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Claims  |
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We claim:
1. A device for providing perspective and distortion corrected views of a
selected portion of a field of view in a desired format, said device
comprising:
an imaging system for receiving selected optical and infrared images of
said selected portion of a field of view and for producing output signals
corresponding to said selected optical and infrared images;
a lens attached to said imaging system for conveyance of said selected
optical and infrared images to said imaging system;
image capture circuitry for receiving and providing digitized signals from
said output signals from said imaging system;
input image memory circuitry for receiving said digitized signals from said
image capture circuitry;
image transform circuitry for processing said digitized signals from said
input image memory circuitry according to selected viewing pan, tilt,
rotation and magnification degrees and for producing output signals
according to a combination of said digitized signals and said selected
viewing pan, tilt, rotation and magnification degrees;
output image memory circuitry for receiving said output signals from said
image transform circuitry;
an input for selected user and external computer input to select said pan,
tilt, rotation and magnification degrees, and for converting said selected
viewing pan, tilt, rotation and magnification degrees for input to said
image transform circuitry to control said processing of said image
transform circuitry; and
an output connected to said output image circuitry for recording said
perspective and distortion corrected views according to said selected
viewing pan, tilt, rotation and magnification degrees.
2. A surveillance device for providing perspective corrected views of a
selected portion of perspective distorted optical images from an
environment into a desired format, said device comprising:
an imaging system for receiving optical images from the environment and for
producing output signals corresponding to said perspective distorted
optical images, said imaging system including a wide angle lens for
optical conveyance of said optical images to a video camera within said
imaging system and positioned within the environment, said optical images
to said video camera being perspective distorted by said wide angle lens;
image capture circuitry for receiving, and producing digitized signals
from, said output signals from said imaging system;
input image memory circuitry for receiving said digitized signals from said
image capture circuitry;
image transform circuitry for processing said digitized signals in said
input memory circuitry according to selected viewing angles of pan, tilt,
rotation and magnification degrees for producing output signals of
perspective corrected images according to a combination of said digitized
signals and said selected viewing angles of pan, tilt, rotation and
magnification degrees;
output image memory circuitry for receiving said output signals from said
image transform circuitry;
an input for selecting said viewing pan, tilt, rotation and magnification
degrees, and for producing signals to control said processing of said
image transform circuitry as to said viewing pan, tilt, rotation and
magnification degrees; and
an output connected to said output image circuitry for recording said
perspective corrected views according to said selected viewing pan, tilt,
rotation and magnification degrees.
3. The device of claim 2 wherein said imaging system further comprises a
video recorder for receiving and recording said output signals of said
video camera for selective input to said image capture circuitry.
4. The device of claim 2 further comprising a further input for inputting
control signals to said image transform circuitry to achieve simultaneous
multiple perspective corrected views in said output and selected scanning
of said video camera.
5. The device of claim 4 wherein a plurality of video cameras are within
the environment, each video camera being provided with a wide angle lens,
and wherein said selected scanning of said video camera by said further
input comprises selecting between incremental effective movement of
optical images of a single video camera and switching between optical
images of different of said plurality of video cameras in the environment.
6. The device of claim 4 wherein said input and said further input includes
selective computer and user inputs.
7. The device of claim 4 wherein said further input includes discrete
switches to control said processing of said image transform circuitry.
8. The device of claim 7 further comprising at least one alarm device
operated by said further input means and by said discrete switches.
9. The device of claim 1 wherein said image transform circuitry is
programmed to implement the following two equations:
##EQU7##
where: A=(cos.phi.cos.differential.-sin.phi.sin.differential.cos.beta.)
B=(sin.phi.cos.differential.+cos.phi.sin.differential.cos.beta.)
C=(cos.phi.sin.differential.+sin.phi.cos.differential.cos.beta.)
D=(sin.phi.sin.differential.-cos.phi.cos.differential.cos.beta.)
and where:
R=radius of the image circle
.beta.=zenith angle
.differential.=Azimuth angle in image plane
.phi.=Object plane rotation angle
m=Magnification
u,v=object plane coordinates
x,y=image plane coordinates.
10. The device of claim 2 wherein said image transform circuitry is
programmed to implement the following two equations:
##EQU8##
where: A=(cos.phi.cos.differential.-sin.phi.sin.differential.cos.beta.)
B=(sin.phi.cos.differential.+cos.phi.sin.differential.cos.beta.)
C=(cos.phi.sin.differential.+sin.phi.cos.differential.cos.beta.)
D=(sin.phi.sin.differential.-cos.phi.cos.differential.cos.beta.)
and where:
R=radius of the image circle
.beta.=zenith angle
.differential.=Azimuth angle in image plane
.phi.=Object plane rotation angle
m=Magnification
u,v=object plane coordinates
x,y=image plane coordinates.
11. A surveillance device for providing perspective corrected views of a
selected portion of perspective distorted optical images from an
environment into a desired format, said device comprising:
an imaging system for receiving optical images from the environment and for
producing output signals corresponding to said perspective distorted
optical images, said imaging system including a wide angle lens for
optical conveyance of said optical images to a video camera within said
imaging system and positioned within the environment, said optical images
to said video camera being perspective distorted by said wide angle lens;
image capture circuitry for receiving, and producing digitized signals
from, said output signals from said imaging system;
input image memory circuitry for receiving said digitized signals from said
image capture circuitry;
image transform circuitry for processing said digitized signals in said
input memory circuitry according to selected viewing angles of pan, tilt,
rotation and magnification degrees for producing output signals of
perspective corrected images according to a combination of said digitized
signals and said selected viewing angles of pan, tilt, rotation and
magnification degrees;
output image memory circuitry for receiving said output signals from said
image transform processor circuitry;
an input for selecting said viewing pan, tilt, rotation and magnification
degrees, and for producing signals to control said processing of said
image transform circuitry as to said viewing pan, tilt, rotation and
magnification degrees; and
a further input for inputting control signals to said image transform
circuitry to achieve multiple perspective corrected views in said output
means and selected scanning of said video camera; and
an output connected to said output image circuitry for recording said
perspective corrected views according to said selected viewing pan, tilt,
rotation and magnification degrees;
wherein said image transform circuitry is programmed to implement the
following two equations:
##EQU9##
where: A=(cos.phi.cos.differential.-sin.phi.sin.differential.cos.beta.)
B=(sin.phi.cos.differential.+cos.phi.sin.differential.cos.beta.)
C=(cos.phi.sin.differential.+sin.phi.cos.differential.cos.beta.)
D=(sin.phi.sin.differential.-cos.phi.cos.differential.cos.beta.)
and where:
R=radius of the image circle
.beta.=zenith angle
.differential.=Azimuth angle in image plane
.phi.=Object plane rotation angle
m=Magnification
u,v=object plane coordinates
x,y=image plane coordinates.
12. The device of claim 11 wherein a plurality of video cameras are within
the environment, each of said video cameras being provided with a wide
angle lens, and wherein said selected scanning of said video cameras by
said further input comprises selecting between incremental effective
movement of optical images of a single video camera and switching between
optical images of different of said plurality of video cameras in the
environment.
13. The device of claim 11 wherein said input and said further input
include selective computer and user inputs.
14. The device of claim 11 wherein said further input comprises discrete
switches to input said selected pan, tilt, rotation and magnification
degrees into said image transform circuitry.
15. The device of claim 11 further comprising an output line from said
image transform circuitry to selectively activate a video recorder in said
image transform circuitry and an alarm.
16. The device of claim 14 wherein said further input further comprises at
least one input line for carrying an input signal from external sensors in
the environment as to closure status of discrete switches of said external
sensors.
17. The device of claim 11 further comprising a sensor for determining
existance of output signals from said imaging system and for energizing an
alarm upon determination of absence of said output signals from said
imaging system.
18. The device of claim 14 wherein said further input further comprises at
least one input line for carrying an interrogation signal to said image
transform circuitry to interrogate for system parameters and performance. |
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Claims |
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Description |
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TECHNICAL FIELD
The present invention relates to an apparatus, algorithm, and method for
transforming single perspective-distorted field-of-view images into
multiple non-distorted, normal perspective image at any orientation,
rotation, and magnification within the field-of-view, and for using the
resultant system for surveillance applications. The viewing direction,
orientation, and magnification are controlled by either computer or remote
control means. More particularly, this apparatus is the electronic
equivalent of a mechanical pan, tilt, zoom, and rotation camera viewing
system with no moving mechanisms, and is typically utilized for automatic
or manual surveillance of a selected environment.
BACKGROUND ART
Camera viewing systems are utilized 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. The majority
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 applications 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.
References that may be relevant to the evaluation of the present invention
are U.S. Pat. Nos.: 4,772,942 issued to M. J. Tuck on Sep. 20, 1988;
5,023,725 issued to D. McCutchen on Jun. 11, 1991; 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.
Accordingly, it is an object of the present invention to provide an
apparatus that can provide an image of any portion of the viewing space
within a selected field-of-view without moving the apparatus, and then
electronically correct for visual distortions of the view.
It is another object of the present invention to provide horizontal
orientation (pan), vertical orientation (tilt) and rotational orientation
(rotation) of the viewing direction with no moving mechanisms.
It is another object of the present invention to provide the ability to
magnify or scale the image (zoom in and out) electronically.
It is another object of the present invention to provide electronic control
of the image intensity (iris level).
It is another object of the present invention to be able to accomplish pan,
tilt, zoom, rotation, and iris adjustments with simple inputs made by a
lay person from a joystick, keyboard controller, or computer controlled
means.
It is also an object of the present invention to provide accurate control
of the absolute viewing direction and orientations using said input
devices.
A further object of the present invention is to provide the ability to
produce multiple images with different orientations and magnifications
simultaneously from a single input image.
Another object of the present invention is to be able to provide these
images at real-time video rates, e.g. thirty transformed images per
second, and to support various display format standards such as the
National Television Standards Committee RS-170 signal format and/or higher
resolution formats currently under development.
It is also an object of the present invention to provide a system that can
be used for automatic or manual surveillance of selected environments,
with optical views of these environments corrected electronically to
remove distortion so as to facilitate this surveillance.
These and other objects of the present invention will become apparent upon
consideration of the drawings hereinafter in combination with a complete
description thereof.
DISCLOSURE OF THE INVENTION
In accordance with the present invention, there is provided an
omnidirectional viewing system that produces the equivalent of pan, tilt,
zoom, and rotation within a selected field-of-view with no moving parts.
Further, the present invention includes means for controlling this
omnidirectional viewing in surveillance applications. This device includes
a means for digitizing an incoming or prerecorded video image signal,
transforming a portion of the video image based upon operator or
preselected commands, and producing one or more output images that are in
correct perspective for human viewing. In one embodiment, the incoming
image is produced by a fisheye lens which has a wide angle field-of-view.
This image is captured into an electronic memory buffer. A portion of the
captured image, either in real time or as prerecorded, containing a
region-of-interest is transformed into a perspective correct image by an
image processing computer. The image processing computer provides direct
mapping of the image region-of-interest into a corrected image using an
orthogonal set of transformation algorithms. The viewing orientation is
designated by a command signal generated by either a human operator or
computerized input. The transformed image is deposited in a second
electronic memory buffer where it is then manipulated to produce the
output image or images as requested by the command signal. This is coupled
with appropriate alarms and other outputs to provide a complete
surveillance system for selected environments.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a schematic block diagram of the signal processing portion of
the present invention illustrating the major components thereof.
FIG. 2 is an exemplary drawing of a typical fisheye image used as input by
the present invention. Lenses having other field-of-view values will
produce images with similar distortion, particularly when the
field-of-view is about eighty degrees or greater.
FIG. 3 is an exemplary drawing of the output image after correction for a
desired image orientation and magnification within the original image.
FIG. 4 is a schematic diagram of the fundamental geometry that the present
invention embodies to accomplish the image transformation.
FIG. 5 is a schematic diagram demonstrating the projection of the object
plane and position vector into image plane coordinates.
FIG. 6 is a block diagram of the present invention as utilized for
surveillance/inspection applications incorporating the basic
transformation of video images obtained with, for example, wide angle
lenses to correct for optical distortions due to the lenses, together with
the control of the surveillance/inspection and appropriate alarm systems.
FIGS. 7A and 7B, together, show a logic flow diagram illustrating one
specific embodiment of controller operation for manual and automatic
surveillance operations of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
In order to minimize the size of the camera orientation system while
maintaining the ability to zoom, a camera orientation system that utilizes
electronic image transformations rather than mechanisms was developed.
While numerous patents on mechanical pan-and-tilt systems have been filed,
no approach using strictly electronic transforms and wide angle optics is
known to have been successfully implemented. In addition, the
electro-optical approach utilized in the present invention allows multiple
images to be extracted from the output of a single camera. These images
can be then utilized to energize appropriate alarms, for example, as a
specific application of the basic image transformation in connection with
a surveillance system. As utilized herein, the term "surveillance" has a
wide range including, but not limited to, determining ingress or egress
from a selected environment. Further, the term "wide angle" as used herein
means a field-of-view of about eighty degrees or greater. Motivation for
this device came from viewing system requirements in remote handling
applications where the operating envelop of the equipment is a significant
constraint to task accomplishment.
The principles of the optical transform utilized in the present invention
can be understood by reference to the system 10 of FIG. 1. (This is also
set forth in the afore-cited U.S. patent application Ser. No. 07/699,366
that is incorporated herein by reference.) Shown schematically at 11 is a
wide angle, e.g., a fisheye, lens that provides an image of the
environment with a 180 degree field-of-view. The lens is attached to a
camera 12 which converts the optical image into an electrical signal.
These signals are then digitized electronically 13 and stored in an image
buffer 14 within the present invention. An image processing system
consisting of an X-MAP and a Y-MAP processor shown as 16 and 17,
respectively, performs the two-dimensional transform mapping. The image
transform processors are controlled by the microcomputer and control
interface 15. The microcomputer control interface provides initialization
and transform parameter calculation for the system. The control interface
also determines the desired transformation coefficients based on
orientation angle, magnification, rotation, and light sensitivity input
from an input means such as a joystick controller 22 or computer input
means 23. The transformed image is filtered by a 2-dimensional convolution
filter 18 and the output of the filtered image is stored in an output
image buffer X9. The output image buffer 19 is scanned out by display
electronics 20 to a video display device 21 for viewing.
A range of lens types can be accommodated to support various fields of
view. The lens optics 11 correspond directly with the mathematical
coefficients used with the X-MAP and Y-MAP processors 16 and 17 to
transform the image. The capability to pan and tilt the output image
remains even though a different maximum field of view is provided with a
different lens element.
The invention can be realized by proper combination of a number of optical
and electronic devices. The lens 11 is exemplified by any of a series of
wide angle lenses from, for example, Nikon, particularly the 8 mm F2.8.
Any video source 12 and image capturing device 13 that converts the
optical image into electronic memory can serve as the input for the
invention such as a Videk Digital Camera interfaced with Texas
Instrument's TMS 34061 integrated circuits. Input and output image buffers
14 and 19 can be constructed using Texas Instrument TMS44C251 video random
access memory chips or their equivalents. The control interface can be
accomplished with any of a number of microcontrollers including the Intel
80C196. The X-MAP and Y-MAP transform processors 16 and 17 and image
filtering 19 can be accomplished with application specific integrated
circuits or other means as will be known to persons skilled in the art.
The display driver can also be accomplished with integrated circuits such
as the Texas Instruments TMS34061. The output video signal can be of the
NTSC RS-170, for example, compatible with most commercial television
displays in the United States. Remote control 22 and computer control 23
are accomplished via readily available switches and/or computer systems
that also will be well known. These components function as a system to
select a portion of the input image (fisheye or other wide angle) and then
mathematically transform the image to provide the proper prospective for
output. The keys to the success of the invention include:
(1) the entire input image need not be transformed, only the portion of
interest;
(2) the required mathematical transform is predictable based on the lens
characteristics; and
3) calibration coefficients can be modified by the end user to correct for
any lens/camera combination supporting both new and retrofit applications.
The transformation that occurs between the input memory buffer 14 and the
output memory buffer 19, as controlled by the two coordinated
transformation circuits 16 and 17, is better understood by referring to
FIGS. 2 and 3. The image shown in FIG. 2 is a rendering of the image of a
grid pattern produced by a fisheye lens. This image has a field-of-view of
180 degrees and shows the contents of the environment throughout an entire
hemisphere. Notice that the resulting image in FIG. 2 is significantly
distorted relative to human perception. Similar distortion will be
obtained even with lesser field-of-view lenses. Vertical grid lines in the
environment appear in the image plane as 24a, 24b, and 24c. Horizontal
grid lines in the environment appear in the image plane as 25a, 25b, and
25c. The image of an object is exemplified by 26. A portion of the image
in FIG. 2 has been corrected, magnified, and rotated to produce the image
shown in FIG. 3. Item 27 shows the corrected representation of the object
in the output display. The results shown in the image in FIG. 3 can be
produced from any portion of the image of FIG. 2 using the present
invention. The corrected perspective of the view is demonstrated by the
straightening of the grid pattern displayed in FIG. 3. In the present
invention, these transformations can be performed at real-time video rates
(e.g., thirty times per second), compatible with commercial video
standards.
The transformation portion of the invention as described has the capability
to pan and tilt the output image through the entire field of view of the
lens element by changing the input means, e.g. the joystick or computer,
to the controller. This allows a large area to be scanned for information
as can be useful in security and surveillance applications. The image can
also be rotated through any portion of 360 degrees on its axis changing
the perceived vertical of the displayed image. This capability provides
the ability to align the vertical image with the gravity vector to
maintain a proper perspective in the image display regardless of the pan
or tilt angle of the image. The invention also supports modifications in
the magnification used to display the output image. This is commensurate
with a zoom function that allows a change in the field of view of the
output image. This function is extremely useful for inspection and
surveillance operations. The magnitude of zoom provided is a function of
the resolution of the input camera, the resolution of the output display,
the clarity of the output display, and the amount of picture element
(pixel) averaging that is used in a given display. The invention supports
all of these functions to provide capabilities associated with traditional
mechanical pan (through 180 degrees), tilt (through 180 degrees), rotation
(through 360 degrees), and zoom devices. The digital system also supports
image intensity scaling that emulates the functionality of a mechanical
iris by shifting the intensity of the displayed image based on commands
from the user or an external computer.
The postulates and equations that follow are based on the image
transformation portion of the present invention utilizing a wide angle
lens as the optical element. These also apply to other field-of-view lens
systems. There are two basic properties and two basic postulates that
describe the perfect wide angle lens system. The first property of such a
lens is that the lens has a 2.pi. steradian field-of-view and the image it
produces is a circle. The second property is that all objects in the
field-of-view are in focus, i.e. the perfect wide angle lens has an
infinite depth-of-field. The two important postulates of this lens system
(refer to FIGS. 4 and 5) are stated as follows:
Postulate 1: Azimuth angle invariability
For object points that lie in a content plane that is perpendicular to the
image plane and passes through the image plane origin, all such points are
mapped as image points onto the line of intersection between the image
plane and the content plane, i.e. along a radial line. The azimuth angle
of the image points is therefore invariant to elevation and object
distance changes within the content plane.
Postulate 2: Equidistant Projection Rule
The radial distance, r, from the image plane origin along the azimuth angle
containing the projection of the object point is linearly proportional to
the zenith angle .beta., where .beta. is defined as the angle between a
perpendicular line through the image plane origin and the line from the
image plane origin to the object point. Thus the relationship:
r=k.beta. (1)
Using these properties and postulates as the foundation of the lens system,
the mathematical transformation for obtaining a perspective corrected
image can be determined. FIG. 4 shows the coordinate reference frames for
the object plane and the image plane. The coordinates u,v describe object
points within the object plane. The coordinates x,y,z describe points
within the image coordinate frame of reference.
The object plane shown in FIG. 4 is a typical region of interest to
determine the mapping relationship onto the image plane to properly
correct the object. The direction of view vector, DOV[x,y,z], determines
the zenith and azimuth angles for mapping the object plane, UV, onto the
image plane, XY. The object plane is defined to be perpendicular to the
vector, DOV[x,y,z].
The location of the origin of the object plane in terms of the image plane
[x,y,z] in spherical coordinates is given by:
x=D sin.beta. cos.differential.y=D sin.beta.sin.differential.z=D
cos.beta.(2)
where D=scaler length from the image plane origin to the object plane
origin, .beta. is the zenith angle, and .delta. is the azimuth angle in
image plane spherical coordinates. The origin of object plane is
represented as a vector using the components given in Equation 1 as:
DOV[x,y,z]=[Dsin.beta.cos.differential., Dsin.beta.sin.differential.,
Dcos.beta.] (3)
DOV[x,y,z] is perpendicular to the object plane and its scaler magnitude D
provides the distance to the object plane. By aligning the YZ plane with
the direction of action of DOV[x,y,z], the azimuth angle .differential.
becomes either 90 or 270 degrees and therefore the x component becomes
zero resulting in the DOV[x,y,z] coordinates:
DOV[x,y,z]=[0, -Dsin.beta., Dcos.beta.] (4)
Referring now to FIG. 5, the object point relative to the UV plane origin
in coordinates relative to the origin of the image plane is given by the
following:
x=u y=v cos.beta.z=v sin.beta. (5)
therefore, the coordinates of a point P(u,v) that lies in the object plane
can be represented as a vector P [x, y, z ] in image plane coordinates:
P[x,y,z]=[u, vcos.beta., vsin.beta.] (6)
where P[x,y,z] describes the position of the object point in image
coordinates relative to the origin of the UV plane. The object vector
O[x,y,z] that describes the object point in image coordinates is then
given by:
O[x,y,z]=DOV[x,y,z]+P[x,y,z] (7)
O[x,y,z]=[u, vos.beta.-Dsin.beta., vsin.beta.+Dcos.beta.] (8)
Projection onto a hemisphere of radius R attached to the image plane is
determined by scaling the object vector O[x,y,z] to produce a surface
vector S[x,y,z]:
##EQU1##
By substituting for the components of O[x,y,z] from Equation 8, the vector
S[x,y,z] describing the image point mapping onto the hemisphere becomes:
##EQU2##
The denominator in Equation 10 represents the length or absolute value of
the vector O[x,y,z] and can be simplified through algebraic and
trigonometric manipulation to give:
##EQU3##
From Equation 11, the mapping onto the two-dimensional image plane can be
obtained for both x and y as:
##EQU4##
Additionally, the image plane center to object plane distance D can be
represented in terms of the image circular radius R by the relation:
D=mR (14)
where m represents the scale factor in radial units R from the image plane
origin to the object plane origin. Substituting Equation 14 into Equations
12 and 13 provides a means for obtaining an effective scaling operation or
magnification which can be used to provide zoom operation.
##EQU5##
Using the equations for two-dimensional rotation of axes for both the UV
object plane and the XY image plane the last two equations can be further
manipulated to provide a more general set of equations that provides for
rotation within the image plane and rotation within the object plane.
##EQU6##
where:
A=(cos.phi.cos.differential.-sin.phi.sin.differential.cos.beta.)
B=(sin.phi.cos.differential.+cos.phi.sin.differential.cos.beta.) (19)
C=(cos.phi.sin.differential.+sin.phi.cos.differential.cos.beta.)
D=(sin.phi.sin.differential.-cos.phi.cos.differential.cos.beta.)
and where:
R=radius of the image circle
.beta.=zenith angle
.delta.=Azimuth angle in image plane
.phi.=Object plane rotation angle
m=Magnification
u,v=object plane coordinates
x,y=image plane coordinates
The Equations 17 and 18 provide a direct mapping from the UV space to the
XY image space and are the fundamental mathematical result that supports
the functioning of the present omnidirectional viewing system with no
moving parts. By knowing the desired zenith, azimuth, and object plane
rotation angles and the magnification, the locations of x and y in the
imaging array can be determined. This approach provides a means to
transform an image from the input video buffer to the output video buffer
exactly. Also, the image system is completely symmetrical about the
zenith, therefore, the vector assignments and resulting signs of various
components can be chosen differently depending on the desired orientation
of the object plane with respect to the image plane. In addition, these
postulates and mathematical equations can be modified for various lens
elements as necessary for the desired field-of-view coverage in a given
application.
The input means defines the zenith angle, .beta., the azimuth angle,
.differential., the object rotation, .phi., and the magnification, m.
These values are substituted into Equations 19 to determine values for
substitution into Equations 17 and 18. The image circle radius, R, is a
fixed value that is determined by the camera lens and element
relationship. The variables u and v vary throughout the object plane
determining the values for x and y in the image plane coordinates.
From the foregoing, it can be seen that a wide angle lens provides a
substantially hemispherical view that is captured by a camera. The image
is then transformed into a corrected image at a desired pan, tilt,
magnification, rotation, and focus based on the desired view as described
by a control input. The image is then output to a television display with
the perspective corrected. Accordingly, no mechanical devices are required
to attain this extensive analysis and presentation of the view of an
environment through 180 degrees of pan, 180 degrees of tilt, 360 degrees
of rotation, and various degrees of zoom magnification.
As indicated above, one application for the perspective correction of
images obtained with a motionless wide angle camera is in the field of
surveillance. The term "surveillance" is meant to include inspection and
like operations as well. It is often desired to continuously or
periodically view a selected environment to determine activity in that
environment. The term "environment" is meant to include such areas as
rooms, warehouses, parks and the like. This activity might be, for
example, ingress or egress of some object relative to that environment. It
might also be some action that is taking place in that environment. It may
be desired to carry out this surveillance either automatically at the
desired frequency (or continuously), or upon demand by an operator. The
size of the environment may require more than one motionless camera for
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