Estimation of the Visibility Distance by Stereovision: a Generic Approach

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May 16
-
18, 2005
-

Tsukuba Science City, Japan


Machine Vision Applications 2005

Estimation of the Visibility Distance

by Stereovision: a Generic Approach

Nicolas Hautière, Raphaël Labayrade, Didier Aubert

LIVIC (LCPC
-
INRETS)

Vehicle
-
Infrastructure
-
Driver Interactions Unit

Versailles
-

France


May 16
-
18, 2005
-

Tsukuba Science City, Japan


Machine Vision Applications 2005

Measurement of Visibility Distance


Our work is based on a definition of the
International Commission on Illumination [1]


«

The meteorological visibility is the greatest distance
at which a black object of suitable dimensions can be
recognized by day against the horizon sky.

»


[1] CIE, 1987. International Lighting Vocabulary, CIE

Publ. No. 17.4.

May 16
-
18, 2005
-

Tsukuba Science City, Japan


Machine Vision Applications 2005

Previous work


We developed a Koschmieder’s Law based method [2]:


detecting daylight fog,


estimating the meteorological visibility.

Extraction of a target region

Composition of a measurement bandwidth

Measurement and derivative of the luminance curve

Extraction of an inflection point

V
met

= 50m

Instanciation of Koschmieder’s Law

Estimation the meteorological visibility

[2] N. Hautière, D. Aubert.
Driving assistance

: Automatic fog detection and

measure of the visibility distance
. 10
th

ITS World, Madrid, 2003.

May 16
-
18, 2005
-

Tsukuba Science City, Japan


Machine Vision Applications 2005

Discussion


The method needs only one camera, and the
presence of the road and the sky in the image to run
properly.



The method is restricted to daylight fog situations.


=>

Development of a new generic approach

including a new visibility distance:


Measurement of the distance to the most distant object
in the scene having a contrast above 5 %.


+

-

May 16
-
18, 2005
-

Tsukuba Science City, Japan


Machine Vision Applications 2005

New Visibility Distance

d

V
mob

(a)

V
max



V
mob

mobilized visibility distance,


The distance to the most distant
object in the scene having a
contrast above 5 %.




V
max

mobilizable visiblity distance,




V
met
meteorological visibility distance.


The greatest distance at which a
black object of suitable dimensions
can be recognized by day against
the horizon sky.

With a contrast theshold of 5 %, we
found the following relationship:

V
mob


V
max


V
met

d

V
mob

V
max

(b)

May 16
-
18, 2005
-

Tsukuba Science City, Japan


Machine Vision Applications 2005

Generic approach

1.
Computation of a depth map of the
vehicle environment,

2.
Extraction of picture elements having a
contrast above 5 %,

3.
Estimation of the mobilized visibility
distance.

May 16
-
18, 2005
-

Tsukuba Science City, Japan


Machine Vision Applications 2005

Depth computation by stereovision [3]

Grabbing the left and right images

Computing a disparity map

Computing the “v
-
disparity”


representation

Extracting global surfaces

Improving the disparity map and

extracting the obstacle areas

[3] R. Labayrade, D. Aubert. In
-
Vehicle Obstacles Detection and Characterization by

Stereovision. IEEE ICVS, Graz, Austria, 2003.

May 16
-
18, 2005
-

Tsukuba Science City, Japan


Machine Vision Applications 2005

Depth computation by stereovision

Results

May 16
-
18, 2005
-

Tsukuba Science City, Japan


Machine Vision Applications 2005



Construction of the border associated with s:

F(s)={(x,x
1
) / x


V
4
(x
1
) and Min(f(x),f(x
1
))

s<Max(f(x),f(x
1
))





Computation of the mean contrast associated with s:

Computation of C>5%

Principle of Köhler’s binarization technique [4]

f(x
1
)

f(x)

C
x,x1
(s)

s

x

x
1

F(s)

[4] R. Köhler
. A segmentation technique based on tresholding.
CVGIP, 15:319
-
338, 1981




s


[0,255]



We find s
0

so as:



Finally, the evaluated contrast on F(s) is 2C(s
0
).


where

May 16
-
18, 2005
-

Tsukuba Science City, Japan


Machine Vision Applications 2005

Computation of C>5%


Adaptation to the logarithmic contrast used by CIE




Algorithmic optimizations


MIN
-
MAX images precomputations,


Sliding vicinities,


Parallelization…


Before:

14 s

on a full image 360x288


Now:


350 ms



Good properties: robustness to noise, precision of edges
detection

May 16
-
18, 2005
-

Tsukuba Science City, Japan


Machine Vision Applications 2005

Computation of C>5%

Results

May 16
-
18, 2005
-

Tsukuba Science City, Japan


Machine Vision Applications 2005

Estimation of the mobilized visibility
distance.


Horizon line

Computation time

on a 2.4 GHz PC

Image 360x288

60 ms

May 16
-
18, 2005
-

Tsukuba Science City, Japan


Machine Vision Applications 2005

Experimental results

Sunny weather

May 16
-
18, 2005
-

Tsukuba Science City, Japan


Machine Vision Applications 2005

Experimental results

Foggy weather

May 16
-
18, 2005
-

Tsukuba Science City, Japan


Machine Vision Applications 2005

Experimental results

Night foggy weather

May 16
-
18, 2005
-

Tsukuba Science City, Japan


Machine Vision Applications 2005

Conclusion


We have presented a generic method:



estimating the mobilized visibility distance,



based on the stereovision«

v
-
disparity

» approach,



computing the local contrast above 5 %,



performed within 60 ms on a current
-
day PC,



reliable in lots of meteorological and illumination
conditions.

May 16
-
18, 2005
-

Tsukuba Science City, Japan


Machine Vision Applications 2005

Thank you for your attention !