Image analysis – Applications – 3-d or stereo imaging analysis
Reexamination Certificate
1998-10-09
2002-04-23
Mehta, Bhavesh (Department: 2621)
Image analysis
Applications
3-d or stereo imaging analysis
C382S285000, C345S629000
Reexamination Certificate
active
06377701
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a calibration method and device, a device for generating calibration data and a method thereof, and information providing medium; whereby information regarding the position of an object in 3-dimensional space is calculated from 2-dimensional images obtained by imaging devices which perform imaging of the object.
2. Description of the Related Art
There is a known stereo camera system serving as a 3-dimensional position detecting device, in which a plurality (e.g., two) of video cameras (hereafter simply referred to as “cameras”) are used to comprise a so-called stereo camera by which an object in a 3-dimensional space is imaged and the position of the object in the 3-dimensional space is determined based on the 2-dimensional images obtained by the imaging.
Details of a stereo camera system are disclosed in detail in MASATOSHI OKUTOMI and TAKEO KANEIDE: “Stereo Matching Using Multiple Base-Line Lengths”, Institute of Electronics, Information and Communication Engineers Journal D-II, Vol. J75-D-II. No. 8, pp. 1317-1327 (August 1992), and so forth.
With a stereo camera system, an object whose positional information in 3-dimensional space is to be obtained is imaged by multiple cameras, and information regarding the position of the object in 3-dimensional space can be obtained from the positional information of the object projected on a light-receiving plane (hereafter referred to as “screen”) of the photo-electric converting devices (e.g., CCD) of each camera. Accordingly, in the event that there is positional information of an object existing at a certain position within a 3-dimensional space, and an object at that position, the correlated relation with the positional information of the object projected on the screen of each camera (correlated relation of position information) must be determined beforehand. The process of obtaining this correlated relation of position information is referred to as “calibration”, and is carried out by a calibration device.
FIG. 8
is an external perspective view of a known calibration device for performing calibration. In
FIG. 8
, pipes
106
and
107
are included in the same plane in a 3-dimensional space, and a carriage
108
is provided so as to smoothly move along the pipes
106
and
107
. Attached to the carriage
108
is a stereo camera, comprised of a first camera
101
and a second camera
102
which have been integrally joined by means of a metal piece
103
.
The pipes
106
and
107
are inscribed with scale marks, so as to enable measuring the distance that the carriage
108
slides. A plate
109
with a square lattice-work pattern drawn thereupon is provided in a direction perpendicular to the direction of sliding of the carriage
108
. The horizontal direction of the square lattice-work serves as the X-axis, the vertical direction thereof as the Y-axis, and the direction of sliding, i.e., the direction perpendicular to the square lattice-work is the Z-axis. Z>0 holds for the side of the plate
109
on which the camera is provided. Such a 3-dimensional coordinates system with the X-axis, Y-axis, and Z-axis, is defined as a “world coordinates” system.
Calibration measurement is performed by shifting the carriage
108
carrying the aforementioned stereo camera along the Z-axis, and imaging the plate
109
from two positions.
FIG. 9
is a diagram describing a case in which imaging is performed from two positions, viewing the device shown in
FIG. 8
from directly above.
First, the first camera
101
and the second camera
102
are fixed at a certain position P
1
, the plate
109
is imaged such that the square lattice-work pattern is recorded, following which the first camera
101
and the second camera
102
are slid along the Z-axis to another position P
2
by a distance of M by means of sliding the carriage
108
, and the plate
109
is imaged once more. Here,
FIG. 9
shows the first camera
101
and the second camera
102
being moved in a direction away from the plate
109
, but this direction of sliding may be reversed.
Thus, the 2-dimensional images obtained by means of sliding a stereo camera comprised of the first camera
101
and the second camera
102
and imaging the plate
109
can also be obtained by means of an arrangement wherein the stereo camera is fixed and the plate
109
is shifted instead as well, as shown in FIG.
10
.
That is to say, the same 2-dimensional images can be obtained by an arrangement such as shown in
FIG. 10
, wherein the first camera
101
and the second camera
102
are fixed to a certain position P
1
, the plate
109
is imaged such that the square lattice-work pattern is recorded, following which the plate
109
is slid along the Z-axis by a distance of M to another position P
2
in a direction away from the first camera
101
and the second camera
102
, and the plate
109
is imaged once more at that position.
In
FIG. 10
, with the lower left corner of the square lattice-work pattern drawn on the plate before moving the plate by a distance of M (first square lattice-work pattern Q
1
) serving as the origin point and also as the origin for the world coordinates system, the position (i, j) on the first square lattice-work pattern Q
1
for the plate
109
is (i, j, O) on the world coordinates. Also, the position (i, j) on the second square lattice-work pattern Q
2
after the plate
109
has been shifted by a distance of M is (i, j, −M) on the world coordinates.
FIG. 11
shows the first camera
101
, and the first square lattice-work Q
1
and second square lattice-work Q
2
on the plate
109
. The optical center of the first camera
101
is
01
, and positional information of the object is case upon the screen serving as the light-receiving surface of a CCD
122
or the like. For example, let us say that coordinates position (p, q) at the first square lattice-work Q
1
is projected, and coordinates position (r, s) at the second square lattice-work Q
2
is projected. Incidentally, the coordinates of positions other than upon the vertical and horizontal lines in the grid can be calculated by interpolation.
Giving the same description once more using world coordinates, 3-dimensional coordinates positions (p, q, O) and (r, s, −M) are projected onto the coordinates position (h, k) on the CCD
122
. That is, in the event that the 2-dimensional coordinates position (h, k) and the 3-dimensional coordinates positions (p, q, O) and (r, s, −M) are connected by a line N, all points on this line N are projected onto the coordinates position (h, k) on the CCD
122
.
Accordingly, the line N represents a correlated relation (correlated relation of position information) between positional information of objects in a 3-dimensional space (in this case, coordinates in the world coordinates system), and 2-dimensional information obtained by imaging the object (in this case, coordinates on the 2-dimensional coordinates system on the CCD
122
).
This line N can be calculated as follows:
(x−r)/(p−r)=(y−s)/(q−s)=(z+M)/M
In the same manner as calculating line N, lines projected on other coordinates positions as collections of points in the 3-dimensional space are also calculated for the other 2-dimensional coordinate systems on the CCD, as well. The same is also carried out with the second camera
102
.
Thus, by calculating all lines for the first camera
101
and the second camera
102
, calibration of the stereo camera system is completed.
The positional information of an object in the 3-dimensional space can be calculated as follows, using a stereo camera system which has been calibrated as described above.
First, an object is imaged using the stereo camera. For example, let us say that the object
127
shown in
FIG. 127
is projected at the position (a, b) on the screen
122
of the first camera
101
and the position (c, d) on the screen
128
of the second camera
102
. The lines
130
and
131
on the world coordinates system corresponding with the positions (a,
Bayat Ali
Bell Boyd & Lloyd LLC
Mehta Bhavesh
LandOfFree
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