1,240 research outputs found
Progressive Transient Photon Beams
In this work we introduce a novel algorithm for transient rendering in
participating media. Our method is consistent, robust, and is able to generate
animations of time-resolved light transport featuring complex caustic light
paths in media. We base our method on the observation that the spatial
continuity provides an increased coverage of the temporal domain, and
generalize photon beams to transient-state. We extend the beam steady-state
radiance estimates to include the temporal domain. Then, we develop a
progressive version of spatio-temporal density estimations, that converges to
the correct solution with finite memory requirements by iteratively averaging
several realizations of independent renders with a progressively reduced kernel
bandwidth. We derive the optimal convergence rates accounting for space and
time kernels, and demonstrate our method against previous consistent transient
rendering methods for participating media
Photorealistic physically based render engines: a comparative study
PĂ©rez Roig, F. (2012). Photorealistic physically based render engines: a comparative study. http://hdl.handle.net/10251/14797.Archivo delegad
Manifold Path Guiding for Importance Sampling Specular Chains
Complex visual effects such as caustics are often produced by light paths
containing multiple consecutive specular vertices (dubbed specular chains),
which pose a challenge to unbiased estimation in Monte Carlo rendering. In this
work, we study the light transport behavior within a sub-path that is comprised
of a specular chain and two non-specular separators. We show that the specular
manifolds formed by all the sub-paths could be exploited to provide coherence
among sub-paths. By reconstructing continuous energy distributions from
historical and coherent sub-paths, seed chains can be generated in the context
of importance sampling and converge to admissible chains through manifold
walks. We verify that importance sampling the seed chain in the continuous
space reaches the goal of importance sampling the discrete admissible specular
chain. Based on these observations and theoretical analyses, a progressive
pipeline, manifold path guiding, is designed and implemented to importance
sample challenging paths featuring long specular chains. To our best knowledge,
this is the first general framework for importance sampling discrete specular
chains in regular Monte Carlo rendering. Extensive experiments demonstrate that
our method outperforms state-of-the-art unbiased solutions with up to 40x
variance reduction, especially in typical scenes containing long specular
chains and complex visibility.Comment: 14 pages, 19 figure
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
Exploring heterogeneous computing with advanced path tracing algorithms
The CG research community has a renewed interest on rendering algorithms based on path space integration, mainly due to new approaches to discover, generate and exploit relevant light paths while keeping the numerical integrator unbiased or, at the very least, consistent. Simultaneously, the current trend towards massive parallelism and heterogeneous environments, based on a mix of conventional computing units with accelerators, is playing a major role both in HPC and embedded platforms. To efficiently use the available resources in these and future systems, algorithms and software packages are being revisited and reevaluated
to assess their adequateness to these environments. This paper assesses the performance and scalability of three different path based algorithms running on homogeneous servers (dual multicore Xeons) and heterogeneous systems (those multicore plus manycore Xeon and NVidia Kepler GPU devices).
These algorithms include path tracing (PT), its bidirectional counterpart (BPT) and the more recent Vertex Connect and Merge (VCM). Experimental results with two conventional scenes (one mainly diffuse, the other exhibiting specular-diffuse-specular paths) show that all algorithms scale well across the different platforms, the actual scalability depending on whether shared data structures are accessed or not (PT vs. BPT vs. VCM).This work was supported by COMPETE: POCI-01-0145FEDER-007043 and FCT (Fundação para a Ciência e Tecnologia) within Project Scope (UID/CEC/00319/2013), by the Cooperation Program with the University of Texas at Austin and co-funded by the North Portugal Regional Operational Programme (ON.2 - O Novo Norte), under the National Strategic Reference Framework, through the European Regional Development Fund
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
Classification of Global Illumination Algorithms
This article describes and classifies various approaches for solving
the global illumination problem. The classification aims to show the similarities
between different types of algorithms. We introduce the concept of Light Manager,
as a central element and mediator between illumination algorithms in a
heterogeneous environment of a graphical system. We present results and analysis
of the implementation of the described ideas
Galactic Outflows and Photoionization Heating in the Reionization Epoch
We carry out a new suite of cosmological radiation hydrodynamic simulations
and explore the relative impacts on reionization-epoch star formation of
galactic outflows and photoionization heating. By itself, an extragalactic
ultraviolet background (EUVB) suppresses the luminosity function by less than
50% at z=6, overproducing the observed galaxy abundance by a factor of 3-5.
Galactic outflows restore agreement with observations without preventing
Population II star formation from reionizing the Universe by z=6. The resulting
EUVB suppresses star formation in halos with virial temperatures below 10^5K
but has a weaker impact in more massive halos. Nonetheless, the low-mass halos
contribute up to 50% of all ionizing photons owing to the EUVB's inhomogeneity.
Overall, star formation rate scales as halo mass M_h to the 1.3-1.4 in halos
with M_h=10^{8.2--10.2}\msun. This is a steeper dependence than is often
assumed in reionization models, boosting the expected power spectrum of 21
centimeter fluctuations on large scales. The luminosity function rises steeply
to at least M_1600=-13, indicating that reionization was driven by faint
galaxies (M_1600 >= -15) that have not yet been observed. Our models cannot
simultaneously explain observations of galaxies, the cosmic microwave
background, and the intergalactic medium. Increased dynamic range will
alleviate the existing discrepancies, but observations may still require
additional physics such as a variable ionizing escape fraction (abridged).Comment: 23 pages, 15 Figures, accepted to Ap
Path Throughput Importance Weights
Many Monte Carlo light transport simulations use multiple importance sampling
(MIS) to weight between different path sampling strategies. We propose to use
the path throughput to compute the MIS weights instead of the commonly used
probability density per area measure. This new formulation is equivalent to the
previous approach and results in the same weights as well as implementation.
However, it is more intuitive and can help in understanding the effects of
modifications to the weight function. We show some examples of required
modifications which are often neglected in implementations. Also, our new
perspective might help to derive MIS strategies for new samplers in the future.Comment: 7 pages, 1 figur
Simulations of a Scintillator Compton Gamma Imager for Safety and Security
We are designing an all-scintillator Compton gamma imager for use in security
investigations and remediation actions involving radioactive threat material.
To satisfy requirements for a rugged and portable instrument, we have chosen
solid scintillator for the active volumes of both the scatter and absorber
detectors. Using the BEAMnrc/EGSnrc Monte Carlo simulation package, we have
constructed models using four different materials for the scatter detector:
LaBr_3, NaI, CaF_2 and PVT. We have compared the detector performances using
angular resolution, efficiency, and image resolution. We find that while PVT
provides worse performance than that of the detectors based entirely on
inorganic scintillators, all of the materials investigated for the scatter
detector have the potential to provide performance adequate for our purposes.Comment: Revised text and figures, Presented at SORMA West 2008, Published in
IEEE Transactions on Nuclear Scienc
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