Art of Science 2013 Online Gallery
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Mirror sphere
Sema Berkiten (graduate student)
Department of Computer Science
In computer vision, there are several methods to create a 3-D model of
an object. One
of them, called "photometric stereo," uses multiple images of the
object under different
light directions. In this 3-D reconstruction technique, we need to
calculate surface
normals of the object as an intermediate step, and this picture is the
result of that step.
The image depicts the surface normals of a mirrored sphere. The
"surface normal" is the
direction perpendicular to a surface, and in this visualization
different normal directions
are represented with colors. For example, red means the object surface
is facing to
the right, green means the object surface is facing upwards, and blue
means the
object surface is facing towards the viewer, and other colors are
combinations of these
directions. The surface normals depicted in this image are not all
geometrically correct
because the algorithm assumes that the surface is not shiny like a
mirror, so what we
see in this image are actually some artifacts caused by highlights and
shadows.
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