Rear-view monitor for use in vehicles

Details Rear-view monitor for use in vehicles Rear-view monitor for use in vehicles

2000-02-29

2001-04-17

Tong, Nina (Department: 2632)

Communications: electrical

External condition vehicle-mounted indicator or alarm

C340S435000, C340S903000, C340S937000, C348S118000, C348S148000, C348S149000, C382S104000, C701S001000

Reexamination Certificate

active

06218960

ABSTRACT:

BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to a rear-view monitor for use in vehicles and, more specifically, to a rear-view monitor that warns a driver to respond to an vehicle approaching from the rear with regard to one's own vehicle by taking images of road in the rear of one's own vehicle with an image pickup device such as a video camera mounted on one's own vehicle such as a motor vehicle and then, by detecting a vehicle approaching from the rear using road images thus obtained.
(2) Description of the Related Art
Several rear-view monitoring and warning systems have hitherto been proposed in the past, for example, Japanese Patent Publication No. 2641562, Japanese Patent Application Laid-Open No. H6-107096 and H7-50769. The systems are capable of monitoring the rear road in order to prevent a possible collision with an overtaking vehicle from occuring by correctly sizing a situation of the overtaking vehicle traveling an adjacent either right or left traffic lane and then, warning a driver of possibility of collision with such overtaking vehicle traveling the adjacent lane when a driver is about to chang the traveling lane.
According to the proposed systems, in order to detect an overtaking vehicle traveling the adjacent lane quickly and securely without performing an excessive image processing, lanes on the road are distinguished by recognizing white lines, i.e. lane dividing lines, using road images taken by a video camera, and a monitoring range is set to the adjacent lane in accordance with this discrimination so that an amount of image processing for detecting an approaching vehicle within an adjacent lane, i.e. a monitoring range set up in the road images taken by a video camera, is reduced.
Apparatuses that employ a detection system by optical flow are disclosed in Japanese Patent Application Laid-Open No. H6-107096 and H7-50769, features of which are explained with reference to
FIGS. 7 and 8
in the following.
FIG. 7
is a block diagram illustrating an assembly of a conventional rear-view monitoring and warning system for vehicles, which contains an image pickup unit
10
as an image pickup device such as a video camera
11
, a data processing unit
30
as a computing system, and a speaker
42
as a warning means.
The image pickup unit
10
is mounted at the rear side of a vehicle such as on a trunk lid so as to take road images of the rear with regard to the traveling vehicle. The data processing unit
30
contains a CPU
31
as a central processing unit operating in accordance with an operation program, a ROM
32
for memorizing the operation program of the CPU
31
and predetermined settings, and a RAM
33
for provisionally memorizing data required upon computation by the CPU
31
. The speaker
42
mounted on the vehicle warns a driver of a danger by sounding or warning in accordance with a signal from the CPU
31
in the data processing unit
30
.
FIGS. 8A and 8B
illustrate a change in images taken by the image pickup unit
10
mounted at the rear portion of the vehicle.
FIG. 8A
is an image taken at a time t and
FIG. 8B
at a time t+&Dgr;t. In each figure, shown are an overtaking vehicle
200
traveling in the rear with regard to one's own vehicle, a traffic sign
300
disposed along a road
500
, and a building
400
along the road
500
.
Supposing that one's own vehicle is traveling straight along a flat road, with time passing by, i.e. accompanied by the vehicle traveling, the traffic sign
300
and building
400
are relatively leaving from the vehicle, resulting in that the images of the traffic sign
300
and building
400
become small. That is, in the figures, images of the traffic sign
300
and building
400
taken at the time t shown in
FIG. 8A
is smaller than those taken at the time t+&Dgr;t shown in FIG.
8
B.
In the following, the optical flows are explained with reference to these figures.
In these figures, to be considered are a plurality of marked points selected in the images taken at the time t (see
FIG. 8A
) such as: marked points
201
a
and
202
a
for the overtaking vehicle
200
;
301
a
,
302
a
and
303
a
for the traffic sign
300
; and
401
a
and
402
a
for the building
400
. Similarly, to be considered are marked points such as:
201
b
and
202
b
for the overtaking vehicle
200
;
301
b
,
302
b
and
303
b
for the traffic sign
300
; and
401
b
and
402
b
for the building
400
in the images taken at the time t+&Dgr;t (see FIG.
8
B). Then, each combination between corresponding marked points, for example
201
a
and
201
b
, gives a velocity vector such as
201
F,
202
F,
301
F,
302
F,
303
F,
401
F and
402
F as shown in
8
C. These velocity vectors are defined as the optical flows.
Here, it can be understood that the optical flow radially appears from a focus of expansion (hereinafter, FOE) defined as an infinitely far point or a vanishing point in the figures. When one's own vehicle is traveling straight, the FOE corresponds to just the opposite direction to which the vehicle is traveling.
When one's own vehicle is traveling, an optical flow of an object going away from the vehicle is a convergent vector heading toward the FOE, while an optical flow of an object approaching the vehicle is a divergent vector away from the FOE. Accordingly, the optical flows
201
F and
202
F (shown in
FIG. 8C
) are divergent vectors, indicating that the vehicle
200
is approaching one's own vehicle, in other wards, that the vehicle
200
is traveling faster than one's own vehicle.
Regarding a size of the optical flow, the size is large when a difference in velocity between one's own vehicle and an object is large and also when a distance therebetween is short. In the following, this matter is explained with reference to the attached drawings.
FIG. 9
illustrates an optical arrangement of the image pickup unit
10
, in which
11
a
is a lens of the video camera in the image pickup unit
10
,
11
b
is an image plane of the video camera, f is a distance between the lens
11
a
and the image plane
11
b
, P (X
a
, Y
a
, Z
a
) is an arbitrary point of the overtaking vehicle, and p (X
a
, y
a
) is a point corresponding to the point P on the image plane
11
b.
On this occasion, the following formula is given on the basis of similar figures in triangles:
X
a
=f·X
a
/Z
a
  (1)
Transforming the formula (1) and then, differentiating with respect to time gives the following formula (2):
X
a
′=(&Dgr;x
a
/&Dgr;t·Z
a
+x
a
·Z
a
′)/f  (2)
A x-component u of an optical flow is given by the following formula (3):
u=&Dgr;x
a
/&Dgr;t  (3)
Hence, the following formula (4) is derived from the formula (3):
Z
a
=(f·X
a
′−x
a
·Z
a
′)/u  (4)
Here, Z
a
′ denotes a difference in velocity between the overtaking vehicle (
200
in
FIG. 8
) traveling the same lane or the adjacent lane and one's own vehicle on which the image pickup unit
10
is mounted. Assuming this difference in velocity to be −&agr;, the formula (4) is expressed by the following formula (5):
Z
a
=(f·X
a
′+x
a
·&agr;)/u  (5)
Hence, the x-component u of the optical flow, is expressed by the following formula (6):
u=(f·X
a
′+x
a
·&agr;)/Z
a
  (6)
By the way, Y
a
, i.e. Y-coordinate of the point P, can be derived in the similar way.
Consequently, according to the formula (6), when Z is small, i.e. a distance between one's own vehicle and the overtaking vehicle
200
traveling the same lane or the adjacent lane is short, or when a is large, i.e. the difference in velocity between one's own vehicle and the overtaking vehicle
200
is large, an x-component of the optical flow becomes large. These relations are the same with respect to the Y-direction.
Accordingly, the size of the optical flow becomes large when the distance between one's own vehicle and the overtaking vehicle
200
is short, and when t

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