BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to a method of identifying an object capable
of identifying rod-like objects to be detected from an image data comprising one
picture of a plurality of said objects in various orientations.
2. Description of the Prior Art
According to a prior art method of identifying an object to be detected
(hereinafter, merely called an object) the object is photographed with an image
pick-up device of an industrial television (ITV) camera for example, the photographed
picture is scanned, and a bright and dark pattern (brightness pattern) comprising
image data of a predetermined number of picture elements which are contiguous in
the direction of scanning is compared with a reference pattern which has been
prepared previously and representing the brightness of the object. Such a method
is taught by US-A-3 959 771 With this method, however, in spite of the fact that
the picture is inputted with multistage tones, the actual processing of the data
is made after converting the data into binary codes, such method is practical where
electrical component parts can be assembled under satisfactory opitcal environment
and high quality binary picture image can be obtained relatively readily. However,
any special light source for image pick-up cannot be available so that the object
is photographed under the influence of solar light, as the brightness pattern of
the object varies greatly, correct identification of the pattern is impossible.
Furthermore, background and noise may cause erroneous identification.
In the method of identifying an object by comparison of patterns,
where the objects arranged in a predetermined direction, for example substantially
perpendicularly to the direction of scanning, detection is possible, but the objects
such as rods or logs 10 are randomly distributed as shown in Fig.1, it has been
impossible to detect the object in all directions. Furthermore, as in a factory
in which directions of illumination are not uniform so that brightness is influenced
by solar light, the brightness pattern in the transverse direction varies according
to the direction of the object. For this reason, detection of objects which are
randomly directed is very difficult.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a novel method of identifying
rod-like objects capable of correctly identifying a proper object even under an
adverse optical environment or in a states in which the objects contact with each
other or are distributed randomly.
In view of the above background, it is an object of the present invention
to provide a novel method of detecting rod-like objects capable of detecting rod-like
objects randomly oriented even under an adverse optical environment.
There is also provided a method of identifying rod-like objects characterized
by the steps of sequentially extracting a set of object brightness patterns including
a predetermined number picture elements which are contiguous in a predetermined
scanning direction, from picture element data in a predetermined field of view
in which a plurality of the rod-like objects to be identified are scattered while
shifting the brightness patterns by one picture element in the scanning direction;
comparing the object brightness patterns with a prepared reference pattern representing
brightnesses of a predetermined number of picture elements in a transverse direction
of the objects; where the brightness pattern in the transverse direction of the
objects varies in accordance with the orientations of the objects, preparing reference
brightness patterns in the transverse direction of the objects lying substantially
perpendicularly to the horizontal, vertical, right 45° upper and right 45° lower
directions in the predetermined field of view, in each of the four directions;
extracting object brightness patterns in each of four scanning directions of the
horizontal, vertical, right 45° upper and right 45° lower directions in the field
of view, from the picture image data in the predetermined field of view; and utilizing
one of the prepared four reference brightness patterns selected in accordance with
the direction of scanning of the object brightness pattern [as a reference pattern
utilized as a reference] for comparison with the object brightness pattern, thereby
identifying randomly oriented scattered rod-like objects.
In the accompanying drawings:
- is a plan view showing rods randomly distributed
- is a block diagram showing an electric circuit for forming a reference pattern;
- is a graph showing a plurality of brightness patterns and a reference pattern
- is a diagrammatic representaion of four rods respectively extending in directions
orthogonal to four directions of scanning and one example of directions of illumination
for these logs;
- Fig.5a - 5d
- are graphs showing one example of reference patterns prepared for respective
rods 10a - 10d shown in Fig.4;
- is a flow chart showing one example of the steps of the method of identifying
objects by using the four reference patterns described above;
A method of preparing the reference pattern and a method of extracting
the brightness pattern will now be described. According to this invention, four
reference patterns are prepared and a reference pattern corresponding to the direction
of extraction of the brightness pattern (scanning direction) is used.
In Fig.2, when the ITV camera 11 photographs rods 10 scattering on
the floor of a factory, a monitor 42 displays a picture of the plurality of rods
in response to the image data sent from the ITV camera 11. Further, the monitor
42 displays a cursor 2a freee to move in the vertical and horizontal directions
of the monitor picture by the manipulation of a cursor shifting lever 43.
A brightness pattern derive out circuit 44 is provided for deriving
out a brightness pattern comprising the picture image data comprising ten contiguous
picture elements from the image data inputted to the monitor 42. More particularly,
the derive out circuit 44 derives out a brightness pattern in a scanning direction
designated by a scanning direction designation switch taking the shifted position
of the cursor 2a as a reference when a write switch 45 is closed. The scanning
direction designation switch 46 is constructed to designate either one of the horizontal
direction (shown by arrow A), the vertical direction (shown by arrow B), right
45° upper direction (shown by arrow C) and right 45° lower direction (shown by
A brightness pattern memory device 47 temporarily stores a plurality
of brightness patterns derived out by the brightness pattern derive out circuit
44, while a reference pattern forming circuit 48 forms an optimum reference pattern
from the plurality of brightness patterns. As the method of forming the reference
pattern from the plurality of brightness patterns, may be used a method using.
Lagrage's method of indefinite multipliers or a method for obtaining an average
value or a center value.
The reference pattern prepared in this manner is stored in a memory
area of the reference pattern memory device 49 corresponding to the direction of
scanning designated by the scanning direction designation switch 46.
To prepare the reference pattern, either one of the four scanning
directions, for example, the horizontal direction shown by arrow A is selected
by operating the scanning direction designation switch 46. While viewing the picture
on the monitor 42, the operator searches a picture image of the rod in a direction
substantially perpendicular to the direction A and then manipulates the cursor
shifting lever 43 to shift the cursor to the central position P&sub1; of the picture.
Thereafter, the operator turns ON the write switch 45. By repeating many times
the operation described above, a plurality of sets of the brightness patterns in
the transverse direction of the rod substantially perpendicular to the direction
A would be stored in the brightness pattern memory device 47, and the reference
pattern is formed by the reference pattern forming circuit 48 based on the plurality
of sets of the brightness patterns. Fig.3 shows the relationship among 4 sets of
brightness patterns shown by symbols (□, ○, Δ and x and the reference
pattern (&peseta;) prepared from these brightness patterns.
Where direction D is designated as the scanning direction, a reference
pattern in this scanning direction can be prepared by shifting the cursor 2a to
the center position P&sub2; of the rod perpendicular to the designated direction.
As above described, the reference pattern memory device 49 stores
four reference patterns corresponding to the four scanning directions.
Where rods 10a, 10b, 10c and 10d present respectively in the orthogonal
directions A, B, C and D as shown in Fig.4, and when the rods are illuminated in
the direction of arrow E, the reference patterns formed for rods 10a, 10b, 10c
and 10d would have different patterns as shown in Figs. 5a - 5d.
One example of the method of identifying an object by using the four
reference patterns will be described in the following with reference to a flow
chart shown in Fig.6. At step 50 it is made n = 1 to designate the scanning direction
of the picture image data of one picture. Then at step 51 a reference pattern corresponding
to n is read out from the reference pattern memory device 49. As above described,
the reference pattern memory device 49 is constructed to store reference patterns
in the four scanning directions so that the reference patterns can be read out
according to the value of n.
Then at step 52 it is made i = 1 for designating the position of
one end of the scanning direction corresponding to n. At step 53, the brightness
pattern of data of a predetermined number of elements which are contigous in the
scanning direction which corresponds to n are read out from the picture image
data of one picture corresponding to the position of i. At step 54, the brightness
pattern is compared with the read out reference pattern to judge whether the read
out brightness pattern is the brightness pattern of the cross-section of the rod
or not. When the result of judgment is NO, at step 55 the position of the rod is
detected based on the position of i when the brightness pattern is that of the
cross-section and to store this position. When the result of judgment at step 54
is YES, the programm is transferred to step 56 to store position detection. At
step 55, 1 is added to i, and at step 57 a judgment is made as to whether the position
of i is the scanning completion position or not. If the result of this judgment
is NO, the program is returned to step 53 at which a new brightness pattern displaced
by one picture element in the scanning direction corresponding to n is read out.
By executing the processings and judgments until completion of a scanning, it
is possible to detect and store the cross-sectional position of a rod presenting
within ±22.5° about a direction orthogonal to the direction of scanning corresponding
to n. When the position is the scanning completion position, 1 is added to n to
designates another scanning position at step 58.
At step 59, a judgment is made as to whether the detection of rods
in each of the four scanning directions has been executed or not. When n is less
than 4, the program is returned to step 51. At this time, at step 51, a new reference
pattern is read out from the reference memory device corresponding to the renewed
value of n. Thereafter, the scanning is made in a scanning direction corresponding
to n by using the read out reference pattern for detecting the cross-sectional
position of the rod in the same manner as above described. When detection of the
rod in each of the four scanning directions completes, n becomes 5 thus ending
the direction of rods of one picture.
As above described, presence or absence (cross-sectional position)
of a plurality of rods scattered in all directions can be detected. Further, the
information of the position of the rod detected in such way is applied to a handling
robbot, for example, so that it is used when the robbot correctly grasps the rod.
Furthermore, in this embodiment, rods were used as the objects to
be detected, however, this invention can be applied to other rod-like objects with
cross-sectional configuration, for example, a hexagonal cross-section.
As described, since according to this invention, the rod-like object
is scanned in four discrete directions so as to use an optimum reference pattern
for each scanning direction, it is possible to accurately detect objects scattered
in all orientations irrespective of the position of the source of illumination.