Showing papers on "Optical transfer function published in 2023"

Trifocal Intraocular Lens Selection: Predicting Visual Function From Optical Quality Measurements

Abstract: To apply in vitro quality metrics to assess and compare three trifocal intraocular lenses (IOLs).The optical performance of the AT LISA tri 839MP (Carl Zeiss Meditec AG), AcrySof IQ PanOptix (Alcon Laboratories, Inc), and TECNIS Synergy (Johnson & Johnson Vision) was compared. The modulation transfer function (MTF) metrics were obtained using an optical bench set-up. A polychromatic light source and a model cornea inducing chromatic and spherical aberrations were used to mimic in vivo characteristics. The area under the MTF was calculated at each defocus position, which served as a parameter in a nonlinear formula applied to predict postoperative visual acuity (VA).All of the studied IOLs had a predicted VA of 0.2 logMAR or better throughout the range of 0.00 to -3.00 diopters (D). Simulated VA differences between the IOLs were negligible (< 0.01 logMAR) at the far point. Although the three models were comparable at -1.00 D, at -2.00 D the AT LISA tri 839MP's VA was 0.06 and 0.08 logMAR worse than with the TECNIS Synergy and AcrySof IQ PanOptix, respectively. At near focus, the AcrySof IQ PanOptix's estimated VA was 0.06 logMAR (40 cm); for the AT LISA tri 839MP and TECNIS Synergy, it was 0.06 and 0.03 logMAR, respectively, at 36 cm.Although simulated distance VA was comparable between the studied models, differences can be found in the intermediate focus' position and quality and the expected reading distance. Therefore, simulations of defocus curves from optical quality metrics provide insight into IOL characteristics and highlight differences between the IOLs, which may guide the selection of a trifocal lens based on patients' needs. [J Refract Surg. 2023;39(2):111-118.].

Development and x-ray imaging performance of Tb-doped GdAlO3-αAl2O3 submicron-diameter phase-separated scintillator fibers

Abstract: Scintillators are key components in high-energy x-ray detectors for x-ray computed tomography, which are applied in medical diagnosis, nondestructive testing, and security inspection. Scintillators in x-ray imaging are required to have both high spatial resolution and sensitivity; however, a trade-off between spatial resolution and sensitivity exists. To improve the sensitivity of a scintillator, its thickness must be increased; however, spatial resolution deteriorates with increasing thickness. Here, we developed a well-aligned Tb-doped GdAlO3- αAl2O3 phase-separated scintillator fiber (PSSF) with a diameter of 1.25- μm by a micro-pulling-down method. The luminescence, scintillation, and imaging performances of a grown PSSF sample were evaluated. X-ray-induced radioluminescence measurements of the sample showed Tb3+ 4f–4f emissions in the wavelength range of 470–700 nm, and the maximum emission peak was at 550 nm. The contrast transfer function at 10 lp/mm was 82% for both 270 and 500 μm-thick PSSF samples. We calculated the luminescence index, which is the product of the scintillator’s light yield and sensitivity, of the samples and compared their values with commercially available conventional CsI:Tl columnar scintillators. The Tb-doped GdAlO3- αAl2O3 PSSF exhibits higher contrast transfer function and luminescence index values at above 60 keV x-ray region compared with the tested conventional scintillators.

Assessment of micro-vibrations effect on the quality of remote sensing satellites images

Abstract: Recently, there is a growing interest in analysing the degrading effect of satellite micro-vibrations due to the rapid growth in satellite technologies and the urgent need to precisely extract a huge amount of information from satellite images. Different kinds of micro-vibration have a notable effect on the quality of satellite images. The main objective of this paper is to demonstrate and analyse the effect of all types of micro-vibration on the quality of images acquired by high-resolution satellites. An algorithm to simulate micro-vibrations is proposed. A very high-resolution satellite image from the Pleiades-neo satellite is selected as an example to be used in addressing the degrading effects of micro-vibrations. In this paper, the modulation transfer function (MTF) is used as a major function to model the degradation that has been conducted. Also, several quality metrics are used to quantitatively assess the degradation. The key result of this paper is the significant effect of micro-vibrations on the quality of remote sensing satellite images which is attributed to the main influential parameters. These parameters like blur diameter, vibration displacement, number of Time Delay and Integration (TDI) stages of the camera, and the ratio of the integration time to the vibration period.

Design and Optical Analysis of a Refractive Aspheric Intraocular Lens with Extended Depth of Focus

Abstract: To obtain a continuous range of clear vision for pseudophakic eyes, a design of intraocular lens (IOL) with extended depth of focus (EDoF) was proposed. The IOL was optimized with a multi-configuration approach based on a pseudophakic eye model and the optical performances of the designed IOL were analyzed. The modulation transfer function (MTF) values remain above 0.2 at 50 lp/mm for object distance ranging from 0.35 m to infinity in both photopic vision and mesopic vision over a field of 4°. The optical performances remain stable when the pupil diameter changes from 2.25 mm to 5 mm. Besides, the presented theoretical analyses show the designed IOL has good optical performances for polychromatic light and corneal asphericity. The above shows that the IOL exhibits an excellent ability for pseudophakic eyes to see the object in a continuous range of distance.

Development and testing of a multi-spectral and multi-field of view imaging system for space-based signature detection and tracking of hypersonic vehicles

Abstract: Hypersonic glide vehicles can glide several thousand kilometers through the Earth’s atmosphere at hypersonic Mach numbers. Their inherent characteristics make them difficult to detect by both ground-based and spacebased sensors. The Universitat der Bundeswehr M¨unchen aims to demonstrate the capability of the Multispectral Object Sensing by Artificial Intelligence-processed Cameras (MOSAIC) experiment to detect and track radiation signatures of hypersonic glide vehicles from Low Earth Orbit on-board the small-satellite ATHENE-1. The payload consists of a cryo-cooled mid-wave infrared sensor with a pixel count of more than 1MPx. The use of variable optics increases flexibility with regards to spatial and spectral resolution. Spectral filter selection is based on atmospheric simulations. A 25MPx color imager sensitive in the visible spectrum is implemented together with a fixed focal length lens for complementary cross validation of detection by postprocessing onground. Both imagers are processed on-board the satellite by a high-performance computer that accelerates artificial intelligence image processing methods. All components used are commercial-off-the-shelf components that are tested and modified for their application in space at the Universit¨at der Bundeswehr M¨unchen. Two test set-ups are developed to characterize the modulation transfer function of the optical systems. Besides an ISO 12233 approach in the visible spectrum, an infinite-conjugate back-illuminated set-up is implemented for the infrared system. This study outlines design drivers and their specific solution approaches for an early warning system for a small-satellite application. A brief analysis of the radiometric budget forms the basis for a further preliminary design. Finally, test set-ups for performance validation are outlined.

The effects of pupil decenter on the human eye vision

Abstract: This study is about the human eye decentering effect on visual performance, and determining the tolerance decenter ranges with different pupil’s diameter. The pupil diameters are used (2.5, 6, and 10)mm, and decentration values are (-1 to 1) mm. The modulation transfer function (MTF) and the tolerance area of MTF, wave aberration, and image simulation are evaluated as acceptance criteria for comparing the visual performance. This work bases on the Liou and Brennan eye model (LBME) by using Zemax optical software. The results indicate that the visual eye performance is adversely affected when the decentration exceeds (±0.9, ±2.15, and ±3.89) mm, for pupil’s diameters (2.5, 6, and 10)mm, respectively.

Performance-Enhanced Static Modulated Fourier Transform Spectrometer with a Spectral Reconstruction

Abstract: A static modulated Fourier transform spectrometer has been noted to be a compact and fast evaluation tool for spectroscopic inspection, and many novel structures have been reported to support its performance. However, it still suffers from poor spectral resolution due to the limited sampling data points, which marks its intrinsic drawback. In this paper, we outline the enhanced performance of a static modulated Fourier transform spectrometer with a spectral reconstruction method that can compensate for the insufficient data points. An enhanced spectrum can be reconstructed by applying a linear regression method to a measured interferogram. We obtain the transfer function of a spectrometer by analyzing what interferogram can be detected with different values of parameters such as focal length of the Fourier lens, mirror displacement, and wavenumber range, instead of direct measurement of the transfer function. Additionally, the optimal experimental conditions for the narrowest spectral width are investigated. Application of the spectral reconstruction method achieves an improved spectral resolution from 74 cm−1 when spectral reconstruction is not applied to 8.9 cm−1, and a narrowed spectral width from 414 cm−1 to 371 cm−1, which are close to the values of the spectral reference. In conclusion, the spectral reconstruction method in a compact static modulated Fourier transform spectrometer effectively enhances its performance without any additional optic in the structure.

MTF as a performance indicator for AI algorithms?

Abstract: The modulation-transfer function (MTF) is a fundamental optical metric to measure the optical quality of an imaging system. In the automotive industry it is used to qualify camera systems for ADAS/AD. Each modern ADAS/AD system includes evaluation algorithms for environment perception and decision making that are based on AI/ML methods and neural networks. The performance of these AI algorithms is measured by established metrics like Average Precision (AP) or precision-recall-curves. In this article we research the robustness of the link between the optical quality metric and the AI performance metric. A series of numerical experiments were performed with object detection and instance segmentation algorithms (cars, pedestrians) evaluated on image databases with varying optical quality. We demonstrate with these that for strong optical aberrations a distinct performance loss is apparent, but that for subtle optical quality differences – as might arise during production tolerances – this link does not exhibit a satisfactory correlation. This calls into question how reliable the current industry practice is where a produced camera is tested end-of-line (EOL) with the MTF, and fixed MTF thresholds are used to qualify the performance of the camera-under-test.

Method to suppress the effects of micro-vibration for MTF measurement in a high-resolution electro-optical satellite payload

Abstract: Sensitivity to micro-vibration generated in an optical alignment ground facility increases with the optical aperture of the electro-optical payload mounted on the remote sensing satellite. The micro-vibration distorts the edge spread function (ESF) and changes the modulation transfer function (MTF) value during MTF measurements. Here, an ESF reconstruction network (ESFNet) is proposed to reconstruct the ESF distorted by micro-vibration. A proxy ground-truth ESF dataset for stable training of the proposed ESFNet via a supervised learning method is introduced. The proposed method is robust against both overfitting and underfitting for distorted parts of the ESF caused by micro-vibration. Experiments using ESF obtained in the facility with real micro-vibration show that the measurement error of MTF is around 0.02% when the ESFs are reconstructed using the proposed ESFNet.

MTF Measurement by Slanted-Edge Method Based on Improved Zernike Moments

Abstract: The modulation transfer function (MTF) is an important parameter for performance evaluation of optical imaging systems in photogrammetry and remote sensing; the slanted-edge method is one of the main methods for measuring MTF. To solve the problem of inaccurate edge detection by traditional methods under the conditions of noise and blur, this paper proposes a new method of MTF measurement with a slanted-edge method based on improved Zernike moments, which firstly introduces the Otsu algorithm to automatically determine the Zernike moment threshold for sub-pixel edge detection to precisely locate the edge points, then obtains LSF through edge point projection, ESF sampling point acquisition, smoothing, fitting, taking ESF curve differential and Gaussian fitting, and finally, accurately obtaining MTF by LSF Fourier transform and modulo normalization. Based on simulation experiments and outdoor target experiments, the reliability of the proposed algorithm is verified by the deviations of slanted-edge angle and MTF measurement, and the tolerance degree of edge detection to noise and ambiguity are analyzed. The results show that compared with ISO 12233, OMNI-sine method, Hough transform method and LSD method, this algorithm has the highest edge detection accuracy, the maximum tolerance of noise and ambiguity, and also improves the accuracy of MTF measurement.

Simulation Analysis on the Performance of a Circular-Edge Technique in Measurements of the Modulation Transfer Function

Abstract: The modulation transfer function (MTF) plays an important role in characterizing medical imaging systems. For such characterization, the circular-edge technique has become a prevalent task-based methodology. When determining the MTF with complicated task-based measurements, error factors must be well understood to properly interpret the results. In this context, the aim of this work was to study the changes in measurement performance in the analysis of the MTF using a circular edge. To eliminate the systematic error related to the measurement and suitably manage the error factors, images were generated by Monte Carlo simulation. Further, a performance comparison with the conventional method was conducted; in addition, the influence of the edge size and contrast and the setting error of the center coordinates were investigated. The difference from the true value and the standard deviation relative to the average value were applied to the index as the accuracy and precision, respectively. The results demonstrated that the smaller the circular object used and the lower the contrast, the grater the deterioration in the measurement performance. Furthermore, this study clarified the underestimating of the MTF in proportion to the square of the distance with respect to the setting error of the center position, which is important for the synthesis of the edge profile. Evaluations in the backgrounds wherein there are multiple factors affecting the results are complex, and the system users must properly judge the validity of the characterization results. These findings provide meaningful insight in the context of MTF measurement techniques.

A Novel Detector Geometry for X-Ray CT

Abstract: State-of-the-art X-ray computed tomography (CT) scanners all employ the conventional detector geometry which forms an arc concentric to the X-ray source. While each collected projection forms an equiangular dataset, the distance of each projection sample to the iso-center is nonuniformly spaced. During the cone-beam to parallel-beam conversion, both channel-wise and view-wise rebinning are required, leading to a degraded spatial resolution and an increased aliasing artifact. In this article, we propose a novel detector geometry that acquires evenly spaced projection samples relative to the iso-center and only view-wise rebinning is required to form a parallel dataset. To ensure that the detector cell size is independent of the cell position, the source-to-detector distance varies as a function of the detector fan-angle. Each detector module is tilted to guarantee the orthogonality of the detector surface to the X-ray. Extensive computer simulations were performed to demonstrate the efficacy of our design. Spatial resolution was measured with the modulation transfer function (MTF) and the proposed design offers a 12.6% improvement. When the equiangular configuration was retuned to match the spatial resolution, the proposed design exhibits an 8.8% noise reduction. In addition, aliasing artifacts were significantly reduced at locations away from the iso-center.

Image Contrast Enhancement by Using LED Annular Oblique Illumination in Bright-Field Microscopy

Abstract: Köhler illumination is the most used method for evenly illuminating a sample in bright-field microscopy. However, Köhler illumination cannot provide optimum contrast and high resolution simultaneously. The image contrast for Köhler illumination can be enhanced at the expense of lateral resolution. In this paper, we discuss the main causes of contrast loss with Köhler illumination by simulating unsymmetrical interference, incoherent superposition, and modulation transfer function. We present a method to increase the image contrast by combining the annular oblique illumination with normalization and blind deconvolution. With the progress of optoelectronic devices, the greater advantages of annular oblique illumination will become apparent. The experimental results achieved by using LED annular oblique illumination prove the feasibility of the proposed method.

Design and Metrological Analysis of a Backlit Vision System for Surface Roughness Measurements of Turned Parts

Abstract: The focus of this study is to design a backlit vision instrument capable of measuring surface roughness and to discuss its metrological performance compared to traditional measurement instruments. The instrument is a non-contact high-magnification imaging system characterized by short inspection time which opens the perspective of in-line implementation. We combined the use of the modulation transfer function to evaluate the imaging conditions of an electrically tunable lens to obtain an optimally focused image. We prepared a set of turned steel samples with different roughness in the range Ra 2.4 µm to 15.1 µm. The layout of the instrument is presented, including a discussion on how optimal imaging conditions were obtained. The paper describes the comparison performed on measurements collected with the vision system designed in this work and state-of-the-art instruments. A comparison of the results of the backlit system depends on the values of surface roughness considered; while at larger values of roughness the offset increases, the results are compatible with the ones of the stylus at lower values of roughness. In fact, the error bands are superimposed by at least 58% based on the cases analyzed.

Modulation transfer function variation through anisotropic turbulence in biological tissue

Abstract: Analysis of the long-exposure modulation transfer function (MTF) is performed for optical imaging using plane and spherical waves through anisotropic turbulence in biological tissues. To obtain the MTF, the wave structure functions of plane and spherical waves are obtained in closed-form expressions. Results are presented depending on various parameters of the turbulent medium and optical beam. The positive effect of anisotropy on optical imaging is remarkable in turbulent biological tissues. Besides scattering and absorption, taking anisotropy into account as well as turbulence will lead to a more accurate description of the performance of the medical imaging systems that use optical spectrums in biological tissues.

Effect of Higher Order Aberrations and Intraocular Scatter on Optical Quality Based on an Optical Eye Model

Abstract: The impact of intraocular scatter and higher order aberrations (HOAs) on ocular optical quality was investigated. An optical eye model was constructed using the measured ocular aberrations, corneal surfaces, axial length, and scatter fraction, and the impact of HOAs and scatter on modulation transfer functions (MTFs) was studied based on the newly established optical eye model. For uniform intraocular scatter, the monochromatic and polychromatic MTF decreased as the HOAs or scatter fractions increased independently at each spatial frequency, which implied that both were essential for visual quality. In addition, the scatter effect on MTF was more significant for the eye with less HOA. The combined deterioration effect of these two factors on the MTF was less than their summation, suggesting a potential compensatory mechanism between HOAs and scatter.

Modulation transfer function simulation methodology on CMOS image sensors using add-on structures for near infrared applications

Abstract: Silicon-based Complementary Metal Oxide Semiconductor (CMOS) image sensors are widely used for visible range detection systems. However, when it comes to near-infrared-range (NIR) applications like face recognition or Augmented/Virtual Reality (AR/VR), these sensors are much less efficient. This is due to the poor absorption of Silicon at such wavelengths. A well-known solution studied in-depth over the past few years to address this issue consists of etching diffractive structures into the Silicon. The incoming light is therefore diffracted inside the photodiode, increasing the optical path, and thus improving the Quantum Efficiency (QE) of the pixel. However, the Modulation Transfer Function (MTF) of the sensor is degraded in return on account of the increased light flux crossing from one pixel to the other, being eventually absorbed in the wrong pixel, an optical crosstalk that ends up degrading the MTF. Here, using Finite Difference Time Domain (FDTD) simulations of precisely the same Slanted Edge method as used in MTF characterization, we positively evaluate a new methodology to simulate the MTF of the sensor. We compared simulated results with characterization ones on actual pixels in several distinct configurations. We studied sensors’ MTF without any diffractive structures and others with various structures designed to influence the MTF more specifically in one direction (horizontal or vertical) at 940 nm. We demonstrated good agreements between simulations and characterizations, showing highly correlated tendencies across the whole studied set and giving us parameter predictive power on the MTF for future innovative pixel designs.

Single-shot refractive index imaging using spectral multiplexing and optical transfer function reshaping (Conference Presentation)

Abstract: Quantitative phase imaging (QPI) techniques require multiple measurements to obtain the refractive index (RI) distribution of a sample. Here, we present a single-shot RI imaging method using spectral multiplexing and optical transfer function reshaping. In the present method, we simultaneously measure three intensity images of a sample with three optimized illumination patterns. Deconvolution of the measured intensity images is then performed to obtain the RI distribution of the sample. As a proof-of-concept, we measured both microspheres and biological cells.

Design and implementation of plenoptic imaging system with reduced aberrations

Abstract: Industrial inspection is critical for 3D semiconductor manufacturing process and automated optical inspection for 3D ICs has attracted a lot of attention in these years. Plenoptic imaging systems, based on a micro-lens array, acquire light field from parallax and computes 3D information with lower costs. To reduce aberrations from the optical design with microlens array, especially for off-axial micro lenses, the design flow for plenoptic imaging systems is proposed. Based on the parameters designed from paraxial approximation, lateral image quality is optimized by a commercial optical design software, and then depth-related performances are estimated from the simulated images of the optical system. The experimental system for validation is tested quantitatively with modulation transfer function (MTF), by the slanted-edge method of ISO 12233. The difference of MTF between the paraxial and off-axial regions is approximately 0.02, which is within the repeatability error 0.03. Moreover, the synthesized images of a PCIe card refocused on the chip and the board clearly show the elements at the refocusing depth only. The depth map and the all-in-focus image are estimated to build a 3D model. However, significant artifacts appear on depth maps when lighting is not uniform. With combination of the ring light and coaxial light, the depth maps of objects with different surface properties can be estimated with less artifacts. Furthermore, accuracy and resolution can be enhanced by deep-learning technologies, which will be implemented in the future.

Single-shot refractive index slice imaging using spectrally multiplexed optical transfer function reshaping

Abstract: The refractive index (RI) of cells and tissues is crucial in pathophysiology as a noninvasive and quantitative imaging contrast. Although its measurements have been demonstrated using three-dimensional quantitative phase imaging methods, these methods often require bulky interferometric setups or multiple measurements, which limits the measurement sensitivity and speed. Here, we present a single-shot RI imaging method that visualizes the RI of the in-focus region of a sample. By exploiting spectral multiplexing and optical transfer function engineering, three color-coded intensity images of a sample with three optimized illuminations were simultaneously obtained in a single-shot measurement. The measured intensity images were then deconvoluted to obtain the RI image of the in-focus slice of the sample. As a proof of concept, a setup was built using Fresnel lenses and a liquid-crystal display. For validation purposes, we measured microspheres of known RI and cross-validated the results with simulated results. Various static and highly dynamic biological cells were imaged to demonstrate that the proposed method can conduct single-shot RI slice imaging of biological samples with subcellular resolution.