36 research outputs found
Fast Back-Projection for Non-Line of Sight Reconstruction
Recent works have demonstrated non-line of sight (NLOS) reconstruction by
using the time-resolved signal frommultiply scattered light. These works
combine ultrafast imaging systems with computation, which back-projects the
recorded space-time signal to build a probabilistic map of the hidden geometry.
Unfortunately, this computation is slow, becoming a bottleneck as the imaging
technology improves. In this work, we propose a new back-projection technique
for NLOS reconstruction, which is up to a thousand times faster than previous
work, with almost no quality loss. We base on the observation that the hidden
geometry probability map can be built as the intersection of the three-bounce
space-time manifolds defined by the light illuminating the hidden geometry and
the visible point receiving the scattered light from such hidden geometry. This
allows us to pose the reconstruction of the hidden geometry as the voxelization
of these space-time manifolds, which has lower theoretic complexity and is
easily implementable in the GPU. We demonstrate the efficiency and quality of
our technique compared against previous methods in both captured and synthetic
dat
Bidirectional Rendering of Vector Light Transport
On the foundations of many rendering algorithms it is the symmetry between the path traversed by light and its adjoint path starting from the camera. However, several effects, including polarization or ¿uorescence, break that symmetry, and are de¿ned only on the direction of light propagation. This reduces the applicability of bidirectional methods that exploit this symmetry for simulating effectively light transport. In this work, we focus on how to include these non-symmetric effects within a bidirectional rendering algorithm. We generalize the path integral to support the constraints imposed by non-symmetric light transport. Based on this theoretical framework, we propose modi¿cations on two bidirectional methods, namely bidirectional path tracing and photon mapping, extending them to support polarization and ¿uorescence, in both steady and transient stat
A Radiative Transfer Framework for Spatially-Correlated Materials
We introduce a non-exponential radiative framework that takes into account
the local spatial correlation of scattering particles in a medium. Most
previous works in graphics have ignored this, assuming uncorrelated media with
a uniform, random local distribution of particles. However, positive and
negative correlation lead to slower- and faster-than-exponential attenuation
respectively, which cannot be predicted by the Beer-Lambert law. As our results
show, this has a major effect on extinction, and thus appearance. From recent
advances in neutron transport, we first introduce our Extended Generalized
Boltzmann Equation, and develop a general framework for light transport in
correlated media. We lift the limitations of the original formulation,
including an analysis of the boundary conditions, and present a model suitable
for computer graphics, based on optical properties of the media and statistical
distributions of scatterers. In addition, we present an analytic expression for
transmittance in the case of positive correlation, and show how to incorporate
it efficiently into a Monte Carlo renderer. We show results with a wide range
of both positive and negative correlation, and demonstrate the differences
compared to classic light transport
Recent advances in transient imaging: A computer graphics and vision perspective
Transient imaging has recently made a huge impact in the computer graphics and computer vision fields. By capturing, reconstructing, or simulating light transport at extreme temporal resolutions, researchers have proposed novel techniques to show movies of light in motion, see around corners, detect objects in highly-scattering media, or infer material properties from a distance, to name a few. The key idea is to leverage the wealth of information in the temporal domain at the pico or nanosecond resolution, information usually lost during the capture-time temporal integration. This paper presents recent advances in this field of transient imaging from a graphics and vision perspective, including capture techniques, analysis, applications and simulation
Analyzing interfaces and workflows for light field editing
With the increasing number of available consumer light field cameras, such as Lytro, Raytrix, or Pelican Imaging, this new form of photography is progressively becoming more common. However, there are still very few tools for light field editing, and the interfaces to create those edits remain largely unexplored. Given the extended dimensionality of light field data, it is not clear what the most intuitive interfaces and optimal workflows are, in contrast with well-studied two-dimensional (2-D) image manipulation software. In this work, we provide a detailed description of subjects' performance and preferences for a number of simple editing tasks, which form the basis for more complex operations. We perform a detailed state sequence analysis and hidden Markov chain analysis based on the sequence of tools and interaction paradigms users employ while editing light fields. These insights can aid researchers and designers in creating new light field editing tools and interfaces, thus helping to close the gap between 4-D and 2-D image editing
Second-order Occlusion-aware Volumetric Radiance Caching
Accurate simulation of light transport in participating media is expensive, due to the many sca ering events. However, the band- limiting e ect of sca ering in media makes this kind of light trans- port very suitable for adaptive sampling and reconstruction tech- niques. In this work we present a novel algorithm that adaptively samples radiance from sparse points in the medium using up-to second-order occlusion-aware derivatives to determine when in- terpolation is appropriate. We derive our metric from each point’s incoming light eld. We use a proxy triangulation-based repre- sentation of the radiance re ected by the surrounding medium and geometry to e ciently compute the rst- and second-order derivatives of the radiance at the cache points while accounting for occlusion changes. We validate the quality of our approach on a self-contained two-dimensional model for light transport in media. en we show how our results generalize to practical three- dimensional scenarios, where we show much be er results while reducing computation time up to a 30% compared to previous work
Recent advances in transient imaging: A computer graphics and vision perspective
Transient imaging has recently made a huge impact in the computer graphics and computer vision fields. By capturing, reconstructing, or simulating light transport at extreme temporal resolutions, researchers have proposed novel techniques to show movies of light in motion, see around corners, detect objects in highly-scattering media, or infer material properties from a distance, to name a few. The key idea is to leverage the wealth of information in the temporal domain at the pico or nanosecond resolution, information usually lost during the capture-time temporal integration. This paper presents recent advances in this field of transient imaging from a graphics and vision perspective, including capture techniques, analysis, applications and simulation
Second-Order Occlusion-Aware Volumetric Radiance Caching
We present a second-order gradient analysis of light transport in
participating media and use this to develop an improved radiance caching
algorithm for volumetric light transport. We adaptively sample and interpolate
radiance from sparse points in the medium using a second-order Hessian-based
error metric to determine when interpolation is appropriate. We derive our
metric from each point's incoming light field, computed by using a proxy
triangulation-based representation of the radiance reflected by the surrounding
medium and geometry. We use this representation to efficiently compute the
first- and second-order derivatives of the radiance at the cache points while
accounting for occlusion changes.
We also propose a self-contained two-dimensional model for light transport in
media and use it to validate and analyze our approach, demonstrating that our
method outperforms previous radiance caching algorithms both in terms of
accurate derivative estimates and final radiance extrapolation. We generalize
these findings to practical three-dimensional scenarios, where we show improved
results while reducing computation time by up to 30\% compared to previous
work