catadioptric system and a reverse continuous zoom system was adopted, and the pupil was matched and connected reasonably. A proper pupil position was determined, then, the ghost often appeared in the image plane in zoom process was eliminated. By reasonable matching the focal power of the main system and the zoom system, the secondary spectrum was minimized. By using the CODE V software to optimize and balance the aberration of every focal length, all the aberration of focal positions in the zoom optical system were corrected and balanced, and the image plane was consistency strictly. Thus, the imaging quality of each focus is favorable. Experiments show that the full field average Modulation Transfer Function (MTF) of each focus at the Nyquist frequency is over than 0.524, which meets the system requirements.

RESEARCH ON THE THREE ANGULAR RESOLUTION OF TERRESTRIAL LASER SCANNING

Abstract. Terrestrial laser scanning technology has been applied more and more widely in the field of Surveying and mapping. Although requirements of the accuracy for different laser scanner survey may differ considerably, spatial resolution is an important aspect, which can be divided into range and angular components. The latter is a focus of this paper and is governed primarily by scanning interval, laser beam width and angle quantisation. An ultimate goal of this research is to derive the relationship and simplified formula between scanning interval and the angular quantisation when the EIFOV(Effective Instantaneous Field of View) is equal to the scanning interval; the relationship and simplified formula of scanning interval and the angular quantisation when the EIFOV is equal to the laser beam width, and the relationship and simplified formula of the theoretical minimum EIFOV and the angular quantisation. Firstly, this paper introduces the EIFOV model and the AMTF(Average Modulation Transfer Function) model. Secondly, the dimensionless AMTF and EIFOV generic model are proposed. Thirdly, the above relathionships are deduced，which are ellipse or hyperbola, and the three simplified formulas are proposed. The simplified formulas have direct significance on the angular resolution's calculation and the scanning interval setting.

Evolutionary algorithms in airborne surveillance systems: image enhancement via optimal sightline control

Airborne electro-optic systems require precise control of the camera line-of-sight vector to prevent unwanted and possibly mission-critical degradation of image quality. This is particularly true for long-range surveillance missions or operation in low signal-to-noise ratio environments. Recent work has shown that pixel smear during camera integration (jitter) can be reduced if adaptive friction compensation ‘shapes’ the jitter frequency content in addition to reducing the energy content. This article expands upon that work by automating the tuning process for the sightline control parameters using a genetic algorithm (GA) with a novel fitness function – the average modulation transfer function. The efficacy of this cost function is illustrated first through tuning of the traditional rate loop proportional + integral controller gains and second via tuning of a bespoke adaptive friction compensator. It is shown in both cases that controllers tuned using the GA with this fitness function are significantly better than the current root-mean-square figure of merit typically employed in stabilization loop design.

Point spread function and optical transfer function of a misaligned hypertelescope

Analytical expressions for an instantaneous spectral point spread function (PSF) and an instantaneous spectral optical transfer function of a misaligned hypertelescope without delay lines, and containing circular and/or annular collecting mirrors, are presented. The formulas are deduced on the basis of the Fresnel approach to the Kirchhoff diffraction theory. Numerical results obtained for the system containing 60 identical annular mirrors, illustrate the pupil densification properties of the hypertelescope and the influence of random spatial and angular positioning errors of the optical elements on the average PSF (APSF), and on the average modulation transfer function (AMTF) calculated for the errors obeying specified probability distributions. The APSF and the AMTF give the opportunity to estimate the influence of the alignment errors on the resulting image quality in the hypertelescope image plane. This estimation can be used to produce the necessary requirements to the accuracy of the mirror control system and to the accuracy of the optical element alignment in dependence on the values of the exit pupil densification and the desirable resolution capability of the hypertelescope. The notion of the PSF and the modulation transfer function for off-axis beams can be useful for evaluation of a hypertelescope field of view.

Aspheric intraocular lenses: effect of residual spherical aberration on objective quality of vision

Abstract Purpose To assess the impact of residual spherical aberration (SA) on objective quality of vision in pseudophakic patients. Methods 15 patients (25 eyes) were divided into 2 groups: 13 eyes received an aspherical AcriSmart36A® generating a negative SA, 12 eyes received a zero‐aberration AcriSmart46LC®. Postoperative evaluations were conducted 6 months after a 1.8mm micro incision cataract surgery. Aberrometric measurements were done for a standardized pupil size of 5 mm in mesopic conditions using Wavescan Aberrometer®. Modulation Transfer Function (MTF), Strehl ratio and depth of field were measured with Objective Quality Analysis System®. Results Best corrected 100% LogMar distance visual acuity (BCVA) was similar in both groups (p=0.89). 20% and 9% BCVA was increased in 36A® group (p=0.009 and 0.005). Mesopic contrast sensitivity was better and total spherical aberration were significantly less with 36A® IOL(SA=0.075±0.05 μm with 36A® and 0.20±0.05 μm with 46LC®,p=0,0002). Coma and trefoil were not different between the two groups (p&gt;0,05). 36A® induced better image quality with an average MTF of 32.7±9.6 c/deg with 36A® and 23.8±8.1 c/deg with 46LC®, p=0.0002. The 36A® group had 1D less depth of focus than the 46LC® group at 6 months : respectively 1.3±0.59D and 2.27±0.63D. For the whole population, depth of focus appeared to be correlated with SA (r2=0.28, p=0.02) and with trefoil (r2=0.49, p=0.0009). Conclusion While reducing total ocular SA, aspheric IOLs improved mesopic contrast sensitivity, quality of vision with greater MTF values. Reduction of aberrations may be responsible for reduced depth of focus with 36A® IOLs. However, residual trefoil aberrations may be advantageous for depth of focus and reading ability.

Optimization of design and operating parameters of a space-based optical-electronic system with a distributed aperture

Using a gradient optimization method with objective functions formulated in terms of a signal-to-noise ratio (SNR) calculated at given values of the prescribed spatial ground resolution, optimization problems of geometrical parameters of a distributed optical system and a charge-coupled device of a space-based optical-electronic system are solved for samples of the optical systems consisting of two and three annular subapertures. The modulation transfer function (MTF) of the distributed aperture is expressed in terms of an average MTF taking residual image alignment (IA) and optical path difference (OPD) errors into account. The results show optimal solutions of the optimization problems depending on diverse variable parameters. The information on the magnitudes of the SNR can be used to determine the number of the subapertures and their sizes, while the information on the SNR decrease depending on the IA and OPD errors can be useful in design of a beam combination control system to produce the necessary requirements to its accuracy on the basis of the permissible deterioration in the image quality.

Polynomial phase masks for extending the depth of field of a microscope

A polynomial phase mask is designed and fabricated for enhancing the depth of field of a microscope by more than tenfold. A generic polynomial of degree 31 that consists of 16 odd power terms is optimized by simulated annealing with a realistic average modulation transfer function (MTF) iteratively set as the target MTF. Optical experimental results are shown.

Intercomparison of methods for image quality characterization. I. Modulation transfer functiona)

The modulation transfer function (MTF) and the noise power spectrum (NPS) are widely recognized as the most relevant metrics of resolution and noise performance in radiographic imaging. These quantities have commonly been measured using various techniques, the specifics of which can have a bearing on the accuracy of the results. As a part of a study aimed at comparing the relative performance of different techniques, in this paper we report on a comparison of two established MTF measurement techniques: one using a slit test device [Dobbins et al., Med. Phys. 22, 1581-1593 (1995)] and another using a translucent edge test device [Samei et al., Med. Phys. 25, 102-113 (1998)], with one another and with a third technique using an opaque edge test device recommended by a new international standard (IEC 62220-1, 2003). The study further aimed to substantiate the influence of various acquisition and processing parameters on the estimated MTF. The slit test device was made of 2 mm thick Pb slabs with a 12.5 microm opening. The translucent edge test device was made of a laminated and polished Pt(0.9)Ir(0.1). alloy foil of 0.1 mm thickness. The opaque edge test device was made of a 2 mm thick W slab. All test devices were imaged on a representative indirect flat-panel digital radiographic system using three published beam qualities: 70 kV with 0.5 mm Cu filtration, 70 kV with 19 mm Al filtration, and 74 kV with 21 mm Al filtration (IEC-RQA5). The latter technique was also evaluated in conjunction with two external beam-limiting apertures (per IEC 62220-1), and with the tube collimator limiting the beam to the same area achieved with the apertures. The presampled MTFs were deduced from the acquired images by Fourier analysis techniques, and the results analyzed for relative values and the influence of impacting parameters. The findings indicated that the measurement technique has a notable impact on the resulting MTF estimate, with estimates from the overall IEC method 4.0% +/- 0.2% lower than that of Dobbins et al. and 0.7% +/- 0.4% higher than that of Samei et al. averaged over the zero to cutoff frequency range. Over the same frequency range, keeping beam quality and limitation constant, the average MTF estimate obtained with the edge techniques differed by up to 5.2% +/- 0.2% from that of the slit, with the opaque edge providing lower MTF estimates at lower frequencies than those obtained with the translucent edge or slit. The beam quality impacted the average estimated MTF by as much as 3.7% +/- 0.9% while the use of beam limiting devices alone increased the average estimated MTF by as much as 7.0% +/- 0.9%. While the slit method is inherently very sensitive to misalignment, both edge techniques were found to tolerate misalignments by as much as 6 cm. The results suggest the use of the opaque edge test device and the tube internal collimator for beam limitation in order to achieve an MTF result most reflective of the overall performance of the imaging system and least susceptible to misalignment and scattered radiation. Careful attention to influencing factors is warranted to achieve accurate results.

In-field evaluation of the modulation transfer function and the signal-to-noise ratio of electronic-display devices

— This paper describes a charged-coupled device (CCD) camera, which was developed for in-field evaluation of the image quality of electronic-display devices [such as cathode-ray tubes (CRTs) and liquid-crystal displays (LCDs)] used for medical applications. Contrary to traditional cameras for display-image-quality evaluation, this CCD camera does not require a sophisticated x-y-z translation stage for mounting and adjustment. Instead, it is handheld and pressed by gentle pressure against the display screen. It is controlled by a software package which was originally developed for display calibration according to the DICOM 14 gray-scale standard display function (GSDF). This software package controls the camera gain when measurements are made at different display luminance, display test patterns, performs image analysis and displays the results of the measurements and calculations. The work concentrated on the measurement of modulation transfer function (MTF) and of signal-to-noise ratio (SNR) per display pixel. The MTF is derived from the Fourier transform of the line spread function (LSF). The single-display-pixel SNR is derived from the integration of the noise power spectrum (NPS) of a camera image taken of a display with a uniform luminance. It is demonstrated that the device can produce repeatable results in terms of MTF and SNR. MTFs were measured on three monochrome CRTs and five monochrome LCDs in order to study repeatability and similar quantities. The MTF was measured on a 5-Mpixel LCD yielding values that lie within 3.5% of the average MTF at the Nyquist frequency and 4.0% of the maximum total sharpness (∫ MTF2 df). The MTF was also measured on a 9-Mpixel LCD, yielding values that lie within 9.0% of the average MTF at the Nyquist frequency and 8.0% of the maximum total sharpness. The SNR was measured eight times on a 3-Mpixel monochrome LCD at nine digital driving levels (DDLs). At a DDL of 185, the mean SNR was 15.694 and the standard deviation (Stdv) was 0.587. At a DDL of 65, the mean SNR was 5.675 and Stdv was 0.120.