Scheimpflug Principle Research Articles

On-site calibration method for an underwater stereoscopic camera system based on Scheimpflug principle

On-site calibration method for an underwater stereoscopic camera system based on Scheimpflug principle

Personalized Lens Correction Improves Quantitative Fundus Autofluorescence Analysis.

Quantitative fundus autofluorescence (QAF) currently deploys an age-based score to correct for lens opacification. However, in elderly people, lens opacification varies strongly between individuals of similar age, and innate lens autofluorescence is not included in the current correction formula. Our goal was to develop and compare an individualized formula. One hundred thirty participants were examined cross-sectionally, and a subset of 30 participants received additional multimodal imaging 2-week post-cataract-surgery. Imaging included the Scheimpflug principle, anterior chamber optical coherence tomography (AC-OCT), lens quantitative autofluorescence (LQAF), and retinal QAF imaging. Among the subset, least absolute shrinkage and selection operator regression and backward selection was implemented to determine which lens score best predicts the QAF value after lens extraction. Subsequently, a spline mixed model was applied to the whole cohort to quantify the influence of LQAF and Scheimpflug on QAF. Age and LQAF measurements were found to be the most relevant variables, whereas AC-OCT measurements and Scheimpflug were eliminated by backward selection. Both an increase in Scheimpflug and LQAF values were associated with a decrease in QAF. The prediction error of the spline model (mean absolute error [MAE] ± standard deviation) of 32.2 ± 23.4 (QAFa.u.) was markedly lower compared to the current age-based formula MAE of 96.1 ± 93.5. Both smooth terms, LQAF (P < 0.01) and Scheimpflug (P < 0.001), were significant for the spline mixed model. LQAF imaging proved to be the most predictive for the impact of the natural lens on QAF imaging. The application of lens scores in the clinic could improve the accuracy of QAF imaging interpretation and might allow including aged patients in future QAF studies.

Broadband continuous-wave differential absorption lidar for atmospheric remote sensing of water vapor.

What we believe to be a novel low-cost broadband continuous-wave water vapor differential absorption lidar (CW-DIAL) technique has been proposed and implemented by combing the Scheimpflug principle and the differential absorption method. The broadband CW-DIAL technique utilizes an 830-nm high-power multimode laser diode with 3-W output power as a tunable light source and a CMOS image sensor tilted at 45° as the detector. A retrieval algorithm dedicated for the broadband CW-DIAL technique has been developed to obtain range-resolved water vapor concentration from the DIAL signal. Atmospheric remote sensing of water vapor has been carried out on a near-horizontal water vapor path to validate the performance of the broadband CW-DIAL system. The retrieved water vapor concentration showed a good consistency with those measured by an air quality monitoring station, with a correlation coefficient of 0.9669. The fitting error of the water vapor concentration is found to be less than 10%. Numerical simulation studies have revealed that the aerosol-induced error on the water vapor concentration is below 5% with a background water vapor concentration of 5 g/m3 for most atmospheric conditions. The experimental results have successfully demonstrated the feasibility of the present broadband CW-DIAL technique for range-resolved water vapor remote sensing.

Comparison of Corneal Higher-order Aberrations Measured by Scheimpflug Camera and Placido Disc-based Topography in Korean Patients

Purpose: We compared corneal higher-order aberration (HOA) measurements between the Pentacam&lt;sup&gt;®&lt;/sup&gt; HR (PC), which uses the Scheimpflug principle, and the iTrace&lt;sup&gt;TM&lt;/sup&gt; aberrometer (IT), which evaluates Placido disc topography.Methods: We retrospectively analyzed 109 eyes of 87 patients without a history of ocular surface disease during the period from January 2021 to December 2022; both devices were used on the same day. We calculated the root mean square values (μm) of corneal total HOA and of the corneal 3rd- and 4th-order HOA at a pupil diameter of 4 mm. Data were compared by Bland-Altman plots for agreement analysis and Pearson correlation coefficient for correlation analysis.Results: There was no significant difference in the total HOA (&lt;i&gt;p&lt;/i&gt; = 0.145), coma (&lt;i&gt;p&lt;/i&gt; = 0.309), or secondary astigmatism (&lt;i&gt;p&lt;/i&gt; = 0.080) between the PC and IT measurements; all other HOAs significantly differed between devices (&lt;i&gt;p&lt;/i&gt; &lt; 0.001). In the correlation analysis, the total HOA (r = 0.605, &lt;i&gt;p&lt;/i&gt; &lt; 0.001) and coma (r = 0.634, &lt;i&gt;p&lt;/i&gt; &lt; 0.001) were moderately correlated between the two devices; the other HOAs showed low degree of correlations. In the Bland-Altman plot analysis, all HOAs showed low agreement between the two devices.Conclusions: Corneal total HOA and coma measured by the two devices were significantly correlated between the two devices, but other HOAs showed significant differences in measurement and low correlations. Therefore, corneal HOA measurements cannot be interpreted interchangeably between the two devices.

4D hyperspectral surface topography measurement system based on the Scheimpflug principle and hyperspectral imaging.

A four-dimensional (4D) hyperspectral surface topography measurement (HSTM) system that can acquire uniform inelastic signals [three-dimensional (3D) spatial data] and reflection/fluorescence spectra of an object is proposed. The key components of the system are a light-sheet profilometer based on the Scheimpflug principle and a hyperspectral imager. Based on the mapping relationships among the image coordinate systems of the two imaging subsystems and the coordinate system of the real space, the spectral data can be assigned to the corresponding 3D point cloud, forming a 4D model. The spectral resolution is better than 4nm. 700nm, 546nm, and 436nm are selected as the three primary colors of red, green, and blue to restore the color. The 4D hyperspectral surface reconstruction experiments of philodendron and chlorophytum have shown the good performance of the proposed HSTM system and the great application potential for plant phenotype and growth analysis in agriculture.

Design of an optical illumination system for a long wave infrared scene projector based on diffraction characteristics.

This study proposes an optical illumination system design based on vector diffraction characteristics and the Scheimpflug principle to determine an optimal relationship between illumination uniformity, energy utilization, and system size in an infrared scene projector. We investigate the influence of digital micromirror device (DMD) diffraction efficiency at different incidence angles on energy utilization rate and establish a two-dimensional diffraction grating model to determine the optimal incidence angle of the DMD beam. We demonstrate that the optical illumination system of a long-wave infrared (LWIR) scene projector based on diffraction characteristics can simulate an infrared scene with a compact structure, high energy efficiency, and high uniformity.

Line laser scanning microscopy based on the Scheimpflug principle for high-resolution topography restoration and quantitative measurement.

A line laser scanning microscopy system with a larger depth of field based on the Scheimpflug principle is proposed for high-resolution surface topography restoration and quantitative measurement on miniature non-transparent samples. An imaging model based on the Scheimpflug principle is established, and a calibration method without system parameters is derived, which is further extended to a microscopic system. The measuring range of the system is 5m m×4m m×x m m, where x is the movement distance of the displacement stage. In the z-axis direction, the relative error of measurement is about 1% when z is of the millimeter level and less than 7% when z is of the micron level, and the spatial resolution is better than 3.8µm. In the y-axis direction, the relative error of measurement is less than 5%. Finally, three-dimensional scanning of two samples with different surfaces is carried out to verify the feasibility of the system. The experimental results show that our system has the capability of high-resolution topography restoration and can be applied in industrial production scenarios such as automatic measurement and intelligent identification.

Spatial monitoring of flying insects over a Swedish lake using a continuous-wave lidar system.

We have used a continuous-wave bi-static lidar system based on the Scheimpflug principle in measurements on flying insects above, and in the vicinity of, a small lake located in a forested area in Southern Sweden. The system, which operates on triangulation principles, has a high spatial resolution at close distance, followed by a subsequent decline in resolution further from the sensor, related to the compact system design with a separation of transmitter and receiver by only 0.81 m. Our study showed a strong increase in insect abundance especially at dusk, but also at dawn. Insect numbers decreased over water compared to over land, and larger insects were over-represented over water. Further, the average size of the insects increased at night compared to day time.

Corneal curvature and thickness – Scheimpflug

AbstractAlthough the Scheimpflug principle was first described over a century ago, the clinical use of Scheimpflug camera in anterior segment imaging started only a decade ago. Scheimpflug imaging has since advanced significantly and modern instruments provide comprehensive imaging and topographic data of the anterior segment using a noncontact method. It provides anterior and posterior surface topography of the cornea that is derived from true elevation measurements. Approximately 25 000 data points are used to calculate topographic corneal thickness, corneal curvature, anterior chamber angle, volume, and height. Pachymetry and topography of the entire anterior and posterior surface of the cornea from limbus to limbus are calculated and displayed. Keratoconus detection maps may be generated to assist in the classification and diagnosis of keratoconus prior to contact lens fitting or refractive surgery. Zernike wavefront representation of the anterior and posterior surface of the cornea may be calculated based on the measured height data. In this presentation the clinical applications and limitations of Scheimpflug imaging will also be discussed.

Composition of sharp-focused image by rotation of Scheimpflug camera

A Scheimpflug camera has an image sensor tilted intentionally with respect to the lens. As the sensor and the lens are not parallel, the sharp-focused subject plane is slanted with respect to the camera according to the lens formula; this is known as the Scheimpflug principle. Therefore, if the camera is rotated about the optical axis, the sharp-focused plane covers a volume of the subject space. In this study, an application of the Scheimpflug camera is proposed to obtain a sharp-focused image with an extended depth of field (DOF) everywhere in the image. Off-the-shelf optical parts are used to implement the camera. A set of images are acquired by rotating the camera about an optical axis and the sharp-focused image is composed by selecting the focused pixels in the set of original images based on the focus measure. The experimental results show that the final composed image has a sharp focus in every region although each original image has a regional blur in the image plane. The focus measure of the composed image is 3–4 times higher than that of the original images.

Multispectral Scheimpflug: Imaging Degraded Books That Open less Than 30 Degrees

This paper presents an imaging system that reads texts from books that open less than 30 degrees (due to their fragile bindings) and whose paper quality is degraded. In particular, the system operates on the Scheimpflug principle to correct the geometric distortion necessarily introduced when imaging barely open books. We introduce the guiding principles behind such a system, discuss how it is calibrated and set up, present the results of imaging two dime novels from early twentieth century, both with fragile bindings, and discuss lessons we learned.

Microscopic fringe projection profilometry systems in Scheimpflug condition and performance comparison

The high-frequency fringe images provided by magnifying lenses with low distortion render the microscopic fringe projection profilometry (MFPP) with better measurement accuracy. In order to extend the depth of field limited in the microscopic environment, the Scheimpflug principle is commonly used in both single-camera-based and multi-camera-based MFPP systems by increasing the mutual overlap range of different views in the object space. In this paper, to compare the performance of single-camera-based and dual-camera-based MFPP systems, we set up MFPP systems and performed 3D measurements of plates, standard balls, and some specifically designed samples. By analyzing the various factors affecting measurement accuracy and integrity, we verified and concluded that the dual-camera-based system wins in measurement accuracy while the single-camera-based system has better integrity, which may provide a reference for the system design in the implementation of industrial applications.

Crosstalk reduction in tabletop multiview display with fog screen

Fog screens offer a great advantage to be used as scattering screens in three-dimensional displays. In the absence of a fixed rigid form, fog screens work as screens without any physical obstruction. The density of water droplets can be regulated to adjust the screen's transparency and scattering level. This study proposes a method for crosstalk reduction between adjacent viewing windows by decreasing the divergence of view of the projector, with concentration lenses. By applying the Scheimpflug principle, we also reduce the keystone effect, which occurs when the fog screen is slanted with respect to the optical axis. In this study, we have realized a tabletop multiview fog display without any structures on the table and established that the proposed method is feasible for decreasing crosstalk effectively.

In situ size and motility measurement of aquatic invertebrates with an underwater stereoscopic camera system using tilted lenses

Abstract In situ observation of traits of aquatic organisms, including size and motility, requires three‐dimensional measurements that are commonly done with a stereoscopic imaging system. However, to observe traits of small aquatic invertebrates, the imaging system requires relatively high magnification, which results in a small overlapping volume between the two cameras of a conventional stereoscopic system. The provision of a larger shared volume would therefore be of great advantage, especially, when the organism abundance is low. We implement a stereoscopic system that utilizes a tilted lens approach, known as the Scheimpflug principle, to increase the common imaging volume of two cameras. The system was calibrated and tested in the laboratory and then deployed in a saltmarsh to observe water boatmen Trichocorixa californica. Processing of the image data from the field deployments resulted in the simultaneous estimation of the traits of body length and swimming speed of the aquatic insects. Our stereo setup with tilted lenses increased the sampling volume by 3.1 times compared to a traditional stereo setup with the same optical parameters. The in situ data and subsequent processing reveal that the instrument can capture stereoscopic images that resolve both body length and swimming speed of the aquatic insects. Results indicate that the relationship between the body length and the swimming speed of the water boatmen is linear in the log–log space with an exponent of . Furthermore, the insects experience Reynold's number in the range of –. Our results demonstrated that the system can be used to observe key traits of small aquatic organisms in an ecologically relevant context. This work expands the capability of underwater imaging systems to measure important traits of an individual aquatic invertebrate in its natural environment and aids in providing a trait‐based approach to zooplankton ecology.

Stereo digital image correlation with improved depth of field using tilt-shift photography

Stereo digital image correlation (DIC) is a non-contacting technique to obtain full-field displacement and strain fields from the surface of a deforming object by comparing images recorded before and after deformation. With stereo measurement techniques, out-of-plane measurements are often limited by the depth of field achieved in an image. Tilt-shift photography uses the Scheimpflug principle to improve depth of field by rotating the image plane with respect to the camera sensor. This is implemented using a tilt-shift lens mount, which imposes an angle of tilt between the lens and the camera sensor. In this stereo-DIC study, images were taken using a range of stereo camera angles with either the lens tilted or not tilted to impose the Scheimpflug effect. A series of rigid body displacements were then measured for each combination of stereo and tilt angles. An evaluation of the means and standard deviations of the measurements shows that Scheimpflug adjustment offers minimal improvement when measuring rigid body displacements, but significant improvement at reducing artificial strains.

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.

Real-time line-structured light measurement system based on Scheimpflug principle

Real-time line-structured light measurement system based on Scheimpflug principle

Design method for the high optical efficiency and uniformity illumination system of the projector.

How to balance the optical efficiency, illumination uniformity and the size of the illumination system is a challenging task in projector design. In this paper, we present a mathematical model describing the relationship between optical energy of the illumination system and the optical parameters and an optimization design method considering the light intensity distribution of the light source. By using the proposed method, two illumination systems are designed with different types of the digital micromirror device chips. In addition, we also propose a non-coaxial system to solve the deformation problem caused by the large flip angle of the DMD chip and further improve the illumination uniformity based on Scheimpflug principle. The optical efficiency and illumination uniformity of the illumination systems were verified and analyzed. The results indicate that the systems designed by the proposed method can provide a good design scheme and obtain a satisfactory utilization rate of the optical energy and higher uniformity.

Corneal Biomechanical Assessment with Ultra-High-Speed Scheimpflug Imaging During Non-Contact Tonometry: A Prospective Review.

BackgroundIn recent years, increasing interest has arisen in the application of data from corneal biomechanics in many areas of ophthalmology, particularly to assist in the detection of early corneal ectasia or ectasia susceptibility, to predict corneal response to surgical or therapeutic interventions and in glaucoma management. Technology has evolved and, recently, the Scheimpflug principle was associated with a non-contact air-puff tonometer, allowing a thorough analysis of corneal biomechanics and a biomechanically corrected intraocular pressure assessment, opening up new perspectives both in ophthalmology and in other medical areas. Data from corneal biomechanics assessment are being integrated in artificial intelligence models in order to increase its value in clinical practice.ObjectiveTo review the state of the art in the field of corneal biomechanics assessment with special emphasis to the technology based on ultra-high-speed Scheimpflug imaging during non-contact tonometry.SummaryA meticulous literature review was performed until the present day. We used 136 published manuscripts as our references. Both information from healthy individuals and descriptions of possible associations with systemic diseases are described. Additionally, it exposed information regarding several fields of ocular pathology, from cornea and ocular surface through areas of refractive surgery and glaucoma until vascular and structural diseases of the chorioretinal unit.

Evaluation of systematic errors for the continuous-wave NO2 differential absorption lidar employing a multimode laser diode.

The NO2-differential absorption lidar (NO2-DIAL) technique has been of great interest for atmospheric NO2 profiling. Comprehensive studies on measurement errors in the NO2-DIAL technique are vital for the accurate retrieval of the NO2 concentration. This work investigates the systematic errors of the recently developed continuous-wave (CW) NO2-DIAL technique based on the Scheimpflug principle and a high-power CW multimode laser diode. Systematic errors introduced by various factors, e.g., uncertainty of the NO2 differential absorption cross-section, differential absorption due to other gases, spectral drifting of the λon and λoff wavelengths, wavelength-dependent extinction and backscattering effect, have been theoretically and experimentally studied for the CW-DIAL technique. By performing real-time spectral monitoring on the emission spectrum of the laser diode, the effect of spectral drifting on the NO2 differential absorption cross-section is negligible. The temperature-dependent NO2 absorption cross-section in the region of 220-294 K can be interpolated by employing a linear fitting method based on high-precision absorption spectra at 220, 240, and 294 K. The relative error for the retrieval of the NO2 concentration is estimated to be less than 0.34% when employing the interpolated spectrum. The primary interference molecule is found to be the glyoxal (CHOCHO), which should be carefully evaluated according to its relative concentration in respect to NO2. The systematic error introduced by the backscattering effect is subjected to the spatial variation of the aerosol load, while the extinction-induced systematic error is primarily determined by the difference between the aerosol extinction coefficients at λon and λoff wavelengths. A case study has been carried out to demonstrate the evaluation of systematic errors for practical NO2 monitoring. The comprehensive investigation on systematic errors in this work can be of great value for future NO2 monitoring using the DIAL technique.