7 research outputs found
Accelerated volumetric reconstruction from uncalibrated camera views
While both work with images, computer graphics and computer vision are inverse problems. Computer graphics starts traditionally with input geometric models and produces image sequences. Computer vision starts with input image sequences and produces geometric models. In the last few years, there has been a convergence of research to bridge the gap between the two fields.
This convergence has produced a new field called Image-based Rendering and Modeling (IBMR). IBMR represents the effort of using the geometric information recovered from real images to generate new images with the hope that the synthesized
ones appear photorealistic, as well as reducing the time spent on model creation.
In this dissertation, the capturing, geometric and photometric aspects of an IBMR system are studied. A versatile framework was developed that enables the reconstruction of scenes from images acquired with a handheld digital camera. The proposed system targets applications in areas such as Computer Gaming and Virtual Reality, from a lowcost perspective. In the spirit of IBMR, the human operator is allowed to provide the high-level information, while underlying algorithms are used to perform low-level computational work. Conforming to the latest architecture trends, we propose a streaming voxel carving method, allowing a fast GPU-based processing on commodity hardware
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
Interactive dynamic objects in a virtual light field
National audienceThis report builds upon existing work on Virtual Light Fields (VLF). A previous VLF implementation allows interactive walkthrough of a static globally illuminated scene on a modern desktop computer. This report outlines enhancements to this implementation which allow movable geometry to be added to existing VLF solutions. Two diffuse shading modes are implemented for the dynamic geometry. A fast simple mode which approximates the emitters in the VLF using OpenGL light sources and a slower advanced mode which approximates the diffuse inter-reflection and soft shadows received on the dynamic geometry using information from the VLF. In both modes the dynamic geometry casts hard shadows onto existing diffuse geometry in the scene. Both modes can achieve interactive rates on a high specification modern desktop computer, although advanced mode is limited to simple dynamic objects due to the expensive diffuse gathering step. Potential optimisations are discussed
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
Simulating Photon Mapping for Real-time Applications
This paper introduces a novel method for simulating photon mapping for real-time applications. First we introduce a new method for selectively redistributing photons. Then we describe a method for selectively updating the indirect illumination. The indirect illumination is calculated using a new GPU accelerated final gathering method and the illumination is then stored in light maps. Caustic photons are traced on the CPU and then drawn using points in the framebuffer, and finally filtered using the GPU. Both diffuse and non-diffuse surfaces can be handled by calculating the direct illumination on the GPU and the photon tracing on the CPU. We achieve real-time frame rates for dynamic scenes