Pixel Size Of Camera Research Articles

Analysis of the accuracy of cadastral surveys using UaVs

This article is dedicated to analyzing the accuracy of cadastral surveys using uncrewed aerial vehicles (UAVs). It explores the efficiency and precision of surveys conducted with UAVs in the context of cadastral work. The article examines the methods and technologies used to ensure high accuracy of geospatial data in the cadastral field through UAVs. Utilizing cutting-edge technologies and analyzing research results, the article highlights the possibilities and limitations of UAV applications in cadastral surveys and land mapping tasks. The research findings can benefit geodesy, cartography, and cadastre professionals, as well as developers and operators of uncrewed aerial vehicles. This work investigates a network of phototriangulation conducted using uncrewed aerial vehicles (UAVs). Network parameters evaluated include the number of images, flight altitude, camera focal length, image size, pixel size, and coverage area. The images were processed using Agisoft Metashape Professional software. The main results of automatic image measurement are provided, including the number of tie points in the network, average ray intersection residuals, and random root mean square errors of ground points. The work shows that the provided accuracy characteristics need to provide more information for a reliable assessment of results. Despite optimistic results, the accuracy distribution may need to be improved for confident cadastral data quality. A modernized software complex for phototriangulation calculation, BlockMSG, was used for a more detailed assessment. It is noted that the calculation results correspond to all initial data of the Agisoft Metashape program but without additional information and analysis of possible errors. The paper also discusses the importance of measurement accuracy and its impact on creating a 3D cadastre. Data on the distribution of linear errors of points are presented, indicating the importance of choosing the number of images to obtain accurate coordinates. The primary focus is the need for a thorough analysis of results and possible error sources to ensure high-quality cadastral data. Keywords: accuracy, cadastral surveys, unmanned aerial vehicles (UAVs), geodetic methods, geospatial data, analysis.

Super-resolution image reconstruction of a neutron thick pinhole imaging system using image denoiser prior based on half quadratic splitting method

Thick pinhole imaging system is a powerful tool to diagnose intense pulsed radiation sources. However, high spatial resolution of a thick pinhole imaging system cannot be achieved due to the limitation of field of view (FOV) and detection efficiency. In this paper, we propose a novel super-resolution image reconstruction algorithm to improve the spatial resolution of a practical thick pinhole imaging system designed for 14.1 MeV neutrons with 100 mm FOV. Point spread function (PSF) of the imaging system is obtained through complete simulation methods, indicating that the spatial resolution of the imaging system is about 500 μ m. A 4 × super-resolution image reconstruction algorithm using image denoiser as implicit image prior, named image denoiser prior, based on half quadratic splitting (HQS) method is firstly applied to restore more details of neutron sources. The results show that the proposed algorithm performs better than the Richardson-Lucy (RL) algorithm with fewer artifacts and sharper boundaries in reconstructed images. Notably, at a low noise level, the proposed algorithm can surpass the Nyquist sampling limit of 200 μ m, which is determined by the equivalent camera pixel size, to achieve a spatial resolution of 150 μ m.

In situ three-dimensional reconstruction of laser powder bed fusion parts by light field camera

The assessment of output quality in the laser powder bed fusion process entails the analysis of the three-dimensional morphology of the manufactured parts, which plays a crucial role in quality control to prevent metallurgical defects. This study proposes a novel approach of three-dimensional reconstruction for laser powder bed fusion parts using a light field camera. Initially, a consistency method for high-precision camera calibration was explored to determine the virtual camera pixel size and coefficient of effective focal length of light field camera. Subsequently, the model based light field epipolar-plane image Unet is designed to obtain disparity information without any data augmentation techniques. By leveraging both binocular and light field optical paths, a robust mapping relationship of the disparity, depth, and visually coherent three-dimensional contour was established. Finally, the three-dimensional contours of laser powder bed fusion parts were reconstructed by the established mapping with a single exposure of the light field camera. The proposed method enables three-dimensional contour visualization of laser powder bed fusion parts from multi-view perspectives, which facilitates in situ monitoring of the spattering distance, three-dimensional spatial points and lines of the printed layers and contours of printed parts. With a calibration error of 50 μm and resolution of 180 μm for the light field camera (Lytro illum camera), the maximum relative and absolute errors between reconstructed three-dimensional spatial points were 4.33 % and 260 μm respectively when compared with theoretical dimension, and 0.5 % and 210 μm respectively when compared with manufactured dimension. The maximum root-mean-square error of reconstructed three-dimensional contour surfaces was found to be 1.55 mm. This study represents the first application of a light field camera for in situ three-dimensional reconstruction of laser powder bed fusion parts, which notably can be obtained from only a single round of calibration and exposure, enabling seamless monitoring of their surface morphology and facilitating online quality control. These advancements have vast potential for enhancing high-end additive manufacturing.

Improved spatial speckle contrast model for tissue blood flow imaging: effects of spatial correlation among neighboring camera pixels.

Speckle contrast analysis is the basis of laser speckle imaging (LSI), a simple, inexpensive, noninvasive technique used in various fields of medicine and engineering. A common application of LSI is the measurement of tissue blood flow. Accurate measurement of speckle contrast is essential to correctly measure blood flow. Variables, such as speckle grain size and camera pixel size, affect the speckle pattern and thus the speckle contrast. We studied the effects of spatial correlation among adjacent camera pixels on the resulting speckle contrast values. We derived a model that accounts for the potential correlation of intensity values in the common experimental situation where the speckle grain size is larger than the camera pixel size. In vitro phantom experiments were performed to test the model. Our spatial correlation model predicts that speckle contrast first increases, then decreases as the speckle grain size increases relative to the pixel size. This decreasing trend opposes what is observed with a standard speckle contrast model that does not consider spatial correlation. Experimental data are in good agreement with the predictions of our spatial correlation model. We present a spatial correlation model that provides a more accurate measurement of speckle contrast, which should lead to improved accuracy in tissue blood flow measurements. The associated correlation factors only need to be calculated once, and open-source software is provided to assist with the calculation.

Practical Talbot wavemeter

A wavemeter using the near-field Talbot diffraction is simplified. High accuracy wavelength measurement can be obtained from each spacing between two adjacent maximum intensities of the periodicity along multiples of the Talbot distance. Our experimental results are confirmed by our calculations. In contrast to the previous works, we use a diffraction grating with sufficiently large grating period. Therefore, the setup is practical and the pixel size of camera used to measure the interference pattern can be large. Moreover, the obtained Talbot patterns are sharp without using a post-image processing. According to our recent setup, we use the grating with a period of 12.5 μm. With visible light lasers, the Talbot distances are in the range of a few hundred of micrometers. These distances are much larger than a pixel size of normal camera. An external cavity diode laser with rubidium saturated absorption spectroscopy is used to calibrate our setup. High accuracy at 1 pm can be achieved.

Crystal optics simulations for delineation of the three-dimensional cellular nuclear distribution using analyzer-based refraction-contrast computed tomography

Refraction-contrast computed tomography (RCT) using a refractive angle analyzer of Si perfect crystal can reconstruct the three-dimensional structure of biological soft tissue with contrast comparable to that of stained two-dimensional pathological images. However, the blurring of X-ray beam by the analyzer has prevented improvement of the spatial resolution of RCT, and the currently possible observation of tissue structure at a scale of approximately 20 µm provides only limited medical information. As in pathology, to differentiate between benign and malignant forms of cancer, it is necessary to observe the distribution of the cell nucleus, which is approximately 5–10 µm in diameter. In this study, based on the X-ray dynamical diffraction theory using the Takagi–Taupin equation, which calculates the propagation of X-ray energy in crystals, an analyzer crystal optical system depicting the distribution of cell nuclei was investigated by RCT imaging simulation experiments in terms of the thickness of the Laue-case analyzer, the camera pixel size and the difference in spatial resolution between the Bragg-case and Laue-case analyzers.

Systematic error analysis and parameter design of a vision-based phase estimation method for ultra-precision positioning.

Ultra-precision position measurement is increasingly important in advanced manufacturing such as the semiconductor industry and fiber optics or photonics. A vision-based phase estimation method we proposed previously performs position measurement by imaging a 2D periodic pattern. In this paper, systematic errors of this method are analyzed and derived mathematically, which are classified into two types: spectrum leakage error caused by image truncation and window function modulation, and sub-pixel error resulting from discrete Fourier transform (DFT) intensity interpolation. Key design parameters are concluded including pattern period T, camera pixel size t and resolution N, as well as the type of window function used. Numerical simulations are conducted to investigate the relationship between the phase errors and design parameters. Then an error reduction method is proposed. Finally, the improved performance of parameter optimization is validated by a comparative experiment. Experimental results show the measurement errors of the prototype are within ∼2 nm in X or Y axis, and ∼1µrad in axis, which reaches the sub-pixel accuracy better than 10-3pixel.

Single-shot pixel super-resolution phase imaging by wavefront separation approach

We propose a novel approach for lensless single-shot phase retrieval, which provides pixel super-resolution phase imaging. The approach is based on a computational separation of carrying and object wavefronts. The imaging task is to reconstruct the object wavefront, while the carrying wavefront corrects the discrepancies between the computational model and physical elements of an optical system. To reconstruct the carrying wavefront, we do two preliminary tests as system calibration without an object. Essential for phase retrieval noise is suppressed by a combination of sparse- and deep learning-based filters. Robustness to discrepancies in computational models and pixel super-resolution of the proposed approach are shown in simulations and physical experiments. We report an experimental computational super-resolution of 2μm, which is 3.45× smaller than the resolution following from the Nyquist-Shannon sampling theorem for the used camera pixel size of 3.45μm. For phase bio-imaging, we provide Buccal Epithelial Cells reconstructed with a quality close to the quality of a digital holographic system with a 40× magnification objective. Furthermore, the single-shot advantage provides a possibility to record dynamic scenes, where the frame rate is limited only by the used camera. We provide amplitude-phase video clip of a moving alive single-celled eukaryote.

Influence of spectral characteristics of light sources on measuring space camera modulation transfer function

Modulation transfer function (MTF) measurement is a major means to evaluate the imaging quality of a space camera. The influence caused by the spectral characteristic of light source on the MTF results is not negligible, because the transmittance and color aberration of optical systems, and quantum efficiency of the space camera detectors are all spectrally related. Thus, MTF results tested by different light sources are different from each other. To address this problem, we propose a method to analyze the influence of spectral characteristics of light sources on measuring the MTF of space cameras. In addition, the devices and methods are designed to calibrate the spectral response and monochrome point spread function (PSF) of space camera. A Sigma lens (focal length: 1000mm, F number: 5.6) and a Cannon EOS 5DSR camera (pixel size: 4.14 μm) are combined into an experimental space camera, whose spectral response is calibrated with a monochromator (Omno30300, NBeT) and a spectral radiometer (FieldSpec, ASD). We calibrate the monochrome PSF of the Sigma lens with the same monochromator and a CCD (PIXIS 1024, Princeton Instruments, pixel size: 13 μm) micro-measuring system (20X objective). During the calibration of spectral response and monochrome PSF, the same collimator (focus: 5000 mm, F number: 10) is used. With using the proposed method and those calibrating data, we compute the theoretical values of the MTF of a space camera measured separately with five different light sources. The results indicate that MTF measured by a xenon lamp is greatly different from those MTFs measured by the other four light sources. Comparisons of those theoretically calculated MTFs, separately, show that the MTF measured by a tungsten halogen lamp is greater than the MTF measured by a xenon lamp at each spatial frequency. The deviation between those two lamps reaches a maximum value of 0.075 in the medium-high frequency zone. Furthermore, in order to verify those theoretical conclusions, a platform including a collimator and the previous space camera is constructed. The MTFs measured by a tungsten halogen lamp and a xenon lamp are computed with the slanted-edge method respectively. The results demonstrate that the distributions and deviations of the MTFs tested by those two lamps are identical to those theoretical results at each spatial frequency, with the maximum deviation being 0.057. The theoretical and experimental results demonstrate that the suggested method can accurately calculate the influence of spectral characteristics of light sources on measuring MTF of space cameras. The proposed method can also be adopted to investigate the influence of spectral characteristics of light sources on MTF of optical systems in the design or test stages.

First analysis of the misaligned leading edges of ITER-like plasma facing units using a very high resolution infrared camera in WEST

Twelve ITER-like plasma-facing units made of tungsten were exposed in the WEST tokamak divertor, with three plasma-facing units (PFUs) significantly overexposed to plasma heat flux: one sharp-edged PFU (vertical misalignment h = 0.8 mm) and two chamfered PFUs (h =0.6 mm and 0.3 mm, respectively). This paper describes the first temperature analysis obtained with a very high spatial resolution infrared camera (pixel size ∼ 0.1 mm) on the misaligned PFU edges and shows the consistency obtained on the parallel heat flux derived from these measurements. The analysis is focused on the hottest areas of the PFU misaligned leading edges, since the temperature detection threshold of the VHR camera is high (Tthreshold,BB ≈ 370 °C). The heat flux parallel to the magnetic field lines is assessed by matching the toroidal temperature profile in the vicinity of the leading edge with 3D finite element modelling. The tungsten emissivity assumed in this study is 0.6, which is consistent with laboratory measurements for damaged PFUs. For the three PFUs studied (with different vertical misalignments, incident angles, geometries), the derived parallel heat flux is similar, and consistent with independent measurements by a Fiber Bragg grating embedded in a graphite PFU at another toroidal location, giving confidence in future experiments using the same settings.

Influence of projector pixel shape on ultrahigh-resolution 3D shape measurement.

The state-of-art three-dimensional (3D) shape measurement with digital fringe projection (DFP) techniques assume that the influence of projector pixel shape is negligible. However, our research reveals that when the camera pixel size is much smaller than the projector pixel size in object space (e.g., 1/5), the shape of projector pixel can play a critical role on ultimate measurement quality. This paper evaluates the performance of two shapes of projector pixels: rectangular and diamond shaped. Both simulation and experimental results demonstrated that when the camera pixel size is significantly smaller than the projector pixel size, it is advantageous for ultrahigh resolution 3D shape measurement system to use a projector with rectangular-shaped pixels than a projector with diamond-shaped pixels.

Method for 3-D Scene Reconstruction Using Fused LiDAR and Imagery From a Texel Camera

Reconstructing a 3-D scene from aerial sensor data creating a textured digital surface model (TDSM), consisting of a LiDAR point cloud and an overlaid image, is valuable in many applications including agriculture, military, surveying, and natural disaster response. When collecting LiDAR from an aircraft, the navigation system accuracy must exceed the LiDAR accuracy to properly reference returns in 3-D space. Precision navigation systems can be expensive and often require full-scale aircraft to house such systems. Synchronizing the LiDAR sensor and a camera, using a texel camera calibration, provides additional information that reduces the need for precision navigation equipment. This paper describes a bundle adjustment technique for aerial texel images that allows for relatively low-accuracy navigation systems to be used with low-cost LiDAR and camera data to form higher fidelity terrain models. The bundle adjustment objective function utilizes matching image points, measured LiDAR distances, and the texel camera calibration and does not require overlapping LiDAR scans or ground control points. The utility of this method is proven using a simulated texel camera and unmanned aerial system (UAS) flight data created from aerial photographs and elevation data. A small UAS is chosen as the target vehicle due to its relatively inexpensive hardware and operating costs, illustrating the power of this method in accurately referencing the LiDAR and camera data. In the 3-D reconstruction, the 1- $\sigma $ accuracy between LiDAR measurements across the scene is on the order of the digital camera pixel size.

Blind Star Identification Algorithm

In this paper, a new algorithm called blind star identification is presented to identify the stars in night sky images without using the intrinsic parameters of the star sensor camera (focal length, principal point, and pixel size), and in lost in space mode. The accuracy and reliability of the proposed algorithm were successfully validated by using the real night sky images and Monte Carlo simulations. Accordingly, the proposed algorithm was successfully able to identify in more than 90% of the images containing more than five stars and no wrong identification was observed in the Monte Carlo simulations. On the other hand, the rotation around the optical axis, which cannot be estimated using vector observations, should be minimized in the process of designing and manufacturing the star sensor and carefully measured in the ground calibration, like as the aberration and lens distortion. Ultimately, another advantage of this algorithm is the simultaneous use of planar and interstellar angles. This advantage leads to data redundancy and greater reliability of the algorithm so that the performance of the algorithm is guaranteed under severe error conditions.

A Search for High-Frequency Coronal Brightness Variations in the 21 August 2017 Total Solar Eclipse

We report on a search for short-period intensity variations in the green-line (Fe xiv 530.3 nm) emission from the solar corona during the 21 August 2017 total eclipse viewed from Idaho in the United States. Our experiment was performed with a much more sensitive detection system, and with better spatial resolution, than on previous occasions (1999 and 2001 eclipses), allowing fine details of quiet coronal loops and an active-region loop system to be seen. A guided 200-mm-aperture Schmidt–Cassegrain telescope was used with a state-of-the-art CCD camera having 16-bit intensity discrimination and a field-of-view (0.43^{ circ } times 0.43^{circ }) that encompassed approximately one third of the visible corona. The camera pixel size was 1.55 arcseconds, while the seeing during the eclipse enabled features of {approx}, 2 arcseconds (1450 km on the Sun) to be resolved. A total of 429 images were recorded during a 122.9 second portion of the totality at a frame rate of 3.49~mbox{s}^{-1}. In the analysis, we searched particularly for short-period intensity oscillations and travelling waves, since theory predicts fast-mode magneto-hydrodynamic (MHD) waves with short periods may be important in quiet coronal and active-region heating. Allowing first for various instrumental and photometric effects, we used a wavelet technique to search for periodicities in some 404mbox{,}000 pixels in the frequency range 0.5,mbox{--},1.6mbox{ Hz} (periods 2 seconds to 0.6 seconds). We also searched for travelling waves along some 65 coronal structures. However, we found no statistically significant evidence in either. This negative result considerably refines the limit that we obtained from our previous analyses, and it indicates that future searches for short-period coronal waves may be better directed towards Doppler shifts as well as intensity oscillations.

A large area high resolution imaging detector for fast atom diffraction

We describe a high resolution imaging detector based on a single 80 mm micro-channel-plate (MCP) and a phosphor screen mounted on a UHV flange of only 100 mm inner diameter. It relies on standard components and we describe its performance with one or two MCPs. A resolution of 80 $\mu m$ rms is observed on the beam profile. % which is limited by the camera pixel size. At low count rate, individual impact can be pinpointed with few $\mu m$ accuracy but the resolution is probably limited by the MCP channel diameter. The detector has been used to record the diffraction of fast atoms at grazing incidence on crystal surfaces (GIFAD), a technique probing the electronic density of the topmost layer only. The detector was also used to record the scattering profile during azimuthal scan of the crystal to produce triangulation curves revealing the surface crystallographic directions of molecular layers. It should also be compatible with reflection high energy electron (RHEED) experiment when fragile surfaces require a low exposure to the electron beam.

Aliasing, coherence, and resolution in a lensless holographic microscope.

We have shown that the maximum achievable resolution of an in-line lensless holographic microscope is limited by aliasing and, for collimated illumination, cannot exceed the camera pixel size. This limit can be achieved only when the optimal conditions on the spatial and temporal coherence state of the illumination are satisfied. The expressions defining the configuration, delivering maximum resolution with given spatial and temporal coherence of the illumination, are obtained. The validity of these conditions is confirmed experimentally.

Speckle suppression in off-axis lensless Fourier transform digital holography

Speckle noise suppression in off-axis lensless Fourier transform digital holography by laterally shifting of object is analyzed quantitatively. Speckle decorrelation is directly proportional to the object displacement therefore object is shifted by three different amounts to test its effect on the speckle contrast reduction that is pixel size of camera, averaged speckle size and resolution pixel size of reconstruction plane. Phase-only spatial light modulator (LCOS) is used in object beam path to introduce the lateral shift in its position digitally without mechanical efforts by displaying a grating function. In comparison with the typical methods, the externally input lateral position shifts of object are controlled accurately, which makes the system effective and practicable. Averaged reconstructed results for three quantitative object lateral position shifts are compared and it has been found that the object shift by resolution pixel size of reconstruction plane shows better speckle contrast reduction and is in good agreement with the theoretical prediction.

Parameter optimization for through-focus scanning optical microscopy.

It is important to economically and non-destructively analyze three-dimensional (3-D) shapes of nanometer to micrometer scale objects with sub-nanometer measurement resolution for emerging high-volume nanomanufacturing, especially for process control. High-throughput through-focus scanning optical microscopy (TSOM) demonstrates promise for such applications. TSOM uses a conventional optical microscope for 3-D shape metrology by making use of the complete set of through-focus, four-dimensional optical data. However, a systematic study showing the effect of various parameters on the TSOM method is lacking. Here we present the optimization of the basic parameters such as illumination numerical aperture (NA), collection NA, focus step height, digital camera pixel size, illumination polarization, and illumination wavelength to achieve peak performance of the TSOM method.

Monte Carlo studies of medium-size telescope designs for the Cherenkov Telescope Array

We present studies for optimizing the next generation of ground-based imaging atmospheric Cherenkov telescopes (IACTs). Results focus on mid-sized telescopes (MSTs) for CTA, detecting very high energy gamma rays in the energy range from a few hundred GeV to a few tens of TeV. We describe a novel, flexible detector Monte Carlo package, FAST (FAst Simulation for imaging air cherenkov Telescopes), that we use to simulate different array and telescope designs. The simulation is somewhat simplified to allow for efficient exploration over a large telescope design parameter space. We investigate a wide range of telescope performance parameters including optical resolution, camera pixel size, and light collection area. In order to ensure a comparison of the arrays at their maximum sensitivity, we analyze the simulations with the most sensitive techniques used in the field, such as maximum likelihood template reconstruction and boosted decision trees for background rejection. Choosing telescope design parameters representative of the proposed Davies–Cotton (DC) and Schwarzchild–Couder (SC) MST designs, we compare the performance of the arrays by examining the gamma-ray angular resolution and differential point-source sensitivity. We further investigate the array performance under a wide range of conditions, determining the impact of the number of telescopes, telescope separation, night sky background, and geomagnetic field. We find a 30–40% improvement in the gamma-ray angular resolution at all energies when comparing arrays with an equal number of SC and DC telescopes, significantly enhancing point-source sensitivity in the MST energy range. We attribute the increase in point-source sensitivity to the improved optical point-spread function and smaller pixel size of the SC telescope design.

Time Super-Resolution Fluorescence Imaging by Event Correlation Microscopy

Fluorescence imaging at low light intensities requires relatively long imaging frames, with severe limitations on the time resolution that can be achieved when dynamic changes are recorded. To overcome this limitation, a method named Event COrrelation Microscopy (ECOM) was developed, which can be applied when imaging is performed together with a precisely timed stimulation event. The method takes advantage of the fact that for a step change in fluorescence intensity, the intensity reported by the frame during which the step occurs depends on the time of the step within the frame. The method is based on averaging a large number of responses timed randomly with respect to the imaging frames. The step response function of the ECOM method was derived theoretically and extends over the duration of 2 frames with a sigmoid time course. This step response function agrees perfectly with the step response determined experimentally. The time point of the intensity step can be determined with a precision that depends on the signal-to-noise ratio (SNR) of the averaged signal. For image acquisition with 200 ms frames in frame transfer mode, the standard deviation σt of the time determination is approximately σt=225/SNR. ECOM therefore provides time super-resolution beating the time resolution of imaging frames. The method shares similarity with localization microscopy techniques such as STORM/PALM, which provide spatial super-resolution beyond the limits of camera pixel size. ECOM was successfully applied to the study of transmitter release events from chromaffin cells revealing a rapid conformational change in SNAP-25 that precedes fusion pore formation by 90±10 ms (Zhao et al. 2013 PNAS 110: 14249-14254.) Supported by ERC Advanced Grant No. 322699.