Diffuse Reflection Components Research Articles

Learning physically based material and lighting decompositions for face editing

Lighting is crucial for portrait photography, yet the complex interactions between the skin and incident light are expensive to model computationally in graphics and difficult to reconstruct analytically via computer vision. Alternatively, to allow fast and controllable reflectance and lighting editing, we developed a physically based decomposition through deep learned priors from path-traced portrait images. Previous approaches that used simplified material models or low-frequency or low-dynamic-range lighting struggled to model specular reflections or relight directly without intermediate decomposition. However, we estimate the surface normal, skin albedo and roughness, and high-frequency HDRI maps, and propose an architecture to estimate both diffuse and specular reflectance components. In our experiments, we show that this approach can represent the true appearance function more effectively than simpler baseline methods, leading to better generalization and higher-quality editing.

A Modified BRDF Model Based on Cauchy-Lorentz Distribution Theory for Metal and Coating Materials

This paper presents a modified Bidirectional Reflectance Distribution Function (BRDF) model based on the Cauchy–Lorentz distribution that accurately characterizes the reflected energy distribution of typical materials, such as metals and coatings in hemispherical space. The proposed model overcomes the problem of large errors in classical models when detecting angles far away from the specular reflection angle by dividing the reflected light into specular reflection, directional diffuse reflection, and ideal diffuse reflection components. The newly added directional diffuse reflection component is represented by the Cauchy–Lorentz distribution, and its parameters are directly obtained from experimental measurement curves without distribution fitting. Surface morphology and model parameters are determined through measurements, and the comparison between simulation and actual measurement results shows that the modified BRDF model is in excellent agreement with the measured data. The proposed model not only achieves higher accuracy and universality, but it also represents a significant advancement in the field of BRDF modeling research. Its contributions have profound implications for advancing the state of the art in BRDF modeling, as well as having a broader impact on computer graphics and computer vision domains.

Three Dimensional Shape Reconstruction via Polarization Imaging and Deep Learning

Deep-learning-based polarization 3D imaging techniques, which train networks in a data-driven manner, are capable of estimating a target’s surface normal distribution under passive lighting conditions. However, existing methods have limitations in restoring target texture details and accurately estimating surface normals. Information loss can occur in the fine-textured areas of the target during the reconstruction process, which can result in inaccurate normal estimation and reduce the overall reconstruction accuracy. The proposed method enables extraction of more comprehensive information, mitigates the loss of texture information during object reconstruction, enhances the accuracy of surface normal estimation, and facilitates more comprehensive and precise reconstruction of objects. The proposed networks optimize the polarization representation input by utilizing the Stokes-vector-based parameter, in addition to separated specular and diffuse reflection components. This approach reduces the impact of background noise, extracts more relevant polarization features of the target, and provides more accurate cues for restoration of surface normals. Experiments are performed using both the DeepSfP dataset and newly collected data. The results show that the proposed model can provide more accurate surface normal estimates. Compared to the UNet architecture-based method, the mean angular error is reduced by 19%, calculation time is reduced by 62%, and the model size is reduced by 11%.

Age‐related changes in surface reflection, diffuse reflection, and subsurface scattering light of facial skin: Luminance value measured by the system for the optical properties of facial skin

AbstractWe have developed a system that separates and measures the optical properties of skin that determine its visual quality, that is, the surface reflection, diffuse reflection, and subsurface scattering components of the skin. This system includes two polarization filters that separate light from the skin into a surface reflection component image and a diffuse reflection component image. Furthermore, by using a projector as a light source and irradiating the skin using a high‐frequency binary illumination pattern, the subsurface scattering component image alone can be separated and generated. Application of an algorithm that calculates the luminance value Y for each component image not only makes it possible to analyze each light signal from the skin quantitatively, but also enables understanding of how each light signal is related to the skin's overall appearance. Using the proposed system, we performed a survey of 154 Japanese women aged from their 20s to their 70s and analyzed age‐related changes in the optical properties of their skin. The results revealed the following. First, the luminance value Y of the surface reflection from the cheek and its standard deviation within the analysis area increase with age. Second, the Y value of diffuse reflection from the skin decreases with age. Third, the amount of light in the subsurface scattering components also decreases with age. The proposed system is expected to be suitable for a wide range of applications, including color science, and various studies of the appearance of human skin.

AvatarMe++: Facial Shape and BRDF Inference With Photorealistic Rendering-Aware GANs.

Over the last years, with the advent of Generative Adversarial Networks (GANs), many face analysis tasks have accomplished astounding performance, with applications including, but not limited to, face generation and 3D face reconstruction from a single "in-the-wild" image. Nevertheless, to the best of our knowledge, there is no method which can produce render-ready high-resolution 3D faces from "in-the-wild" images and this can be attributed to the: (a) scarcity of available data for training, and (b) lack of robust methodologies that can successfully be applied on very high-resolution data. In this paper, we introduce the first method that is able to reconstruct photorealistic render-ready 3D facial geometry and BRDF from a single "in-the-wild" image. To achieve this, we capture a large dataset of facial shape and reflectance, which we have made public. Moreover, we define a fast and photorealistic differentiable rendering methodology with accurate facial skin diffuse and specular reflection, self-occlusion and subsurface scattering approximation. With this, we train a network that disentangles the facial diffuse and specular reflectance components from a mesh and texture with baked illumination, scanned or reconstructed with a 3DMM fitting method. As we demonstrate in a series of qualitative and quantitative experiments, our method outperforms the existing arts by a significant margin and reconstructs authentic, 4K by 6K-resolution 3D faces from a single low-resolution image, that are ready to be rendered in various applications and bridge the uncanny valley.

Development of a System to Measure the Optical Properties of Facial Skin using a 3D Camera and Projector

We have developed a system to measure both the optical properties of facial skin and the three-dimensional shape of the face. To measure the three-dimensional facial shape, our system uses a light-field camera to provide a focused image and a depth image simultaneously. The light source uses a projector that produces a high-frequency binary illumination pattern to separate the subsurface scattering and surface reflections from the facial skin. Using a dichromatic reflection model, the surface reflection image of the skin can be separated further into a specular reflection component and a diffuse reflection component. Verification using physically controlled objects showed that the separation of the optical properties by the system correlated with the subsurface scattering, specular reflection, or diffuse reflection characteristics of each object. The method presented here opens new possibilities in cosmetology and skin pharmacology for measurement of the skin's gloss and absorption kinetics and the pharmacodynamics of various external agents.

Optimization of ray tracing algorithm for Laser Radar Cross Section calculation based on material Bidirectional Reflection Distribution Function

This paper studied the Laser Radar Cross Section (LRCS) of the target scale model by using the Bidirectional Reflection Distribution Function (BRDF) of materials and the Monte Carlo method for reverse ray tracing. The results of the research are shown through data from the satellite scale model. On the basis of the classification of the roughness of different materials and in conjunction with probability density distribution, we adopted a non-uniform sampling method to improve the split-ray collection method in the spatial distribution of scattering energy in the reverse ray tracing algorithm. By conducting the typical Monte Carlo simulation of a simple dihedron and comparing the theoretical calculation results, we tested and verified the correctness of the proposed method. We analyzed the difference between the primary and secondary scattering results of the target LRCS with different conditions. The calculation results show that for rough materials, if only primary scattering is considered in a plurality of detection directions, a large calculation error will occur, so the influence of the secondary scattering must be considered; and the contribution of the diffuse reflection component to the secondary scattering is more significant. Finally, we compared the secondary scattering of different rough materials to describe the circumstances of secondary scattering in which diffuse reflection conditions need to be considered. In addition, the inverse Monte Carlo method used in this paper to calculate the multiple scattering of the LRCS of the target can effectively improve the calculation speed of the acquisition processing. This improves the reliability of the calculation results while taking into account the estimated speed.

Research and implementation of digital 3D panoramic visual communication technology based on virtual reality

SummaryBased on the digital three‐dimensional (3D) panoramic technology of sequence pictures, the static pictures are stitched together to form a 360‐degree panoramic image, which can truly reproduce the real scene. Panoramic images are widely used, making this technology a hot spot in the research of virtual reality technology. This paper completes the research content of the application value of the digital 3D panorama, the key technology of digital 3D panorama technology, and the design and display of 3D panorama campus through practical application. This article comprehensively introduces the hardware equipment of panoramic technology and the technical requirements of panoramic image acquisition in the field of practical application, and combines the actual cases to systematically produce panoramic image stitching, panoramic image generation, and virtual roaming campus construction; 3D panoramic technology is a brand‐new form of viewing images, discussing and studying the artistic expression of 3D panoramic images, and researching its innovative application in visual communication art. In this paper, the chromaticity calibration of digital camera and projection equipment is used to eliminate the coupling difference between the two; then estimate the spectral reflectance of the three‐color channel of the object and separate the specular reflection component and the diffuse reflection component, at the same time correct the color and specular reflectance of the object itself, and analyze the influence of reflection on the color of the projection light source. This article describes the design ideas and key technologies of the school's 3D panoramic walkthrough system, describes in detail the process of the system from demand analysis to system design and finally realization, and focuses on the production method of panoramic images and the main functional modules in the walkthrough system. At the end, the system was tested, and the existing problems were analyzed, and solutions were provided. Research shows that when the roaming system has 3,000 concurrent users, it can read a single scene for about 3 s on average.

An effective framework for 3D shape measurement of specular surface based on the dichromatic reflection model

Fringe projection profilometry based on phase-shift method has been commonly used for three-dimensional measurement. However, measuring the specular surface is always a challenging task since the specular area cannot present original intensity information. This paper presents a novel framework for measuring objects with specular surfaces. Firstly, a set of phase-shifted fringe patterns with maximum intensity value is projected onto the specular surface. Then, the dichromatic reflection model is developed to theoretically decompose an image into specular and diffuse reflection components, which identifies specular pixels more robustly and effectively than judging by saturation only. Secondly, since the location and intensity of specular areas are acquired, the best projection intensity corresponding to the specular areas can be determined by fitting a power function that transforms captured specular reflection components to projected intensities, aiming to minimize specular areas and decrease specular reflection components. It should be stated here that the assumption based on this paper is that the fewer specular reflection components, the fewer measurement errors. Subsequently, the adaptive fringe patterns, which are constructed using the best projection intensity, are reprojected for phase recovery. Thirdly, it is reasonable that there still exist regions where the specular reflection components are too high. For these information-loss areas, the pixel inpainting technique is adopted when extracting the disparity map. Finally, the ultimate result combines adaptive fringe reconstruction with pixel inpainting. The experiment results verify that the proposed measurement framework can effectively and robustly perform three-dimensional reconstruction of various objects with specular surfaces.

Study on reflection characteristics of underwater target and laser echo power

For the design of the underwater laser detection system, the echo power equation of underwater target is derived, and the effects of water’s attenuation coefficient and incident angle on target's echo power are analyzed. The bidirectional reflection distribution function (BRDF) of the single-station model is used to study the reflection characteristics of the target. The influence of the correlation coefficients of specular and diffuse reflection components on the reflected light intensity of special axisymmetric targets is studied. The signal-to-noise ratio (SNR) values of three types of target under different surface BRDF are given. The simulation results show that the larger the attenuation coefficient is, the smaller the echo power received, and the incidence angle is closer to 90°, the echo power is equal to 0. A smaller surface slope or a larger diffuse reflected coefficient will cause a smaller reflected intensity.

The Impact of Light Polarisation on Light Field of Scenes with Multiple Reflections

The article describes the role of polarisation in calculation of multiple reflections. A mathematical model of multiple reflections based on the Stokes vector for beam description and Mueller matrices for description of surface properties is presented. On the basis of this model, the global illumination equation is generalised for the polarisation case and is resolved into volume integration. This allows us to obtain an expression for the Monte Carlo method local estimates and to use them for evaluation of light distribution in the scene with consideration of polarisation. The obtained mathematical model was implemented in the software environment using the example of a scene with its surfaces having both diffuse and regular components of reflection. The results presented in the article show that the calculation difference may reach 30 % when polarisation is taken into consideration as compared to standard modelling.

Polarization-based extracting diffuse reflection from light-field of object surface

<sec>The reflection light field of surface of the Non-Lambertian body in nature has both specular reflection and diffuse reflection components. In the process of three-dimensional(3D) reconstruction, image matching and pattern recognition are based on the ideal Lambert body. The imaging effect is limited due to the presence of specular reflection components, and the accuracy of feature recognition is low. In order to obtain the diffuse reflection component accurately, a large number of studies have been conducted for a long time, which can be mainly divided into two parts: intensity- and polarization-based separation techniques. The intensity-based separation algorithm is limited in many aspects due to the prior knowledge, such as light source chromaticity, direction and image color information. With the maturity of detection technology, the acquisition and interpretation of multi-dimensional physical properties of light-field have made great progress of the utilization of polarization characteristics of light wave. Compared with traditional intensity imaging technology, the polarization imaging technology has strongr and many advantages in highlighting targets. However, in traditional polarization-based separation techniques, it is often necessary to assume that the diffuse light is completely unpolarized, which is used in some specific cases but not universally.</sec><sec>In this work, we report a method to obtain the diffuse reflection components of the target surface based on the polarization characteristics of the light-field. According to Fresnel's law and Lawrence B. Wolff's reflection model, the reflected light-field on the target surface can be divided into diffuse and specular components with partial polarization. The partial polarization characteristics of diffuse and specular components are explored in depth and the Stokes vector is used to calculate the minimum light intensity of each pixel modulated by polarizer, which is completely unpolarized light. By subtracting completely unpolarized light from the obtained polarized sub-images, the diffuse and specular components in the polarized part satisfy the linear constraint model. Based on the independent component analysis (ICA) model, the diffuse and specular components in the polarized part are regarded as independent and non-interfering additive vectors. The singular value decomposition method and optical relevancy of mutual information are used to determine the optimal mix coefficients matrix of the subcomponents in the linear constrained model. Thus, the diffuse components are accurately acquired and explained from the complex reflected light-field. </sec><sec>Simulation and experimental results show that the algorithm mentioned above can accurately obtain the optimal mix coefficients’ matrix without the prior knowledge of illuminant chromaticity, or direction or image chromatic information, or others. This technique can accurately obtain and remove the specular reflection part, at the same time, restore the diffuse light intensity which is covered by the specular reflection and conforms to the change trend of the surface shape. Meanwhile, the pretty good results also demonstrate that the proposed separation method has the strong stability and wide applicability. This technology does not have to make the assumption that 3D imaging technology and computer vision algorithms such as pattern recognition rely on natural objects as ideal Lambert bodies, and it can eleminate the influence of complex reflected light-field on target results, which makes passive remote 3D imaging technology more applicable and more robust.</sec>

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.

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.

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.

Deceiving ability of typical natural objects used for false target in laser decoy jamming

Aiming at the application of natural objects false target in laser decoy jamming, its deceiving ability characterized by decoy airspace was calculated and analyzed. On the premise of full considering the reflection characteristics of target, the intensity of jamming-indicating laser, atmospheric laser attenuation coefficient, and other factors, the analysis model of decoy jamming ability for false target was established under the condition of suppression coefficient K (≥1). Furthermore, the effectual decoy airspace of common natural objects was analyzed under typical condition. The results show that the effective cheating airspace of false target is closely related to the type of targets, and the deceiving ability of vegetation, gravel and diffuse reflection objects is enhanced in turn under the same conditions. There exists a mirror reflection component that is much smaller than the diffuse reflection component in the decoy airspace of vegetation and gravel natural objects, and the variation of the incident angle of jamming laser has obvious influence on the distribution of effectual decoy airspace. However, there is no obvious trend change rule for the decoy airspace of vegetation targets with the incidence angle. The research results are instructive for the reasonable application of typical natural objects used for false target.

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.