when does a camera see rain? department of computer science columbia university kshitiz garg shree...
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When Does a Camera See Rain?
Department of Computer Science
Columbia University
Kshitiz GargShree K. Nayar
ICCV ConferenceOctober 2005, Beijing, China
Sponsors:NSF, DARPA
When is Rain Visible?
Rain
[Garg and Nayar, ICCV 05]
Visibility of Rain Depends Strongly on Camera Parameters ( Exposure time, Aperture size, Focus distance )
Defining the Visibility of RainIn
tens
ity
Inte
nsity
Time (Frames) Time (Frames)
Visibility: Variance due to a Volume of Rain
Intensity of a Rain Streak
Back
gro
un
dzm Rzm
Fog like
0I
Rzmzm
NoiseLevel
Distance
Change in Intensity
)(00 br LLT
kI
mzz
z
zI m
00Ibw
wI
cd
Dependence on Defocus
Dependence on Exposure Time
mzz
Rain Region[Garg and Nayar, ICCV 05]
Streak’s width
Radius of blur circle
Dependence on Distance
Visibility and Volume of Rain
z
)()()(),( 22 zIzwznzI ddr
Back
gro
un
dz
mRz
Numberof drops
Intensity ChangeStreakWidth
dzzII rr ),()( 22 T
zNfGLL
v
ak br
),,()( 0
2
0
Variance
Layer of Rain:
Volume of Rain:
Rain Properties Camera Properties
Scene Properties
[Garg and Nayar, ICCV 05]
Experimental Verification of Rain Visibility
0 2 4 6 8 10
1
2
3
F-number (N)Exposure time
Visibility
0 10 20 30 40 50
1
2
Distance of Focus Plane z0 (m) (ms)0 40 80 120
1
4
8
Visibility Visibility
T
zNfGLL
v
akI brr
),,()()( 0
2
02
Theoretical Visibility
Measured Visibility(with error bars)
Camera Parametes
F-num (Aperture)
Exposure Time
Focus Distance
zoom
Scene Near Depth Exposure F-numberMotion Distance Range (m) Time (ms) slow close large 66 14
small 33 4.4
far large 33 6
small 33 2 fast close large X X
small X X
far large 8 6
small 8 2.4
Optimal Settings for Rain Removal
Slow: Motion< 15 pixels/secClose: z < Rain Visible Region Small: z < Rain Visible Region
Scene with Fast Motion
Default camera settings
F-number =12 Exposure time = 8 ms Focus plane = 100 m
Scene with Fast Motion
F-number decreased from 12 2.4
F-number = 2.4 Exposure time = 8 ms Focus plane = 100 m
Scene with Large Depth
Exposure time Increased from 16 66 ms
F-number =14 Exposure time = 66 ms Focus plane=10 m
Panning Video in Rain
Default camera settingsExposure time =16 ms F-
num=14
Optimal camera settings Exposure time =33 ms F-
num=6
Implications for Vision Algorithms
Default camera settingsExposure time =16 ms F-
num=14
Optimal camera settings Exposure time =33 ms F-
num=6
[KLT feature tracker code from Stan Birchfield]
Enhancing the Visibility of Rain: Rain Gauge
Moderate Rain Video Heavy Rain VideoBackgrou
nd
Sampled Rain Volume
Backgrou
nd
Sampled Rain Volume
Type of Rainfall Camera parameters (f, N, z0, T)
Measured rain rate mm/hr
Reported rain rate* mm/hr
(a) Light (7095, 3.8, 3, 16) 1.34 0.763
(b) Moderate (5148, 4.4, 3, 4) 3.215 2.28
(c) Heavy (3300, 1.8, 3, 4) 14.28 11.17
Summary
Contributions
Future Work
Camera Based Rain Gauge
Analysis of Visibility of Rain
Camera Parameters for Removal of Rain
Limitations
A Camera-Lens system that automatically detects rain in videos and sets optimal camera parameters for reducing rain during image acquisition
Not as effective in very heavy rain and for scenes with close by and fast-moving objects
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