Constant Magnification Research Articles

Double vision: 2D and 3D mosquito trajectories can be as valuable for behaviour analysis via machine learning

BackgroundMosquitoes are carriers of tropical diseases, thus demanding a comprehensive understanding of their behaviour to devise effective disease control strategies. In this article we show that machine learning can provide a performance assessment of 2D and 3D machine vision techniques and thereby guide entomologists towards appropriate experimental approaches for behaviour assessment. Behaviours are best characterised via tracking—giving a full time series of information. However, tracking systems vary in complexity. Single-camera imaging yields two-component position data which generally are a function of all three orthogonal components due to perspective; however, a telecentric imaging setup gives constant magnification with respect to depth and thereby measures two orthogonal position components. Multi-camera or holographic techniques quantify all three components.MethodsIn this study a 3D mosquito mating swarm dataset was used to generate equivalent 2D data via telecentric imaging and a single camera at various imaging distances. The performance of the tracking systems was assessed through an established machine learning classifier that differentiates male and non-male mosquito tracks. SHAPs analysis has been used to explore the trajectory feature values for each model.ResultsThe results reveal that both telecentric and single-camera models, when placed at large distances from the flying mosquitoes, can produce equivalent accuracy from a classifier as well as preserve characteristic features without resorting to more complex 3D tracking techniques.ConclusionsCaution should be exercised when employing a single camera at short distances as classifier balanced accuracy is reduced compared to that from 3D or telecentric imaging; the trajectory features also deviate compared to those from the other datasets. It is postulated that measurement of two orthogonal motion components is necessary to optimise the accuracy of machine learning classifiers based on trajectory data. The study increases the evidence base for using machine learning to determine behaviours from insect trajectory data.Graphical

Magnification of a multi-focus infinity corrected microscope

The problem of image magnification in a bright field multi-focus imaging microscope is discussed. Such microscope allows simultaneous observation of two objects axially separated by a distance that exceeds the depth-of-field of the microscope, so-called multi-planar imaging. It is shown that the tunable lens required for operation of the microscope can be used in constant magnification imaging in the single focus regime, but not in multi-focus. Additionally, it is presented that the microscope allows for multi-planar imaging with satisfactory quality with a selected magnification of the image of one of the two objects. While the microscope uses a thermal lens as the tunable lens, the scheme of the optical setup needed to achieve the desired operation of the microscope is universal and applies to all kinds of tunable lenses used in microscopy.

Phase contrast micro-CT with adjustable in-slice spatial resolution at constant magnification

Objective. To report on a micro computed tomography (micro-CT) system capable of x-ray phase contrast imaging and of increasing spatial resolution at constant magnification. Approach. The micro-CT system implements the edge illumination (EI) method, which relies on two absorbing masks with periodically spaced transmitting apertures in the beam path; these split the beam into an array of beamlets and provide sensitivity to the beamlets’ directionality, i.e. refraction. In EI, spatial resolution depends on the width of the beamlets rather than on the source/detector point spread function (PSF), meaning that resolution can be increased by decreasing the mask apertures, without changing the source/detector PSF or the magnification. Main results. We have designed a dedicated mask featuring multiple bands with differently sized apertures and used this to demonstrate that resolution is a tuneable parameter in our system, by showing that increasingly small apertures deliver increasingly detailed images. Phase contrast images of a bar pattern-based resolution phantom and a biological sample (a mouse embryo) were obtained at multiple resolutions. Significance. The new micro-CT system could find application in areas where phase contrast is already known to provide superior image quality, while the added tuneable resolution functionality could enable more sophisticated analyses in these applications, e.g. by scanning samples at multiple scales.

Design and characterization of a varifocal camera system with an extended depth of field and focal range.

This paper presents the design and characterization of a compact and affordable varifocal camera system. With its entrance pupil located in front as the first element for easy access, the camera system offers a working F/# as low as 2, is capable of focusing across a wide depth range from optical infinity to as close as 4 diopters through an electrically tunable lens, and maintains nearly constant angular magnification through the focus range by placing the focusing element at proximity to the entrance pupil. These unique features can find a myriad of applications such as image-based head-mounted display calibration and extended depth of field (EDOF) imaging. The paper further demonstrates a single-shot EDOF imaging function by utilizing its property of nearly constant angular magnification through focus scanning.

Nonlinear optimization considering target feature points for bitelecentric camera calibration: experimental study.

The telecentric camera has found extensive application in microscopy imaging due to its remarkable attributes of maintaining constant magnification and minimal distortion within its depth of field. In telecentric imaging technology, the accuracy of measurements frequently hinges upon the calibration precision of the telecentric camera. In real-world scenarios, the shallow depth of field characteristic of telecentric cameras often leads to out-of-focus targets during the capturing process, which in turn results in the inability to accurately extract pixel coordinates of feature points, making it difficult for optimization algorithms to converge to the optimal value. We propose a nonlinear optimization algorithm based on pixel coordinates of optimized feature points for bitelecentric cameras. Incorporating pixel coordinates into the optimization process yields the theoretically optimal solution based on bitelecentric camera model. The obtained pixel coordinates are used for second initial value estimation, followed by the optimization of all parameters. Compared to existing methods, the proposed approach significantly reduces reprojection errors under both blurry and clear target conditions. Experimental results demonstrate superior performance in processing blurry defocused images.

Simulation of the temporal resolution uniformity of a dilation framing camera.

The temporal resolution uniformity of a time-dilation framing camera is studied, and the ideal photocathode (PC) pulse curve is determined, while the temporal magnification factor is kept constant. To obtain the ideal curve, a series of linear pulses with the same slope are superposed. The variance in the temporal resolution and the number of linear pulses required are compared, while the superposition results with different slopes are used as the PC voltage. As the slope of the linear pulses decreases, the variance decreases, which means that the uniformity of the temporal resolution is improved, but the number of linear pulses required increases. In this study, linear pulses with a slope of 1V/ps are superposed. Nine linear pulses with a front edge time of 200ps, amplitude of 200V, and flat top time of 1ns are superimposed to approximate the ideal PC pulse curve with a constant temporal magnification factor of 10; the trigger times of the pulses are 0, 0, 0, 185, 200, 350, 450, 605, and 790ps. When the superposition result is applied as the PC voltage and the measured signal is synchronized to the PC pulse at 128ps-1ns, the temporal resolution error is within 5%.

Extended the depth of field and zoom microscope with varifocal lens

Extending the depth of field (DOF) is especially essential in thick and 3D sample imaging. However, it's difficult to achieve both large DOF and high resolution in a zoom microscope. Currently, the use of optical sectioning to expand DOF still has the problem of inconstant magnification. Here, we develop an extended the depth of field (EDOF) and zoom microscope, which can realize EDOF with constant magnification and high resolution. Besides, the proposed microscope can achieve optical axial scanning at different NA and magnifications in real time without any mechanical movement. The proposed varifocal lens is employed to realize optical axial scanning, zooming, and keeping constant magnification when extending the DOF. Experimental results show that the proposed microscope can realize a continuous optical zoom of 10–40×, NA from 0.14 to 0.54, and the DOF of microscope can be extended to 1.2 mm.

Preparation of Porous Biomass-Derived Carbon Material and Its Sodium Storage Capacity

Biomass-derived porous carbon(BDPC)was designed and prepared from Qamgur,a biomass from Xinjiang,China,as the carbon precursor,by pre-carbonization and activation,while retaining Qamgur’s inherent pore structure.The microstructure,phase composition and pore structure of the material were analyzed by scanning electron microscope(SEM),X-ray diffraction(XRD),Raman spectroscopy,X-ray photoelectron spectroscopy(XPS)and nitrogen adsorption desorption test;The electrochemical properties of the material as a sodium storage anode were characterized by cyclic voltammetry,constant current charge-discharge, cycling,magnification and electrochemical impedance measurements.The results show that BDPC- 600 has good sodium storage performance because it contains nitrogen and oxygen heteroatoms(the contents are 3.36 at.% and 7.61 at.%,respectively).At 0.1A/g current density,after 100 cycles of charge and discharge,the reversible capacity is 187.7mAh/g,and the capacity retention rate is 88.7%.In addition, BDPC-900 has excellent magnification performance due to its large specific surface area(2396.60 m2/g)and pore volume(1.70cm3/g).

Constrained nonlinear optimization method for accurate calibration of a bi-telecentric camera in a three-dimensional microtopography system.

Telecentric cameras are widely used in the field of microscopic imaging because of their constant magnification and tiny distortion in the depth of field. Camera calibration has always been a key step in the field of computer vision. Usually, the precise parameters of the telecentric camera are obtained by nonlinear optimization; however, the randomness of the optimization algorithm without proper constraints will cause the results to be inconsistent with reality. Existing studies paid little attention to this issue; therefore, we show a reliable optimization approach for the bi-telecentric camera in a structured illumination three-dimensional microtopography measurement system. In this method, the distortion-free camera parameters are solved through a closed-form solution. Then a nonlinear optimization algorithm with constraining the world coordinates of the precise calibration target is proposed to refine the global parameters, leading to the calibration results being more accurate and authentic. The real experiments are conducted to verify the feasibility of the proposed method. The comparative experiments with the exiting approach are then carried out, manifesting that the proposed method enjoys advantages in terms of both reprojection error and operating efficiency. Additionally, the average offset of the world coordinates on the calibration target derived from the proposed method verifies its effectiveness and reasonability.

Design of a stigmatic lens implementing a required ray mapping.

We consider a method for designing stigmatic lenses implementing required ray mappings. A ray mapping relates the angular coordinates of the rays at the image points with the angular coordinates of the rays coming from the object. The calculation of a stigmatic lens with a required ray mapping is reduced to solving an explicit ordinary differential equation. As examples, we design stigmatic lenses satisfying the Abbe sine condition, the Herschel's condition, and the constant angular magnification condition.

Deep multiple-instance learning for abnormal cell detection in cervical histopathology images

Cervical cancer is a disease of significant concern affecting women's health worldwide. Early detection of and treatment at the precancerous stage can help reduce mortality. High-grade cervical abnormalities and precancer are confirmed using microscopic analysis of cervical histopathology. However, manual analysis of cervical biopsy slides is time-consuming, needs expert pathologists, and suffers from reader variability errors. Prior work in the literature has suggested using automated image analysis algorithms for analyzing cervical histopathology images captured with the whole slide digital scanners (e.g., Aperio, Hamamatsu, etc.). However, whole-slide digital tissue scanners with good optical magnification and acceptable imaging quality are cost-prohibitive and difficult to acquire in low and middle-resource regions. Hence, the development of low-cost imaging systems and automated image analysis algorithms are of critical importance. Motivated by this, we conduct an experimental study to assess the feasibility of developing a low-cost diagnostic system with the H&E stained cervical tissue image analysis algorithm. In our imaging system, the image acquisition is performed by a smartphone affixing it on the top of a commonly available light microscope which magnifies the cervical tissues. The images are not captured in a constant optical magnification, and, unlike whole-slide scanners, our imaging system is unable to record the magnification. The images are mega-pixel images and are labeled based on the presence of abnormal cells. In our dataset, there are total 1331 (train: 846, validation: 116 test: 369) images. We formulate the classification task as a deep multiple instance learning problem and quantitatively evaluate the classification performance of four different types of multiple instance learning algorithms trained with five different architectures designed with varying instance sizes. Finally, we designed a sparse attention-based multiple instance learning framework that can produce a maximum of 84.55% classification accuracy on the test set.

Calibration and rectification of bi-telecentric lenses in Scheimpflug condition

In the lens-based imaging model, the Scheimpflug principle is expressed as the object plane, the image plane, and the lens plane intersect in a line. With this principle, the focused object plane in the lens's object side can be tilted by placing a tilted sensor at the image side of the lens; thereby, multi-cameras can be focused on the same object space with an overlapping field of view and depth of field. For Scheimpflug cameras, additional tilt angles between the camera sensor and the optical axis are introduced, which has been well studied in pinhole cameras' calibration methods. Telecentric lens, as a commonly used lens type, has constant magnification in the axial direction and has a wide range of applications in close-range photogrammetry. To calibrate and rectify the telecentric lenses in Scheimpflug conditions, we derived a concise imaging model by expressing the sensor tilt angles and the lens magnification into a simplified intrinsic matrix. Based on the derived imaging model, an integrated calibration algorithm without solving the tilt angles and a stereo-rectification method for stereo matching are developed. The effectiveness and accuracy of the proposed methods are verified by experiments, including the comparison with the traditional telecentric model and pinhole model. Combined with the experimental results, we analyzed the potential impact of the extrinsic rotation matrix's ambiguity, verified whether the lens distortion affects the re-projection error, and discussed how the calibration posture influences the calibration accuracy.

Variation and dispersal of PM10 and PM2.5 during COVID-19 lockdown over Kolkata metropolitan city, India investigated through HYSPLIT model

The higher concentration of PM10 and PM2.5 in the lower atmosphere is severely harmful for human health and it also makes visibility diminution along with weather and climate modifications. The main objective is to find out the spatiotemporal variation and dispersal of PM10 and PM2.5 along with COVID-19 infection in the dusty city Kolkata. The consecutive two years PM10 and PM2.5 data of different stations have been obtained from State Pollution Control Board, Govt. of West Bengal. Forward trajectory analysis has been done through HYSPLIT (Hybrid Single Particle Lagrangian Integrated Trajectory) model to find the path and direction of air particles. The result showed that the various meteorological or environmental factors (such as temperature, relative humidity, wind, wind speed, pressure and gusty wind) and geographical location regulate the spatiotemporal variation of PM10 and PM2.5. These factors like high temperature with relative humidity and strong wind influence to disperse the particulate matters from north to south direction from city to outside during summer in Kolkata metropolitan city. During summer (both pre and lockdown years), the height of particles is extended up to 1000 m owing to active atmospheric ventilation whereas in winter it is confined within 100 m. The HYSPLIT model clearly specified that the particles dispersed from south, south-west to north and north east direction due to strong wind. The constant magnification of PM10 and PM2.5 in the lower atmosphere leads to greater frequency of COVID-19 infections and deaths. In Kolkata, the one of the crucial reasons of high infection and deaths (COVID-19) is co-morbidity of people.

Incoherent digital holographic spectral imaging with high accuracy of image pixel registration* *Project supported by the National Natural Science Foundation of China (Grant Nos. 61505178, 61307019, and 11504333) and the Natural Science Foundation of Henan Province, China (Grant Nos. 18A140032, 15A140038, and 16A140035).

Fresnel incoherent correlation holography (FINCH) is a unique three-dimensional (3D) imaging technique which has the advantages of scanning-free, high resolution, and easy matching with existing mature optical systems. In this article, an incoherent digital holographic spectral imaging method with high accuracy of spectral reconstruction based on liquid crystal tunable filter (LCTF) and FINCH is proposed. Using the programmable characteristics of spatial light modulator (SLM), a series of phase masks, none of whose focal lengths changes with wavelength, is designed and made. For each wavelength of LCTF output, SLM calls three phase masks with different phase constants at the corresponding wavelength, and CCD records three holograms. The spectral images obtained by this method have a constant magnification, which can achieve pixel-level image registration, restrain image registration errors, and improve spectral reconstruction accuracy. The results show that this method can not only obtain the 3D spatial information and spectral information of the object simultaneously, but also have high accuracy of spectral reconstruction and excellent color reproducibility.

Telecentric design for digital-scanning-based HiLo optical sectioning endomicroscopy with an electrically tunable lens.

Confocal endoscopy has been widely used to obtain fine optically sectioned images. However, confocal endomicroscopic images are formed by point-by-point scanning in both lateral and axial directions, which results in long image acquisition time. Here, an endomicroscope with telecentric configuration is presented to achieve nonmechanical and rapid axial scanning for volumetric fluorescence imaging. In our system, optical sectioning in wide-field fashion is obtained through HiLo imaging with a digital micromirror device. Axial scanning, without mechanical moving parts, is conducted by digital focus adjustment using an electrically tunable lens, offering constant magnification and contrast. We demonstrate imaging performance of our system with optically sectioned images using fluorescently labeled beads, as well as ex vivo mice cardiac tissue samples. Our system provides multiple advantages, in terms of improved scanning range, and reduced image acquisition time, which shows great potentials for three-dimensional biopsies of volumetric biological samples.

Incoherent digital holographic color imaging with high accuracy image registration

Fresnel incoherent correlation holography is a new technology which can record incoherent object holograms and has important applications in biomedical imaging and 3D remote sensing. The problem of image fusion registration in hyperspectral imaging, three groups of double lens phase masks with constant focal lengths at 492 nm, 562 nm and 672 nm were designed and fabricated. The spatial light modulator called the masks of three wavelengths in turn and recorded the holograms of the objects under the corresponding wavelengths, which owed to the spatial light modulator were programmable. Because of the three-color recorded light was modulated by the corresponding wavelength mask, the spot position size of the CCD surface was the same. The reconstructed images had constant lateral magnification, which could improve the image registration accuracy and avoid complicated spatial registration algorithm of spectral images. The system truly achieved high-precision registration and real-time fusion of holographic color imaging. The color 3D image obtained from the dice holograms had high color reconstruction after numerical reconstruction and color fusion.

A Simple Device and Biplanar Technique to Improve Precision When Templating for Total Joint Arthroplasty

Accurate templating for arthroplasty procedures depends on reliably estimating image magnification. The authors designed a simple device and technique to accomplish this. It is a wedge with four 25-mm balls staggered at different heights, each representing a potential marker. The proper ball to use as the scaling marker is identified on an orthogonal view on the basis of its relationship with the anatomic feature of interest. Reviewing x-rays with known acetabular component diameters, the authors found that the staggered balls technique had a scaling error of 1.48±0.89%. Assuming a constant 20% magnification for all x-rays resulted in an error of 1.65±1.59%. Although similarly accurate, the difference in precision was found to be significant (P=0.012). The constant magnification method resulted in 2 outliers with >4% error, whereas there were no outliers with the novel technique. Staggered marker balls combined with orthogonal imaging is accurate and improves the precision of estimating radiograph magnification.

A compact system for intraoperative specimen imaging based on edge illumination x-ray phase contrast

A significant number of patients receiving breast-conserving surgery (BCS) for invasive carcinoma and ductal carcinoma in situ (DCIS) may need reoperation following tumor-positive margins from final histopathology tests. All current intraoperative margin assessment modalities have specific limitations. As a first step towards the development of a compact system for intraoperative specimen imaging based on edge illumination x-ray phase contrast, we prove that the system’s dimensions can be reduced without affecting imaging performance.We analysed the variation in noise and contrast to noise ratio (CNR) with decreasing system length using the edge illumination x-ray phase contrast imaging setup. Two-(planar) and three-(computed tomography (CT)) dimensional imaging acquisitions of custom phantoms and a breast tissue specimen were made. Dedicated phase retrieval algorithms were used to separate refraction and absorption signals. A ‘single-shot’ retrieval method was also used, to retrieve thickness map images, due to its simple acquisition procedure and reduced acquisition times. Experimental results were compared to numerical simulations where appropriate.The relative contribution of dark noise signal in integrating detectors is significant for low photon count statistics acquisitions. Under constant exposure factors and magnification, a more compact system provides an increase in CNR. Superior CNR results were obtained for refraction and thickness map images when compared to absorption images. Results indicate that the ‘single-shot’ acquisition method is preferable for a compact CT intraoperative specimen scanner; it allows for shorter acquisition times and its combination of the absorption and refraction signals ultimately leads to a higher contrast. The first CT images of a breast specimen acquired with the compact system provided promising results when compared to those of the longer length system.

Design of a compact dual-view endoscope based on a hybrid lens with annularly stitched aspheres

We present a compact dual-view endoscope objective lens with a field of view (FOV) of ±80°and F/# of 3.4. The endoscope consists of two optical configurations for increasing FOV within the volume constraint. The front view configuration is a fisheye lens with a FOV of ±55°, and the side view configuration is a panoramic annular lens that covers the remaining FOV. The two configurations are combined by a hybrid lens that consists of center refractive portion and side catadioptric portion. Both the front and rear surfaces of the hybrid lens are aspherized with the use of annularly stitched Q-type aspheres. Thus, a compact endoscope is successfully implemented with fewer lenses, with a total length of 11.5 mm and a maximum diameter of 5.5 mm. The modulation transfer function at 167 lp/mm is above 0.4 over the entire FOV. The relative illumination is more than 0.65 and the optical distortion is within 10%. Moreover, the near telecentric condition is fulfilled and supports constant magnification focusing.

Depth estimation of steel cracks using laser and image processing techniques

Crack detection is needed to maintain safety and its automation is a must when human-based inspection cannot be made due to space limitations and/or hazards. In this study, an automatic crack depth measurement method using image processing and laser methods is developed. Measurement of maximum actual depths is done using Keyence (VK-X100) laser microscope. Microscope capture crack image segments using 1/3 in. (8.5 mm) sensor color charge-coupled device(CCD) camera with high resolution and 10x constant magnification. Depths are also calculated using the updated Make3D toolbox. Measured and calculated depths are compared for 11 cracked specimens with 105 segments. The comparison showed that the minimum and overall average error between measured and calculated depths are about 6.13% and 28.22% respectively.