Patent Publication Number: US-2011069148-A1

Title: Systems and methods for correcting images in a multi-sensor system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and the benefit of U.S. Provisional Patent Application Ser. No. 61/244,514, filed Sep. 22, 2009, and entitled “Systems and Methods for Correcting Images in a Multi-Sensor System”, the entire contents of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The systems and methods described herein relates generally to multi-sensor imaging, and more specifically to an optical system having a plurality of lenses, each offset from one or more sensors for, among other things, stabilizing an image and minimizing distortions due to perspective. 
     BACKGROUND 
     Surveillance systems are commonly installed indoors in supermarkets, banks or houses, and outdoors on the sides of buildings or on utilities poles to monitor traffic in the environment. These surveillance systems typically include still and video imaging devices such as cameras. It is particularly desirable for these surveillance systems to have a wide field of view and generate panoramic images of a zone or a space under surveillance. In this regard, conventional surveillance systems generally use a single mechanically scanned camera that can pan, tilt and zoom. Panoramic images may be formed by using such a camera combined with a panning motor to shoot multiple times and then stitching the images captured each time. However, these mechanically scanned camera systems consume a lot of power, require plenty of maintenance and are generally very bulky. Furthermore, motion within an image may be difficult to detect from simple observation of a monitor screen because of the movement of the camera itself can generate undesirable visual artifacts. 
     Panoramic images may also be formed by using multiple cameras, each pointing in a different direction, in order to capture a wide field of view. With the advent of multi-sensor imaging devices capable of generating panoramic images by stitching together individual images from individual sensors, there has been an interest in adapting these multi-sensor imaging devices for surveillance and other applications. However, seamless integration of the multiple resulting images is complicated. The image processing required for multiple cameras or rotating cameras to obtain precise information on position and azimuth of an object takes a long time and is not suitable for most real-time applications. Accordingly, there is a need for improved surveillance systems capable of capturing panoramic images. 
     It is also desirable that cameras used in surveillance systems be mounted in locations that are relatively out of plain sight and are free from obstructions. Generally, to prevent obstructions from obscuring line of sight, these cameras (single or multi-sensor) are often mounted in a relatively high position and angled downward. However, images obtained from angled sensors tend to be distorted, and stitching together these images, to form a panorama, tend to be difficult and imperfect. 
     Accordingly, there is a need for improved systems and methods for multi-sensor imaging 
     SUMMARY 
     As noted above, and as the inventors have identified, the angled orientation of many surveillance camera systems makes creating high-fidelity panoramic images from stitched individual images difficult. In particular, the inventors have identified that adjacent images obtained from angled cameras cannot be easily lined up and are mismatched from each other because each image suffers from distortion due to perspective (e.g., when the camera is angled downwards, vertical lines on the image tend to converge). Moreover, if the image subject or the camera platform is dynamic or moving, motion blur may be introduced. Consequently, stitching these images together requires significant interpolation of data, which in and of itself is likely to generate inaccurate results. The inventors have overcome these problems by developing systems and methods, described herein, that are directed to multi-sensor panoramic imaging systems having lenses offset from their respective sensors. By introducing an offset between the lenses and their respective sensors, the inventors have successfully shifted the field of view of the camera without substantially tilting it. Thus a multi-sensor surveillance camera located high above the ground can capture images below without much perspective distortion. Inventors have not only identified that perspective distortion adversely impacts stitching together images captured by a multi-sensor camera, but have resolved the problem by shifting the optical axis of the camera relative to the center of the sensor so as to limit distortion due to perspective. As described in more detail below, each sensor in a multi-sensor surveillance camera located high above the ground may be able to capture an image of a scene below without perspective distortion. Consequently, images from each sensor may be stitched together easily and accurately. 
     For purposes of clarity, and not by way of limitation, the systems and methods may be described herein in the context of multi-sensor imaging with variable or offset optical and imaging axes. However, it may be understood that the systems and methods described herein may be applied to provide for any type of imaging. Moreover, the systems and methods described herein can be used for a variety of different applications that benefit from a wide field of view. Such applications include, but not limited to, surveillance and robotics. 
     In one aspect, the systems and methods described herein include a multi-sensor system for imaging a scene. The multi-sensor system includes a plurality of cameras and a processor. Each camera may include a lens and sensor. The lens typically includes an optical axis or a principle optical axis. The sensor may be positioned behind the lens for receiving light from the scene. The sensor includes an active area for imaging a portion of the scene. The sensor may also include an imaging axis, perpendicular to the active area and intersecting a center region of the active area. The optical axis may be offset from the imaging axis so that the camera may record images having minimized distortion due to perspective. In certain embodiments, the plurality of cameras includes at least two cameras having overlapping fields of view. The processor may include circuitry for receiving images recorded by the sensors, and generating a panoramic image by combining the image from each of the plurality of cameras. 
     In certain embodiments, the plurality of cameras are positioned above the scene and the optical axis is vertically offset from the imaging axis such that optical axis is below the imaging axis. In other embodiments, the plurality of cameras are positioned below the scene and the optical axis is vertically offset from the imaging axis such that optical axis is above the imaging axis. 
     The multi-sensor system may include one or more offset mechanisms connected to one or more lenses for shifting the optical axis relative to the imaging axis. In certain embodiments, these offset mechanisms include at least one prism. In other embodiments, the offset mechanism includes a combination of one or more motors, gears and other mechanical components capable of moving lenses and/or sensors. The offset mechanism may be coupled to a processor and the processor may include circuitry for controlling the offset mechanism and shifting the one or more lenses. In certain embodiments, the multi-sensor system includes a detection mechanism configured to detect movement in the scene. In such embodiments, the processor includes circuitry for controlling the offset mechanism based on movement detected by the detection mechanism. 
     Additionally and optionally, the multi-sensor system may include one or more offset mechanisms connected to one or more sensors for shifting the imaging axis relative to the optical axis. The offset mechanism may be coupled to the processor and the processor may include circuitry for controlling the offset mechanism and shifting the one or more sensors. In certain embodiments, the processor includes circuitry for changing the active area on one or more sensors, thereby shifting one or more imaging axes. The active area may be smaller than the surface area of the sensor. In such embodiments, the processor may include circuitry for changing the addresses of one or more photosensitive elements to be read out. In other embodiments, the active area substantially spans the sensor. 
     In certain embodiments, the cameras are arranged on a perimeter of a circular region for spanning a 360 degree horizontal field of view. The plurality of cameras may be optionally mounted on a hemispherical or planar surface. The multi-sensor system may include an arrangement whereby the plurality of cameras includes two cameras arranged horizontally adjacent to one another with partially overlapping fields of view. In certain embodiments, the multi-sensor system may include a plurality of cameras and/or sensors arranged in multiple rows to form a two-dimensional array of cameras and/or sensors. Additionally and optionally, the plurality of cameras may be mounted on a moving platform and the offset between the optical axis and the imaging axis may be determined based on the motion of the moving platform. 
     In another aspect, the systems and methods described herein include methods for imaging a scene. The methods include providing a first camera having a first field of view and a second camera having a second field of view that at least partially overlaps with the first field of view. The first and second cameras may each include a lens and a sensor. The lens may include an optical axis offset from an axis perpendicular to the sensor and intersecting near a center of an active area of the sensor. The methods include recording a first image of a portion of a scene on the active area at the first camera, and recording a second image of a portion of the scene on the active area at the second camera. The methods may further include receiving at a processor the first image and the second image, and generating a panoramic image of the scene by combining the first image with the second image. 
     The methods may include providing a plurality of cameras positioned adjacent to at least one of the first and second camera. In certain embodiments, the methods further include determining a position for the first and second camera in relation to the location of the scene. In such embodiments, the methods may include selecting the offset between the optical axis and the imaging axis in each of the first and second camera based at least on the location of the scene relative to the position of the first and second camera. 
     The offset between the optical axis and imaging axis in at least one of the first and the second camera may be generated by physically offsetting at least one of the lens and sensor. Additionally and optionally, the active area may be smaller than the sensor in at least one of the first and second camera, and the offset between the optical axis and imaging axis in the first and the second camera may be generated by changing the active area on the sensor in at least one of the first and second camera. Changing the active area may include, among other things, changing a portion of photosensitive elements being read out. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The foregoing and other objects and advantages of the systems and methods described will be appreciated more fully from the following further description thereof, with reference to the accompanying drawings wherein: 
         FIGS. 1A-C  depict a single-sensor imaging system having an optical axes parallel to an imaging axis, according to an illustrative embodiment of the invention; 
         FIG. 2  depicts the components of a multi-sensor imaging system, according to an illustrative embodiment of the invention; 
         FIGS. 3A-D  depict a multi-sensor imaging system having two cameras for imaging a scene, according to an illustrative embodiment of the invention; 
         FIG. 4A-D  depict another multi-sensor imaging system having two horizontally-angled cameras for imaging a scene, according to an illustrative embodiment of the invention; 
         FIG. 5  depicts a multi-sensor imaging system for imaging a scene from a vertically-angled perspective, according to an illustrative embodiment of the invention; 
         FIG. 6  depicts a method for generating a single image from two overlapping images of a scene; 
         FIGS. 7A and 7B  depict a multi-sensor imaging system having offset lens-sensor pairs for imaging a scene, according to an illustrative embodiment of the invention; 
         FIGS. 7C and 7D  depict a method for generating a single image from two overlapping images of a scene generated by imaging system of  FIGS. 7A and 7B  according to an embodiment of the invention; 
         FIGS. 8A and 8B  depict a horizontally-angled, multi-sensor imaging system having offset lens-sensor pairs for imaging a scene, according to an illustrative embodiment of the invention; 
         FIGS. 8C and 8D  depict a method for generating a single image from two overlapping images of a scene generated by imaging system of  FIGS. 8A and 8B  according to an embodiment of the invention; 
         FIGS. 9A-C  depict alternate systems and methods for imaging a scene based on the active area of the sensor, according to illustrative embodiments of the invention; 
         FIG. 10  depicts a multi-sensor imaging system for imaging a panoramic scene, according to an illustrative embodiment of the invention; 
         FIG. 11  depicts an exemplary camera having an offset lens-sensor pair, according to an illustrative embodiment of the invention. 
         FIG. 12  is a flowchart depicting an exemplary process for imaging a scene, according to an illustrative embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS 
     To provide an overall understanding, certain illustrative embodiments will now be described, including a multi-sensor imaging system with variable optical and imaging axes. However, it will be understood by one of ordinary skill in the art that the systems and methods described herein may be adapted and modified for other suitable applications and that such other additions and modifications will not depart from the scope thereof. 
       FIG. 1A-C  depicts a single sensor imaging system  100 , with an imaging sensor  102  and a lens  104 . A side view of imaging system  100  is depicted in  FIG. 1A , and a back view of system  100  is depicted in  FIG. 1B , from the perspective of the leftmost block arrow in  FIG. 1A . The axis passing through the center of the imaging sensor  102  (and perpendicular to the plane of sensor  102 ), the imaging axis, is substantially collinear to the axis of the lens  104 , the optical axis. These collinear axes are represented by a single axis  108 . Axis  108  is also collinear with the axis associated with the plane of image target  106 , which is the axis perpendicular to the plane  106  and intersecting the center of the imaged area of the target. The imaging sensor  102  may be able to capture an image  110  of target  106  through lens  104 . In one example, if the target  106  is a series of parallel lines, then the imaging system  100  may be able to capture image  110  of target  106 . Because the imaging axis of the imaging sensor  102 , the optical axis of the lens  104 , and the imaged area of target  106  are collinear, the parallel lines of target  106  will appear as generally parallel lines in image  110 . 
     Image  110  represents the field of view of system  100 . In particular, image  110  represents that portion of target  106  that is captured by sensor  102  in system  100 . In certain embodiments, the coverage of the lens is greater than the area of the sensor. Consequently, image  110  may represent an area that is less than the area of target  106  and less than the coverage of the lens. The field of view of the system  100  is typically that portion of the target  106  which is captured by the system  100 , in this case image  110 . The field of view (horizontal or vertical) is roughly directly proportional to the dimensions of the sensor array (horizontal or vertical) and distance of the target  106  from the system  100 , and inversely proportional to the focal length of lens  104 . In the example of a surveillance system, the field of view is often times below the camera. Consequently, as described with reference to  FIG. 5 , the camera would need to be angled downward so that the desired portion of the target falls within the system&#39;s field of view. When the system is angled downward, the parallel lines in image  110  are no longer parallel due to perspective distortion. In a multi-sensor imaging system, such perspective distortion is especially undesirable because stitching images from the multiple sensors becomes more difficult. As will be described with reference to FIGS.  2  and  7 - 9 , to resolve this issue, the lens  102  may be shifted so that the field of view of the system shifts downwards without having to angle the camera downward. 
       FIG. 2  depicts an illustrative multi-sensor imaging system  200  having two sensors positioned substantially adjacent to each other, according to an illustrative embodiment. In particular, system  200  includes imaging sensors  202   a  and  202   b  and associated lenses  204   a  and  204   b  that are positioned substantially adjacent to each other. Generally, system  200  may include two or more imaging sensors and associated lenses arranged vertically or horizontally with respect to one another without departing from the scope of the systems and methods described herein. 
     In certain embodiments, the imaging sensors  202   a  and  202   b  may include or be connected to one or more light meters (not shown). The sensors  202   a  and  202   b  are connected to exposure circuitry  220 . The exposure circuitry  220  may be configured to determine an exposure value for each of the sensors  202   a  and  202   b . In certain embodiments, the exposure circuitry  220  determines the best exposure value for a sensor for imaging a given scene. The exposure circuitry  220  is optionally connected to miscellaneous mechanical and electronic shuttering systems  222  for controlling the timing and intensity of incident light and other electromagnetic radiation on the sensors  202   a  and  202   b . The sensors  202   a  and  202   b  may optionally be coupled with one or more filters  224 . In certain embodiments, filters  224  may preferentially amplify or suppress incoming electromagnetic radiation in a given frequency range. Lenses  204   a  and  204   b  may be any suitable type of lens or lens array, and may be coupled with one or more offset mechanisms (not shown) that allow the optical axes of the lenses to shift with respect to the optical axes of their associated sensors. In some embodiments, the sensors may also be coupled with one or more offset mechanisms that allow sensor optical axes to shift with respect to lens optical axes. The offset mechanisms may also enable the lenses and/or sensors to tilt with respect to their associated sensors and/or lenses. The offset mechanisms may enable all of the lenses and/or sensors to shift and/or tilt simultaneously, or may allow one or more lenses and/or sensors to shift and/or tilt independent of the other lenses and sensors. The offset mechanisms may be coupled to processor  228 . In some embodiments, the offset mechanisms may include one or more prisms (not shown) that allow the optical axes of the lenses and the sensors to shift with respect to each other. For example, the one or more prisms may be able to shift and/or tilt in order to redirect the light passing between the lenses and the sensors. 
     In some embodiments, sensor  202   a  includes an array of photosensitive elements (or pixels) distributed in an array of rows and columns (not shown). The sensor  202   a  may include a charge-coupled device (CCD) imaging sensor. In certain embodiments, the sensor  202   a  includes a complementary metal-oxide semiconductor (CMOS) imaging sensor. In certain embodiments, the sensor  202   b  is similar to the sensor  202   a . The sensor  202   b  may include a CCD and/or CMOS imaging sensor. The sensors  202   a  and  202   b  may be positioned adjacent to each other, either vertically or horizontally. The sensors  202   a  and  202   b  may be included in an optical head of an imaging system. In certain embodiments, the sensors  202   a  and  202   b  may be configured, positioned or oriented to capture different fields-of-view of a scene. The sensors  202   a  and  202   b  may be angled depending on the desired extent of the field of view. During operation, incident light from a scene being captured may fall on the sensors  202   a  and  202   b . In certain embodiments, the sensors  202   a  and  202   b  may be coupled to a shutter and when the shutter opens, the sensors  202   a  and  202   b  are exposed to light. The light may then converted to a charge in each of the photosensitive elements in sensors  202   a  and  202   b , which may then be transferred to output amplifier  226 . In certain embodiments, the active imaging area of an imaging sensor (i.e. the portion of the sensor exposed to light) may be smaller than the total imaging area of the imaging sensor. In some embodiments, the size and/or position of the active imaging area of an imaging sensor may be varied. Varying the size and/or position of the active imaging area may be done by selecting the appropriate rows, columns, and/or pixels of the imaging sensor to read out, and in some embodiments, may be performed by processor  228 . 
     The sensors can be of any suitable type and may include CCD imaging sensors, CMOS imaging sensors, or any analog or digital imaging sensor. The sensors may be color sensors. The sensors may be responsive to electromagnetic radiation outside the visible spectrum, and may include thermal, gamma, multi-spectral and x-ray sensors. The sensors, in combination with other components in the imaging system  100 , may generate a file in any format, such as the raw data, GIF, JPEG, TIFF, PBM, PGM, PPM, EPSF, X11 bitmap, Utah Raster Toolkit RLE, PDS/VICAR, Sun Rasterfile, BMP, PCX, PNG, IRIS RGB, XPM, Targa, XWD, PostScript, and PM formats on workstations and terminals running the X11 Window System or any image file suitable for import into the data processing system. Additionally, the system may be employed for generating video images, including digital video images in the .AVI, .WMV, .MOV, .RAM and .MPG formats. 
     The processor  228  may include microcontrollers and microprocessors programmed to receive data from the output amplifier  226  and exposure values from the exposure circuitry  220 . In particular, processor  114  may include a central processing unit (CPU), a memory, and an interconnect bus. The CPU may include a single microprocessor or a plurality of microprocessors for configuring the processor  228  as a multi-processor system. The memory may include a main memory and a read-only memory. The processor  114  and/or the databases  230  also include mass storage devices having, for example, various disk drives, tape drives, FLASH drives, etc. The main memory also includes dynamic random access memory (DRAM) and high-speed cache memory. In operation, the main memory stores at least portions of instructions and data for execution by a CPU. 
     The mass storage  230  may include one or more magnetic disk or tape drives or optical disk drives, for storing data and instructions for use by the processor  228 . At least one component of the mass storage system  230 , possibly in the form of a disk drive or tape drive, stores the database used for processing the signals measured from the sensors  202   a  and  202   b . The mass storage system  230  may also include one or more drives for various portable media, such as a floppy disk, a compact disc read-only memory (CD-ROM), DVD, or an integrated circuit non-volatile memory adapter (i.e. PC-MCIA adapter) to input and output data and code to and from the processor  228 . 
     The processor  228  may also include one or more input/output interfaces for data communications. The data interface may be a modem, a network card, serial port, bus adapter, or any other suitable data communications mechanism for communicating with one or more local or remote systems. The data interface may provide a relatively high-speed link to a network, such as the Internet. The communication link to the network may be, for example, optical, wired, or wireless (e.g., via satellite or cellular network). Alternatively, the processor  228  may include a mainframe or other type of host computer system capable of communications via the network. 
     The processor  228  may also include suitable input/output ports or use the interconnect bus for interconnection with other components, a local display, keyboard or other local user interface  232  for programming and/or data retrieval purposes. 
     In certain embodiments, the processor  228  includes circuitry for an analog-to-digital converter and/or a digital-to-analog converter. In such embodiments, the analog-to-digital converter circuitry converts analog signals received at the sensors to digital signals for further processing by the processor  228 . 
     The components of the processor  228  are those typically found in imaging systems used for portable use as well as fixed use. In certain embodiments, the processor  228  includes general purpose computer systems used as servers, workstations, personal computers, network terminals, and the like. In fact, these components are intended to represent a broad category of such computer components that are well known in the art. Certain aspects of the systems and methods described herein may relate to the software elements, such as the executable code and database for the server functions of the imaging system  200 . 
     Generally, the methods described herein may be executed on a conventional data processing platform such as an IBM PC-compatible computer running the Windows operating systems, a SUN workstation running a UNIX operating system or another equivalent personal computer or workstation. Alternatively, the data processing system may comprise a dedicated processing system that includes an embedded programmable data processing unit. 
     Certain of the processes described herein may also be realized as one or more software components operating on a conventional data processing system such as a UNIX workstation. In such embodiments, the processes may be implemented as a computer program written in any of several languages well-known to those of ordinary skill in the art, such as (but not limited to) C, C++, FORTRAN, Java or BASIC. The processes may also be executed on commonly available clusters of processors, such as Western Scientific Linux clusters, which may allow parallel execution of all or some of the steps in the process. 
     Certain of the methods described herein may be performed in either hardware, software, or any combination thereof, as those terms are currently known in the art. In particular, these methods may be carried out by software, firmware, or microcode operating on a computer or computers of any type, including pre-existing or already-installed image processing facilities capable of supporting any or all of the processor&#39;s functions. Additionally, software embodying these methods may comprise computer instructions in any form (e.g., source code, object code, interpreted code, etc.) stored in any computer-readable medium (e.g., ROM, RAM, magnetic media, punched tape or card, compact disc (CD) in any form, DVD, etc.). Furthermore, such software may also be in the form of a computer data signal embodied in a carrier wave, such as that found within the well-known Web pages transferred among devices connected to the Internet. Accordingly, these methods and systems are not limited to any particular platform, unless specifically stated otherwise in the present disclosure. 
       FIGS. 3A-D  depict the illustrative multi-sensor imaging system  200 , with adjacent imaging sensors  202   a  and  202   b , lenses  204   a  and  204   b , and target  306 , which is a series of parallel, dashed lines oriented vertically.  FIG. 3A  and  FIG. 3B  show side and top views of imaging system  200 , respectively. In this particular embodiment, the imaging sensors  202   a  and  202   b  are separated from each other by some distance X in a horizontal direction, as shown in  FIG. 3B . Imaging sensor  202   a  and lens  204   a  have axes (imaging axis and optical axis, respectively) that are collinear and represented by axis  308   a , and imaging sensor  202   b  and lens  204   b  have optical axes that are collinear and represented by axis  308   b . Both axis  308   a  and axis  308   b  are perpendicular to the plane of target  306 . Because imaging sensors  202   a  and  202   b  are offset from each other and have parallel optical axes, each sensor will capture an image of a slightly different portion of target  306 . In other words each sensor-lens pair has a different, but overlapping, field of view. For example, sensor  202   a  may capture portion  310   a  of target  306 , shown in image  312   a  of  FIG. 3C , and sensor  202   b  may capture portion  310   b  of target  306 , shown in image  312   b  of  FIG. 3C . In certain embodiments, the captured portions may have an overlap portion  310   c , imaged by both sensor  202   a  and sensor  202   b . As in  FIG. 1 , because each sensor-lens pair has optical axes perpendicular to the surface of target  306  and collinear with the optical axes of the captured portions  310   a  and  310   b  of target  306 , the resultant captured images will appear as parallel, dashed lines. After image capture, the two images  312   a  and  312   a  may be stitched together to form image  104  in  FIG. 3D  by aligning along overlap region  316 , which corresponds to overlap portion  310   c . Image stitching may be accomplished by hardware, such as processor  228 , or software. Because the target lines in both images  312   a  and  312   b  are parallel, the images may be matched and stitched together with relatively little image processing and/or data interpolation required. 
       FIGS. 4A-D  depict a multi-sensor imaging system  400 , similar to the imaging system  200  described in  FIGS. 3A-D . Multi-sensor imaging system  400  includes adjacent imaging sensors  402   a  and  402   b , lenses  404   a  and  404   b , and target  306 , which in this example is a series of parallel, dashed lines oriented vertically. However, system  400  differs from system  200  in the orientation of the imaging sensors and lenses. Instead of the sensors being parallel to each other, in system  400  the sensors  402   a  and  402   b  are tilted horizontally with respect to each other. Although the now-tilted sensor optical axes  408   a  and  408   b  are no longer parallel to the plane of target  306 , and hence are no longer collinear with the optical axes of the captured portions, the captured images  412   a  and  412   b  (corresponding to portions  410   a  and  410   b  of target  306 ) will still show parallel vertical lines, because the sensors are not tilted vertically. Hence, the images may still be matched and stitched together with relatively little image processing and/or data interpolation. However, matching these images may be more difficult if the sensors-lens pairs were tilted vertically instead of horizontally. 
       FIG. 5  depicts a side view of multi-sensor imaging system  200  imaging a target whose surface is tilted along an axis parallel to the sensor offset direction. In this situation, the target dashed lines will not appear as parallel lines in the images  508   a  and  508   b , because the optical axes of the sensor-lens pairs are not perpendicular to the plane of the target. Instead, the parallel dashed lines will appear to converge toward the bottom of the image, as shown in images  508   a  and  508   b . Stitching the images  508   a  and  508   b  together in this situation may require extensive image processing, because the overlap areas in the images do not match, as they did in the situation depicted in  FIG. 3D . 
     More particularly,  FIG. 6  depicts a method for generating a single image from two overlapping images of a tilted scene via image processing. First, an image  602  similar to image  508   a  in  FIG. 5  may be captured. Image  602  may then be processed so that the converging lines become parallel lines, resulting in modified image  604   a . This processing step may involve data interpolation based on the original image data. Modified image  604   a  may then be stitched together along an overlap region  608  with another modified image  604   b  to form the final image  606 . However, the final image  606  will likely have lower resolution and fidelity than a similar stitched image  314  ( FIG. 3E ), because of the image processing necessary to transform the converging lines into parallel lines. Image processing such as data interpolation generally results in loss of image data, resolution, and fidelity in the overlap region of the image and possibly elsewhere in the image, which may be undesirable. 
       FIGS. 7A-D  depict a method for generating a single image from two overlapping images of a scene at an angle according to an embodiment. In multi-sensor imaging system  700 , shown in a side view ( FIG. 7A ) and a top view ( FIG. 7B ), the lenses have been offset from their original positions along a direction Y. After this offset, while the optical axes  708   a  and  708   b  of the sensors  702   a  and  702   b  are still parallel to the optical axes  710   a  and  710   b  of lenses  704   a  and  704   b  and the optical axes  714   a  and  714   b  of imaged areas  712   a  and  712   b  and perpendicular to the plane of target  706 , the axes are no longer collinear. In this configuration, the field of view of the imaging sensors through the lenses changes depending on the offset of the lenses, but the parallel lines of target  706  will not longer appear to be converging in a captured image. Instead, the parallel target lines will remain parallel in captured images, as shown in overlapping images  716   a  and  716   b  in  FIG. 7C . Therefore, stitching the overlapping images  716 A and  716 B together along overlap region  718  to form final image  720  as shown in  FIG. 7D  may no longer require extensive image processing and data interpolation, resulting in less data loss and higher image resolution and fidelity. 
       FIGS. 8A-D  depict a method for generating a single image from two overlapping images of a scene at an angle according to another embodiment. Multi-sensor imaging system  800 , shown in a side view ( FIG. 8A ) and a top view ( FIG. 8B ), is similar to the imaging system  700  shown in  FIGS. 7A-D , but differs in the orientation of the imaging sensors and lenses. In multi-sensor imaging system  800 , shown in a side view ( FIG. 8A ) and a top view ( FIG. 8B ), the lenses have been offset from their original positions along a direction Y. After this offset, the optical axes  808   a  and  808   b  of the sensors  802   a  and  802   b  are not parallel to the optical axes  810   a  and  810   b  of lenses  804   a  and  804   b . In other words, instead of the sensors being parallel to each other, in system  800  the sensors are tilted horizontally with respect to each other. Although the now-tilted sensor optical axes  808   a  and  808   b  are no longer parallel to the plane of target  806 , the captured images  812   a  and  812   b  will still show parallel vertical lines, because the sensors are not tilted vertically. Hence, the images may still be matched along overlap region  810   c  and stitched together with relatively little image processing and/or data interpolation, resulting in less data loss and higher image resolution and fidelity. 
       FIGS. 9A-C  depict alternate methods for imaging a scene, according to illustrative embodiments. In one method, depicted in  FIG. 9A , instead of offsetting the lens  904   b , the imaging sensor  902   b  may be offset, as shown by the arrow Y. This may provide the same effect as the lens offset depicted in  FIGS. 7A-D . In another method, depicted in a side view ( FIG. 9B ) and a front view ( FIG. 9C ), instead of physically offsetting either the lens  904   b  or the imaging sensor  902   b , an active imaging area  906   b  of imaging sensor  902   b  may be offset. In this embodiment, the offset of the active imaging area  906   b  may be accomplished by changing the portion of the photosensitive element array that is read out. For example, in  FIG. 9C , the photosensitive elements between columns  908   a  and  908   b  and rows  910   a  and  910   b  may be read out. The size and position of the active imaging area  906   b  may be varied simply by varying the addresses of the photosensitive elements to be read out. Moreover, the shape of the active imaging area  906   b  may also be controlled by varying the read-out photosensitive elements. For example, the active imaging area may be a rectangle, a square, a triangle, or any other shape. In some embodiments, two or more of the above methods may be combined. For example, an imaging system may have sensors, lenses, and active imaging areas that may be offset, independent of each other. 
     In certain embodiments, instead of panning or tilting the entire imaging system in order to change the field of view, only the lenses, sensors, or active imaging areas may be moved. The lenses and/or sensors may be shifted, tilted, or moved toward and/or away from each other. The lenses and/or sensors may be able to shift or be offset along any combination of the X, Y, and Z axes of a Cartesian coordinate system. For example, the lenses and/or sensors may be shifted from side to side (along an X-axis) or top-to-bottom/bottom-to-top (along Z-axis). In some embodiments, each lens, sensor, and/or active area may move independently of the other lenses, sensors, and/or active areas. In certain embodiments, the imaging system may include more than two sensors. These sensors may be mounted on a flat surface, a hemisphere or any other planar or nonplanar surface. 
       FIG. 10  depicts a multi-sensor imaging system  1000 , according to an illustrative embodiment. In particular, imaging system  1000  includes a plurality of cameras  1002  arranged about the perimeter of a circular mount  1006 . Each camera  1002  is facing a direction corresponding to a different, but overlapping, field of view. In certain embodiments, the multi-sensor imaging system  1000  may include a second row of cameras  1002  arranged in a circular mount below circular mount  1006 . The second row of cameras  1002  may be arranged vertically below the gaps between the cameras  1002  in circular mount  1006 . Alternatively, the second row of cameras  1002  may be arranged vertically adjacent to cameras  1002  in circular mount  1006 . The multi-sensor imaging system  1000  may include a plurality of rows of cameras of  1002  to form a two-dimensional array of cameras. The plurality of cameras may be arranged in any suitable without departing from scope of the systems and methods described herein. 
     The imaging system  100  includes a processor  1012 , a detector  1014  such as a motion detector, and a user interface  1016  which may include computer peripherals and other interface devices. The processor  1012  includes circuitry for receiving images from the cameras  1002  and combining these images to form a panoramic image of the scene. The processor  1012  may include circuitry to perform other functions including, but not limited to, operating the cameras  1002 , and operating motion and offset mechanism. The processor  1012  is connected to a detector  1014 , a user interface  1016  and other optional components (not shown). The detector  1014  includes circuitry for scanning a scene and/or detecting motion. In certain embodiments, upon detection, the detector  1014  may communicate related information to the processor  1012 . The processor  1012 , based on the information from the detector  1014 , may operate one or more cameras  1002  to image a particular portion of the scene. The imaging system  1000  may further include other devices and components as depicted with reference to  FIG. 2 . 
     The camera  1002  includes a lens  1004  and a sensor. The lens  1004  is housed in lens housing  1008  and the sensor is housed in sensor housing  1010 . The sensor housing  1010  may optionally include processing circuitry for performing one or more functions of the processor  1012 . As will be described in more detail with reference to  FIG. 11 , the sensor housing  1010  may further include an offsetting mechanism for shifting the optical axis of the lens relative to the imaging axis of the active area of the sensor. In particular,  FIG. 11  depicts an exemplary camera  1100 , to be used in a multi-sensor imaging system such as systems  200 ,  400 ,  700 ,  800 ,  900  and  1000 . Camera  1100  includes a sensor  1102  positioned behind a lens  1104 . The lens  1104  is positioned within housing  1108  and the sensor  1102  is positioned within housing  1106 . 
     The lens  1104  may be a single lens or a lens system comprising a plurality of optical devices such as lens, prisms, beam splitters, mirrors, and the like. The sensor  1102  may include one or more active areas that may partially or completely span the area of the sensor. The lens  1104  may include an optical axis or a principle optical axis  1122  that pass through the center of the lens  1104 . The sensor  1102  may include an imaging axis  1120  that passes through the sensor  1102  and intersects the center or substantially near the center of an active area of the sensor  1102 . The optical axis  1122  and the imaging axis  1120  are separated by an offset D. 
     The offset D may be generated by at least one of shifting the lens  1104 , the sensor  1102  or modifying the active area on the sensor  1102 . The lens housing  1108  includes an offset mechanism  1110  for moving the lens  1104  along direction C. The direction C is along the direction parallel to the plane of the lens  1104  and the sensor  1102 . The sensor housing  1106  also includes an offset mechanism  1112  for moving the sensor  1102  along direction B. The direction B is along the direction parallel to the plane of the lens  1104  and the sensor  1102 . In certain embodiments, camera  1100  includes an optical offset mechanism  1116  such as a prism. Prisms and other optical devices may be used to shift and offset the optical axis  1122  of lens  1104 . 
     The camera  1100  is mounted on a moving platform  1114 . The moving platform  1114  moves the camera along direction A. As will be described below with reference  FIG. 12 , the offset D may be selected based on, among other things, the location of the camera in relation to the scene being imaged and movement along direction A. For example, a surveillance camera mounted high on a wall to monitor movement on the ground, may be moved up and down the wall. As the camera is moved down the wall and towards the ground, the offset between the optical axis and the imaging axis may be reduced. On the other hand, as the camera is moved up the wall and away from the ground, the offset between the optical axis and the imaging axis may be increased. The offset D may be selected and dynamically adjusted and adapted so that the field of view of a moving camera remains substantially constant. 
       FIG. 12  is a flow chart depicting a process  1200  for imaging a scene, according to an illustrative embodiment. The process  1200  includes providing a multi-sensor imaging system having a plurality of cameras having offset optical and imaging axes (step  1202 ). Such an imaging system and corresponding cameras may be similar to imaging systems and cameras in  FIGS. 1-11 . The process further includes selecting an offset between the optical and imaging axis. In certain embodiments, the camera may have a fixed offset. The offset may be selected based on, among other things, the location of the camera in relation to the scene being imaged and the desired field of view. In other embodiments, the offset may be selected based on the movement of the camera. A processor may control the movement of various components of the imaging system to dynamically, and optionally in real-time, adjust and modify the offset. The process  1200  further includes recording images on each of the plurality of cameras (step  1206 ). A processor may be configured to receive these recorded images. The process  1200  includes stitching these images together to form a panoramic image (step  1210 ). 
     Variations, modifications, and other implementations of what is described may be employed without departing from the spirit and scope of the invention. More specifically, any of the method and system features described above or incorporated by reference may be combined with any other suitable method or system features disclosed herein or incorporated by reference, and is within the scope of the contemplated inventions. The systems and methods may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The foregoing embodiments are therefore to be considered in all respected illustrative, rather than limiting of the invention. The teachings of all references cited herein are hereby incorporated by reference in their entirety.