Global Illumination Model Research Articles

Real-time volume rendering for three-dimensional fetal ultrasound using volumetric photon mapping

Three-dimensional (3D) fetal ultrasound has been widely used in prenatal examinations. Realistic and real-time volumetric ultrasound volume rendering can enhance the effectiveness of diagnoses and assist obstetricians and pregnant mothers in communicating. However, this remains a challenging task because (1) there is a large amount of speckle noise in ultrasound images and (2) ultrasound images usually have low contrasts, making it difficult to distinguish different tissues and organs. However, traditional local-illumination-based methods do not achieve satisfactory results. This real-time requirement makes the task increasingly challenging. This study presents a novel real-time volume-rendering method equipped with a global illumination model for 3D fetal ultrasound visualization. This method can render direct illumination and indirect illumination separately by calculating single scattering and multiple scattering radiances, respectively. The indirect illumination effect was simulated using volumetric photon mapping. Calculating each photon’s brightness is proposed using a novel screen-space destiny estimation to avoid complicated storage structures and accelerate computation. This study proposes a high dynamic range approach to address the issue of fetal skin with a dynamic range exceeding that of the display device. Experiments show that our technology, compared to conventional methodologies, can generate realistic rendering results with far more depth information.

Precomputed low-frequency lighting in cinematic volume rendering.

Cinematic Rendering (CR) employs physical models such as ray tracing and global illumination to simulate real-world light phenomena, producing high-quality images with rich details. In the medical field, CR can significantly aid doctors in accurate diagnosis and preoperative planning. However, doctors require efficient real-time rendering when using CR, which presents a challenge due to the substantial computing resources demanded by CR's ray tracing and global illumination models. Precomputed lighting can enhance the efficiency of real-time rendering by freezing certain scene variables. Typically, precomputed methods freeze geometry and materials. However, since the physical rendering of medical images relies on volume data rendering of transfer functions, the CR algorithm cannot utilize precomputed methods directly. To improve the rendering efficiency of the CR algorithm, we propose a precomputed low-frequency lighting method. By simulating the lighting pattern of shadowless surgical lamps, we adopt a spherical distribution of multiple light sources, with each source capable of illuminating the entire volume of data. Under the influence of these large-area multi-light sources, the precomputed lighting adheres to physical principles, resulting in shadow-free and uniformly distributed illumination. We integrated this precomputed method into the ray-casting algorithm, creating an accelerated CR algorithm that achieves more than twice the rendering efficiency of traditional CR rendering.

Approximate Image-Space Multidirectional Occlusion Shading Model for Direct Volume Rendering

Understanding and perceiving three-dimensional scientific visualizations, such as volume rendering, benefit from visual cues produced by the shading models. The conventional approaches are local shading models since they are computationally inexpensive and straightforward to implement. However, the local shading models do not always provide proper visual cues since non-local information is not sufficiently taken into account for the shading. Global illumination models achieve better visual cues, but they are often computationally expensive. It has been shown that alternative illumination models, such as ambient occlusion, multidirectional shading, and shadows, provide decent perceptual cues. Although these models improve upon local shading models, they still require expensive preprocessing, extra GPU memory, and a high computational cost, which cause a lack of interactivity during the transfer function manipulations and light position changes. In this paper, we proposed an approximate image-space multidirectional occlusion shading model for the volume rendering. Our model was computationally less expensive compared to the global illumination models and did not require preprocessing. Moreover, interactive transfer function manipulations and light position changes were achievable. Our model simulated a wide range of shading behaviors, such as ambient occlusion and soft and hard shadows, and can be effortlessly applied to existing rendering systems such as direct volume rendering. We showed that the suggested model enhanced the visual cues with modest computational costs.

Research on Application of Virtual Reality Technology in Virtual Marine Environment

Xie, J., 2019. Research on application of virtual reality technology in virtual marine environment. In: Li, L.; Wan, X.; and Huang, X. (eds.), Recent Developments in Practices and Research on Coastal Regions: Transportation, Environment and Economy. Journal of Coastal Research, Special Issue No. 98, pp. 223–226. Coconut Creek (Florida), ISSN 0749-0208.Virtual reality technology is a technology that generates a high-fidelity simulation environment by computer and enables users to immerse in the environment through a variety of sensor interfaces, thus realizing direct interaction between users and the virtual environment. Virtual environment is the application representation space of virtual reality technology, which is a visual platform integrating various technologies. For specific applications, building a three-dimensional, high-fidelity, and interactive virtual environment system is an important topic in the application of virtual reality technology. In this paper, simple illumination model and global illumination model are discussed, and the algorithm for parametric surface is discussed. In addition, the application of OpenGL in illumination model and texture mapping is also introduced. Taking the construction of virtual marine environment as an example, this paper develops a virtual marine environment system based on it. This paper introduces the simulation and simulation of ocean waves based on OpenGL wave spectrum by the method of equal energy.

Illumination estimation for augmented reality based on a global illumination model

With the rapid development of 3D technology, the illumination consistency plays an important role in realistic rendering of virtual objects which are superimposed into the real scene. In this paper we proposed a new approach to estimate illumination, given the images of a scene. Our algorithm is designed from principles in optics, which is based on a global illumination model. First, we get the images of a scene and perform scene reconstruction using images. Then, a photon emission hemispherical model is built for emitting photons into the scene. The photons are traced, meanwhile the result is stored in multiple photon maps. Finally, the estimated illumination is obtained by estimating the photon radiance value in the photon emission hemispherical model. Experiments on our newly collected real scene databases and virtual scene databases show the accuracy of our method subjectively and objectively. By comparing with related work, it is found that more accurate results can be obtained using the global illumination inversely.

Patch-based Stereo Direct Visual Odometry Robust to Illumination Changes

In this paper, we present a patch-based direct visual odometry (DVO) that is robust to illumination changes at a sequence of stereo images. Illumination change violates the photo-consistency assumption and degrades the performance of DVO, thus, it should be carefully handled during minimizing the photometric error. Our approach divides an incoming image into several buckets, and patches inside each bucket own its unique affine illumination parameter to account for local illumination changes for which the global affine model fails to account, then it aligns small patches placed at temporal images. We do not distribute affine parameters to each patch since this yields huge computational load. Furthermore, we propose a prior weight as a function of the previous pose in a constant velocity model which implies that the faster a camera moves, the more likely it maintains the constant velocity model. Lastly, we verify that the proposed algorithm outperforms the global affine illumination model at the publicly available micro aerial vehicle and the planetary rover dataset which exhibit irregular and partial illumination changes due to the automatic exposure of the camera and the strong outdoor sunlight, respectively.

CT cinematic rendering for pelvic primary tumor photorealistic visualization.

Pelvic tumors can be both complicated and challenging, and computed tomography (CT) has played an important role in the diagnosis and treatment planning of these conditions. Cinematic rendering (CR) is a new method of 3D imaging using CT volumetric data. Unlike traditional 3D methods, CR uses the global illumination model to produce high-definition surface details and shadow effects to generate photorealistic images. In this pictorial review, a series of primary pelvic tumor cases are presented to demonstrate the potential value of CR relative to conventional volume rendering (VR). This technique holds great potential in disease diagnosis, preoperative planning, medical education and patient communication.

A BSSRDF model for efficient rendering of fur with global illumination

Physically-based hair and fur rendering is crucial for visual realism. One of the key effects is global illumination, involving light bouncing between different fibers. This is very time-consuming to simulate with methods like path tracing. Efficient approximate global illumination techniques such as dual scattering are in widespread use, but are limited to human hair only, and cannot handle color bleeding, transparency and hair-object inter-reflection. We present the first global illumination model, based on dipole diffusion for subsurface scattering, to approximate light bouncing between individual fur fibers. We model complex light and fur interactions as subsurface scattering, and use a simple neural network to convert from fur fibers' properties to scattering parameters. Our network is trained on only a single scene with different parameters, but applies to general scenes and produces visually accurate appearance, supporting color bleeding and further inter-reflections.

Multi-scale Visualization of Molecular Architecture Using Real-Time Ambient Occlusion in Sculptor.

The modeling of large biomolecular assemblies relies on an efficient rendering of their hierarchical architecture across a wide range of spatial level of detail. We describe a paradigm shift currently under way in computer graphics towards the use of more realistic global illumination models, and we apply the so-called ambient occlusion approach to our open-source multi-scale modeling program, Sculptor. While there are many other higher quality global illumination approaches going all the way up to full GPU-accelerated ray tracing, they do not provide size-specificity of the features they shade. Ambient occlusion is an aspect of global lighting that offers great visual benefits and powerful user customization. By estimating how other molecular shape features affect the reception of light at some surface point, it effectively simulates indirect shadowing. This effect occurs between molecular surfaces that are close to each other, or in pockets such as protein or ligand binding sites. By adding ambient occlusion, large macromolecular systems look much more natural, and the perception of characteristic surface features is strongly enhanced. In this work, we present a real-time implementation of screen space ambient occlusion that delivers realistic cues about tunable spatial scale characteristics of macromolecular architecture. Heretofore, the visualization of large biomolecular systems, comprising e.g. hundreds of thousands of atoms or Mega-Dalton size electron microscopy maps, did not take into account the length scales of interest or the spatial resolution of the data. Our approach has been uniquely customized with shading that is tuned for pockets and cavities of a user-defined size, making it useful for visualizing molecular features at multiple scales of interest. This is a feature that none of the conventional ambient occlusion approaches provide. Actual Sculptor screen shots illustrate how our implementation supports the size-dependent rendering of molecular surface features.

The Research and Application on Illumination Model Algorithm of Oilfield Virtual Reality System

Realistic graphics for virtual reality system has been a hot research at home and abroad, the illumination model mapping and its application of the algorithms is one of the key level to achieve realistic scenes. This paper introduced the illumination model mapping and classification of the algorithms, focused on ray tracing algorithms and bounding box technology of the global illumination model which were realized in the oilfield virtual reality system and have been achieved good results.

Global Illumination Technique for Aircraft Infrared Signature Calculations

There is an increasing need of infrared signature knowledge of aerospace vehicles, both for defense and civilian applications, such as stealth technology, sensor design, and aerial obstacle detection for unmanned aerial vehicles. Models have been developed for this purpose by manufacturers or research laboratories, in order to predict infrared signatures of targets in the specific fields investigated. In some circumstances, it may be necessary to model complex radiative phenomena, such as diffuse reflections between different parts of the airframe, to improve the infrared target signature accuracy, or to help experimental image interpretation. An aircraft infrared signature modeling code, developed at ONERA, has been upgraded with a global illumination model, based on a Monte Carlo ray tracer, in order to evaluate the influence of these effects. First, this paper presents the main characteristics of the code and the principles of the rendering method. Next, comparisons are accomplished with another simulation tool and experimental data as well. The benefit of this approach in aircraft infrared signature computation is then discussed.

The Research and Implementation of Illumination Technology in the 3D GIS Visualization

Building mountains as the basic model for illumination model in the system of 3DGIS visualization. The establishing of this model adopts the approach of the global illumination model combine with the local reflection model and also the combination of shading and shadow. Complete the drawing of the shadow in the global illumination model ,using the shadow algorithm of Ray tracing as the main algorithm for drawing shadow, take advantage of shadow volume algorithm as the additional algorithm for shadow; complete the drawing of the shading in the local reflection model ,using the Blinn proportion algorithm as the main algorithm. Select the single ideal fixed point source as the light source of the illumination model. The results of this experimental show that the approach of combination of global and local model is feasible, the selection of the shadow and shading algorithms are also can reference.

Rendering Grass Blowing in the Wind with Global Illumination

We have simulated a time varying wind field using the lattice Boltzmann model, and its effect on blades of grass with a simple mass-spring model. We present a global illumination model for multiple scattering of incident sun and sky illumination within the field of grass. We model the grass as a continuous distribution of infinitesimal colored scattering flakes and solve a system of differential equations for the radiance transport. We repeat this for a collection of grass bending directions and amounts, and then interpolate the solutions when rendering animations of blowing grass.

Efficient reuse of paths for random walk radiosity

Global illumination algorithms take into account not only the direct illumination but also the indirect one, i.e., all reflections of light. Radiosity is one global illumination model which relies on computing the amount of light transferred between the surfaces in a scene, assuming these surfaces to be ideal diffuse or Lambertian reflectors. Numerous algorithms have been proposed to find the radiosity solution of an environment. Some of them use Monte Carlo random paths. The main drawback of such techniques is their high computational cost, due to the large number of samples (paths) needed to obtain an acceptable result. The reuse of paths is a valid strategy to reduce this cost. This article analyzes in detail the techniques of reusing paths in the radiosity context for both static scenes and light animation. A noticeable gain has been obtained in our experiments.

Construction of a realistic scene in virtual turning based on a global illumination model and chip simulation

Research on the virtual machining environment is one of the key parts of virtual manufacturing technology. According to the features of virtual turning, this paper proposes a simplified Whitted lighting model based on the analysis of Phong and other local illumination models. Moreover, to obtain natural lighting effects, a local ray tracing algorithm is given to calculate the light intensity of every position during the course of simulation. This method cannot simulate the machining environment accurately, but also can reduce the calculation time. Further, to obtain a more realistic machining scene, the paper deduces the transfer matrix from the chip coordinate to the feeding coordinate so that the chip model can be integrated into the whole machining scene. Finally, an example of a virtual cutting scene is shown to demonstrate the effects of the global illumination model and chip simulation. The data needed for the construction of the scene and for chip simulation is obtained from a C616 lathe. This study plays an important role in richening virtual manufacturing theory and promoting the development of advanced manufacturing technology.

A spectrally based framework for realistic image synthesis

Realistic image synthesis provides principles and techniques for creating realistic imagery based on models of real-world objects and behaviors. It has widespread applications in 3D design, computer animation, and scientific visualization. While it is common to describe light and objects in terms of colors, this approach is not sufficiently accurate and cannot render many spectral phenomena such as interference and diffraction. Many researchers have explored spectral rendering and proposed several methods for spectral representation, but none satisfy all representation criteria such as accuracy, compactness and efficiency. Furthermore, previous studies have focused on distinct behaviors of natural phenomena but few on their commonality and generality, and it is difficult to combine existing algorithms to simulate complex processes. This thesis proposes solutions to these problems within a spectrum-based rendering framework. The pipeline begins by loading spectra from a database to specify light sources and objects, then generates a spectral image based on local and global illumination models, projects the spectral image into a CIE image, and finally converts the CIE image into an RGB image for display or a CIELab image for evaluation. In spite of omitting the light phase information, it is shown that this approach suffices to generate all optical effects important for realistic image synthesis. As components of the new framework, a heuristic method is proposed for deriving spectra from colors and an error metric is provided for evaluating synthesized images. The new spectral representation proposed in this thesis is called the composite model. Its key point is to decompose any spectrum into a smooth background and a collection of spikes. The smooth part can be represented by Fourier coefficients and a spike by its location and height. A re-sampling technique is proposed to improve performance. Based upon the characteristics of human perception, the sufficiency of a low-dimensional representation is shown analytically. This model improves upon existing methods with aspect to accuracy, compactness and efficiency, and offers an effective vehicle for rendering optical effects involving spiky spectra. Using the proposed framework and composite spectral model, this thesis develops new illumination models for rendering a number of optical effects including dispersion, interference, diffraction, fluorescence, and volume absorption. The rendered images closely correspond to their real-world counterparts. Overall, this thesis improves realistic image synthesis by expanding its rendering capabilities. It may serve as a basis for a more sophisticated rendering environment for high-quality computer image generation.

Rendering + modeling + animation + postprocessing = computer graphics

Nowadays, students coming into a computer graphics course have seen movies that have fantastic graphics effects (e.g., Toy Story, A Bug's Life and the Star War series). These students have also acquired a certain level of graphics knowledge by playing games and reading popular magazines. Their expectations are certainly high for their first graphics course. Moreover, many deep and powerful theories were developed during the past decade. Either because these topics are too new or because they are too difficult to teach, they are frequently only sketched or even skipped in favor of a "programming" approach. Hence, what a student learns in an introductory course might only be some programming skills using a graphics API, usually OpenGL, along with some fundamental computer graphics knowledge. Students are only exposed a little to modern developments which are frequently used by the graphics industry for creating fantastic special effects or realistic images.At Michigan Technological University, we have three computer graphics related courses: an introduction to graphics course, a computing with geometry course for junior and senior students and an advanced graphics course for graduate students. We also have graduate courses on geometric modeling and visualization. The minimum prerequisite of the introductory graphics course is only a sophomore software development course which is usually taken after a data structure course. This introductory course covers essentially all traditional topics with the help of publicly available tools (e.g., GLUT and GLUI) and other tools developed by the instructor of this course. We believe that our current approach is a successful combination of theory and the current popular programming approach using tools. However, we still feel that we need to do more to introduce students to modern theories and developments. While many educators have already observed the need of a new graphics course and proposed some approaches [1], our approach is more ambitious and non-traditional.We believe that graphics consists of four major components: rendering, modeling, animation and postprocessing. The rendering part has become the major topic in typical graphics textbooks and the main thrust of a programming approach. There is nothing wrong with a focus on rendering methods. The problem is that the programming approach cannot cover global illumination models (e.g., ray tracing and radiosity) and volume rendering, because most popular APIs only implement local illumination models. Every scene contains some objects and object building requires the knowledge of modeling. However, building a good and realistic model is not part of any API. Animation is the skill for creating animation sequences and simulating physical events. Finally, postprocessing makes created scenes satisfy additional requirements and requires a special set of 2D operations. Obvious topics should include, but not be limited to, filters, morphing, dithering and other current techniques. Since the programming approach usually cannot go this far to cover all four components, additional course materials and working environments are required. This has become the main thrust of our project.To address this need, our goal is to design a comprehensive introductory computer graphics course that covers all four major components to some depth with a breath-first and learning-by-doing approach. To support this goal, a pedagogical environment is required for students to experiment and visualize important concepts, and to perform a semester-long project of implementing various components. In the following, we discuss a number of problems that prompted us to initiate this project, present a description of our proposed course and its software tools, address the software modules that are currently under development and, finally, make our conclusions.

Color representation in virtual environments

Techniques are suggested for improved color treatment in real-time rendering of synthetic environments. These include the use of emissive textures within a radiosity-based, global illumination model, the addition of dynamic specular highlights to a radiosity-based model, and an alternative approach to full spectral representation that uses a radiosity solution engine in the complex domain. The target application, dynamic rendering of theatrical settings for lighting design, demands both color accuracy and correct treatment of subtle reflections, translucency, and specular highlights. The new techniques appear to provide an appropriate solution. © 1996 John Wiley & Sons, Inc.

Color representation in virtual environments

Techniques are suggested for improved color treatment in real-time rendering of synthetic environments. These include the use of emissive textures within a radiosity-based, global illumination model, the addition of dynamic specular highlights to a radiosity-based model, and an alternative approach to full spectral representation that uses a radiosity solution engine in the complex domain. The target application, dynamic rendering of theatrical settings for lighting design, demands both color accuracy and correct treatment of subtle reflections, translucency, and specular highlights. The new techniques appear to provide an appropriate solution. © 1996 John Wiley & Sons, Inc.

The Heidelberg ray tracing model

The Heidelberg ray tracing model, developed especially for visualization of medical images, is based on a global illumination model and contains a number of application-specific assumptions. It simulates the projection of a scene with well-defined lighting. A detailed description of the model follows an overview of existing and competing illumination procedures.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>