445 research outputs found
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
Instant global illumination on the GPU using OptiX
OptiX, a programmable ray tracing engine, has been recently made available by NVidia, relieving rendering researchers from the idiosyncrasies of efficient ray tracing programming and allowing them to
concentrate on higher level algorithms, such as interactive global illumination.
This paper evaluates the performance of the Instant Global
Illumination algorithm on OptiX as well as the impact of three di fferent optimization techniques: imperfect visibility, downsampling and interleaved sampling. Results show that interactive frame rates are indeed achievable, although the combination of all optimization techniques leads to the appearance of artifacts that compromise image quality. Suggestions are presented on possible ways to overcome these limitations
Autonomous Lighting Agents in Photon Mapping
proceedings of ISVC'05International audienceIn computer graphics, global illumination algorithms such as photon mapping require to gather large volumes of data which can be heavily redundant.We propose both a new characterization of useful data and a new optimization method for the photon mapping algorithm using structures borrowed from Artificial Intelligence such as autonomous agents. Our autonomous lighting agents efficiently gather large amounts of useful data and are used to make decisions during rendering. It induces less photons being cast and shorter rendering times in both photon casting and rendering phase of the photon mapping algorithm which leads to an important decrease of memory occupation and slightly shorter rendering times for equal image quality
Efficient Many-Light Rendering of Scenes with Participating Media
We present several approaches based on virtual lights that aim at capturing the light transport without compromising quality, and while preserving the elegance and efficiency of many-light rendering. By reformulating the integration scheme, we obtain two numerically efficient techniques; one tailored specifically for interactive, high-quality lighting on surfaces, and one for handling scenes with participating media
Refinement criteria for high fidelity interactive walkthroughs
Physically based global illumination rendering at interactive frame rates would enable users to navigate within complex virtual environments, such as archaeological models. These algorithms, however, are computationally too demanding to allow interactive navigation on current PCs. A technique based on image subsampling and spatiotemporal coherence among successive frames is exploited, while resorting to progressive refinement whenever there is available computing power. A physically based ray tracer (Radiance) is used to compute reflected radiance at the model's triangles vertices. Progressive refinement is achieved increasing the sampling frequency by subdividing certain triangles and requesting shading information for the resulting vertices. This paper proposes and evaluates different criteria for selecting which triangles to subdivide. A random criterium and two criteria based on Normalized Luminance Differences are evaluated: one operating on image space, the other on object space. Results, obtained with a model of an old roman town, show that the object space criterium is able to locate and represent visual discontinuities, such as shadows, and does so requiring less triangle subdivisions than the other two.Fundação para a Ciência e a Tecnologia (FCT) - POSI/CHS/42041/2001
High fidelity walkthroughs in archaeology sites
Comunicação apresentada no 6th International Symposium on Virtual Reality, Archaeology and Cultural Heritage (VAST 2005), Pisa, Italy, 8-11 Novembro 2005.Fast and affordable computing systems currently support walkthroughs into virtual reconstructed sites, with fast frame
rate generation of synthetic images. However, archaeologists still complain about the lack of realism in these interactive tours,
mainly due to the false ambient illumination. Accurate visualizations require physically based global illumination models
to render the scenes, which are computationally too demanding.
Faster systems and novel rendering techniques are required: current clusters provide a feasible and
affordable path towards these goals, and we developed a framework to support smooth virtual walkthroughs,
using progressive rendering to converge to high fidelity images whenever computing power surplus is available.
This framework exploits spatial and temporal coherence among
successive frames, serving multiple clients that share and
interact with the same virtual model, while maintaining each its
own view of the model. It is based on a three-tier architecture:
the outer layer embodies light-weight visualization clients, which
perform all the user interactions and display the final images
using the available graphics hardware; the inner layer is a
parallel version of a physically based ray tracer running on a
cluster of off-the-shelf PCs; in the middle layer lies the shading
management agent (SMA), which monitors the clients' states,
supplies each with properly shaded 3D points, maintains a cache of
previously rendered geometry and requests relevant shading samples
to the parallel renderer, whenever required.
A prototype of a high fidelity walkthrough in the archaeologic
virtual model of the roman town of Bracara Augusta was developed,
and the current evaluation tests aimed to measure the performance
improvements due to the use of SMA caches and associated parallel
rendering capabilities. Preliminary results show that interactive
frame rates are sustainable and the system is highly responsive.Fundação para a Ciência e Tecnologia (FCT) - POSI/CHS/42041/2001
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