Specular Reflectance Properties Research Articles

An effective MID-based visual defect detection method for specular car body surface

The quality control of car body surfaces is one of the most important tasks in automotive manufacturing, which can directly affect the appearance of cars and purchasing experience of consumers. However, current car body defect detection methods rely mostly on manual inspection, which is subjective, inaccurate, and labor intensive. One of the biggest challenges of automated defect detection is that the specular reflection properties of car body surfaces make obtaining high-quality defect images extremely difficult. This article proposes a novel method called modulated intensity decoding (MID), in which preset encoded fringe patterns are projected onto the surface of a car body, and a camera is used to capture images after the patterns are reflected by the surface. By decoding the captured reflection images, high-quality surface defective decoded (SDD) images are obtained, which preserve the appearance of the defects and effectively highlight the defects against the background. Comparison experiments are performed on detecting and classifying the car body surface defects using four typical object detection networks to demonstrate the effectiveness of the proposed method. The results indicate that our method is far superior to that of conventional approaches using a square-wave-like-pattern light source.

A Method for Point Cloud Accuracy Analysis Based on Intensity Information.

Three-dimensional laser scanning has emerged as a prevalent measurement method in numerous high-precision applications, and the precision of the obtained data is closely related to the intensity information. Comprehending the association between intensity and point cloud accuracy facilitates scanner performance assessment, optimization of data acquisition strategies, and evaluation of point cloud precision, thereby ensuring data reliability for high-precision applications. In this study, we investigated the correlation between point cloud accuracy and two distinct types of intensity information. In addition, we presented methods for assessing point cloud accuracy using these two forms of intensity information, along with their applicable scopes. By examining the percentage intensity, we analyzed the reflectance properties of the scanned object's surface employing the Lambertian model. Our findings indicate that the Lambertian circle fitting radius is inversely correlated with the scanner's ranging error at a constant scanning distance. Experimental outcomes substantiate that modifying the surface characteristics of the object enables the attainment of higher-precision point cloud data. By constructing a model associating the raw reflectance intensity with ranging errors, we developed a single-point error ellipsoid model to assess the accuracy of individual points within the point cloud. The experiments revealed that the ranging error model based on the raw intensity is solely applicable to point cloud data unaffected by specular reflectance properties. Moreover, the devised single-point error ellipsoid model accurately evaluates the measurement error of individual points. Both analytical methods can be utilized to evaluate the performance of the scanner as well as the accuracy of the acquired point cloud data, providing reliable data support for various high-precision applications.

Morphological, optical and electrochemical properties of tin(II) 2,3-naphthalocyanine for organic electronic applications

Herein, tin(II) 2,3-naphthalocyanine (SnNC) organic dye was successfully thermally deposited onto different optical transparent substrates such as glass, quartz, ITO, and FTO. FE-SEM technique reveals that SnNC film shows a uniform and symmetrical spherical-shaped with an average diameter of ∼50 nm. Annealing up to 473 K for 4 h increases the crystallite size of SnNC thin film. SnNC thin film shows absorption bands centered at 858 nm, 313 nm, and 249 nm with two shoulders at 775 nm and 350 nm. We present the absorbance, specular transmittance, specular reflectance and fluorescence properties of SnNc deposited on the different transparent substrates. The oscillator strengths (f) and the electric dipole strength (q2) of SnNC thin film were estimated from the molar absorptivity () spectra. According to the Tauc model, two optical gap transitions were estimated as 1.03 eV and 3.48 eV. Annealing up to 473 K for 4 h slightly increases them to 1.15 eV and 3.59 eV, respectively. At excitation wavelength = 360 nm, two emission bands were observed at around 403 nm and 674 nm. Upon annealing at 373 K and 473 K, the real part of the refractive index of SnNC thin film decreases, which is correlated with a decrease in mass density. Electrochemical HOMO—LUMO band gaps of SnNC estimated from the cyclic voltammetry (CV) measurements () agree well with the observed optical energy gap estimated from the optical measurements. The wide range absorption, emission, good thermal stability, suitable optical band gap, and electrochemical properties, prove an effective example of organic dye suitable for organic electronic applications.

Improved structured light system based on generative adversarial networks for highly-reflective surface measurement

Gray code pattern structured light projection technology is widely used in industrial inspection due to its good robustness and anti-noise performance. Gray code pattern technology projects a sequence of encoded fringe patterns with black and white strips onto the scanned object in order to measure its height distribution. However, if the scanned object has strong specular reflection properties, the acquired encoded fringe images tend to miss significant amounts of local area information. As a result, the measured three-dimensional point clouds contain many missing points, and hence the measurement accuracy is severely degraded. To address this problem, the present study proposes a novel fringe-inpainting system based on a generative adversarial network framework, to repair the fringe features in the regions of the scanned surface in which the local information is lost. The performance of the proposed fringe-inpainting system is compared with that of several other advanced highly-reflective surface measurement technologies reported in the literature. The experimental results show that the proposed method significantly outperforms these techniques and yields an excellent encoded fringe inpainting for all of the considered objects.

Quantification of supplied laser energy and its relationship with powder melting process in PBF-LB/P using near-infrared laser

This study discusses the quantitative understanding of the laser input energy considering the optical properties and its effect on the melting process of powder materials in PBF-LB/P using a near-infrared laser. With the increased use of near-infrared lasers for PBF-LB/P in recent years, the influence of the input energy loss due to transmission and reflection on the powder melting process must be considered. Therefore, the modified energy melt ratio (Modified EMR), which is the ratio of the input energy to the energy required to melt the powder material, was proposed as a new energy supply index in this study. The energy absorbed by the powder layer was estimated from the transmission and diffuse reflection properties obtained in a previous study and the specular reflection properties obtained in this study. The powder layer thickness was determined by considering the consolidation of the powder layer, which affected the optical properties. The parts were fabricated with various optical properties, powder bed temperatures, and input energies to evaluate part density, which is closely related to the melting process. Compared to conventional indices, such as the energy density or EMR, the relationship between the Modified EMR and part density was more consistent, regardless of the optical properties and powder bed temperature. This study also investigated the effect of the laser heating of the layer below the powder layer on the melting process of the powder layer. The optical properties of a thin plate simulating the underlying layer were obtained, and the temperature increase in the underlying layer was determined from the known transmittance of the powder layer. It was concluded that heating the underlying layer does not accelerate the melting of the powder layer even at low powder bed temperatures, which require the highest laser energy for melting the powder material.

Optical design of photometric techniques for specular reflection

Photometric techniques are one of the three-dimensional image reconstruction technologies. It is used in various fields, especially surface analysis because it focuses on extracting surface information such as texture and color. Photometric techniques perform the 3D reconstruction using light sources and a camera. If the object has specular reflection properties, then an error may occur in the reconstructed data according to the noise of intensity in acquired images. For the solution of these problems, the optical system is configurated by dome light and coaxial light, and the non-uniformity area is defined and is derived by mathematical formulas in this paper. In order to verify the validity of the formulas, various simulations and experiments have been conducted. As a result, it was confirmed that the proposed optical design method could be used as a new technique for the uniform optical system.

Wave-based non-line-of-sight imaging using fast f-k migration

Imaging objects outside a camera's direct line of sight has important applications in robotic vision, remote sensing, and many other domains. Time-of-flight-based non-line-of-sight (NLOS) imaging systems have recently demonstrated impressive results, but several challenges remain. Image formation and inversion models have been slow or limited by the types of hidden surfaces that can be imaged. Moreover, non-planar sampling surfaces and non-confocal scanning methods have not been supported by efficient NLOS algorithms. With this work, we introduce a wave-based image formation model for the problem of NLOS imaging. Inspired by inverse methods used in seismology, we adapt a frequency-domain method, f-k migration, for solving the inverse NLOS problem. Unlike existing NLOS algorithms, f-k migration is both fast and memory efficient, it is robust to specular and other complex reflectance properties, and we show how it can be used with non-confocally scanned measurements as well as for non-planar sampling surfaces. f-k migration is more robust to measurement noise than alternative methods, generally produces better quality reconstructions, and is easy to implement. We experimentally validate our algorithms with a new NLOS imaging system that records room-sized scenes outdoors under indirect sunlight, and scans persons wearing retroreflective clothing at interactive rates.

15‐1: Application of the Optical Measurement Methodologies of IEC and ISO Standards to Reflective E‐Paper Displays

This paper explores applying the optical characterization methodologies in IEC 62679 and ISO 9241 to reflective e‐paper displays (EPDs). Measurements of specular and diffuse reflection properties are presented. Simulations and measurements show that EPDs fulfill the ISO requirements for minimum contrast ratio over a wide range of illumination conditions.

Experimental and rendering-based investigation of laser radar cross sections of small unmanned aerial vehicles

Laser imaging systems are prominent candidates for detection and tracking of small unmanned aerial vehicles (UAVs) in current and future security scenarios. Laser reflection characteristics for laser imaging (e.g., laser gated viewing) of small UAVs are investigated to determine their laser radar cross section (LRCS) by analyzing the intensity distribution of laser reflection in high resolution images. For the first time, LRCSs are determined in a combined experimental and computational approaches by high resolution laser gated viewing and three-dimensional rendering. An optimized simple surface model is calculated taking into account diffuse and specular reflectance properties based on the Oren–Nayar and the Cook–Torrance reflectance models, respectively.

Probabilistic mapping of flood-induced backscatter changes in SAR time series

The information content of flood extent maps can be increased considerably by including information on the uncertainty of the flood area delineation. This additional information can be of benefit in flood forecasting and monitoring. Furthermore, flood probability maps can be converted to binary maps showing flooded and non-flooded areas by applying a threshold probability value pF=0.5. In this study, a probabilistic change detection approach for flood mapping based on synthetic aperture radar (SAR) time series is proposed. For this purpose, conditional probability density functions (PDFs) for land and open water surfaces were estimated from ENVISAT ASAR Wide Swath (WS) time series containing >600 images using a reference mask of permanent water bodies. A pixel-wise harmonic model was used to account for seasonality in backscatter from land areas caused by soil moisture and vegetation dynamics. The approach was evaluated for a large-scale flood event along the River Severn, United Kingdom. The retrieved flood probability maps were compared to a reference flood mask derived from high-resolution aerial imagery by means of reliability diagrams. The obtained performance measures indicate both high reliability and confidence although there was a slight under-estimation of the flood extent, which may in part be attributed to topographically induced radar shadows along the edges of the floodplain. Furthermore, the results highlight the importance of local incidence angle for the separability between flooded and non-flooded areas as specular reflection properties of open water surfaces increase with a more oblique viewing geometry.

Tailored specular reflectance properties of bulk Cu based novel intermetallic alloys

Significant research has been pursued to develop solar selective metallic coatings using a variety of coating deposition techniques, with limited attempts to assess the properties of bulk metallic materials for solar energy applications. In developing bulk solar reflectors with good reflectance in the entire solar range, we report a new class of reflector materials based on Cu–Sn intermetallics with tailored substitution of aluminium or zinc. Our experimental results suggest that the arc melted–suction cast Cu (78.8at%)–Al (21.2at%) alloy with nanoscale surface roughness can exhibit a combination of 89% bulk specular reflectance and 83% bulk solar reflectance, together with a hardness of 2GPa. We show that the present alloy design approach paves the way for further opportunities of tuning the spectral properties of this new class of solar reflector material.

Progressive transition from resonant to diffuse reflection in anisotropic colloidal films

ABSTRACTThe synthesis and characterization of highly ordered three‐dimensional photonic crystals have been the subjects of intense study over the past two decades due to the unique ability of these structures to control light at the nanoscale. Building on that work in recent years, increasing interest is now focused on the unique optical properties of disordered and quasi‐ordered photonic structures. We present a study of the effects of shape anisotropy and disorder on the specular reflection properties of polymer‐based colloidal films comprised of rod‐shaped subunits of varying aspect ratio. We characterize the specular reflectance properties of these films as a function of their increasing levels of disorder, demonstrating progressive transition from resonant reflection to diffuse reflection. The onset of the diffuse reflection is governed by particle size. © 2014 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys. 2014, 52, 611–617

Inverse Rendering of Faces with a 3D Morphable Model

In this paper, we present a complete framework to inverse render faces with a 3D Morphable Model (3DMM). By decomposing the image formation process into geometric and photometric parts, we are able to state the problem as a multilinear system which can be solved accurately and efficiently. As we treat each contribution as independent, the objective function is convex in the parameters and a global solution is guaranteed. We start by recovering 3D shape using a novel algorithm which incorporates generalization error of the model obtained from empirical measurements. We then describe two methods to recover facial texture, diffuse lighting, specular reflectance, and camera properties from a single image. The methods make increasingly weak assumptions and can be solved in a linear fashion. We evaluate our findings on a publicly available database, where we are able to outperform an existing state-of-the-art algorithm. We demonstrate the usability of the recovered parameters in a recognition experiment conducted on the CMU-PIE database.

Variational estimation of inhomogeneous specular reflectance and illumination from a single view

Estimating the illumination and the reflectance properties of an object surface from a few images is an important but challenging problem. The problem becomes even more challenging if we wish to deal with real-world objects that naturally have spatially inhomogeneous reflectance. In this paper, we derive a novel method for estimating the spatially varying specular reflectance properties of a surface of known geometry as well as the illumination distribution of a scene from a specular-only image, for instance, recovered from two images captured with a polarizer to separate reflection components. Unlike previous work, we do not assume the illumination to be a single point light source. We model specular reflection with a spherical statistical distribution and encode its spatial variation with a radial basis function (RBF) network of their parameter values, which allows us to formulate the simultaneous estimation of spatially varying specular reflectance and illumination as a constrained optimization based on the I-divergence measure. To solve it, we derive a variational algorithm based on the expectation maximization principle. At the same time, we estimate optimal encoding of the specular reflectance properties by learning the number, centers, and widths of the RBF hidden units. We demonstrate the effectiveness of the method on images of synthetic and real-world objects.

Using specularities in comparing 3D models and 2D images

We aim to create systems that identify and locate objects by comparing known, 3D shapes to intensity images that they have produced. To do this we focus on verification methods that determine whether a known model in a specific pose is consistent with an image. We build on prior work that has done this successfully for Lambertian objects, to handle a much broader class of shiny objects that produce specular highlights. Our core contribution is a novel method for determining whether a known 3D shape is consistent with the 2D shape of a possible highlight found in an image. We do this using only a qualitative description of highlight formation that is consistent with most models of specular reflection, so no specific knowledge of an object’s specular reflectance properties is needed. This allows us to treat non-Lambertian image effects as a positive source of information about object identity, rather than treating them as a potential source of noise. We then show how to integrate information about highlights into a system that also checks the consistency of Lambertian reflectance effects. Also, we show how to model Lambertian reflectance using a reference image, rather than albedos, which can be difficult to measure in shiny objects. We test each aspect of our approach using several different data sets. We demonstrate the potential value of our method of handling specular highlights by building a system that can locate shiny, transparent objects, such as glassware, on table tops. We demonstrate our hybrid methods on pottery, and our use of reference images with face recognition experiments.

Reflectance modeling for a textured object under uncontrolled illumination from high dynamic range maps

During the past several years, considerable work has been presented on the methods for measuring and modeling the observed reflectance properties of materials. However, most of these works have been done under controlled lighting configurations, and require a constant bidirectional reflectance distribution function (BRDF), which is a measure of the amount of light scattered by a medium from one direction into another, or a homogeneous material over the object regions. This paper discusses a method to estimate the reflectance properties of a textured object under uncontrolled illumination. Assuming that the object has a constant specular reflectance property over its surface, the BRDF can be approximated as a constant specular component and a spatially varying diffuse component. The proposed method will first approximate the illumination distribution of a scene from a set of high dynamic range (HDR) radiance maps of a light probe. Next, a patch on the surface of an object is selected; several HDR intensity maps of the patch taken under different viewing conditions are used to estimate the average specular reflectance parameters of this patch. With the separation of the specular component and the diffuse component of each sample, and using the separated diffuse component, the diffuse reflectance parameters for each point over the surface are next estimated. The test results show that the method is effective for textured objects with constant specular reflectance properties. The method can also be directly applied to objects with piecewise-smooth material, which means that although the surface of an object does not have a constant specular reflectance property; when sub-divided into many smaller meshes, the specular parameter of each mesh can be regarded as uniform.

Measurement of Differential Gloss Using a μ-Goniophotometer

Differential gloss is the term used in print media to describe the condition where areas of a printed image, especially adjacent areas, appear to reflect light in different ways giving these areas varying gloss appearance. This phenomenon is quite common in dry toner electrophotographic imaging and some ink jet imaging technologies where the first surface reflection properties of the toner or ink and the substrate can be markedly different. Also, high density areas composed of multiple layers of toner can have substantially different specular reflection properties than low density areas composed of a sparse layer of toner through which areas of substrate remain visible. Differential gloss, while well known, is difficult to quantify in a meaningful way. Recently, a pilot experiment was conducted that indicated that it may be possible to quantify gloss artifacts using a device called a μ-goniophotometer. This device, previously described in detail in the literature, measures specular reflection at all angles, not just the one equal and opposite angle to the light source as is done with a traditional glossmeter. This device creates a curve or Bi-directional Reflectance Distribution Function (BRDF) for the sample measured. Because it also generates a series of these curves along the length of the sample, a quantification of the variability of the measured specular light, σ, is available. It was this variability that was found to relate to the degree of gloss artifact detected by observers, on average, in flat field images. And it is this variability that was posited to serve as a function of the degree of differential gloss apparent in an image. In the first steps toward testing this theory, experimentation was conducted involving the measurement of patches. The patches were created in conjunction with a differential gloss scaling experiment conducted by the W1.1 Committee on Perceptual Measurement of Gloss. Prints of three scenes were made on equipment exhibiting a range of differential gloss behavior. The prints were visually scaled by observers in several locations across the United States. To make comparative objective measurements, prints of the W1.1 Perceptual Gloss Measurement Committee's patch target were also made. An evaluation of the measured data generated using both a traditional glossmeter as well as the μ-goniophotometer relative to the visual data will be described.

G225 シリカマイクロ粒子最密構造の赤外線反射特性(ふく射)

The reflection property of the close-packed structure of silica micro-spheres consists of specular and diffuse component. The characteristic of close-packed structure appears in specular component. On the other hand, the particulate systems exhibit scattering property. In this paper, the specular and diffuse reflection properties of the close-packed structure assembled with 3μm silica micro-spheres are investigated. The experimental setup is developed for the measurement of spectral reflectance. The measurement is carried out by using an FT-IR spectrometer. The specular component of spectral reflectance is compared with previous experimental result measured by microscopic FT-IR spectrometer. The diffuse reflection is observed blow 5μm in wavelength.

360° shape measurement system for objects having from Lambertian to specular reflectance properties utilizing a novel rangefinder

This paper describes a 360° shape measurement system for objects with various reflectance properties. To date, ordinary laser rangefinding techniques have rarely been used to measure objects having specular reflectance. The ordinary rangefinder is also difficult to apply to objects having hybrid reflectance, i.e. those whose reflectance properties lie between Lambertian and specular. We previously proposed a rangefinder that can be applied to specular objects. The concept of that rangefinder involved the use of a light-stripe projected at a constant incident angle upon the image sensor through the use of shield masks. We propose here a new rangefinder which improves on the previous rangefinder. The main improvements are the placement of a field stop using multiple slits, automatically controlled scanning of the light source, and an automatic gain control for the image sensor. As a result, the new rangefinder allows the automatic measurement of the 360° shapes of objects exhibiting both hybrid reflectance and non-uniform reflectance. We constructed a prototype automatic 360° shape measurement system which utilizes the proposed rangefinder. The experimental results demonstrate that the system can measure the shapes of hybrid objects with almost the same level of accuracy as it can those of Lambertian objects and specular objects. The proposed rangefinder is especially valuable for industrial purposes, since it assures consistent accuracy and high reliability even for objects with unknown reflectance properties.

Texture histograms as a function of irradiation and viewing direction

The textural appearance of materials encountered in our daily environment depends on two directions, the irradiation and viewing direction. We investigate the bidirectional grey level histograms of a large set of materials, obtained from a texture database. We distinguish important categories, relate the various effects to physical mechanisms, and list material attributes that influence the bidirectional histograms. We use a model for rough surfaces with locally diffuse and/or specular reflection properties, a class of materials that commonly occurs, to generate bidirectional histograms and obtain close agreement with experimental data. We discuss several applications of bidirectional texture functions and histograms. In particular, we present a new approach to texture mapping based on bidirectional histograms. For 3D texture, this technique is superior to standard 2D texture mapping at hardly any extra computational cost or memory requirements.