Omnidirectional vision sensor

Details Omnidirectional vision sensor Omnidirectional vision sensor

2001-07-13

2004-09-21

Sikder, Mohammad (Department: 2872)

Optical: systems and elements

Mirror

Plural mirrors or reflecting surfaces

C359S853000, C359S854000, C359S725000, C359S729000

Reexamination Certificate

active

06793356

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vision sensor capable of omnidirectional observation encompassing a viewing range 360 degrees around the vision sensor. In particular, the present invention relates to an omnidirectional vision sensor which is used in a vision system for a monitoring camera system or a mobile robot, etc., and which can obtain field of view information associated with the entire surroundings in real-time.
2. Description of the Related Art
In recent years, various omnidirectional vision sensors have been proposed as input devices through which visual information covering a broad range is to be input to any device coupled to the omnidirectional vision sensors, with a view to developing applications for monitoring camera systems or mobile robots, etc.
The following techniques are known, for example:
{circle around (1)} a method in which images which are captured by means of a single rotating camera are linked together (Japanese Laid-Open Publication No. 10-105840, entitled “System for automatically detecting an intruding object”);
{circle around (2)} a method in which images which are captured by means of a rotating plate mirror are linked together (Japanese Laid-Open Publication No. 11-4373, entitled “Method and apparatus for constructing omnidirectional panoramic images”);
{circle around (3)} a method in which omnidirectional images are captured at one time by means of a plurality of fixed cameras (Japanese Laid-Open Publication No. 11-164292, entitled “Image generation device, image presentation device, image generation method and image synthesis method”);
{circle around (4)} a method in which an image from a wide field of view is captured at one time by means of a wide-angle lens such as a fish-eye lens (Japanese Laid-Open Publication No. 11-355763, entitled “Monitor system and monitor method”); and
{circle around (5)} a method in which an image is captured at one time by means of a reflection mirror of a special shape such as a spherical, conical, hyperbolic, etc., shape (Japanese Laid-Open Publication No. 11-218409, entitled “Method and apparatus for measuring three-dimensional information”).
Method {circle around (1)} mentioned above involves acquiring images of the surroundings by means of a single television camera which is placed on an electrically actuated base and is rotated by 360 degrees, where the images are linked together by image processing. By using this method, it is possible to acquire omnidirectional images with a relatively high resolution. However, since the camera is rotated while acquiring images, it is impossible to acquire omnidirectional images at one time, thus the resultant image is no longer a real-time image.
Method {circle around (2)} mentioned above involves rotating a mirror by 360 degrees so as to acquire images of the surroundings which are reflected by the mirror are captured by means of a fixed camera, where the images are linked together by image processing. Thus, it is possible to acquire omnidirectional images with a relatively high resolution, as is the case with method {circle around (1)}. However, since the mirror is rotated while acquiring images, it is impossible to acquire omnidirectional images at one time, thus resultant image is no longer a real-time image, as is the case with method {circle around (1)}.
Methods {circle around (1)} and {circle around (2)} mentioned above utilize a mechanical means for rotating a camera or a mirror, respectively, thus requiring some sort of maintenance work for the mechanical means in order to enable operation over a long period of time. Accordingly, methods {circle around (3)} to {circle around (5)} mentioned above have been proposed as methods which enable a one-time acquisition of omnidirectional images without employing any mechanical means.
Method {circle around (3)} mentioned above involves acquiring omnidirectional images at one time by employing a plurality of fixed cameras, and is advantageous from the perspective of obtaining images in real-time. Moreover, since no special mechanical means is required, this method is suitable for long periods of use, and provides for good reliability. However, there is a problem in that the use of a plurality of camera leads to an increased system cost.
Methods {circle around (4)} and {circle around (5)} mentioned above employ a wide-angle lens or a reflection mirror of a specific shape to enable a one-time acquisition of an image from a wide field of view. As is the case with method {circle around (3)} mentioned above, this method is advantageous from the perspective of obtaining images in real-time, and, since no special mechanical means is required, this method is suitable for long periods of use and provides for good reliability. Furthermore, unlike method {circle around (3)} mentioned above, only one camera is required, thereby reducing the system cost. However, with methods {circle around (4)} and {circle around (5)}, it is impossible to acquire complete omnidirectional images encompassing 360 degrees. In other words, the resultant field of view includes a blind spot(s).
Hereinafter, the field of view and blind spots which are inherent in methods {circle around (4)} and {circle around (5)} mentioned above will be described with reference to
FIGS. 6
to
10
. Each plane of
FIGS. 6
to
10
is a vertical plane which contains a central axis therein, with a camera being disposed below a lens or a mirror.
FIG. 6
illustrates a field of view in the case where a wide-angle lens
10
is employed in method {circle around (4)} mentioned above. When the system is constructed so that the wide-angle lens
10
is disposed with its convex portion “up” (as shown in FIG.
6
), with the imaging means including a camera being located below the wide-angle lens
10
, it would be possible to acquire an image from the space above a horizontal plane extending 360 degrees around the lens, an image of only an upper half of the surrounding sphere along the vertical direction can be captured. That is, the lower half of the surrounding sphere is left as a blind spot.
FIG. 7
illustrates a field of view in the case where a conical mirror
20
is employed as a body-of-revolution mirror in method {circle around (5)} mentioned above. While the images captured by this method encompass a horizontal span covering 360 degrees around the mirror, the mirror face presents an obstacle along the vertical direction, creating a blind spot above and below the horizontal span. In other words, a blind spot exists in the “front” of the camera (imaging means).
FIG. 8
illustrates a field of view in the case where a spherical mirror
30
is employed as a body-of-revolution mirror in method {circle around (5)} mentioned above. While the images captured by this method encompass a horizontal span covering 360 degrees around the mirror, the mirror face presents an obstacle along the vertical direction, creating a blind spot above the horizontal span. In other words, a blind spot exists in the “front” of the camera (imaging means).
FIG. 9
illustrates a field of view in the case where a hyperbolic mirror
40
is employed as a body-of-revolution mirror in method {circle around (5)} mentioned above. While the images captured by this method encompass a horizontal span covering 360 degrees around the mirror, the mirror face presents an obstacle along the vertical direction, creating a blind spot above the horizontal span. In other words, a blind spot exists in the “front” of the camera (imaging means).
FIG. 10
illustrates a field of view in the case where a parabolic mirror
50
is employed as a body-of-revolution mirror in method {circle around (5)} mentioned above. While the images captured by this method encompass a horizontal span covering 360 degrees around the mirror, the mirror face presents an obstacle along the vertical direction, creating a blind spot above the horizontal span. In other words, a blind spot exists in the “front” of the camera (imaging means).
Thus, according to any of methods {circle around (4)} and {circl

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