lighting is widely assumed in computer vision. However, many scenes are
illuminated by near light sources. An advantage of near lighting is that the
intensity fall-off from the light source encodes scene depth. A drawback is
that exact estimation of this depth requires the 3D position of the light
source. In this paper, we analyze what kinds of depth cues are possible
under uncalibrated near point
lighting. A stationary scene is illuminated by a point source that is moved
approximately along a line or in a plane. We observe the brightness profile
at each pixel and demonstrate how to obtain three novel cues: plane-scene
intersections, depth ordering and mirror symmetries. These cues are defined
with respect to the line/plane in which the light source moves, and not the
camera viewpoint. Plane-Scene Intersections are detected by finding those
scene points that are closest to the light source path at some time
instance. Depth Ordering for scenes with homogeneous BRDF is obtained by
sorting pixels according to their shortest distances from a plane
containing the light source. Mirror Symmetry pairs for scenes with
homogeneous BRDFs are detected by reflecting scene points across a plane in
which the light source moves. We show analytic results for Lambertian
objects and demonstrate empirical evidence for a variety of other BRDFs.
Depth Cues from Uncalibrated Near-field Lighting"
S.J. Koppal and S.G Narasimhan,
IEEE International Conference on Computer Vision (ICCV),
Poster and Presentation
Poster at ICCV 2007
Our experiments were done by hand-waving a Lamina BL-4000 LED point light
source in front of scene viewed by a Canon 1D Mark II camera. In all of
our experiments we do not have the position of the light source and the
camera is uncalibrated.
scene be illuminated by a point source moving along a line. We show that
scene points intersected by a plane perpendicular to the light source
will exhibit a brightness maxima. By simply detecting intensity maxima at
every frame, we produce plane-scene intersections similar to those
obtained by sweeping a sheet of light over the scene.
point light source moving in a plane illuminates a homogeneous scene
under orthographic viewing. Under certain conditions, it is possible to
obtain an ordering of the scene in terms of perpendicular distances to
this ’base plane’. Changing the base plane in which the light
source is being moved gives scene depth orderings with respect to
orthographic camera views a scene illuminated by a light source moving
along a line. We detect mirror symmetries by reflecting scene points
across a plane containing the light source path. These symmetric pairs of
scene points will observe identical incident angles and light source
distances. Therefore, they can be detected by simply matching scene
points with the same brightnesses over time.
(Video Result Playlist)
2007 Video with Audio (use Apple Quicktime 6.0):
This video is a compilation of the main results of this project (50 MB).
Intersections (use Apple Quicktime 6.0):
We show plane-scene intersections for different objects, as well as an
example of how the results are very similar to those obtained from
Ordering (use Apple Quicktime 6.0):
depth ordering of a scene is used as a “pseudo depth” to
visualize the object in 3D.