Patent Application
20070115355
This invention relates generally to video surveillance systems and, more particularly, to calibrating presets for a pan/tilt/zoom capable camera assembly.
Surveillance video cameras associated with complex surveillance systems, such as those found in gaming establishments, schools, and shopping malls, are typically placed in transparent domes mounted in ceilings or other supports, such as on poles in a parking lot. In such systems, camera operators typically use a joystick type control to affect pan and tilt movements of various controllable cameras of the system. Zoom, focus, and iris functions of lenses coupled to these cameras are typically controlled by the joystick and/or a keypad having discrete keys marked with these functions. A video switching matrix selectively couples video outputs from the cameras to a plurality of monitors, with the switching matrix controlled, for example, through the use of the keypad.
At least some known surveillance applications include a plurality of cameras communicatively coupled to a lesser number of monitors or displays, which are all controlled manually and/or semi-automatically by the camera operator or controlled automatically by the surveillance system and monitored by the operator. In the areas under surveillance, camera operators need to be proficient with using the surveillance system and be thoroughly familiar with the layout of the areas being observed. To be effective, an operator must, within a short period of time, be able to switch one or more cameras to a particular view, such as a particular slot machine or gaming table. This may be accomplished using “presets” or addresses that direct a camera to a predetermined view by issuing a simple command rather than by selecting a particular camera from the plurality of cameras, recognizing the direction the camera is pointed and issuing pan, tilt, and zoom commands to point the camera to the desired view.
At least some known camera assemblies equipped with “preset” controls use, for example, servo mechanisms to position the camera to internally stored pan, tilt, zoom, focus, and iris positions. With this data, a plurality of “preset” views for each camera may be stored in the camera and used to direct the respective camera to a one, or a sequence, of these preset views responsive to operating a key on the keypad or from logic in a system control that automatically determines a desired view.
A camera that has greater than ninety degrees of travel in the tilt axis can address a preset from two perspectives. However, for the two perspectives to appear identical to the operator a calibration is used to remove positioning errors caused by mechanical and parallax distortions.
In one embodiment, a video camera assembly includes a video camera, a pan mechanism configured to rotate the video camera about a pan axis, a tilt mechanism coupled to the pan mechanism wherein the tilt mechanism is configured to rotate the video camera about a tilt axis, and a controller communicatively coupled to the pan and tilt mechanisms. The controller is configured to receive a first image of a view acquired from a first address, receive a second image of the view acquired from a second address wherein the second address is different from the first address, compare the first image to the second image, and determine an offset between the first address and the second address using the comparison.
In another embodiment, a method of calibrating a video camera assembly is provided. The video camera assembly includes a video camera and at least one of a pan mechanism, a tilt mechanism, and a zoom for defining a field of view of the camera, the pan mechanism configured to rotate the video camera about a pan axis, the tilt mechanism configured to rotate the video camera about a tilt axis. The method includes acquiring a first image of a view using a first camera assembly positional address, acquiring a second image of the view using a second camera assembly positional address, the second camera assembly positional address being a conjugate address with respect to the first camera assembly positional address, comparing the first and second images to determine an offset between the first and second images, and applying the offset to each camera assembly positional address and conjugate address.
In yet another embodiment, a method of operating a video camera assembly is provided. The video camera assembly includes a video camera and at least one of a pan mechanism, a tilt mechanism, and a zoom for defining a field of view of the video camera. The method includes receiving a preset command, determining an address from a plurality of addresses associated with the preset command, transmitting movement commands to the at least one of a pan mechanism, a tilt mechanism, and a zoom, and repositioning the camera assembly in response to the movement commands to a position associated with the address.
As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.
Lens assembly 116 views an area of a location 132, which may be remote from control panel 102 and is in a field of view 134 and along a viewing axis 136 of lens assembly 116. Images of location 132 are converted by camera 106 into an electrical video signal, which is transmitted to display monitor 104.
In the exemplary embodiment, control panel 102 includes an X-Y control joystick 140 that is used to generate pan and tilt commands. A plurality of rocker-type switches 142 are used to control a zoom 144, a focus 146, and an iris 148 of lens assembly 116. In an alternative embodiment, joystick 140 includes a twist actuation that is used to control the zoom of camera 106. Joystick 140 may also incorporate triggers and/or buttons to facilitate operating various controls associated with system 100. Control panel 102 also includes a numeric keypad 150 for entering numbers and values. In an alternative embodiment, control panel 102 may include an alpha or alphanumeric keypad (not shown) for entering text as well as numbers. Control panel 102 further includes a plurality of preset switches 152 that may be programmed to execute macros that automatically control the actions of camera 106 and/or lens assembly 116. A plurality of buttons 154 may be used, for example, for predetermined control functions and/or user-defined functions, for example, a camera selection in a multi-camera video surveillance system. A display 156 may be used to display a status of video surveillance system 100 or may be used to display parameters associated with a selected camera.
A processor 158 receives programmed instructions, from software, firmware, and data from memory 160 and performs various operations using the data and instructions. Processor 158 may include an arithmetic logic unit (ALU) that performs arithmetic and logical operations and a control unit that extracts instructions from memory 160 and decodes and executes them, calling on the ALU when necessary. Memory 160 generally includes a random-access memory (RAM) and a read-only memory (ROM), however, there may be other types of memory such as programmable read-only memory (PROM), erasable programmable read-only memory (EPROM) and electrically erasable programmable read-only memory (EEPROM). In addition, memory 160 may include an operating system, which executes on processor 158. The operating system performs basic tasks that include recognizing input, sending output to output devices, keeping track of files and directories and controlling various peripheral devices.
The term processor, as used herein, refers to central processing units, microprocessors, microcontrollers, reduced instruction set circuits (RISC), application specific integrated circuits (ASIC), logic circuits, and any other circuit or processor capable of executing the functions described herein. Memory 160 may include storage locations for the preset macro instructions that may be accessible using one of the plurality of preset switches 142.
As used herein, the terms “software” and “firmware” are interchangeable, and include any computer program stored in memory for execution by processor 158, including RAM memory, ROM memory, EPROM memory, EEPROM memory, and non-volatile RAM (NVRAM) memory. The above memory types are exemplary only, and are thus not limiting as to the types of memory usable for storage of a computer program.
In various embodiments, processor 158 and memory 160 are located external to camera 106 such as in control panel 102 or in a PC or other standalone or mainframe computer system capable of performing the functions described herein.
In the exemplary embodiment, video surveillance system 100 is a single camera application, however, various embodiments of the present invention may be used within a larger surveillance system having additional cameras which may be either stationary or moveable cameras or some combination thereof to provide coverage of a larger or more complex surveillance area. In an alternative embodiment, one or more video recorders (not shown) are connected to control panel 102 to provide for recording of video images captured by camera 106 and other cameras in system 100.
Each of the first address and the second address are used to point camera 106 at a view that is associated with a preset. A preset records the address of a view such that camera 106 may be automatically pointed in the direction of the view at a later time with little or no additional user actions. In the exemplary embodiment, two addressees are stored. A first address of the view is stored when the preset is commanded for that view. A second address is computed and stored. The second address includes conjugate corrections for the first address and corrections for mechanical inaccuracies between the first address and the second address, for example, due to camera parallax, lens variation from direct video to flip video, and tolerances of pan mechanism 202 and tilt mechanism 208.
To calibrate the first and second addresses such that the view imaged from either the first or second address is perceived to be the same by the user, an image acquired at the first address is compared to an image acquired at the second, conjugate address. In the exemplary embodiment, a pixel by pixel correlation is performed to determine a pan and tilt offset between the first and second images. In various other embodiments, other image difference algorithms are used to determine the offset, for example, locating a subimage in the first image that substantially matches a subimage in the second image is used. Controller 102 registers the images using determined landmarks in each image and determines correction factors that can be applied to the second address such that a view imaged using either address is perceived by the user as the same view. Once correction factors are determined, the first and second images may be discarded and the corrections are stored in memory associated with the preset addresses.
During operation, when the preset is selected, controller 102 determines the shortest path from the current address to the selected preset address. In one embodiment, the shortest path may be determined using a combination of angular distances camera 106 would need to be rotated to reach either preset address. In other embodiments, the shortest path may be determined using a time it would take for camera 106 to reach either preset address, for example, if pan mechanism 202 is capable of faster rotation than tilt mechanism 208.
In the exemplary embodiment, a plurality of preset commands are stored in memory, such as memory 160. Each preset may be selected manually by the user or be selected automatically by controller 102 in response to execution of programmed instructions in software. Each of the plurality of preset commands are associated with a plurality of addresses wherein each address position orients camera 106 to substantially the same view. During operation, when a preset is selected, one address of the plurality of addresses is determined to be closest to the current position. Being closest relates to the shortest angular distance between the current position and the preset address position or the shortest transit time from the current position to the preset address position.
Exemplary embodiments of video surveillance systems and apparatus are described above in detail. The video surveillance system components illustrated are not limited to the specific embodiments described herein, but rather, components of each system may be utilized independently and separately from other components described herein. For example, the video surveillance system components described above may also be used in combination with different video surveillance system components.
A technical effect of the various embodiments of the systems and methods described herein include facilitating operation of the video surveillance system by using images of a preset view to calibrate a preset command.
While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.
