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Digital Camera Patent Abstract
The distance between a first detectable point (5) and a second detectable
point (6) on an object (2) is measured by means of a digital camera
(1) by making a first image (7) comprising said first detectable
point (5), then displacing the camera (1), and subsequently making
an other image (8) comprising said second detectable point (6).
The coordinates of the detectable points (5, 6) on the images (7,8)
are calculated. Two or more overlapping images (7, 8) are made by
the camera (1), whereupon corresponding detectable points (C) in
the overlapping part (9) of overlapping images (7, 8) are detected
in order to determine the displacement of the camera (1).
Digital Camera Patent Claims
1. A method for measuring dimensions of an object (2) by means of
a digital camera (1) provided with image processing means, with
detection means for detecting points (A,B) on the image (7,8), and
with coordinate calculation means for calculating the coordinates
of detected points (A,B) on the image (7,8), whereby the distance
between a first detectable point (A) and a second detectable point
(B) on the object (2) is measured by making a first image (7) comprising
said first detectable point (A), then displacing the field of view
of the digital camera (1), and subsequently making an other image
(8) comprising said second detectable point (B), whereby the coordinates
of said first detectable point (A) on said first image (7) and the
coordinates of said second detectable point (B) on said other image
(8) are calculated, and whereby the displacement of said field of
view is determined in order to calculate said distance between said
first detectable point (A) and said second detectable point (B),
characterized in that two or more overlapping images (7,8) are made
by the digital camera (1), whereupon corresponding detectable points
(C) in the overlapping part (9) of overlapping images (7,8) are
detected, after which the coordinates of said corresponding detectable
points (C) in both images (7,8) are calculated in order to determine
the displacement of said field of view.
2. A method as claimed in claim 1, characterized in that said field
of view is displaced by displacing the digital camera (1) in a direction
perpendicular to its direction of photographing.
3. A method as claimed in claim 1, characterized in that said field
of use is displaced by moving the object (2) to be measured.
4. A method as claimed in claim 1, characterized in that the field
of view is seen by the digital camera (1) through an adjustable
optical device.
5. A method as claimed in any claim 1, characterized in that a
number of overlapping images (7,8) is processed, whereby all images
show a detectable line of the object (2).
6. A system for measuring dimensions of an object (2) comprising
a digital camera (1) provided with image processing means, detection
means for detecting points (A,B) on the image (7,8), and coordinate
calculation means for calculating the coordinates of detected points
(A,B) on the image (7,8), so that the distance between a first detectable
point (A) and a second detectable point (B) on the object (2) can
be measured by making a first image (7) comprising said first detectable
point (A), then displacing the field of view of the digital camera
(1), and subsequently making an other image (8) comprising said
second detectable point (B), whereby the coordinates of said first
detectable point (A) on said first image (7) and the coordinates
of said second detectable point (B) on said other image (8) can
be calculated, and whereby the displacement of said field of view
can be determined in order to calculate said distance between said
first detectable point (A) and said second detectable point (B),
characterized by means for detecting corresponding detectable points
(C) on two overlapping images (7,8), and means for determining the
displacement of the field of view by calculating the coordinates
of corresponding detectable points (C) on an image (7) made before
the displacement and a overlapping image (8) made after the displacement.
Digital Camera Patent Description
[0001] The invention is related to a method for measuring dimensions
of an object by means of a digital camera provided with image processing
means, with detection means for detecting points on the image, and
with coordinate calculation means for calculating the coordinates
of detected points on the image, whereby the distance between a
first detectable point and a second detectable point on the object
is measured by making a first image comprising said first detectable
point, then displacing the field of view of the digital camera,
and subsequently making an other image comprising said second detectable
point, whereby the coordinates of said first detectable point on
said first image and the coordinates of said second detectable point
on said other image are calculated, and whereby the displacement
of said field of view is determined in order to calculate said distance
between said first detectable point and said second detectable point.
The digital camera is preferably a CCD camera (CCD means Charge
Coupled Device), or it is a CMOS camera (CMOS means Complementary
Metal Oxide Semiconductor), or any other digital imaging equipment.
[0002] Such a method for high precision measuring of dimensions
of an object, in particular the dimensions of an opening or gap
in a die for extruding products, and an apparatus to apply the method,
are disclosed in EP-A-0500400. Thereby the field of view is displaced
by displacing the digital camera in a direction perpendicular to
its direction of photographing.
[0003] To measure the distance between two points of an object
by means of a digital camera, the object can be placed in the field
of view of the camera, in a predetermined position and at a predetermined
distance from the camera. Based on the signals from the digital
camera, an image can be processed showing the field of view of the
camera, and showing said two points, provided that these points
are detectable. After the points are detected and after the coordinates
of the two points are calculated, the distance between the two points
can easily be measured, i.e. calculated.
[0004] For example, a point is detectable in case it is a so called
intensity reversing point, i.e. a point on the image at the border
of two different colours, in particular black and white or a dark
and a light colour. Especially in case the representation on the
image shows angular points, sharp curves or crossings of lines,
such points are detectable on the image. After a point on the image
is detected, the coordinates of it can be calculated, so that its
location on the image is exactly determined.
[0005] In case the distance between two the points is larger than
the field of view of the digital camera, the camera can zoom out
to enlarge its field of view. The same can be achieved by increasing
the distance between the digital camera and the object. However,
in such case the accuracy of the measurement will decrease. So,
if the accuracy has to be maintained, zooming out is not an option.
[0006] EP-A-0500400 presents a solution for that problem by making
use of a CCD camera that can be displaced in a direction perpendicular
to the direction of photographing. A first image showing the first
detectable point is made and an other image showing the second detectable
point is made, and furthermore the displacement of the CCD camera
is detected by measuring an X- and Y-coordinate of the CCD camera.
Therefore an X-axis table and a separate Y-axis table are proposed
to determine the position of the CCD camera during photographing.
[0007] The object of the invention is a method for measuring dimensions
of an object by means of a digital camera, whereby the distance
to be measured is larger than the field of view of the digital camera,
and whereby no additional means for determining the displacement
of the field of view of the digital camera are required.
[0008] To accomplish with that object, two or more overlapping
images are made by the digital camera, whereupon corresponding detectable
points in the overlapping portions of overlapping images are detected,
after which the coordinates of said corresponding detectable points
in both images are calculated in order to determine the displacement
of the field of view of the digital camera relative to the object
to be measured.
[0009] Overlapping images means that a certain portion of the object
to be measured, or a certain portion of the surrounding area, appears
on the image that is made before a displacement of the field of
view of the digital camera as well as on the image that is made
after that displacement. Thereby a portion of one image shows the
same representation as a portion of the other image, i.e. both portions
are identical. The displacement of the field of view of the digital
camera between the moments of making the two images can be exactly
determined by detecting detectable points on both said identical
portions and by calculating the coordinates of said points on each
of the two images. The differences of the coordinates correspond
to the displacement of the field of view of the digital camera.
This manner of calculating the displacement of the field of view
can be done by making use of the means that are already present,
so that there is no need for additional means for measuring the
displacement of the digital camera, in particular for mechanical
additional means as proposed in EP-A-0500400.
[0010] In one preferred embodiment said field of view is displaced
by displacing the digital camera in a direction perpendicular to
its direction of photographing. Thereby the digital camera can be
mounted in a frame that can be displaced with respect to the object
to be measured, as is shown in EP-A-0500400.
[0011] In another preferred embodiment said field of use is displaced
by moving the object to be measured with respect to the digital
camera. Because the distance and the direction of the displacement
is determined through the images taken by the digital camera, there
are no special requirements for controlling said displacement. The
object can be displaced over an unknown distance, provided that
there is an appropriate overlap. Such overlap should include one
or more detectable points.
[0012] In still another preferred embodiment the field of view
is seen by the digital camera through an adjustable optical device,
such as one or more movable mirrors and/or lenses. In general, a
relative small movement of a mirror or lens can cause a rather large
displacement of the field of view, and it will be clear the accuracy
when measuring such small movement is low. However, according to
the invention, there is no need for measuring the movement of the
mirror and/or lens, because the result, i.e. the displacement of
the field of view, is measured.
[0013] In one preferred embodiment, a number of overlapping images
is processed, whereby all images show a detectable line of the object.
Such line can be a portion of the contour of the object or a border
between different colours or the like. The field of view can follow
that line and from time to time the digital camera can make a photograph,
so that an image can be processed. The displacement of the field
of view to a next image can be controlled by the shape of the line
on the image, so that the movement of the field of view follows
the line.
[0014] The invention is also related to a system for measuring
dimensions of an object comprising a digital camera provided with
image processing means, detection means for detecting points on
the image, and coordinate calculation means for calculating the
coordinates of detected points on the image, so that the distance
between a first detectable point and a second detectable point on
the object can be measured by making a first image comprising said
first detectable point, then displacing the field of view of the
digital camera, and subsequently making an other image comprising
said second detectable point, whereby the coordinates of said first
detectable point on said first image and the coordinates of said
second detectable point on said other image can be calculated, and
whereby the displacement of said field of view can be determined
in order to calculate said distance between said first detectable
point and said second detectable point, whereby means are present
for detecting corresponding detectable points on two overlapping
images, and means for determining the displacement of the field
of view by calculating the coordinates of corresponding detectable
points on an image made before the displacement and a overlapping
image made after the displacement.
[0015] The invention will now be further elucidated by means of
a description of an embodiment of a measuring system, whereby reference
is made to the drawing comprising figures which are only schematic
representations, in which:
[0016] FIG. 1 shows a measuring system;
[0017] FIG. 2 shows a field of view of the camera; and
[0018] FIG. 3 shows two overlapping fields of view.
[0019] FIG. 1 shows a digital imaging device 1, in this example
a CCD camera, and an object 2 in front of the camera 1. Object 2
is shown in the position as it is seen by the CCD camera 1. Behind
the object 2, seen from the camera 1, there are a light source 3
and a diffuser plate 4. The light source 3 illuminates the diffuser
plate 4, so that the contour of the object 2 can be seen by the
CCD camera 1 as a sharp border between a dark colour (the object
2) and a light colour (the surrounding area, i.e. the diffuser plate).
[0020] The measurement system is furthermore provided with image
processing means to process images based on the signals of the CCD
camera, with detection means for detecting points on a processed
image, and with coordinate calculation means for calculating the
coordinates of detected points on an image.
[0021] In this example, the length of the object 2 must be measured
by means of the measuring system. The length of the object is the
distance between the two ends 5,6 of the object 2, as it is seen
by the CCD camera 1, i.e. in a certain position with respect to
the camera 1. By measuring that dimension of the object 2, a specific
quality of the object 2 can be checked, provided that the accuracy
of the measurement is high enough.
[0022] The CCD camera 1 can be adjusted in such a way that the
whole object 2 is within its field of view, so that an image can
be processed showing the whole contour of the object 2. That image
is shown in FIG. 2, indicated with a striped line. Then the two
ends 5,6 of the object 2 can be detected as point A and point B
on the image, and subsequently the coordinates of these two points
A,B on the image can be calculated, so that the distance between
them can be determined.
[0023] The accuracy of such measurement depends on the number of
picture elements or pixels on the image. In principle, the accuracy
of the calculated coordinates of a detected point on the image corresponds
with the dimension of a pixel (pixel size). And when making use
of special techniques, such as interpolation of grey values, it
is possible to increase the accuracy, but the accuracy will remain
limited.
[0024] To increase the accuracy of the measurement, the CCD camera
1 can zoom in to increase the scale of the represented object 2
on the image, whereby the dimensions of the object 2 on the processed
image are larger. However, the field of view of the CCD camera 1
will decrease accordingly, whereby it may occur that it is not possible
to represent the whole object 2 on one image. In that case, two
overlapping images (i.e. partly overlapping) can be processed, together
showing the whole object 2.
[0025] FIG. 3 shows these two overlapping images 7,8, which are
indicated with a striped line. After the first image 7 is taken
by the CCD camera (i.e. processed by the image processing means
based on the signals of the camera), the camera is displaced in
a direction perpendicular to its direction of photographing, and
subsequently the second image is taken. The said direction of the
displacement of the camera 1 is indicated with arrow 10, whereby
the displacement can have also a component perpendicular to the
plane of the drawing. The two images 7,8 have an overlapping area
9, and together they represent the whole object 2.
[0026] The distance between the two ends 5,6 of the object 2 is
determined as follows. On the first image 7 the lower end 5 of the
object 2 is detected by the detection means as point A, and subsequently
the coordinates of that point A on the first image 7 are calculated
by the coordinate calculation means. Then, on the second image 8
the upper end 6 of the object 2 is detected as point B, and the
coordinates of that point B on the second image 8 are calculated.
The accuracy of the coordinates of both detected points A,B is relative
high, corresponding to the increased scale of the representation
of the object 2 on the images 7,8.
[0027] It will be clear that the distance between point A and point
B can be easily determined after the position of the first image
7 with respect to the second image 8 is known. This mutual relation
between the two images 7,8 is determined by detecting on both images
7,8 the same detectable point, or pattern of points, in the overlapping
area of the two images 7,8. In the described example of an embodiment,
the detectable point C is detected by the detection means. Point
C is a detectable point of the object 2, because it represents a
sharp curve in the contour of the object 2. Then the coordinates
of point C on each of the two images 7,8 are calculated by the coordinate
calculation means. In fact, the differences between the two sets
of coordinates represent the mutual relation of the two images 7,8,
so that the position of the first image 7 with respect to the position
of the second image 8 is determined.
[0028] The detectable point in the overlapping area of two images
can also be the representation of a point that is not present on
the object to be measured, but present on a structure near the object,
for example on the diffuser plate 4. Therefore the diffuser plate
4 can be provided with a pattern of detectable dots and/or lines.
In case the distance between the diffuser plate 4 and the CCD camera
1 is exactly known, the mutual relation of two images can be determined
when the coordinates of a certain detectable point on the represented
diffuser plate 4 in the overlapping area 9 of two images 7,8 are
calculated.
[0029] In the described example of an embodiment the whole object
2 is represented on two images 7,8. However, the invention can also
be applied by making use of more than two images, provided that
each two neighbouring images overlap each other partly, so that
in each overlapping area one or more detectable points can be found.
[0030] When inspecting an object which is much larger than the
field of view of the CCD camera, a number of mutual overlapping
images can be taken, whereby the field of view of the CCD camera
follows a (curved) line, which is detected on the representation
of the object. In case the system has to inspect objects having
a known shape, the field of view can follow a predetermined line.
But in all these cases overlapping images are made, so that the
shape of the object can be checked.
[0031] The embodiment as described above is merely an example of
the method of measuring dimensions and/or the shape of an object;
a great many other embodiments are possible. For example, in case
a difference in colour on the object has to be detected, the light
source 3 in FIG. 1 should not be located behind the object 2 (seen
from the camera 1), but at the other side of the object 3 (in FIG.
1 the right side). |