Novel Depth Cues from Uncalibrated Near-field Lighting

Sanjeev J. Koppal and Srinivasa Narasimhan

Carnegie Mellon University

Sponsors: ONR and NSF

Distant Lighting

Sun

Scene

Parallel Rays

Near-field Lighting

Indoor Night

Underground Underwater

Scene

Calibrated Near Point Light Source

Inverse-square fall-off can give depth information

(Clark 92, Iwahori et al 94, Kao and Fuh 95, Magda et al 01, Zickler et al 02, Prados and Faugeras 05)

1

R 2

Our Key Idea

Scene

Move an uncalibrated point light source in a line or a plane

‘baseline’

Appearance Model

BRDF Illumination and Viewing angles Foreshortening

Distance to Source

Experimental Setup

LED

Scene

Camera

Plane-Scene Intersectionsfor Lambertian Scenes

Light source moves in a line

t = i

Scene

Camera

t = 0

t = n

Maxima in Intensity

Scene

Camera

Plane perpendicular to light source path.

t = i

t = 0

t = n

Lambertian Scenes

Lambertian Model:

Solve for maxima location:

Expression for maxima:

Albedo

Quadratic

Shortest distance to light source path

If D is small, maxima happens at t = i

Moving the Light Source in a Line

Moving the Light Source in a Line

Input Images

Plane-Scene Intersections

Similar to Structured Light

Rough Earthen Pot

Painted House

Metal Office Desk

Wax Candle

Depth Orderingfor Homogeneous Scenes

Light source moves in a plane

Scene

Camera

Integrating the Profile

Integral of Profile:

P

Q

Overlapped Incident Angles

P

Q

S < S if:

Works for convex Lambertian scenes

p q

Moving the Light Source in a Plane

Moving the Light Source in a Plane

Input Images

Depth Ordering

Plotting ordering as a pseudo-depth

Plastic Beach Ball

Plastic Beach Ball

Polyresin Statue

Polyresin Statue

Depth Orderings from Different ‘Views’

Depth Orderings from Left Plane

Depth Orderings from Image Plane

Depth Orderings from Right Plane

Symmetry Pairsfor Homogeneous Scenes

Matching Profiles

Scene

Camera

Matching Profiles

Light source moves in reflection plane

Light source moves in reflection plane

Input Images

Symmetry Pairs

Metal Office Desk

Conclusions• Line or plane paths for a near

light source are a ‘baseline’.

• Depth cues can be obtained

from such uncalibrated light paths.

• The cues are from the light source

‘viewpoint’ and not from the camera.