Image analysis – Applications – Target tracking or detecting
Reexamination Certificate
1997-09-25
2001-10-23
Ahmed, Samir (Department: 2623)
Image analysis
Applications
Target tracking or detecting
C382S280000
Reexamination Certificate
active
06307951
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for detecting a moving body, and more particularly, to a method and apparatus for detecting persons passing through passages or entrances and exits of buildings by processing image signals obtained from a video camera.
2. Prior Art
FIG. 17
illustrates a moving body counting apparatus equipped with a conventional moving body detection apparatus that uses a video camera.
The video camera
11
is installed in a ceiling, etc., over a passage or entrance/exit of a building so that the camera looks down on a monitoring region through which moving bodies such as persons
20
passing through the passage or entrance/exit pass.
Images picked up by the video camera
11
are digitized by an A/D converter
12
, and these digitized images are successively updated in a current image memory
13
at short time intervals, so that the most recent image is stored in the current image memory
13
.
In addition, the output of the current image memory
13
is stored in an immediately-prior image memory
14
, and this immediately-prior image memory
14
sends an image which is one frame prior to the image arriving from the current image memory
13
to a movement judging part
15
.
The movement judging part
15
judges the presence or absence of a moving body by processing the current image stored in the current image memory
13
and the output of the immediately-prior image memory
14
which constitutes an image one frame prior to the current image; and moving body detection signals outputted by this movement judging part
15
are counted by a counting means
16
, and the count value of this counting means
16
is outputted by an output device
17
.
The method used to judge the presence or absence of a moving body in the above conventional moving body counting apparatus will be described in greater detail below.
FIG. 18
shows the image obtained by imaging a passing person. The reference numeral
92
refers to a current image stored in the current image memory
13
, and
91
indicates the image one frame prior to the current image
92
, i. e., the immediately-prior image stored in the immediately-prior image memory
14
. In both of these images, a stationary image
82
is shown in the vicinity of the image
81
of the passing person in order to facilitate discrimination of the amount of movement of the image
81
. The reference numeral
93
is the output of the movement judging part
15
; and this output is an image (hereafter referred to as a “differential image”) which is produced by taking the differences in brightness between the respective picture elements of the current image
92
and the immediately-prior image
91
. In other words, the output is an image which has a differential region
94
(the area indicated by shading) in which the brightness varies between the current image
92
and the immediately-prior image
91
. Furthermore, in order to simplify the description, a region in which there is no overlapping of images
81
of passing persons in the current image
92
and immediately-prior image
91
is shown as the differential region
94
in FIG.
18
. In cases where the area of the differential region
94
(portion indicated by shading) in the differential image
93
exceeds a prescribed threshold value, a passing person
20
is judged to be present by the movement judging part
15
. Thus, in the system illustrated in
FIG. 18
, the aggregate of the video camera
11
, A/D converter
12
, current image memory
13
, immediately-prior image memory
14
and movement judging means
15
functions as a moving body detection apparatus. Next, when a differential region
94
having an area exceeding the threshold value crosses a counting line
95
set within the monitoring region
96
, the counting means
16
performs a counting operation, and the result of this counting operation is outputted by the output device
17
.
However, in the above conventional apparatus, the presence or absence of a passing person
20
is detected on the basis of a differential image
93
obtained by taking differences in brightness between the current image
92
and immediately-prior image
91
. Accordingly, if there are changes in the intensity of illumination in the area being imaged by the video camera
11
or the sensitivity caused by the automatic exposure adjustment function of the video camera
11
changes, then regions where there is a change in brightness may be generated within the monitoring region
96
in spite of the fact that no image
81
of a passing person is present, and a detection signal indicative of a passing person
20
may be erroneously outputted. Accordingly, in such cases, the counting result outputted by the counting means
16
does not match actual conditions.
Furthermore, in the apparatus described above, two image memories are required, i. e., a current image memory
13
and an immediately-prior image memory
14
, which respectively store the current image and an image one frame prior to the current image. Accordingly, it is disadvantageous in terms of cost.
Moreover, in cases where a plurality of moving bodies
20
pass by each other in close proximity, it is difficult to separate and discriminate the respective passing persons
20
as individuals at the instant at which these persons pass by each other; this also lowers the precision of the count.
In the prior art described above, the objectives of detection are passing persons
20
. However, it goes without saying that similar problems arise in cases where moving bodies such as automobiles traveling along a road, etc. are detected.
SUMMARY OF THE INVENTION
Accordingly, the object of the present invention is to prevent any drop in the precision of detection caused by changes in the intensity of illumination in the area monitored by a video camera or changes in the automatic exposure adjustment function of the video camera.
It is another object of the present invention to reduce the number of expensive image memories required.
It is still another object of the present invention to make it possible to separate and discriminate moving bodies which move in a complicated manner so that the moving bodies pass each other in close proximity.
The objects of the invention are accomplished by a moving body detection method which detects moving bodies by processing image data for the moving bodies, and the method comprises:
a process to calculate spatial phases in terms of a time series, said spatial phases being obtained by the operational formula tan
−1
(AS/AC) or cot
−1
(AC/AS) (where AC is a Fourier cosine transformation and AS is a Fourier sine transformation) in a case where image signals obtained as aggregates of picture elements on the basis of picture element data constituting the image data are subjected to a spatial Fourier transformation in a direction which is not perpendicular to the direction of movement of the moving bodies; and
a process to detect the moving bodies on the basis of changes in the calculated spatial phase.
In this method, since the spatial phase of each image signal obtained as an aggregate of picture elements changes as the moving body moves, the spatial phases are calculated as a time series; and the presence or absence of a moving body, as well as the direction of movement of the moving body, can be detected by monitoring changes in this calculated spatial phase.
The objects of the present inventions are further accomplished by a method characterized by the fact that “the aggregates of picture elements are respective blocks produced by dividing the image data into a plurality of lattice forms” in the method above, the presence or absence of blocks in which the direction of change of the spatial phases is different is determined by examining the changes in the spatial phases of the image signals on a block by block basis. In this way, moving bodies which are passing by each other can be detected.
In concrete terms, “brightness signals” may be used as the image signals obtained as aggregates o
Shibuya Satoru
Tanigawa Hiroshi
Ahmed Samir
Giken Trastem Co., Ltd.
Koda & Androlia
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