Optical Modulation Transfer Function Research Articles

Integrating eye rotation and contrast sensitivity into image quality evaluation of virtual reality head-mounted displays

Visual perception on virtual reality head-mounted displays (VR HMDs) involves human vision in the imaging pipeline. Image quality evaluation of VR HMDs may need to be expanded from optical bench testing by incorporating human visual perception. In this study, we implement a 5-degree-of-freedom (5DoF) experimental setup that simulates the human eye geometry and rotation mechanism. Optical modulation transfer function (MTF) measurements are performed using various camera rotation configurations namely pupil rotation, eye rotation, and eye rotation with angle kappa of the human visual system. The measured MTFs of the VR HMD are inserted into a human eye contrast sensitivity model to predict the perceptual contrast sensitivity function (CSF) on a VR HMD. At the same time, we develop a WebXR test platform to perform human observer experiments. Monocular CSFs of human subjects with different interpupillary distance (IPD) are extracted and compared with those calculated from optical MTF measurements. The result shows that image quality, measured as MTF and CSF, degrades at the periphery of display field of view, especially for subjects with an IPD different than that of the HMD. We observed that both the shift of visual point on the HMD eyepiece and the angle between the optical axes of the eye and eyepiece degrade image quality due to optical aberration. The computed CSFs from optical measurement correlates with those of the human observer experiment, with the optimal correlation achieved using the eye rotation with angle kappa setup. The finding demonstrates that more precise image quality assessment can be achieved by integrating eye rotation and human eye contrast sensitivity into optical bench testing.

Theoretical and experimental study on spatial characteristics of a large imaging area streak camera developed for ICF precise diagnostics

The Modulation Transfer Function (MTF) offers an objective measure to assess the imaging performance of streak cameras. This study aims to enhance the diagnostic precision of streak camera used in laser-driven inertial confinement fusion research. We introduce a novel method for evaluating the MTF of a recently developed large imaging area streak tube. This method integrates the electron optical MTF theory and the production of a reticle plate-type photocathode. Using ultraviolet and femtosecond lasers, we established two calibration platforms for the streak camera in both static and dynamic modes. We measured the radius of the electrons reaching fluorescent screen and obtained MTFs. Our findings reveal that the ultimate spatial resolutions at off-axis distances of 1.2, 4.7, 8.2, and 11.7mm are 28.5, 27.2, 26.4, 24.9 lp/mm (static) and 25.0, 22.8, 23.0, 21.2 lp/mm (dynamic). Notably, we successfully charted the ultimate spatial resolution distributions across the streak camera's full imaging area in both modes.

Analysis and Prediction of Image Quality Degradation Caused by Diffraction of Infrared Optical System Turning Marks

This paper addresses the issue of reduced image quality due to annular turning marks formed by single-point diamond turning (SPDT) during the processing of metal-based mirrors and infrared lenses. An ideal single-point diamond turning marks diffraction action model to quantitatively analyze the impact of turning marks diffraction on imaging quality degradation is proposed. Based on this model, a fast estimation algorithm for the optical modulation transfer function of the system under turning marks diffraction (TMTF) is proposed. The results show that the TMTF algorithm achieves high computational accuracy, with a relative error of only 3% in diffraction efficiency, while being hundreds of times faster than rigorous coupled wave analysis (RCWA). This method is significant for reducing manufacturing costs and improving production efficiency, as it avoids the problem of being unable to compute large-size optical systems due to computational resource and time constraints.

Full modulation transfer functions of thick parallel- and focused-element scintillator arrays obtained by a Monte Carlo optical transport model.

Arrays of thick segmented crystalline scintillators are useful x-ray converters for image-guided radiation therapy using electronic portal imaging (EPI) and megavoltage cone-beam computed tomography (MV-CBCT). Ionizing-radiation-only simulations previously showed relatively low modulation transfer function (MTF) in parallel-element arrays because of beam divergence. Hence, a focused-element geometry (matchingthebeamdivergence)has been proposed. The "full" (ionizing and optical) MTF performance of such a focused geometry compared to its radiation-only MTF has, however, not been fully investigated. To study the full MTF performance of such arrays in a more realistic situation in which optical characteristics are also included using an in-house detector model that supports light transport, and quantify the errors in MTF estimation when the optical stage is ignored. First, radiation (x-ray and electron) transport was simulated. Then, transport of the generated optical photons was modeled using ScintSim2, an optical Monte Carlo (MC) code developed in MATLAB for simulation of two-dimensional (2D) parallel- and focused-element scintillator arrays. The full-MTF responses of focused- and parallel-element geometries, for a large array of 3 × 3 mm2 CsI:Tl detector elements of 10, 40, and 60 mm thicknesses, were examined. For each configuration, a composite line spread function (LSF) was calculated to obtain the MTF. At the Nyquist frequency, for 10 mm-thick central elements and 60 mm-thick peripheral parallel elements, full-MTF exhibited a drop of up to 15 and 79 times, respectively, compared with radiation-only MTF. This was found to be partly attributable to the angular distribution of the light emerging from the detector-element exit face and the dependence on its aspect ratio, since the light exiting thicker scintillators exhibited a more forward-directed distribution. Focused elements provided an increase of up to nine times in peripheral-area full MTF values. Full MTF was up to 79 times lower than radiation-only MTF. Focused arrays preserved full MTF by up to nine times compared to parallel elements. The differences in the results obtained with and without inclusion of optical photons emphasize the need to include light transport when optimizing thick segmented scintillation detectors. Besides their application in detector optimization for radiotherapy megavoltage photon imaging, these findings can also be useful for other segmented-scintillator-based imaging systems, for example, in nuclear medicine, or in 2D detection systems for quality assurance of MR-linacs.

Mathematical modeling and experimental verification of aging human eyes polarization sensitivity.

The polarization perception sensitivity of the human eyes affects the perceived polarized image quality. In this paper, we used polarized spatiotemporal structured images to develop a spatiotemporal age mapping of the polarization perception of human eyes. We built an optical modulation transfer function mathematical model of the aging human eyes with spatiotemporal frequency domains and introduced the Stokes vector to analyze the polarized images. The proposed model provides a testing method based on a set of polarization images with spatiotemporal frequencies varying according to the perception of differently aged viewers. Then, we experimentally validated the proposed model by performing polarization perception tests on a group of volunteers. The test method has the diagnostic potential to confirm the health of human eyes and identify potential age-related macular diseases.

Some Contributions to the Study of the Effects of Human Motricities through Nordic Walking

The paper aimed to add new knowledge to the study of Nordic walking. For this purpose, the authors presented the results of some measurements of pulse and contrast sensitivity (CS) at the daily walking tour of several kilometers, in the Nordic walking style. The recorded results were modeled by interpolation and were displayed in the form of graphics and processed images. The profile of the optical modulation transfer (MTF) function was simulated, as a function necessary to evaluate the contrast sensitivity. To this end, the authors evaluated the influence of screen brightness and the random motion due to the effort and fatigue accumulated in the human body by traveling the walking tour. The authors took into account the fact that mobility performance can be measured by the distance traveled, by the time required to cover this distance or by walking speed and, above all, by the variation of the contrast sensitivity following the effort of moving.

Optical satellite image MTF compensation for remote-sensing data production

Modulation Transfer Function (MTF) compensation had been widely used in Remote-Sensing (RS) imagery processing for texture feature enhancement and high-frequency details restoration. In this paper, we propose an optical satellite MTF Compensation (MTFC) method for engineering applications and RS data production. The framework mainly includes Point Spread Function (PSF) model estimation and non-blind image deconvolution. In PSF estimation, we used the iterative total variation algorithm and 2D Gaussian model fitting to reduce the dependence on slant-edge quality and improve the efficiency of PSF measurement. The PSF model estimation error is less than 3% using the results from standard commercial software as an evaluation benchmark. In image deconvolution, we adopted a regularisation-based non-blind deconvolution method using hyper-Laplacian prior. Compared with the widely used methods, the MTF has been improved more than double in high-frequency part. Its processing efficiency and image quality can meet the requirements of RS image products. These results can effectively prove the engineering application value of our proposed method.

Effect of lateral diffusion of photoelectrons in the reflection-mode varied-doping AlGaN photocathode on resolution.

To obtain a high resolution of the reflection-mode AlGaN photocathode by establishing the modulation transfer function (MTF) model of this photocathode, the influence of emission layer thickness Te, electron diffusion length Ld, recombination velocity at back-interface Vb, and optical absorption coefficient α on MTF for varied-doping and uniform-doping Al0.42Ga0.58N photocathodes have been given. The computational results suggest that varied-doping structure has great potentiality in improving both resolution and quantum efficiency of the reflection-mode Al0.42Ga0.58N photocathode. This improvement is mainly attributed to the reduced lateral diffusion of photoelectrons, which is caused by an electric field generated by the varied-doping structure, and hence the photoelectron transportation towards photocathode surface is promoted.

On-orbit thermal deformation prediction for a high-resolution satellite camera

Thermal-structural analysis of satellite camera in the early design phase as well as during the later experimental verification is important due to the extreme thermal environment. The purpose of this work is to numerically investigate the thermal deformation for a high-resolution satellite camera under solar radiation. Based on the on-orbit thermal environment of the geosynchronous orbit, thermal-structural finite element model of the satellite camera is developed and opto-thermo-mechanical analysis of the optical system is proposed. Transient temperature distributions of the satellite camera under different extreme heat loads are obtained. Mirror deformations, translation and rotation have been introduced to the optical analysis and modulation transfer function analysis has been performed. Numerical simulation results reveal the dynamic response of the optical system under transient temperature and the thermal vacuum test predicts the imagery quality of the satellite camera, which can provide guidance for designers to analyze the on-orbit stability for the optical camera.

Comparison of spherical and aspherical intraocular lenses with decentration and tilt error using a physical model of human contrast vision and an image quality metric

PurposeIn this study, two intraocular lenses (spherical IOL SA60AT and aspherical IOL SN60WF) are examined in an eye model under conditions of misalignment (defocus, decentration and tilt). The lenses are rated using the contrast sensitivity function (CSF) based on Barten's physical model. The square root integral (SQRI) method is used as a quality criterion comparable to the subjective image quality assessment of the human eye. MethodsThe IOLs to be tested are decentered from 0 to 1mm and tilted from −5 to +5 degrees in the Navarro eye model (optimized for far-point 6m and pupil aperture 3mm). The defocus of the IOLs is ±0.1mm at the anterior chamber depth (ACD). The optical modulation transfer function (MTF) is simulated with a ray tracing program. The SQRI is calculated using this MTF and the Barten CSF model (for in-focus at aperture 3 and 4.5mm and for defocus at 3mm). ResultsWith increasing decentration, the spherical IOL shows a significantly smaller loss of quality for both apertures compared to the aspherical lens. With an aperture of 4.5mm, the image quality of the aspherical IOL is better for small decentration and tilt. The loss of quality of the spherical IOL increases with increasing tilt in both directions. In contrast, the image quality of the aspherical IOL is reduced under decentration for certain tilt values. For ACD−0.1mm, both IOLs behave similarly to the in-focus situation. For ACD+0.1mm, the influence of tilt without decentration is small for both IOLs. With increasing decentration, the quality loss of the aspherical IOL is similar to that in-focus and greater than that of the spherical lens. ConclusionIn general, under the same conditions the spherical SA60AT displays a lower tolerance in loss of quality of subjective vision with lens alignment errors, in comparison to the aspherical SN60WF, limited by certain combinations of decentration and tilt according to this study. This study shows a way to evaluate IOLs based on the subjective visual performance of the eye.

Optical aberrations and modulation transfer function of a thermal lens for use in imaging.

The optical aberrations of the thermal lens formed in a liquid are reported for the first time as expressed in terms of the Zernike polynomials coefficients. Convection of the liquid in which the thermal lens is formed is shown to strongly modify the lens imaging properties, even for the case of vertical heating laser illumination, as studied herein. The time evolution of the optical properties of the thermal lens is investigated. The direction from which the heating laser beam illuminates the thermo-optical liquid, in which the thermal lens is formed, has been found to be crucial for the lens optical power, type, and level of aberrations observed and the way these lens properties change in time.

Athermalization design for infrared dual-band double-layer harmonic diffractive optical system

In order to achieve the anaberration and athermalization of the infrared dual-band optical system, a new athermalization design based on the negative dispersion property is proposed. The system uses closed four-piece lens which made of combination of three materials to realize the double-band thermal dissipation differential design. The influence of temperature on optical parameters and design method is analyzed. Through a design example, the parameter performance index is discussed. The design results show that the optical modulation transfer function of the medium wave band (3–5 u m) is greater than 0.5, the long wave band (8–10 u m) is greater than 0.25 when the operating temperature is between −60℃ and 200℃, and the Nyquist frequency of the detector is 20lp/mm. The results not only meet the design requirements but also verify the feasibility of the proposed method through the optimization analysis of Zemax software.

Experimental demonstration of wave-front coded imaging with a very low response of the modulation transfer function at the Nyquist frequency.

Wave-front coding (WFC) is a well-known technique that can be used to extend the depth of field (DOF) of incoherent imaging systems. The phase masks make the optical transfer function drop significantly, and digital restoration must be used to obtain a clear image with a largely extended DOF. According to the existing literature, in order to obtain satisfactory restoration results, the optical modulation transfer function (MTF) at the Nyquist frequency is required to be bigger than 0.1, which has already become a popularly accepted design constraint. However, according to our experimental research reported in this paper, this requirement is overly strict. By assembling one already fabricated WFC lens and another camera having physically higher resolution, the MTF of the newly assembled WFC system used in the experimentation has quite a low response at its Nyquist frequency. The experimental results demonstrate that when the optical MTF value at the Nyquist frequency reaches the minimum value of about 0.05, visually satisfactory restoration results can still be obtained as long as the MTF is optimized to be highly insensitive to defocus and the corresponding SNR of the coded intermediate images goes beyond 20 dB at the same time. The experimental results indicate that the overly strict constraint could be alleviated while designing a WFC system.

Theoretical investigations of infrared optical wave modulation transfer function models in anisotropic marine turbulence.

The previously derived marine turbulence modulation transfer function (MTF) adopts the classical assumption of isotropic and Kolmogorov turbulence. However, more theoretical research shows that marine turbulence demonstrates anisotropic non-Kolmogorov properties. In this study, new long-exposure plane and spherical wave MTF models under anisotropic non-Kolmogorov marine turbulence will be investigated. Comparative analyses are performed for the new models and the existing ones that have been developed under the isotropic marine turbulence and the anisotropic terrestrial turbulence cases. It turns out that the anisotropic marine turbulence influences the electro-optical imaging system less than the isotropic marine turbulence does. Also, under the same turbulence strength condition, due to the humidity fluctuations of marine atmosphere, the anisotropic marine turbulence will reduce more severely the quality of electro-optical imaging systems than the anisotropic terrestrial turbulence. Investigations conducted in this paper are beneficial to understand better the electro-optical imaging mechanism in marine atmospheric turbulence media.

Subjective Visual Performance and Objective Optical Quality With Intraocular Lens Glistening and Surface Light Scattering.

To evaluate the long-term effect of glistenings and surface light scattering of intraocular lenses (IOLs) on visual and optical performance after cataract surgery. Pseudophakic eyes that underwent standard phacoemulsification and two types of hydrophobic acrylic spherical IOL implantation without complications for at least 5 years were included in this retrospective study. Participants were divided into the glistenings, surface light scattering, and control groups according to the current condition of the IOLs. Then participants received a follow-up examination including uncorrected and corrected distance visual acuity (UDVA and CDVA), contrast sensitivity, straylight, and intraocular higher order aberrations, as well as point spread function (PSF) and modulation transfer function (MTF). A total of 140 eyes were included in the study. UDVA, CDVA, and glare sensitivity were not significantly different among the three groups (P > .05). However, compared with the control group, the IOLs of the glistenings and surface light scattering groups were associated with significantly lower contrast sensitivity under no glare conditions. Furthermore, eye with glistenings exhibited the highest straylight value (P < .05), whereas no difference was found between the surface light scattering and control groups. In contrast to the control group, the spherical aberration increased and the mean values of PSF and MTF decreased in the glistenings and surface light scattering groups. Both glistenings and surface light scattering tend to impair subjective visual performance, such as contrast sensitivity, and potentially affect objective optical quality, including straylight, spherical aberration, PSF, and MTF. [J Refract Surg. 2018;34(6):372-378.].

Development of novel adjustable focus head mount display for concurrent image-guided treatment applications

Purpose: A conventional see-through head mount display contains many optical lenses, which can be problematic in image-guided treatment applications due to its size, weight, structure, and focus limitation. Therefore, we have designed a new type of see-through head mount display with a reduced number of optical lenses and an adequate optical resolution that can be utilized for image-guided treatment applications.Materials and methods: A new type of adjustable focus head mount display with expanded virtual images and an external treatment space that can be provided to the eyes of a user by enlarging the images of a small display is designed and investigated in this study. This type of head mount display can be used in image-guided treatment applications because of the dual paths of imaging and treatment from the optical systems. Therefore, this system with an adjustable focus function can aid doctors in obtaining images for the treatment of the eyes of patients because every patient has a unique pupil size.Results: The results of the adjustable focus see-through head mount display showed distortion values of +0.36% in the +1 diopter location and −0.55% in the −4 diopter location, and there are less significant modulation transfer function differences within the ±5 diopter locations.Conclusions: Low optical distortions within ±0.5 diopters can help doctors image the eye conditions of patients through fewer image processing techniques. Therefore, the designed adjustable focus head mount display can provide low optical aberrations and high optical modulation transfer function resolutions for image-guided treatment applications.

含有自由曲面的大视场低畸变同轴三反射光学系统设计

Remote sensing mapping applications need optical system with long focal length, wide width, low distortion, small volume, and the optical system can be designed for integration on satellite platform. Through the structure selection, modified coaxial three mirror system is adopted to realize long focal length, wide width and low distortion at the same time. Because of the influence of the second obscuration and large field, the image quality of general aspheric optimization design cannot meet the requirements. Degrees of freedom are increased efficiently by the introduction of free-form surface. After optimization design, the optical design modulation transfer function (MTF) is greater than 0.418 at 72 lp/mm, and the maximum relative distortion is less than 0.00145%. Imaging quality is improved significantly. The free-form surface is tested and fine grinded by the application of computer-generated holography (CGH) technology, the root mean square (RMS) of remnant wavefront error is 0.007, and the peak to valley (PV) value is 0.027, remnant wavefront error meet the requirements of free-form surface irregularity tolerance. Laboratory static MTF is tested after processing and adjustment, the minimum static MTF is 0.225 at 72 lp/mm, the image quality meet the requirements of technical indicators.

高速切换紧凑型双视场无热化红外光学系统设计

In this paper,a refractive optical system with secondary image is adopted to realize 1. 67 F number and 4. 6 zoom ratio,and the ratio between the total length and focal length is 1,and the zooming lens group is driven by solenoid pilot actuated valve switching structure to complete zooming in 60 ms. In addition,an optical passive compensation method is used to realize an athermalized design in the range of- 40 ~ + 50 ℃ by choosing proper optical and structural materials. The design results show that the optical system's modulation transfer function in each field is close to the diffraction limit at different temperatures under the characteristic frequency of 20 lp /mm and the system size is compact with fast FOV switching. Finally,it is proved that this dual-FOV infrared optical system can meet the requirements for application.

紧凑型无热化非制冷红外光学系统设计

With rapid growth of uncooled infrared detector technology, uncooled infrared optical systems are widely used. The uncooled infrared optical system must fulfill the requirements of compact size, large relative aperture, high temperature adaptability and stray light suppression ability. A catadioptric optical system with secondary image is adopted to realize the design parameters of 0.55 ratio of total length and focal length and 0.8 F number. In addition, the optical passive compensation method is used to realize an athermalized design in the temperature range of -40C~50C by matching optical and structural materials properly, and the field stop in the first image can ensure the optical system a high stray light suppression ability. The design result shows that optical system's modulation transfer function in each field is close to the diffraction limit at different temperatures and the system size is compact. Finally, it is proved that this uncooled infrared optical system can meet environmental requirements of airborne and missile application through the actual imaging experiment at high and low temperatures.

大视场时间延迟积分CCD遥感相机的精密定焦

A precise focusing technology for a spliced TDICCD camera was introduced. Firstly, the components of focal plane were assembled to the designed locations on the camera under the circumstance of a constant temperature and vibration-isolation. Then, the Modulation Transfer Function (MTF) of the camera image was obtained through a data acquisition and processing system, the curve of MTF-focus value of every TDICCD image was plotted, and the optimum imaging plane of every TDICCD was obtained. Finally, the common optimum imaging plane of the 8 chips for TDICCD was fitted according to the every single optimum imaging plane obtained above, and then the machining values of the external interfaces of the focal plane components were derived to finish the assembly and adjustment. Precision analysis on the focusing shows that the focusing error is 9.1 m and the relative error to the depth of field is 4.4%. The MTF test indicates that the 8 chips of TDICCD have approximately even MTF values, which are high than the camera's static MTF requirement of 0.2. Obtained results coincide with the variation regularity of the camera's optical MTF values and can provide references for the precise focusing technologies of the same kinds of remote sensing cameras.