Specular Reflection Components Research Articles

Single Image Highlight Removal for Real-Time Image Processing Pipelines

This paper presents a fully automatic method for the separation of diffuse and specular reflection components from a single image. Overall, the mechanisms in which the available methods operate on are computationally costly and do not translate well to modern hardware-implemented image processing pipelines, such as the ones present in consumer electronics. Consequently, the objective of this article is to introduce a simple yet effective method for specular highlight removal. It is based on the dichromatic reflection model and operates through histogram matching in the YCbCr color space. The proposed method performs in real-time. It only uses global image statistics and point-wise intensity transformations. Experimental evaluation shows that the proposed approach has competitive results in comparison to state-of-the-art methods. Limitations of the proposed approach are seldom and are common to most methods available. The proposed method, however, achieves better quality results with much less computational cost, thus enabling feasibility in systems with limited processing power.

Enhancement characteristics of laser-induced plasma confined by hemispherical cavities in different materials

A hemispherical cavity can be used to improve the sensitivity of laser-induced breakdown spectroscopy by increasing the emission spectra of the plasma. In this work, laser-induced plasma plume images were obtained with and without confinement. The results have confirmed that the reason for the signal enhancement caused by the hemispherical cavity was the reflected shockwave “compressing” effect. The dependence of spectral signal enhancement on the material property of the cavities was investigated. Four cavities in different materials, which include K-resin, aluminum alloy, photosensitive resin and nylon, were used to confine the plasma. It has shown that the material physical properties of the cavities influence the enhancement effect. We found that the main influencing factor was surface roughness of the material. Smoother cavity surfaces induced stronger enhancement effects due to the larger specular reflection component of the reflected shockwave and the more intense subsequent interaction between the plasma and shockwave. The spectral intensities of the characteristic lines approximately doubled with surface roughness values changing from 0.2 to 16.1.

Thermal non-line-of-sight imaging from specular and diffuse reflections

This paper presents a non-line-of-sight technique to estimate the position and temperature of an occluded object from a camera via reflection on a wall. Because objects with heat emit far infrared light with respect to their temperature, positions and temperatures are estimated from reflections on a wall. A key idea is that light paths from a hidden object to the camera depend on the position of the hidden object. The position of the object is recovered from the angular distribution of specular and diffuse reflection component, and the temperature of the heat source is recovered from the estimated position and the intensity of reflection. The effectiveness of our method is evaluated by conducting real-world experiments, showing that the position and the temperature of the hidden object can be recovered from the reflection destination of the wall by using a conventional thermal camera.

Measuring, Modeling, and Reproducing Material Appearance from Specular Profile

A method is proposed for measuring, modeling, and reproducing material appearance from the specular profile representing reflectance distribution around a specular highlight. Our method is aimed at opaque materials with a highly glossy surface like plastic, ceramic, and metals. Hence, the material surface is assumed to be not a perfect mirror, but a surface with some roughness. We do not use a gonio-spectrophometer nor an image-based measurement setup. Instead, we make use of a gloss meter with a function to measure the specular profile, containing for glossy materials appearance such as roughness, sharpness, and intensity. The surface reflection is represented as a linear sum of diffuse and specular reflection components, the latter described by the Cook-Torrance model. The specular function represents the glossy surface appearance by a small number of control parameters. Mitsuba rendering system is utilized to perform the rendering algorithms. Finally, the feasibility of the proposed method is examined using different materials.

Luminance edge is a cue for glossiness perception based on low-luminance specular components.

The visual system is considered to employ various image cues from an object image to perceive its glossiness. It has been reported that, surprisingly, even for object images without specular highlights we can perceive glossiness by relying on low-luminance specular components (Kim, Marlow, & Anderson, 2012). This type of perceptual glossiness is referred to as dark gloss. However, it is still unclear whether dark gloss is observed commonly across various objects, and what image features are cues for dark gloss. To address these issues, we performed several psychophysical experiments. First, we measured perceived glossiness for a number of computer-graphics object images with natural specular reflection components (Full condition) and for those without high-luminance components of specular reflections (Dark condition). The results showed that dark gloss (glossiness perception in the Dark condition) was generally observed on almost all object images, while its intensity was rather different across the images. Then we psychologically or computationally measured several image features for the stimulus images, such as luminance edge number, recognizability of reflection images, and some highlight-related features, to examine their relations to perceived glossiness with a multiple regression analysis. The results demonstrated that luminance edge number was most strongly related to glossiness scores among the measured features only for object images with potent dark gloss. These results suggest that luminance edges are an effective cue for dark gloss under certain stimulus conditions.

Degree of polarization modeling based on modified microfacet pBRDF model for material surface

The polarized bidirectional reflectance distribution function (pBRDF) can effectively simulate the degree of polarization (DoP) characteristics of material surface. Most of the existing pBRDF models include a Lambertian constant diffuse scattering component that the scattering and absorption of light inside the material is completely ignored. In this paper, a modified microfacet pBRDF model is proposed for material surface with considering specular reflection and diffuse scattering based on the combination of the microfacet and Kubelka–Munk (K–M) theory. In this model, a scaling parameter is introduced into specular reflection component to adjust the model which contains all the polarization information, and the diffuse scattering component is depolarization modeled following the K–M theory. The expression of DoP is developed from the new pBRDF model that includes the scattering and absorption effects in bulk of material, which makes more reasonable with physical interpretation. Several experiment groups of DoP for coating samples (rough yellow and black paint) are measured by the multi-angle polarization instrument, and then, the model parameters are fitted by least square method based on the experimental data. The results show that the DoP values calculated by the modified microfacet pBRDF model are found to be consistent with the measured DoP values, and can significantly improve the modeling accuracy, which provides theoretical support for polarization remote sensing and object recognition.

Color generation from self-organized metalo-dielectric nanopillar arrays

Abstract Nanostructures composed of dielectric, metallic or metalo-dielectric structures are receiving significant attention due to their unique capabilities to manipulate light for a wide range of functions such as spectral colors, anti-reflection and enhanced light-matter interaction. The optical properties of such nanostructures are determined not only by the shape and dimensions of the structures but also by their spatial arrangement. Here, we demonstrate the generation of vivid colors from nanostructures composed of spatially disordered metalo-dielectric (In/InP) nanopillar arrays. The nanopillars are formed by a single-step, ion-sputtering-assisted, self-assembly process that is inherently scalable and avoids complex patterning and deposition procedures. The In/InP nanopillar dimensions can be changed in a controlled manner by varying the sputter duration, resulting in reflective colors from pale blue to dark red. The fast Fourier transform (FFT) analysis of the distribution of the formed nanopillars shows that they are spatially disordered. The electromagnetic simulations combined with the optical measurements show that the reflectance spectra are strongly influenced by the pillar dimensions. While the specular and diffuse reflectance components are appreciable in all the nanopillar samples, the specular part dominates for the shorter nanopillars, thereby leading to a glossy effect. The simulation results show that the characteristic features in the observed specular and diffused reflectance spectra are determined by the modal and light-scattering properties of single pillars. While the work focuses on the In/InP system, the findings are relevant in a wider context of structural color generation from other types of metalo-dielectric nanopillar arrays.

Calculation of Radiation Heat Exchange in the Model of Specular-Diffuse Reflection and Direct and Diffuse Transmission

The general solution to the radiation exchange problem in the zone method is given in the system of surfaces in the presence of nonparticipating medium for the model of specular-diffuse reflection and direct and diffuse transmission. The reflection indicatrix for all surfaces of the considered system of bodies is assumed as a superposition of diffuse and specular components of reflection, and the transmitted radiation for transparent materials—as a superposition of direct and diffuse transmission. The cornerstone of the offered approach is in obtaining the exchange radiation factors by the semi-analytical method by solving a system of linear algebraic equations that include specular exchange factors or diffuse configuration factors of radiation. This allows one to combine exact computational methods of diffuse reflection and diffuse transmission through diffuse configuration factors with methods of direct ray tracing for accounting of specular reflection and direct transmission. Solutions for all possible particular models of reflection and transmission are provided. The solution for diffuse transmission by the semi-analytical method is obtained for the first time. Results of the numerical experiments confirming accuracy and efficiency of the offered approach are given.

Terrestrial laser scanner intensity correction for the incidence angle effect on surfaces with different colours and sheens

ABSTRACT Laser scanning intensity captures information about the reflectance of target-surfaces and is used for a variety of applications such as data registration, classification, object detection and recognition. To enhance its utility, intensity values often undergo a correction process, which reduces the influence of nuisance parameters on recorded intensity (often range and incidence angle). This study applies and tests the Torrance-Sparrow model to correct intensity for the incidence angle effect in terrestrial laser scanning. Main components of the Torrance-Sparrow model are the geometrical attenuation (G) and microfacet distribution functions (D). Four models of geometrical attenuation and microfacet distribution functions are evaluated, namely, (i) Beckmann, (ii) Trowbridge-Reitz, (iii) GGX, and (iv) shifted gamma distribution (SGD). These models provide different derivations of the functions G and D, which estimate parameters necessary for the Torrance-Sparrow model. Target-surfaces scanned from various incidence angles are used for the assessment. These are painted with eight different colours (white, yellow, red, green, blue, grey, brown, and black) and two sheens (flat and semi-gloss), which create different reflection characteristics (diffuse and specular). Numerical and visual evaluations show that all four models manage to model the specular reflection component of the semi-gloss sheen target-surfaces for all tested colours. However, in flat-sheen surfaces, the Beckmann and SGD models show inferior modelling than GGX and Trowbridge-Reitz for brown, grey, and black colours. In addition, a relative comparison of the roughness parameters and Fresnel factors showed that only the Trowbridge-Reitz model produced reasonable values, based on encountered surface characteristics. Application of the Trowbridge-Reitz model in independent point-cloud data shows how intensity values can be corrected for the incidence angle effect in real cases.

Detecting and Removing Specular Reflectance Components Based on Image Linearization

Shape from Shading and Photometric Stereo are famous approaches to recover the 3D shape from image(s). These approaches can obtain 3D shape from observed gray scale image(s) but it is necessary to estimate reflectance parameters for objects when some specular reflectance components are observed. Specular reflectance is difficult to be handled as diffuse reflectance in general. It is expected to remove specular reflectance component without assuming any kind of reflectance function (reflectance model). This paper proposes a method to remove specular reflection components using 4 observed images taken under 4 different light source directions using relighting approach of diffused reflectance based on image linearization. Results are demonstrated via computer simulation and experiments.

Sequential fitting-and-separating reflectance components for analytical bidirectional reflectance distribution function estimation.

We present a sequential fitting-and-separating algorithm for surface reflectance components that separates individual dominant reflectance components and simultaneously estimates the corresponding bidirectional reflectance distribution function (BRDF) parameters from the separated reflectance values. We tackle the estimation of a Lafortune BRDF model, which combines a nonLambertian diffuse reflection and multiple specular reflectance components with a different specular lobe. Our proposed method infers the appropriate number of BRDF lobes and their parameters by separating and estimating each of the reflectance components using an interval analysis-based branch-and-bound method in conjunction with iterative K-ordered scale estimation. The focus of this paper is the estimation of the Lafortune BRDF model. Nevertheless, our proposed method can be applied to other analytical BRDF models such as the Cook-Torrance and Ward models. Experiments were carried out to validate the proposed method using isotropic materials from the Mitsubishi Electric Research Laboratories-Massachusetts Institute of Technology (MERL-MIT) BRDF database, and the results show that our method is superior to a conventional minimization algorithm.

Inversion of Position for Low Speed Target in Near Space Using Non-resolved Photometric and Astrometric Data

A method for estimating the position parameters of a low speed target (LST) in near space was presented. The estimation method utilizes apparent magnitude, azimuthal angle, and angle of elevation to invert the position of a typical LST, such as a high altitude balloon (HAB). A photometric observation model composed of specular and diffuse reflection components for the LST was established. An astrometric observation model was discussed to deduce the azimuth and elevation of a ground-based opto-electronic detection system for the LST. An extended Kalman filter (EKF) was designed to invert the state parameters of the position and velocity of the LST from photometric and astrometric data. Two sets of simulations were carried out to validate this inversion method. The simulation results show that the simulation errors for the estimated parameters are small, the estimated positions agree with GPS very well, and the non-resolved photometric and angular data can be used to estimate the indirect observable position state parameters for a LST in near space.

BRDF Models for the Impulse Response Estimation in Indoor Optical Wireless Channels

Indoor wireless optical communications (IWOCs) are highly conditioned by the communication channel, which depends on factors, such as the endpoints’ positions and the reflective surfaces inside the room. Reflections have an important impact on the channel properties, since both channel gain and multipath interference are directly affected by reflections. Therefore, the selection of the reflection model used in the channel characterization is a critical decision in order to achieve realistic and accurate channel estimation. Simulation software, for the IWOC channel impulse response estimation, usually simplifies reflections surfaces using basic models, such as the ideal diffuse reflector (Lambertian model) or Phong’s reflection scheme. However, these models do not provide accurate results when are used with some surfaces, like those with a high-level of specular reflection components. In this letter, the integration of new reflection models into the impulse response estimation of the IWOC channels is proposed. These models are based on bidirectional reflectance distribution function theories, such as Blinn’s or Lafortune’s models, which are frequently used in 3D image rendering.

Specular Reflection Separation With Color-Lines Constraint.

According to dichromatic reflection model, the previous methods of specular reflection separation in image processing often separate specular reflection from a single image using patch-based priors. Due to lack of global information, these methods often cannot completely separate the specular component of an image and are incline to degrade image textures. In this paper, we derive a global color-lines constraint from dichromatic reflection model to effectively recover specular and diffuse reflection. Our key observation is from that each image pixel lies along a color line in normalized RGB space and the different color lines representing distinct diffuse chromaticities intersect at one point, namely, the illumination chromaticity. For pixels along the same color line, they spread over the entire image and their distances to the illumination chromaticity reflect the amount of specular reflection components. With global (non-local) information from these color lines, our method can effectively separate specular and diffuse reflection components in a pixelwise way for a single image, and it is suitable for real-time applications. Our experimental results on synthetic and real images show that our method performs better than the state-of-the-art methods to separate specular reflection.

Three-dimensional reconstruction of Roman coins from photometric image sets

A method is presented for increasing the spatial resolution of the three-dimensional (3-D) digital representation of coins by combining fine photometric detail derived from a set of photographic images with accurate geometric data from a 3-D laser scanner. 3-D reconstructions were made of the obverse and reverse sides of two ancient Roman denarii by processing sets of images captured under directional lighting in an illumination dome. Surface normal vectors were calculated by a “bounded regression” technique, excluding both shadow and specular components of reflection from the metallic surface. Because of the known difficulty in achieving geometric accuracy when integrating photometric normals to produce a digital elevation model, the low spatial frequencies were replaced by those derived from the point cloud produced by a 3-D laser scanner. The two datasets were scaled and registered by matching the outlines and correlating the surface gradients. The final result was a realistic rendering of the coins at a spatial resolution of 75 pixels/mm (13-μm spacing), in which the fine detail modulated the underlying geometric form of the surface relief. The method opens the way to obtain high quality 3-D representations of coins in collections to enable interactive online viewing.

Influences of Leaf-Specular Reflection on Canopy BRF Characteristics: A Case Study of Real Maize Canopies With a 3-D Scene BRDF Model

The diffuse and specular components of leaf reflection are both important to determine the leaf optical properties as well as to describe the leaf bidirectional reflectance distribution function (BRDF). However, the specular component is usually ignored in practice in numerous canopy reflectance models that describe the interaction between solar light and vegetated scene components. To evaluate the impact of leaf-specular reflection on canopy bidirectional reflectance factor (BRF) characteristics, we introduce a leaf BRDF model into the radiosity-graphics combined model (RGM; a 3-D scene model) to calculate canopy BRFs with nondiffuse leaves. The modified RGM is validated by comparing simulated BRFs against in situ measured BRFs over real maize canopies. The results show that ignorance of leaf-specular reflection can result in up to 50% of relative error in the blue band (435.8 nm). A series of maize canopies with different leaf angle distributions (LADs) is reconstructed to investigate the effect of five major biophysical/geometrical parameters such as leaf area index, LAD, leaf surface property, view direction, and solar zenith angle on leaf-specular reflection contributions to the canopy BRF. It is demonstrated that increasing the incident solar zenith angle and decreasing the mean leaf angle impact the angular distribution of the canopy BRF more significantly than other factors. The cumulative hemispherical relative and absolute errors of canopy BRF caused by the leaf-specular reflection are often too large to be ignored, even for canopies with rough surface leaves. Moreover, the relative error of BRF in visible waveband shows that, in general, leaf-specular reflection has a large impact than that in near-infrared waveband. However, such impact can be sufficiently accounted for by even just consideration of the first-order leaf-specular reflection in canopy reflectance calculation, leading to a substantial improvement in simulation accuracy for most vegetation canopies.

Three-Dimensional Measurement for Specular Reflection Surface Based on Reflection Component Separation and Priority Region Filling Theory.

Due to the strong reflection property of materials with smooth surfaces like ceramic and metal, it will cause saturation and the highlight phenomenon in the image when taking pictures of those materials. In order to solve this problem, a new algorithm which is based on reflection component separation (RCS) and priority region filling theory is designed. Firstly, the specular pixels in the image are found by comparing the pixel parameters. Then, the reflection components are separated and processed. However, for ceramic, metal and other objects with strong specular highlight, RCS theory will change color information of highlight pixels due to larger specular reflection component. In this situation, priority region filling theory was used to restore the color information. Finally, we implement 3D experiments on objects with strong reflecting surfaces like ceramic plate, ceramic bottle, marble pot and yellow plate. Experimental results show that, with the proposed method, the highlight caused by the strong reflecting surface can be well suppressed. The highlight pixel number of ceramic plate, ceramic bottle, marble pot and yellow plate, is decreased by 43.8 times, 41.4 times, 33.0 times, and 10.1 times. Three-dimensional reconstruction results show that highlight areas were significantly reduced.

Laser Reflection as a Simple Prospect Tool for Nondestructive Quality Control of Charged Lapping Plates

In the present work, a simple laser/detector-based system was assembled and mounted in situ at the production line of the Hitachi hard-disk recording-head facilities in Mexico. The system was set to scan the surface of rotating lapping plates charged during time windows of varying lengths. The specular-reflection component was measured as a function of angular distance along the plate surface. The optical system showed enough sensitivity to follow the incorporation of abrasive into the plate surface. Moreover, two different charging stages were identified. Relevant topographical information could also be extracted. For example, the data distribution skewness was used to identify major surface defects, such as scratches. The reflection-signal spatial pattern was matched to that of the lapping plate topographer (LPT) surface profile by means of a coherence-spectrum analysis. The system assembly is relatively straightforward and it occupies little space. Thus, it could become a compact multitask substitute or complement of larger equipment at the manufacturing line. Note that even when the data analysis performed has led to promising results, the technique still needs to be fine-tuned in order to increase its precision and reliability.

Poststack diffraction imaging using reverse-time migration

We propose a method for imaging small-scale diffraction objects in complex environments in which Kirchhoff-based approaches may fail. The proposed method is based on a separation between the specular reflection and diffraction components of the total wavefield in the migrated surface angle domain. Reverse-time migration was utilized to produce the common image gathers. This approach provides stable and robust results in cases of complex velocity models. The separation is based on the fact that, in surface angle common image gathers, reflection events are focused at positions that correspond to the apparent dip angle of the reflectors, whereas diffracted events are distributed over a wide range of angles. The high-resolution radon-based procedure is used to efficiently separate the reflection and diffraction wavefields. In this study, we consider poststack diffraction imaging. The advantages of working in the poststack domain are its numerical efficiency and the reduced computational time. The numerical results show that the proposed method is able to image diffraction objects in complex environments. The application of the method to a real seismic dataset illustrates the capability of the approach to extract diffractions.

Directional and angular response of construction materials solar properties: Characterisation and assessment

Construction and building materials are generally considered Lambertian, namely they reflect as perfectly diffusive the radiation incident onto their surface. Thus, reflectance and absorptance are assumed to be constant and independent on the incidence and view angles. This assumption is not valid for specular materials, like glass or polished surfaces, where an angular dependence of their optical–radiative properties is observed. However, many opaque construction materials often show a mixed behaviour, which includes specular and diffuse (or scattering) reflectance components. Moreover, the apparent roughness of the materials surface changes according to the angle of incidence of the solar radiation. This issue is relevant for some cool materials, which are polished or treated with other methods to offer a very smooth surface, to increase the solar reflectance.Herein, the angular dependent solar reflectance of the opaque materials and the impact on the solar gains and energy balance of the building envelope is investigated. The off-normal solar spectral reflectance of four typical construction material for roofing and façade systems is measured with a spectrophotometer, equipped with a large integrating sphere, and with a goniophotometer to characterise the directional reflectance. The comparison between reflectance values in the visible band obtained with both devices shows relative variations lower than 2% for materials with prevalent diffusing behaviour. Discrepancies up to 6% are observed for the samples with a perceivable specular component. Solar reflectance angular dependent curves are calculated, starting from measurements, to compare different models to compute the solar gains. A building energy simulation tools is then used to compute the differences between heat fluxes and energy needs obtained with reflectance angular dependent models and with constant solar reflectance. Discrepancies of the thermal fluxes up 0.7kWh/m2 in summer and 0.5kWh/m2 in winter are calculated, with relative variations exceeding 7%. Discrepancies of 1.7kWh/m2 in winter and 1.2kWh/m2 in summer are calculated for the heating and cooling energy uses of a reference building.