Shedding Light on the Weather

1
Shedding Light on the Weather
Srinivasa Narasimhan and Shree
Nayar Computer Science Department Columbia
University
IEEE CVPR Conference June 2003, Madison, USA
Sponsors DARPA Human ID, NSF
2
Computer Vision in Bad Weather
3D Visualization
Computed Dehazed Image
Mild Haze
Dense Haze
3
Light Sources in Bad Weather
Mist
Fog
4
Multiple Scattering in the Atmosphere
Incident Beam
Particle
5
Radiative Transfer
Infinitesimal Scattering Volume
Direction
Exiting Beam Radiance
dR
Incident Beam Radiance
6
Light Source in a Spherical Medium
Isotropic Source
Homogeneous Medium
7
Axially Symmetric Phase Functions
Exiting Direction
Incident Direction
8
Light Source in a Spherical Medium
Isotropic Source
Homogeneous Medium
Spherical Radiative Transfer Equation
Chandrasekhar 1960
Cosine of Angle
Phase Function
Light Field
Optical Thickness
9
Analytic Multiple Scattering Solution
Scattered Light Field
10
Highlights of the Model

• Single and Multiple Scattering

• Absorbing and Purely Scattering Media

• Isotropic and Anisotropic Phase Functions

11
Scattered Light Field vs. Weather Condition
Angular PSF Scattered Light Field at a
Point
12
Validation Multiple Scattering in Milk
13
Model Fit Accuracy
Low Milk Concentration
High Milk Concentration
14
Rendering Glows using Convolution
Original Image
Joint work with Ramamoorthi (submitted to TOG)
15
Single versus Multiple Scattering
Original Image
Joint work with Ramamoorthi (submitted to TOG)
16
Inverse RTE Weather from APSF
17
A Camera-based Weather Station
45 images of a light source (WILD Database ECCV
02)
Ground Truth
Estimated
Ground Truth
Estimated
18
Active Visibility Meter for Ground Truth
19
Summary
20
Prior Work on Radiative Transfer
Chandrasekhar 1960 , Ishimaru 1997
21
Scattering Space of Weather Conditions
Phase Function Parameter, q
1
0
0
10
Optical Thickness, T
22
Axially Symmetric Phase Functions
Incident Direction
23
Effect of Source Visibility
24
Scattering is Everywhere
Computer Vision
Computer Graphics