Occlusion Cameras
Camera Model Design for Alleviating Disocclusion Errors
Summary
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One advantage of image-based rendering
is scene-independent rendering cost. However, rendering a scene with a
single reference depth image produces disocclusion errors: samples are
lacking for surfaces that are visible in the desired view, but not in
the reference view. Even small view changes produce noticeable errors.
We introduce occlusion cameras,
a class of non-pinhole cameras whose rays reach around occluders to
gather samples that are hidden in the reference view but are likely to
become visible in nearby views. These initially hidden samples alleviate
disocclusion errors. Like regular depth images, occlusion-camera images
have a single layer thus the number of samples they contain is bounded
by the image resolution and connectivity is defined implicitly.
Occlusion cameras provide fast projection so reference images are
constructed efficiently with the hardware accelerated feed-forward
pipeline. We have developed two members of the occlusion camera class:
the single pole occlusion camera,
and the depth discontinuity
occlusion camera.
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Single Pole Occlusion Camera (SPOC)
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The SPOC is obtained by applying a
radial 3D distortion to the rays of the reference view. The distortion
is centered at the occluder. A single SPOC covers the entire silhouette
of the occluder, whereas many planar pinhole cameras are needed to
achieve the same effect. Given a scene triangle and an SPOC, a closed
form undistortion expression from the image plane to the triangle plane
allows rasterization in the distorted domain, which is implemented on
the GPU.
SPOC images constructed on the GPU at 11 and 3fps. |
Samples contributed by SPOC highlighted in pink. |
Comparison between using a depth image, an SPOC image,
and original geometry. |
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Depth
Discontinuity Occlusion Camera (DDOC)
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The DDOC is defined by the reference
view and the geometry it
encompasses. The reference planar pinhole camera is 3D distorted at
depth discontinuities. The distortion is fine-grain controlled with a
distortion map, which allows handling complex scenes. The camera model
is customized for every reference view. The DDOC enables fast projection
of 3D points, so the reference image is constructed efficiently with the
feed-forward graphics pipeline. The DDOC reference image provides a
high-quality, bounded-cost approximation of complex scenes.
DDOC reference image. |
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Frames rendered from depth image and DDOC image. |
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3D Display Rendering Acceleration
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Volumetric 3D displays allow the user to explore a 3D
scene free of joysticks, keyboards, goggles, or trackers. For nontrivial
scenes, computing and transferring a 3D image to the
display takes hundreds of seconds, which is a serious bottleneck
for many applications. The OCRI is
a compact scene representation that stores only and all scene
samples that are visible from a viewing volume centered at a
reference viewpoint. The OCRI enables computing and
transferring the 3D image an order of magnitude faster than
when the entire scene is processed. When compared with a depth image, an OCRI provides much improved scene coverage with no increase in rendering cost on the 3D display.
Photo of 3D display bunny model rendered with a Depth Image
viewed from the reference point. |
Photo of 3D display bunny model rendered with an OCRI viewed
from the reference point. |
Photo of 3D display bunny model rendered with Real Geometry
viewed from the reference point. |
Photo of 3D display bunny model rendered with a Depth Image
viewed from 4" left of the reference point. |
Photo of 3D display bunny model rendered with an OCRI viewed
from 4" left of the reference point. |
Photo of 3D display bunny model rendered with a Depth Image
viewed from the side. |
Photo of 3D display bunny model rendered with an OCRI viewed
from the side. |
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