1. Technical Field
This invention relates generally to an apparatus and method for capturing an image having a spherical field-of-view for subsequent viewing. Specifically, the present invention relates to a system involving a single camera having a lens with a field of view of at least 180.degree. and associated method for capturing a first hemispherical image for subsequent combination into the spherical image. Alternatively, when the system comprises two cameras with such lenses mounted in a securely attached back-to-back arrangement, the system and method captures two distinct hemispherical images for subsequent combination into the spherical image. The preferred system includes a single-use, still image camera.
2. Background Art
The discussion of the background art related to the invention described herein relates to two subjects: spherical image capture and subsequent captured image transformations.
Spherical Image Capture
The goal of imaging technology is to make the observer feel as though he or she is part of the image. Prior art systems have partially accomplished this goal. Unfortunately, the ability of prior art systems to make the user feel part of the captured images are proportional to the cost of the image capture system.
Relating to inexpensive image capturing systems, camera companies have introduced disposable cameras. A disposable camera generally refers to a single-use camera that includes film, a lens, and a camera body, all in a single compact shell. The film includes either a single frame of film or multiple frames of film. After the entire roll of film has been exposed, the entire camera is returned for film developing. All the photographer receives back are the developed prints or slides. The manufacturer then recycles the parts from the returned camera, adds film, and ships the camera to a retailer for sale again. Disposable cameras come in various types including regular magnification cameras, telephoto cameras, water resistant cameras, and panoramic cameras.
Images captured by panoramic cameras provide wide angle horizontal images (left to right) but lack wide angle vertical images (up and down). Accordingly, while capturing a wide field-of-view on one plane (horizontal), the photographer loses the wide field-of-view on the other plane (vertical). Rotating the camera only alters the wide angle direction. The following example illustrates this shortcoming. Suppose a photographer desires to capture the grandeur of a dense forest from within the forest. While an image captured by a panoramic camera would include a sweeping cross section of trees (left to right), it would only include, at most, the middle portions of the nearest trees. To capture the forest floor and canopy, the photographer would have to take multiple panoramic photographs from looking almost straight down to looking straight up. The final image of the forest would then only be realized with the laborious task of manually cutting and pasting the different images together. Unfortunately, the left and right ends of the final image become distorted and cannot be easily resolved. The distortions created are similar to those encountered in map-making where one tries to represent a round earth on a flat map. Specifically, objects and relative distances near the extremes of the wide angle image become distorted. Additionally, this approach wastes film.
A slightly more complex panoramic camera employs a scanning drive mechanism which selectively exposes vertical strips of film as the camera scans from extreme to extreme. However, scanning panoramic cameras invariably introduce noise into captured images through vibrations generated from their scanning motions as well as take a relatively long period of time to capture the image.
Other wide-angle image capturing systems exist. For example, IMAX and 70 mm films provide high definition images on a large screen. However, these screens are flat. While a viewer can feel part of the scene when staring straight ahead, this feeling dissipates where the screen ends.
Another imaging system includes the OMNIMAX camera and projection system where an image was recorded and later projected on a spherical screen to produce an image 180 degrees wide, 100 degrees up from the horizon and 20 degrees below. While this system offers significant improvements over a flat screen projection system, the viewer's absorption into the displayed images is limited by the edges of the displayed image.
Another image capture and display system is U.S. Pat. No. 5,023,725 to McCutchen. McCutchen discloses a dodecahedral imaging system which breaks a sphere into 12 discrete polyhedrons. Each section has its own dedicated CCD camera. The images are captured and displayed on the walls of a hemispherical room. This system offers increased resolution through increasing the number of cameras used. However, as the number of cameras increase, the bulk of the imaging system likewise increases. Additionally, each camera has to be perfectly aligned with respect to the other cameras to adequately capture a spherical image. Using McCutcheon's system, increased resolution requires more bulk and more expense. Furthermore, the images of each camera are not integrated together. Accordingly, the system fails to account for the seams between the displayed images. While quickly moving images may mask these edge effects, the edge effects may be more noticeable with slow moving images.
Captured Image Transformations
Camera viewing systems are used in abundance for surveillance, inspection, security, and remote sensing. Remote viewing is critical, for example, for robotic manipulation tasks. Close viewing is necessary for detailed manipulation tasks while wide-angle viewing aids positioning of the robotic system to avoid collisions with the work space. Most of these systems use either a fixed-mount camera with a limited viewing field to reduce distortion, or they utilize mechanical pan-and-tilt platforms and mechanized zoom lenses to orient the camera and magnify its image. In the application where orientation of the camera and magnification of its image are required, the mechanical solution is large in size and can subtend a significant volume making the viewing system difficult to conceal or use in close quarters. Several cameras are usually necessary to provide wide-angle viewing of the work space.
In order to provide a maximum amount of viewing coverage or subtended angle, mechanical pan/tilt mechanisms usually use motorized drives and gear mechanisms to manipulate the vertical and horizontal orientation. An example of such a device is shown in U.S. Pat. No. 4,728,839 issued to J. B. Coughlan, et al, on Mar. 1, 1988. Collisions with the working environment caused by these mechanical pan/tilt orientation mechanisms can damage both the camera and the work space and impede the remote handling operation. Simultaneously, viewing in said remote environments is extremely important to the performance of inspection and manipulation activities.
Camera viewing systems that use internal optics to provide wide viewing angles have also been developed in order to minimize the size and volume of the camera and the intrusion into the viewing area. These systems rely on the movement of either a mirror or prism to change the tilt-angle of orientation and provide mechanical rotation of the entire camera to change the pan angle of orientation. Additional lenses are used to minimize distortion. Using this means, the size of the camera orientation system can be minimized, but "blind spots" in the center of the view result. Also, these systems typically have no means of magnifying the image and or producing multiple images from a single camera.
Further, references that may be relevant to the evaluation of the captured image transformations as described herein include U.S. Pat. Nos. 4,772,942 issued to M. J. Tuck on Sep. 20, 1988; 5,067,019 issued to R. D. Juday on Nov. 19, 1991; and 5,068,735 issued to K. Tuchiya, et al on Nov. 26, 1991.