Television – Panoramic
Reexamination Certificate
1998-06-16
2001-10-16
Kelley, Chris (Department: 2713)
Television
Panoramic
Reexamination Certificate
active
06304285
ABSTRACT:
FIELD OF INVENTION
This invention presents a set of methods and apparatus for omnidirectional stereo imaging. By “omnidirectional imaging system”, we mean a system that is able to acquire images with a field-of-view covering entire hemisphere (180 solid space angle), simultaneously without any mechanical moving part. The field of view of a conventional camera or a light projector can be dramatically increased by employing a reflective mirror properly placed in front of the camera or the projector. A pair of omnidirectional cameras is able to form a unique stereo imaging system that is able to obtain three dimensional images of surrounding scene with 360 degree view angle. A combination of an omnidirectional camera and an omnidirectional structured light projector can also provide a means to obtain quantitative three dimensional measurements of the objects around the camera system. The omnidirectional three dimensional imaging methods and apparatus presented herein may offer unique solutions to many practical systems that need simultaneous 360 degree viewing angle and three dimensional measurement capability.
1. PRIOR ART—EXISTING APPROACHES TO LARGE FOV IMAGING SYSTEM
A number of approaches had been proposed in the past for imaging systems to achieve wide field-of-view (FOV). None of them, however, is able to generate 3D omnidirectional images. In the following paragraphs, we give a briefly survey on the state-of-the-art of current imaging systems that seek to achieve wide FOV.
1.1. Conventional Cameras
Most existing imaging systems employ electronic sensor chips, or still photographic film, to record optical image collected by its optical lens system. The image projection for most camera lenses is modeled as a “pin-hole” with a single center of projection. Since sizes of camera lens and the imaging sensor have their practical limitations, the light rays that can be collected by a camera lens and received by the imaging device typically form a corn with very small opening angle. Therefore, angular field-of-views for conventional cameras are within a range of 5 to 50 degrees. For example, an 8.5 mm F/1.3 camera lens for ½″ CCD (Charge Coupled Device) chip only has an angular FOV of 41.2 degree.
1.2. Fish-Eye Lenses
Optical engineers had designed several versions of wide-viewing-angle lens system, called the fish-eye lens (see [1],[2]). The fish-eye lens features a very short focal length which, when used in place of conventional camera lens, enables the camera to view object for much wider angle (almost 180 degree of hemisphere). In general, the wider FOV, the more complicated design the fish-eye lens has. To obtain a hemispherical FOV, the fish-eye lens must be quite large in dimension, complex in optical design, and hence expensive. Also, it is very difficult to design a fish-eye lens that ensures single view point constraint, i.e., all incoming principal light rays intersect at a single point to form a fixed viewpoint. This is indeed a problem with commercial fish-eye lenses, including Nikon's Fisheye-Nikkor 8-mm f/2.8 lens. The use of fish-eye lenses for wide FOV imaging application has been advocated by [3] and [4], among others. Although the acquired image by fish-eye lenses may prove to be good enough for some visualization applications, the distortion compensation issue has not been resolved, and the high unit-cost remain to be major hurdles for its wide-spread applications. The fish-eye lens technique has the advantage of adopting a statically positioned camera to acquire a wide angle of view. However the nonlinear property resulted from the semi-spherical optical lens mapping make the resolution along the circular boundary of the image very poor, while the field of view corresponding to the circular boundary of the image usually represents a ground or floor where a high resolution of image is required.
1.3. Multi-Camera System or Rotating Imaging Systems
Large field of view of objects may be obtained by using multiple cameras in the same system, each points towards a different direction. However, issues on seamless integration of multiple images is further complicated by the fact that image produced by each camera has different centers of projection. The cost for such a system is usually high. The image processing required by multiple cameras or rotating camera method to obtain a precise information on position and azimuth of an object takes a long time, which is not suitable for real-time battle field modeling and reconnaissance applications.
Another straightforward solution to increasing the FOV of an imaging system is to rotate the entire imaging system about its center of projection (FIG.
1
). An image sequence acquired by the camera at different positions are “stitched” together to obtain a panoramic view of the scene. Such an approach has been recently proposed by several researchers (see [5], [6] [7]). A very interesting approach developed by [8] employs a camera with a non-frontal image detector to scan the world.
The first disadvantage of any rotating image system is that it requires the use of moving parts, and precision positioning devices. A more serious drawback is that such systems lack the capability of simultaneously a acquiring images with wide FOV. Although such system can acquire precise azimuth information in omnidirectional view, the imaging process is time-consuming and the method is not applicable to real-time problems such as avoiding collision against moving obstacles or monitoring scene with mobile objects. This restricts the use of rotating systems to static and non-real-time applications.
In contrast, the invention presented herein, called the omnidirectional camera, is capable of capturing real-time omnidirectional images without using any moving parts. By “omnidirectional images”, we mean images with a field-of-view covering entire hemisphere (180 solid space angle), simultaneously.
FIG. 2
provides a comparison between our Omnidirectional Camera, panoramic camera and conventional cameras. As one can see, a panoramic camera is still not ommidirectional, since it can only provide a wide-angle of FOV at certain time instance, not in all directions.
2. SUMMARY OF THE INVENTION
The primary objective of present invention is to provide a set of simple methods and apparatus to obtain simultaneously omnidirectional stereo images without using any moving parts. The field of view of a conventional camera or a light projector can be dramatically increased by employing a reflective mirror properly placed in front of the camera or the projector. A pair of omnidirectional cameras is able to form a unique stereo imaging system that is able to obtain three dimensional images of surrounding scene with 360 degree view angle. A combination of an omnidirectional camera and an omnidirectional structured light projector can also provide a means to obtain quantitative three dimensional measurements of the objects around the camera system. The omnidirectional three dimensional imaging methods and apparatus presented herein may offer unique solutions to many practical systems that need simultaneous 360 degree viewing angle and three dimensional measurement capability.
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Kelley Chris
Vo Tung
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