Sample-Based Camera
A General Camera Model for Graphics, Visualization, and Vision
Feed-forward reflection rendering
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The
sample-based camera (SBC) is a general camera constructed from a given set of
rays. The first application of SBCs that we have explored is rendering
accurate reflections on curved reflectors at interactive rates. In order to
render reflections with the feed forward graphics pipeline, one has to
compute the image points where a reflected scene point projects. For general
reflectors, the problem of projecting reflected vertices does not have a
closed form solution. The SBC is a collection of BSP trees of pinhole cameras
that jointly approximate the projection function. One BSP tree is built for
each convex component of the reflector. The projection error is controlled by
the user, the typical upper bound we use is 1 pixel.
The method supports change of view, moving objects and reflectors, higher
order reflections, view-dependent lighting of reflected objects, and complex
reflector surface properties. The SBC approach excels in the case of large
smooth reflectors like the ones in the images below. Complex reflectors perturb
the desired image rays considerably: less coherence and more intersections make
the hierarchical space partitioning less efficient. We handle complex reflectors
with a different approach, based on approximating the reflected scene with
impostors. |
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Fresnel
& attenuation with distance effects.
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1st and
2nd order reflections rendered with SBC (left, 30 fps) and
ray tracing (right). Image resolution: 1140x960.
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The class of k-ray cameras
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The SBC provides an efficient
and accurate approximation of a set of rays by leveraging ray coherence. The
initial set of rays is subdivided recursively in bundles until a bundle can
be approximated well enough with a simple camera. A simple camera is a camera
with closed form projection. In the first implementation of SBCs simple
cameras were modeled as planar pinhole cameras. Next we looked at devising
models for the simple cameras that are more powerful, in the sense of
providing a better approximation for a given set of rays. For this we
developed the class of k-ray non-pinhole cameras. A k-ray camera is built
from k given rays and has closed form projection. We have shown that such
cameras exist for k up to 6, when the projection equation has order 4. A
versatile simple camera model is the continuous 3-ray camera (C3RC), since it
offers projection continuity across the edge shared by two adjacent cameras.
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Continuity problem
across shared edge eliminated by continuous 3-ray cameras (C3RCs).
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Images rendered
with two adjacent regular 3-ray cameras and C3RCs, respectively.
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