145 research outputs found
Hardware Acceleration of Progressive Refinement Radiosity using Nvidia RTX
A vital component of photo-realistic image synthesis is the simulation of
indirect diffuse reflections, which still remain a quintessential hurdle that
modern rendering engines struggle to overcome. Real-time applications typically
pre-generate diffuse lighting information offline using radiosity to avoid
performing costly computations at run-time. In this thesis we present a variant
of progressive refinement radiosity that utilizes Nvidia's novel RTX technology
to accelerate the process of form-factor computation without compromising on
visual fidelity. Through a modern implementation built on DirectX 12 we
demonstrate that offloading radiosity's visibility component to RT cores
significantly improves the lightmap generation process and potentially propels
it into the domain of real-time.Comment: 114 page
Virtual light fields for global illumination in computer graphics
This thesis presents novel techniques for the generation and real-time rendering of globally illuminated
environments with surfaces described by arbitrary materials. Real-time rendering of globally illuminated
virtual environments has for a long time been an elusive goal. Many techniques have been developed
which can compute still images with full global illumination and this is still an area of active flourishing
research. Other techniques have only dealt with certain aspects of global illumination in order to speed
up computation and thus rendering. These include radiosity, ray-tracing and hybrid methods. Radiosity
due to its view independent nature can easily be rendered in real-time after pre-computing and storing
the energy equilibrium. Ray-tracing however is view-dependent and requires substantial computational
resources in order to run in real-time.
Attempts at providing full global illumination at interactive rates include caching methods, fast rendering
from photon maps, light fields, brute force ray-tracing and GPU accelerated methods. Currently,
these methods either only apply to special cases, are incomplete exhibiting poor image quality and/or
scale badly such that only modest scenes can be rendered in real-time with current hardware.
The techniques developed in this thesis extend upon earlier research and provide a novel, comprehensive
framework for storing global illumination in a data structure - the Virtual Light Field - that is
suitable for real-time rendering. The techniques trade off rapid rendering for memory usage and precompute
time. The main weaknesses of the VLF method are targeted in this thesis. It is the expensive
pre-compute stage with best-case O(N^2) performance, where N is the number of faces, which make the
light propagation unpractical for all but simple scenes. This is analysed and greatly superior alternatives
are presented and evaluated in terms of efficiency and error. Several orders of magnitude improvement
in computational efficiency is achieved over the original VLF method.
A novel propagation algorithm running entirely on the Graphics Processing Unit (GPU) is presented.
It is incremental in that it can resolve visibility along a set of parallel rays in O(N) time and can
produce a virtual light field for a moderately complex scene (tens of thousands of faces), with complex illumination
stored in millions of elements, in minutes and for simple scenes in seconds. It is approximate
but gracefully converges to a correct solution; a linear increase in resolution results in a linear increase in
computation time. Finally a GPU rendering technique is presented which can render from Virtual Light
Fields at real-time frame rates in high resolution VR presentation devices such as the CAVETM
Implementation and Analysis of an Image-Based Global Illumination Framework for Animated Environments
We describe a new framework for efficiently computing and storing global illumination effects for complex, animated environments. The new framework allows the rapid generation of sequences representing any arbitrary path in a view space within an environment in which both the viewer and objects move. The global illumination is stored as time sequences of range-images at base locations that span the view space. We present algorithms for determining locations for these base images, and the time steps required to adequately capture the effects of object motion. We also present algorithms for computing the global illumination in the base images that exploit spatial and temporal coherence by considering direct and indirect illumination separately. We discuss an initial implementation using the new framework. Results and analysis of our implementation demonstrate the effectiveness of the individual phases of the approach; we conclude with an application of the complete framework to a complex environment that includes object motion
Photorealistic physically based render engines: a comparative study
Pérez Roig, F. (2012). Photorealistic physically based render engines: a comparative study. http://hdl.handle.net/10251/14797.Archivo delegad
Doctor of Philosophy
dissertationReal-time global illumination is the next frontier in real-time rendering. In an attempt to generate realistic images, games have followed the film industry into physically based shading and will soon begin integrating global illumination techniques. Traditional methods require too much memory and too much time to compute for real-time use. With Modular and Delta Radiance Transfer we precompute a scene-independent, low-frequency basis that allows us to calculate complex indirect lighting calculations in a much lower dimensional subspace with a reduced memory footprint and real-time execution. The results are then applied as a light map on many different scenes. To improve the low frequency results, we also introduce a novel screen space ambient occlusion technique that allows us to generate a smoother result with fewer samples. These three techniques, low and high frequency used together, provide a viable indirect lighting solution that can be run in milliseconds on today's hardware, providing a useful new technique for indirect lighting in real-time graphics
Efficient From-Point Visibility for Global Illumination in Virtual Scenes with Participating Media
Sichtbarkeitsbestimmung ist einer der fundamentalen Bausteine fotorealistischer Bildsynthese. Da die Berechnung der Sichtbarkeit allerdings äußerst kostspielig zu berechnen ist, wird nahezu die gesamte Berechnungszeit darauf verwendet. In dieser Arbeit stellen wir neue Methoden zur Speicherung, Berechnung und Approximation von Sichtbarkeit in Szenen mit streuenden Medien vor, die die Berechnung erheblich beschleunigen, dabei trotzdem qualitativ hochwertige und artefaktfreie Ergebnisse liefern
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
Acceleration Techniques for Photo Realistic Computer Generated Integral Images
The research work presented in this thesis has approached the task of accelerating the
generation of photo-realistic integral images produced by integral ray tracing.
Ray tracing algorithm is a computationally exhaustive algorithm, which spawns one ray
or more through each pixel of the pixels forming the image, into the space containing
the scene. Ray tracing integral images consumes more processing time than normal
images. The unique characteristics of the 3D integral camera model has been analysed
and it has been shown that different coherency aspects than normal ray tracing can be
investigated in order to accelerate the generation of photo-realistic integral images.
The image-space coherence has been analysed describing the relation between rays and
projected shadows in the scene rendered. Shadow cache algorithm has been adapted in
order to minimise shadow intersection tests in integral ray tracing. Shadow intersection
tests make the majority of the intersection tests in ray tracing. Novel pixel-tracing
styles are developed uniquely for integral ray tracing to improve the image-space
coherence and the performance of the shadow cache algorithm. Acceleration of the
photo-realistic integral images generation using the image-space coherence information
between shadows and rays in integral ray tracing has been achieved with up to 41 % of
time saving. Also, it has been proven that applying the new styles of pixel-tracing does
not affect of the scalability of integral ray tracing running over parallel computers.
The novel integral reprojection algorithm has been developed uniquely through
geometrical analysis of the generation of integral image in order to use the tempo-spatial
coherence information within the integral frames. A new derivation of integral
projection matrix for projecting points through an axial model of a lenticular lens has
been established. Rapid generation of 3D photo-realistic integral frames has been
achieved with a speed four times faster than the normal generation
Interactive global illumination on the CPU
Computing realistic physically-based global illumination in real-time remains one
of the major goals in the fields of rendering and visualisation; one that has not
yet been achieved due to its inherent computational complexity. This thesis focuses
on CPU-based interactive global illumination approaches with an aim to
develop generalisable hardware-agnostic algorithms. Interactive ray tracing is reliant
on spatial and cache coherency to achieve interactive rates which conflicts
with needs of global illumination solutions which require a large number of incoherent
secondary rays to be computed. Methods that reduce the total number of
rays that need to be processed, such as Selective rendering, were investigated to
determine how best they can be utilised.
The impact that selective rendering has on interactive ray tracing was analysed
and quantified and two novel global illumination algorithms were developed,
with the structured methodology used presented as a framework. Adaptive Inter-
leaved Sampling, is a generalisable approach that combines interleaved sampling
with an adaptive approach, which uses efficient component-specific adaptive guidance
methods to drive the computation. Results of up to 11 frames per second
were demonstrated for multiple components including participating media. Temporal Instant Caching, is a caching scheme for accelerating the computation of
diffuse interreflections to interactive rates. This approach achieved frame rates
exceeding 9 frames per second for the majority of scenes. Validation of the results
for both approaches showed little perceptual difference when comparing
against a gold-standard path-traced image. Further research into caching led to
the development of a new wait-free data access control mechanism for sharing the
irradiance cache among multiple rendering threads on a shared memory parallel
system. By not serialising accesses to the shared data structure the irradiance
values were shared among all the threads without any overhead or contention,
when reading and writing simultaneously. This new approach achieved efficiencies
between 77% and 92% for 8 threads when calculating static images and animations.
This work demonstrates that, due to the
flexibility of the CPU, CPU-based
algorithms remain a valid and competitive choice for achieving global illumination
interactively, and an alternative to the generally brute-force GPU-centric
algorithms
A graphics processing unit based method for dynamic real-time global illumination
Real-time realistic image synthesis for virtual environments has been one of the most actively researched
areas in computer graphics for over a decade. Images that display physically correct illumination of an
environment can be simulated by evaluating a multi-dimensional integral equation, called the rendering
equation, over the surfaces of the environment. Many global illumination algorithms such as pathtracing,
photon mapping and distributed ray-tracing can produce realistic images but are generally unable
to cope with dynamic lighting and objects at interactive rates. It still remains one of most challenging
problems to simulate physically correctly illuminated dynamic environments without a substantial preprocessing
step.
In this thesis we present a rendering system for dynamic environments by implementing a customized
rasterizer for global illumination entirely on the graphics hardware, the Graphical Processing
Unit. Our research focuses on a parameterization of discrete visibility field for efficient indirect illumination
computation. In order to generate the visibility field, we propose a CUDA-based (Compute
Unified Device Architecture) rasterizer which builds Layered Hit Buffers (LHB) by rasterizing polygons
into multi-layered structural buffers in parallel. The LHB provides a fast visibility function for any direction
at any point. We propose a cone approximation solution to resolve an aliasing problem due to
limited directional discretization. We also demonstrate how to remove structure noises by adapting an
interleaved sampling scheme and discontinuity buffer. We show that a gathering method amortized with
a multi-level Quasi Mont Carlo method can evaluate the rendering equation in real-time.
The method can realize real-time walk-through of a complex virtual environment that has a mixture
of diffuse and glossy reflection, computing multiple indirect bounces on the fly. We show that our method
is capable of simulating fully dynamic environments including changes of view, materials, lighting and
objects at interactive rates on commodity level graphics hardware
- …