Three-dimensional Fringe Research Articles

Study on gamma correction for three-dimensional fringe projection measurement based on attention U-Net network

Study on gamma correction for three-dimensional fringe projection measurement based on attention U-Net network

In vitro and in vivo validation of a new three-dimensional fringe projection-based device (AEVA-HE) dedicated to skin surface mapping.

Aging signs are much visible on the surface of the skin that presents different changes: cheeks start to sag, more and deeper wrinkles appear, and pigmentation spotsincrease.Face diagnostic torecommend products includes assessingcutaneous micro-reliefor themicro-depressive networkon the face.Furthermore,there is anincreasing demand for clinical and instrumental methods to provetheefficacy ofanti-agingtreatments.As a result,very accurate and sensitive three-dimensional (3D) devicesare developedand validatedto measure and quantify aging skin andto catch fine anti-aging productsacting on wrinklesand fine lines. AEVA-HE,anon-invasive3Dmethodbased onfringe projectiontechnology, is used to robustly characterize theskinmicro-relieffrom afull-faceacquisitionandfrommultipleextractedzonesof interest.In vitro and in vivo studiesare conductedtoassessthe reproducibility of this systemandits precision towarda standard fringe projection system,DermaTOP. TheAEVA-HEsuccessfully measuredmicro-relief and wrinklesand demonstrated the reproducibility of measurements. AEVA-HEparameters were found highly correlated toDermaTOP. The present work illustrates theperformance of theAEVA-HEdevice and its dedicatedsoftwarekitasa precious tool for quantifying themajor characteristics ofwrinklesappearingwith ageandthus offersa high potential forassessing the effect of anti-wrinkling products.

Single-shot detection of 8 unique monochrome fringe patterns representing 4 distinct directions via multispectral fringe projection profilometry

Spatial resolution in three-dimensional fringe projection profilometry is determined in large part by the number and spacing of fringes projected onto an object. Due to the intensity-based nature of fringe projection profilometry, fringe patterns must be generated in succession, which is time-consuming. As a result, the surface features of highly dynamic objects are difficult to measure. Here, we introduce multispectral fringe projection profilometry, a novel method that utilizes multispectral illumination to project a multispectral fringe pattern onto an object combined with a multispectral camera to detect the deformation of the fringe patterns due to the object. The multispectral camera enables the detection of 8 unique monochrome fringe patterns representing 4 distinct directions in a single snapshot. Furthermore, for each direction, the camera detects two π-phase shifted fringe patterns. Each pair of fringe patterns can be differenced to generate a differential fringe pattern that corrects for illumination offsets and mitigates the effects of glare from highly reflective surfaces. The new multispectral method solves many practical problems related to conventional fringe projection profilometry and doubles the effective spatial resolution. The method is suitable for high-quality fast 3D profilometry at video frame rates.

Lens aberration compensation in interference microscopy

Emergence of products that feature functional surfaces with complex geometries, such as freeform optics in consumer electronics and augmented reality and virtual reality, requires high-accuracy non-contact surface measurement. However, large discrepancies are often observed between the measurement results of optical methods and contact stylus methods, especially for complex surfaces. For interference microscopy, such as coherence scanning interferometry, the three-dimensional surface transfer function provides information about the instrument spatial frequency passband and about lens aberrations that can result in measurement errors. Characterisation and phase inversion of the instrument's three-dimensional surface transfer function yields an inverse filter that can be applied directly to the three-dimensional fringe data. The inverse filtering is shown to reduce measurement errors without using any data processing or requiring any a priori knowledge of the surface. We present an experimental verification of the characterisation and correction process for measurements of several freeform surfaces and an additive manufactured surface. Corrected coherence scanning interferometry measurements agree with traceable contact stylus measurements to the order of 10 nm.

Phase-matching method based on optimization function for three-dimensional fringe projection

An optimization function-based phase-matching method is proposed for the three-dimensional (3-D) fringe projection method. As an essential procedure in 3-D fringe projection metrology, the phase-matching processing has a significant influence on the measurement accuracy. The traditional phase-matching method obtains the corresponding points in different images by comparing the phase-values directly, so its matching precision is easily affected by the phase-measurement error. The proposed method determines the corresponding points automatically and accurately by minimizing the cost function represented by the absolute phase values. The cost function consists of two parts: one for calculating the squared difference of the absolute phase to ensure matching precision, and the other is selected to guarantee optimization convergence. A series of experiments enable us to analyze the precision and effectiveness in practical application.

A finite element analysis of initial stresses and displacements in the tooth and the periodontium in periodontally compromised simulations: Labial versus lingual force application

Introduction: Orthodontics a unique branch in dentistry is inter-related with biology, mathematics and engineering sciences. Biomechanics is fundamental to the practice of orthodontics. Stresses generated at any point during orthodontic treatment are critical in remodeling of bone and type of tooth movement. Aims and Objectives: The aim of the following study is to determine the initial stresses produced in the tooth, periodontal ligament (PDL) and bone when force is applied on the tooth for intrusion and tipping on labial and lingual sides in the presence of varying alveolar bone heights. Materials and Methods: A geometric model generated using AutoCAD (Autodesk, Inc.). Six three-dimensional finite element models of a maxillary central incisor were designed with PDL and varying alveolar bone heights after applying the boundary conditions of the model, force was applied on the tooth. Results: Results were obtained with color coded three-dimensional fringe patterns. Conclusion: Alveolar bone loss causes an increase in the maximum initial stresses relative to the bone heights.

Experimental testing of impact limiters for RAM packages under drop test conditions

In context with new cask designs and their approval procedure, the experimental testing of impact limiters under drop test conditions becomes more and more important in order to assess the damage mechanics behaviour and safety margins for validation reasons. In recent years, various designs of impact limiters have been tested by the Federal Institute for Materials Research and Testing within specific component testing and particularly with regard to type B package design approval procedures. The paper focuses on the experimental realisation of impact limiter tests and presents implemented measurement techniques to determine the amount of deformation and to explain the impact behaviour by means of photogrammetric metrology and three-dimensional fringe projection method, high speed motion analysis and adjusted deceleration measurements.

Quantification of Age-Related Facial Wrinkles in Men and Women Using a Three-Dimensional Fringe Projection Method and Validated Assessment Scales

Whereas the molecular mechanisms of skin aging are well understood, little information is available concerning the clinical onset and lifetime development of facial wrinkles. To perform the first systematic evaluation of the lifetime development of facial wrinkles and sex-specific differences using three-dimensional (3D) imaging and clinical rating. 200 men and women aged 20 to 70 were selected. Wrinkle severity of periorbital, glabellar, and forehead lines was evaluated using 3D imaging and validated assessment scales. Wrinkle severity was greater at all assessed locations with older age. In men, wrinkles manifested earlier and were more severe than in women. In women, periorbital lines were the first visible wrinkles, in contrast to the forehead lines in men. In both sexes, glabellar lines did not clinically manifest before the age of 40. The results of the present study confirm a progressive increase of crow's feet and forehead and glabellar lines in men and women. Although the development of facial wrinkles happens earlier and is more severe in men, perimenopause seems to particularly affect development in women. Clinical ratings and 3D measurements are suitable methods to assess facial wrinkle severity in men and women.

Pulse-width modulation in defocused three-dimensional fringe projection

Shape measurements by fringe projection methods require high-quality sinusoidal fringes. We present a sinusoidal fringe generation technique that utilizes slightly defocused binary fringe projection. The proposed method is a spatial version of the well-known pulse-width modulation (PWM) technique of electrical engineering. PWM is easy to implement using off-the-shelf projectors, and it allows us to overcome the gamma problem (i.e., the nonlinear projector response) in the output light intensity. We will demonstrate that, with a small defocusing level--lower than with other techniques proposed in the literature--a high-quality sinusoidal pattern is obtained. Validation experiments using a commercial video projector are presented.

Spherical Gaussian beam model for prediction of three-dimensional fringe patterns in a laser Doppler anemometer measuring volume

A general and rigorous spherical Gaussian beam model is introduced to predict the threedimensional fringe field based on the paraxial approximation for Gaussian beams. It has been proved that for any dual-beam LDA system with the knowledge of beam cross-angle, waist locations and sizes, the interfering surfaces and the fringe spacings can be obtained by directly solving the phase condition equation in which all the phase terms including the Guoy phase shift are taken into account. As examples, computations were carried out for typical configurations including those with initial phase difference, partial intersection and different waist sizes. The results which are presented in graphical form, for the first time, reveal the detailed three-dimensional fringe fields formed by the interference of two Gaussian beams.