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Circularly Polarized
Spherical Illumination Reflectometry
We present a novel method for surface
reflectometry from a few observations of a scene under a single uniform
spherical field of circularly polarized illumination. The method is based
on a novel analysis of the Stokes reflectance field of circularly polarized
spherical illumination and yields per-pixel estimates of diffuse albedo,
specular albedo, index of refraction, and specular roughness of isotropic BRDFs. To infer these reflectance parameters, we
measure the Stokes parameters of the reflected light at each pixel by
taking four photographs of the scene, consisting of three photographs with
differently oriented linear polarizers in front of the camera, and one additional
photograph with a circular polarizer. The method only assumes knowledge of
surface orientation, for which we make a few additional photometric
measurements. We verify our method with three different lighting setups,
ranging from specialized to off-the shelf hardware, which project either
discrete or continuous fields of spherical illumination. Our technique
offers several benefits: it estimates a more detailed model of per-pixel
surface reflectance parameters than previous work, it requires a relatively
small number of measurements, it is applicable to a wide range of material
types, and it is completely viewpoint independent.
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Estimating
Specular Roughness and Anisotropy from
Second Order Spherical Gradient Illumination
We present a novel method for estimating
specular roughness and tangent vectors, per surface point, from polarized
second order spherical gradient illumination patterns. We demonstrate that
for isotropic BRDFs, only three second order
spherical gradients are sufficient to robustly estimate spatially varying
specular roughness. For anisotropic BRDFs, an
additional two measurements yield specular roughness and tangent vectors
per surface point. We verify our approach with different illumination
configurations which project both discrete and continuous fields of
gradient illumination. Our technique provides a direct estimate of the
per-pixel specular roughness and thus does not require off-line numerical
optimization that is typical for the measure-and-fit approach to classical
BRDF modeling.
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Practical Modeling
and Acquisition of Layered Facial Reflectance
We present a practical method for
modeling layered facial reflectance consisting of specular reflectance, single
scattering, and shallow and deep subsurface scattering. We estimate
parameters of appropriate reflectance models for each of these layers from
just 20 photographs recorded in a few seconds from a single viewpoint. We
extract spatially-varying specular reflectance and single scattering
parameters from polarization-difference images under spherical and point
source illumination. Next, we employ direct-indirect separation to
decompose the remaining multiple scattering observed under
cross-polarization into shallow and deep scattering components to model the
light transport through multiple layers of skin. Finally, we match
appropriate diffusion models to the extracted shallow and deep scattering
components for different regions on the face. We validate our technique by
comparing renderings of subjects to reference photographs recorded from
novel viewpoints and under novel illumination conditions.
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BRDF Acquisition with
Basis Illumination
Realistic
descriptions of surface reflectance have long been a topic of interest in
both computer vision and computer graphics research. In this work, we
describe a novel and fast approach for the acquisition of bidirectional
reflectance distribution functions (BRDFs). We
develop a novel theory for directly measuring BRDFs
in a basis representation by projecting incident light as a sequence of
basis functions from a spherical zone of directions. We derive an
orthonormal basis over spherical zones that is
ideally suited for this task. BRDF values outside the zonal directions are
extrapolated by re-projecting the zonal measurements into a spherical
harmonics basis, or by fitting analytical reflection models to the data.
For specular materials, we experiment with alternative basis acquisition approaches
such as measuring the response to basis defined by an anlytical
model as a way of optically fitting the BRDF to such a representation. We
verify this approach with a compact optical setup that requires no moving
parts and only a small number of image measurements. Using this approach, a
BRDF can be measured in just a few minutes.
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Correlated Visibility
Sampling for Direct Illumination
State-of-the-art importance sampling
strategies for direct illumination take into account the importance of the
incident illumination, as well as the surface BRDF. Hence, these techniques
achieve low variance in unoccluded regions.
However, the resulting images still have noise in partially occluded regions
as these techniques do not take visibility into account during the sampling
process. We introduce the notion of correlated visibility sampling, which
considers visibility in partially occluded regions during the sampling
process, thereby improving the quality of the shadowed regions. We aim to
draw samples in the partially occluded regions according to the triple
product of the incident illumination, BRDF and visibility using Monte Carlo sampling followed by Metropolis sampling.
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Sequential Sampling
for Dynamic Environment Map Illumination
Sampling
complex illumination in the form of environment maps has received a lot of
attention in computer graphics. Recent work in this area has demonstrated
that drawing samples from the product of light and BRDF produces superior
results to other sampling strategies. However, existing methods in this
area consider only individual frames, and do not take advantage of
coherence in animations. In this paper, we introduce a sequential sampling
approach for dynamic environment map illumination. Our algorithm
efficiently samples from the product of illumination and BRDF, while
exploiting temporal coherence. We demonstrate significant performance
benefits over existing methods.
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Bidirectional
Importance Sampling for Direct Illumination
Image-based
representations for illumination can capture complex real-world lighting
that is difficult to represent in other forms. Current importance sampling
strategies for image-based illumination have difficulties in cases where
both the illumination and the surface BRDF contain important high-frequency
detail, for example, when a specular surface is illuminated by an
environment map containing small light sources. We introduce the notion of
bidirectional importance sampling, in which samples are drawn from the
product distribution of both the surface reflectance and the light source
energy. While this approach makes the sample selection process more
expensive, we drastically reduce the number of visibility tests required to
obtain good image quality. As a consequence, we achieve significant quality
improvements over previous sampling strategies for the same compute time.
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Real Illumination
from Virtual Environments
We introduce a method for actively
controlling the illumination in a room so that it is consistent with a
virtual world. In combination with a high dynamic range display, the system
produces both uniform and directional illumination at intensity levels
covering a wide range of real-world environments. It thereby allows natural
adaptation processes of the human visual system to take place, for example
when moving between bright and dark environments. In addition, the
directional illumination provides additional information about the
environment in the user s peripheral field of view. We describe both the
hardware and the software aspects of our system. We also conducted an
informal survey to determine whether users prefer the dynamic illumination
over constant room illumination in an entertainment setting.
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High Dynamic
Range Display Systems
The dynamic range of many real-world
environments exceeds the capabilities of current display technology by
several orders of magnitude. In this paper we discuss the design of two
different display systems that are capable of displaying images with a
dynamic range much more similar to that encountered in the real world. The
first display system is based on a combination of an LCD panel and a DLP
projector, and can be built from off-the-shelf components. While this
design is feasible in a lab setting, the second display system, which
relies on a custom-built LED panel instead of the projector, is more
suitable for usual office workspaces and commercial applications. We
describe the design of both systems as well as the software issues that arise.
We also discuss the advantages and disadvantages of the two designs and
potential applications for both systems.
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Simple Blurry
Reflection with Environment Maps
We
present a technique which uses existing OpenGL capabilities to approximate
the effect of blurry specular reflections and indirect diffuse
illumination. It makes use of environment maps, mipmapping
with level of detail control, and possibly texture borders. The method is
extremely simple to implement, in some cases requiring just a single
additional OpenGL statement.
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