46 research outputs found
Accelerating Ray Shooting Through Aggressive 5D Visibility Pre-processing
We present a new approach to accelerating general ray shooting. Our technique uses a five-dimensional ray space partition and is based on the classic ray-classication algorithm. Where the original algorithmevaluates intersection candidates at run-time, our solution evaluates them as a preprocess.
The offline nature of our solution allows for an adaptive subdivision of ray space. The advantage being, that it allows for the placement of a user set upper bound on the number of primitives intersected.
The candidate sets produced account for occlusion, thereby reducing memory requirements and accelerating the ray shooting process. A novel algorithm which exploits graphics hardware is used to evaluate the candidate sets. It is the treatment of occlusion that allows for the practical precomputation of the ray space partition. This algorithm is called aggressive since it is optimal (no invisible primitives are included), but may result in false exclusion of visible primitives. Error is minimised through the adaptive sampling
Fast and Accurate Visibility Preprocessing
Visibility culling is a means of accelerating the graphical rendering of geometric models. Invisible objects are efficiently culled to prevent their submission to the standard graphics pipeline. It is advantageous to preprocess scenes in order to determine invisible objects from all possible camera views. This information is typically saved to disk and may then be reused until the model geometry changes. Such preprocessing algorithms are therefore used for scenes that are primarily static.
Currently, the standard approach to visibility preprocessing algorithms is to use a form of approximate solution, known as conservative culling. Such algorithms over-estimate the set of visible polygons. This compromise has been considered necessary in order to perform visibility preprocessing quickly. These algorithms attempt to satisfy the goals of both rapid preprocessing and rapid run-time rendering.
We observe, however, that there is a need for algorithms with superior performance in preprocessing, as well as for algorithms that are more accurate. For most applications these features are not required simultaneously. In this thesis we present two novel visibility preprocessing algorithms, each of which is strongly biased toward one of these requirements.
The first algorithm has the advantage of performance. It executes quickly by exploiting graphics hardware. The algorithm also has the features of output sensitivity (to what is visible), and a logarithmic dependency in the size of the camera space partition. These advantages come at the cost of image error. We present a heuristic guided adaptive sampling methodology that minimises this error. We further show how this algorithm may be parallelised and also present a natural extension of the algorithm to five dimensions for accelerating generalised ray shooting.
The second algorithm has the advantage of accuracy. No over-estimation is performed, nor are any sacrifices made in terms of image quality. The cost is primarily that of time. Despite the relatively long computation, the algorithm is still tractable and on average scales slightly superlinearly with the input size. This algorithm also has the advantage of output sensitivity. This is the first known tractable exact solution to the general 3D from-region visibility problem.
In order to solve the exact from-region visibility problem, we had to first solve a more general form of the standard stabbing problem. An efficient solution to this problem is presented independently
Towards Predictive Rendering in Virtual Reality
The strive for generating predictive images, i.e., images representing radiometrically correct renditions of reality, has been a longstanding problem in computer graphics. The exactness of such images is extremely important for Virtual Reality applications like Virtual Prototyping, where users need to make decisions impacting large investments based on the simulated images. Unfortunately, generation of predictive imagery is still an unsolved problem due to manifold reasons, especially if real-time restrictions apply. First, existing scenes used for rendering are not modeled accurately enough to create predictive images. Second, even with huge computational efforts existing rendering algorithms are not able to produce radiometrically correct images. Third, current display devices need to convert rendered images into some low-dimensional color space, which prohibits display of radiometrically correct images. Overcoming these limitations is the focus of current state-of-the-art research. This thesis also contributes to this task. First, it briefly introduces the necessary background and identifies the steps required for real-time predictive image generation. Then, existing techniques targeting these steps are presented and their limitations are pointed out. To solve some of the remaining problems, novel techniques are proposed. They cover various steps in the predictive image generation process, ranging from accurate scene modeling over efficient data representation to high-quality, real-time rendering. A special focus of this thesis lays on real-time generation of predictive images using bidirectional texture functions (BTFs), i.e., very accurate representations for spatially varying surface materials. The techniques proposed by this thesis enable efficient handling of BTFs by compressing the huge amount of data contained in this material representation, applying them to geometric surfaces using texture and BTF synthesis techniques, and rendering BTF covered objects in real-time. Further approaches proposed in this thesis target inclusion of real-time global illumination effects or more efficient rendering using novel level-of-detail representations for geometric objects. Finally, this thesis assesses the rendering quality achievable with BTF materials, indicating a significant increase in realism but also confirming the remainder of problems to be solved to achieve truly predictive image generation
Ray Tracing Gems
This book is a must-have for anyone serious about rendering in real time. With the announcement of new ray tracing APIs and hardware to support them, developers can easily create real-time applications with ray tracing as a core component. As ray tracing on the GPU becomes faster, it will play a more central role in real-time rendering. Ray Tracing Gems provides key building blocks for developers of games, architectural applications, visualizations, and more. Experts in rendering share their knowledge by explaining everything from nitty-gritty techniques that will improve any ray tracer to mastery of the new capabilities of current and future hardware. What you'll learn: The latest ray tracing techniques for developing real-time applications in multiple domains Guidance, advice, and best practices for rendering applications with Microsoft DirectX Raytracing (DXR) How to implement high-performance graphics for interactive visualizations, games, simulations, and more Who this book is for: Developers who are looking to leverage the latest APIs and GPU technology for real-time rendering and ray tracing Students looking to learn about best practices in these areas Enthusiasts who want to understand and experiment with their new GPU
Utilising path-vertex data to improve Monte Carlo global illumination.
Efficient techniques for photo-realistic rendering are in high demand across a wide array of industries. Notable applications include visual effects for film, entertainment and virtual reality. Less direct applications such as visualisation for architecture, lighting design and product development also rely on the synthesis of realistic and physically based illumination. Such applications assert ever increasing demands on light transport algorithms, requiring the computation of photo-realistic effects while handling complex geometry, light scattering models and illumination. Techniques based on Monte Carlo integration handle such scenarios elegantly and robustly, but despite seeing decades of focused research and wide commercial support, these methods and their derivatives still exhibit undesirable side effects that are yet to be resolved. In this thesis, Monte Carlo path tracing techniques are improved upon by utilizing path vertex data and intermediate radiance contributions readily available during rendering. This permits the development of novel progressive algorithms that render low noise global illumination while striving to maintain the desirable accuracy and convergence properties of unbiased methods. The thesis starts by presenting a discussion into optical phenomenon, physically based rendering and achieving photo realistic image synthesis. This is followed by in-depth discussion of the published theoretical and practical research in this field, with a focus on stochastic methods and modem rendering methodologies. This provides insight into the issues surrounding Monte Carlo integration both in the general and rendering specific contexts, along with an appreciation for the complexities of solving global light transport. Alternative methods that aim to address these issues are discussed, providing an insight into modem rendering paradigms and their characteristics. Thus, an understanding of the key aspects is obtained, that is necessary to build up and discuss the novel research and contributions to the field developed throughout this thesis. First, a path space filtering strategy is proposed that allows the path-based space of light transport to be classified into distinct subsets. This permits the novel combination of robust path tracing and recent progressive photon mapping algorithms to handle each subset based on the characteristics of the light transport in that space. This produces a hybrid progressive rendering technique that utilises the strengths of existing state of the art Monte Carlo and photon mapping methods to provide efficient and consistent rendering of complex scenes with vanishing bias. The second original contribution is a probabilistic image-based filtering and sample clustering framework that provides high quality previews of global illumination whilst remaining aware of high frequency detail and features in geometry, materials and the incident illumination. As will be seen, the challenges of edge-aware noise reduction are numerous and long standing, particularly when identifying high frequency features in noisy illumination signals. Discontinuities such as hard shadows and glossy reflections are commonly overlooked by progressive filtering techniques, however by dividing path space into multiple layers, once again based on utilising path vertex data, the overlapping illumination of varying intensities, colours and frequencies is more effectively handled. Thus noise is removed from each layer independent of features present in the remaining path space, effectively preserving such features
Técnicas de aceleración para el método de radiosidad jerárquica
[Resumen]
Uno de los métodos que mejor modelan el comportamiento real de la luz
en la búsqueda del realismo visual en imágenes construidas de forma sintética
es el método de radiosidad. Este método presenta, sin embargo, el
inconveniente de un alto coste computacional, tanto en tiempo de cálculo como
en almacenamiento. Entre las numerosas variantes surgidas con el objetivo de
rebajar la complejidad del método clásico destaca el método de radiosidad
jerárquica, basado en la aplicación de una subdivisión adaptativa de la escena.
El método de radiosidad jerárquica mantiene, no obstante, todavÃa una
elevada complejidad que dificulta su explotación en escenas de gran tamaño.
En este trabajo se han tratado de desarrollar nuevas soluciones para algunos
de los diversos problemas que el método jerárquico de radiosidad plantea.
El primer punto en el que se centra el trabajo es en la determinación
de la visibilidad entre los distintos objetos de una escena (principal cuello
de botella en un algoritmo de iluminación), analizando las principales
soluciones existentes y proponiendo una nueva aproximación al problema,
basada en aprovechar el principio de localidad en el espacio de direcciones
de los rayos lanzados durante el proceso.
Otro aspecto desarrollado en la tesis es la utilización de modelos
geométricos de diferentes complejidades que permitan el tratamiento de
escenas grandes con objetos detallados, independizando la correcta simulación
de la distribución de la energÃa en la escena de la complejidad geométrica
de los objetos que la componen. A este respecto se presenta una propuesta
para el cálculo de la radiosidad jerárquica basada en el uso de esquemas de
subdivisión de superficies.
Por último, en esta tesis se propone una solución paralela para el
aprovechamiento de sistemas distribuidos en la aplicación del método de
radiosidad jerárquica en escenas de gran tamaño, realizando una distribución
real de la geometrÃa de la escena entre todas las memorias del sistema y con
una aproximación multi-hilo para la ejecución, lo que va a permitir un mejor
ajuste de la granularidad utilizada en la paralelización de las tareas.[Resumo]
Uns dos métodos que mellor modelan o comportamento real da luz na
búsqueda do realismo visual en imaxes construidas de forma sintética é o
método de radiosidade. Este método presenta, sen embargo, a desvantaxe dun
alto coste computacional, tanto en tempo de cálculo coma en almacenamento.
Entre as numerosas variantes xurdidas co obxectivo de rebaixar a complexidade
do método clásico sobresae o método de radiosidade xerárquica, baseado na
aplicación dunha subdivisión adaptativa na escea.
O método de radiosidade xerárquica mantén todavÃa, asà a todo, unha
elevada complexidade que dificulta a súa explotación en esceas de gran
tamaño. Neste traballo tratáronse de desenvolver novas solucións para algúns
dos diversos problemas plantexados polo método de radiosidade xerárquica.
O primeiro punto ao que se presta atención no traballo é á
determinación de visibilidade entre os distintos obxectos dunha escea
(principal colo de botella nun algoritmo de iluminación), analizando as
principais solucións existentes e propondo unha nova aproximación ao problema
baseada no aproveitamento do principio de localidade no espazo de direccións
dos raios lanzados durante o proceso.
Outro aspecto desenvolvido na tese é a utilización de modelos
xeométricos de diferente complexidad que permitan o tratamento de esceas
grandes con obxectos moi detallados, independizando a correcta simulación
da distribución da enerxÃa na escea da complexidade xeométrica dos obxectos
que a compoñen. Ao respecto preséntase unha proposta para o cálculo da
radiosidade xerárquica baseada no uso de esquemas de subdivisión de
superficies.
Por último, nesta tese proponse unha solución paralela para o
aproveitamento de sistemas distribuidos na aplicación do método de
radiosidade xerárquica en esceas de gran tamaño, facendo unha distribución
real da xeometrÃa da escea entre todas as memorias do sistema e cunha
aproximación multi-fÃo na execución, o que vai permitir un mellor axuste da
granularidade empregada na paralelización das tarefas.[Absract]
Radiosity is one of the best methods in modelling the physical
behaviour of light in a synthetic scene. However, the main drawback is the
high requirements in terms of computational and storage costs. Hierarchical
radiosity stands out among the different alternatives to reduce complexity
in classic radiosity, applying an adaptive subdivision on scene.
Hierarchical radiosity still presents, anyway, a high complexity that
difficults to process really large scenes. In this work we have developed
new solutions for several of the most common bottenecks presented in
hierarchical radiosity.
Our first goal is to accelerate visibility determination (most
consuming task in global illumination), analysing the main existing solutions
and proposing a new method based in taking advantage of directional coherence
for the rays casted during process.
Other aspect we have touched in the thesis is the use of
multiresolution models that allow to work with very complex geometrical
models in our input scene, isolating geometry detail and illumination detail.
Specifically, we have developed a new method to compute hierarchical radiosity
based on surface subdivision.
Finally, a new parallel solution for computing hierarchical radiosity
on multiprocessor systems, allowing huge input scenes is presented. The
scene is totally distributed (geometrically and computationally) among the
processors in our proposal, and a multi-thread implementation improves the
flexibility in the granularity of the parallel execution
Técnicas de altas prestaciones para métodos de iluminación global
[Resumen] El gran interés en los métodos de iluminación global se debe a sus múltiples
aplicaciones y al realismo de sus imágenes resultantes. La investigación presentada en
esta memoria se centra en mejorar computacionalmente el algoritmo de radiosidad,
planteando estrategias tanto para métodos determinÃsticos como estocásticos.
Respecto de los métodos determinÃsticos, se expondrán nuestras implementaciones
en un sistema distribuido del algoritmo de radiosidad progresiva, utilizando el
paradigma de paso de mensajes. Estas implementaciones están basadas en la división
de la escena de una manera uniforme o no uniforme. Además, se usa la técnica de
las máscaras de visibilidad para el cálculo de visibilidad entre elementos de distintos
subescenas. También se demuestra que estas metodologÃas pueden reducir el tiempo
de ejecución secuencial.
Relativo a las soluciones estocásticas, presentamos dos implementaciones del método
de relajación estocástica de Monte Carlo para radiosidad: en un sistema distribuido
y en una Graphics Processing Unit (GPU). La primera se basa en tres técnicas:
partición de la escena, empaquetamiento de rayos y determinación distribuida del
fin de iteración. En la implementación GPU, además de la partición de la escena se
empleó la simplificación de la malla de elementos y una organización eficiente de la
ejecución de las tareas.[Resumo] O grande interese nos métodos de iluminación global débese ás súas múltiples
aplicacións e ao realismo das súas imaxes resultantes. A investigación presentada
nesta memoria céntrase en mellorar computacionalmente o algoritmo de radiosidade,
formulando estratexias tanto para métodos determinÃsticos como estocásticos.
Respecto dos métodos determinÃsticos, exporanse as nosas implementacións nun
sistema distribuÃdo do algoritmo de radiosidade progresiva, utilizando o paradigma
de paso de mensaxes. Estas implementacións están baseadas na división da escena
dunha maneira uniforme ou non uniforme. Ademais, úsase a técnica das máscaras de
visibilidade para o cálculo de visibilidade entre elementos de distintas subescenas.
Tamén se demostra que estas metodoloxÃas poden reducir o tempo de execución
secuencial.
Relativo as solucións estocásticas, presentamos dúas implementacións do método
de relaxación estocástica de Monte Carlo para radiosidade: nun sistema distribuÃdo
e nunha Graphics Processing Unit (GPU). A primeira baséase en tres técnicas:
partición da escena, empaquetamento de raios e determinación distribuÃda do fin de
iteración. Na implementación GPU, ademais da partición da escena empregouse a
simplificación da malla de elementos e unha organización eficiente da execución das
tarefas.[Abstract] The great interest in global illumination methods is due to their multiple applications
and the realism of the resulting images. The research presented in the
present thesis focuses on computationally improving the radiosity algorithm, proposing
strategies for both deterministic and stochastic approaches.
For deterministic approaches, our implementations of the progressive radiosity
algorithm will be demonstrated in a distributed system , using the message passing
paradigm. These implementations are based on the partitioning of the scene in a
uniform or non uniform manner. Furthermore, the technique of visibility masks is
employed to calculate the visibility between elements in different subscenes. It is also
shown that these methods are capable of reducing the sequential execution time.
With regard to stochastic solutions, we present two implementations of the stochastic
relaxation method for Monte Carlo radiosity: in a distributed system and in
a Graphics Processing Unit (GPU). The first is based on three techniques: partition
of the scene, ray packing strategy and distributed testing of the end of each iteration.
In the GPU implementation, as well as the partition of the scene a simplified
mesh of the elements was used along with an efficient thread scheduling
LIPIcs, Volume 244, ESA 2022, Complete Volume
LIPIcs, Volume 244, ESA 2022, Complete Volum
Proceedings of the International Workshop on Medical Ultrasound Tomography: 1.- 3. Nov. 2017, Speyer, Germany
Ultrasound Tomography is an emerging technology for medical imaging that is quickly approaching its clinical utility. Research groups around the globe are engaged in research spanning from theory to practical applications. The International Workshop on Medical Ultrasound Tomography (1.-3. November 2017, Speyer, Germany) brought together scientists to exchange their knowledge and discuss new ideas and results in order to boost the research in Ultrasound Tomography