The phenomenon of birefringence may be observed when light arrives at an anisotropic crystal surface and refracts through it, causing the incident light ray to split into two rays; these become ...polarized in mutually orthogonal directions, and two images are formed. The principal goal of this paper is the study of the directional issues involved in the behavior of light when refracting through a homogeneous, non-participating medium, including both isotropic and anisotropic media (uniaxial and, for the first time, biaxial). The paper focuses on formulating and solving the non-linear algebraic system that is obtained when the refraction process is simulated using the geometric model of Huygens. The main contribution focuses on the case of biaxial media. In the case of uniaxial media, we rely on symbolic calculus techniques to formulate and solve the problem.
We present a physically based progressive global illumination system that is capable of simulating complex lighting situations robustly by efficiently using both light and eye paths. Specifically, we ...combine three distinct algorithms: point‐light‐based illumination which produces low‐noise approximations for diffuse inter‐reflections, specular gathering for glossy and singular effects and a caustic histogram method for the remaining light paths. The combined system efficiently renders low‐noise production quality images with indirect illumination from arbitrary light sources including inter‐reflections from caustics and allows for simulating depth of field and dispersion effects. Our system computes progressive approximations by continuously refining the solution using a constant memory footprint without the need of pre‐computations or optimizing parameters beforehand.
In 3D reconstruction, appearance is always overlooked compared to geometry and motion. The existing methods prefer texture-based shading, where the reconstructed appearance cannot perform ...re-lighting, thus weakens the authenticity, aesthetic and availability. Although excellent attempts were made in some works at lighting model-based shading in 3D reconstruction, still they fall short of differentiated rendering of materials. In this paper, we propose a method that can make an artistic effect on the recovery of illumination properties in 3D reconstruction from a single RGB-D image. Our method builds adaptive lighting models for different surfaces, which are used in re-lighting and recovering surface properties. We start with the establishment of coordinate system conversion tables for rapidly matching surface parameters and location. Then, a projection-based triangulation method is developed to generate polygonal mesh. After that, we propose a physically based lighting model with few variable parameters to recover surface illumination properties, in order to accurately describe the reflection of light from different materials. Furthermore, we develop an adaptive algorithm for generating parameters. Since the algorithm is based on the surface consistency of albedo over channels and training-less also, it is applicable to a surface of any shape and material, and the physically based lighting model brings a more vivid re-lighting. The obtained experimental results demonstrate that our method could achieve an excellent reconstructed appearance in both artistic view and verisimilitude.
In an animated scene, geometry and lighting often change in an unpredictable way. Rendering algorithms based on Monte Carlo methods are usually employed to precisely capture all features of an ...animated scene. However, Monte Carlo methods typically take a long time to produce a noise-free image. In this paper, we propose a variance reduction technique for Monte Carlo methods which exploits coherence between frames. Firstly, we introduce a dual cone model to measure the incident coherence intersecting camera rays in object space. Secondly, we allocate multiple frame buffers to store image samples from consecutive frames. Finally, the color of a pixel in one frame is computed by borrowing samples from neighboring pixels in current, previous, and subsequent frames. Our experiments show that noise is greatly reduced by our method since the number of effective samples is increased by use of borrowed samples.
Instance segmentation is of great significance for the automatic picking of weakly textured pipes. However, it is hard to acquire synthetic datasets with a robust sim-to-real capability for training ...instance segmentation models due to the domain gap between the synthetic and real images. This paper proposes a method for generating photorealistic images of weakly textured pipes using BlenderProc2 and automatically constructing a synthetic dataset. The innovation of this approach lies in combining Physically-Based Rendering (PBR) with domain randomization techniques to reduce the sim-to-real gap. The presented results on instance segmentation tasks indicate that the Mask R-CNN model with PointRend module achieves a 9.919% improvement in Average Precision (AP) for segmentation and an almost 29% improvement for bounding boxes when trained on images synthesized using the proposed method, compared to training on realistic images combined with data augmentation. Thus, the effectiveness of the proposed method is verified in this study.
Within computer graphics, the field of predictive rendering is concerned with those methods of image synthesis that yield results that do not only look real, but are also radiometrically correct ...renditions of nature, i.e. which are accurate predictions of what a real scene would look like under given lighting conditions.
In order to guarantee the correctness of the results obtained by such techniques, three stages of such a rendering system have to be verified with particular care: the light reflection models, the light transport simulation and the perceptually based calculations used at display time.
In this report, we will concentrate on the state of the art with respect to the second step in this chain. Various approaches for experimental verification of the implementation of a physically based rendering system have been proposed so far. However, the problem of proving that the results are correct is not fully solved yet, and no standardized methodology is available. We give an overview of existing literature, discuss the strengths and weaknesses of the described methods and illustrate the unsolved problems. We also briefly discuss the related issue of image quality metrics.
Recent developments in rendering have provided very realistic images. However, these images rarely show organic objects. We believe that one of the main difficulties of rendering these objects ...realistically is the lack of reflectance and transmittance models oriented to organic materials. In this paper an algorithmic reflectance and transmittance model for plant tissue oriented to computer graphics applications is presented. The model accounts for the three components of light propagation in plant tissues, namely surface reflectance, subsurface reflectance and transmittance, and mechanisms of light absorption by pigments present in these tissues. The model design is based on the available biological information, and it is controlled by a small number of biologically meaningful parameters. Its formulation, based on standard Monte Carlo techniques, guarantees its easy incorporation into most rendering systems. The spectral curves of reflectance and transmittance computed by the model are compared with measured curves from actual experiments.
Recently, physically based rendering (PBR) 1 has become popular with respect to visual realism in the computer graphics field. PBR model is more of a ray tracing calculation than a legacy Lambert or ...Phong model. This technique has become the industry standard for movies and video game developments. This paper refers to a simple model for subsurface light transport in translucent materials with respect to the PBR system. We attempt to simulate a realistic subsurface scattering by choosing to mimic a cake-surface texture, which has a sophisticated translucent material, and nest-like structure that can demonstrate the characteristics of the bidirectional scattering distribution function (BSDF). We used the Arnold engine with 3ds max software for Monte Carlo ray-tracing calculation in CPU. We compared the difference between the photo-scanning map and the procedural shader, which were fed into the displacement channel to achieve a random organic texture of a cake-surface. This approach showed the advantages and disadvantages of these different situations in the PBR workflow. With the knowledge of the examining mathematical model of PBR, we describe that the PBR theory and the practical aspect to validate this procedural shader, can provide more advantages in a variety of material mimic. Finally, the workflow of the experiment can help 3D artists design realistic looking surfaces as effortlessly as possible based on physically accurate formulas.
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