Abstract:
A camera concurrently produces an orthographic map and map spectral content. illumination from an image passes through a phase modulator and the resulting rotating photo-flux phase is converted to an electrical signal by multiple adjacent sensors of detectors of array of detectors. The amount of unwanted illumination reaching the sensors is reduced by a set of baffles that shield and protect the transducers from unwanted out-of-field light and other light sources.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0001]    This invention was made with Government support from DOI-NBC of Ft. Huachuca, Ariz. Support was provided under Contract No. NBCHCD50090 awarded by the U.S. Department of the Interior—National Business Center on behalf of a Department of Defense Agency—Defense Advanced Research Projects Agency. The Government has certain rights in the invention. 
     
    
     RELATED ART 
       [0002]    The disclosure relates to improvements of a ground, exo-atmospheric, or aerial based image capture system comprising a plurality of cameras positioned in a camera mount to capture images. The captured images are stitched together to form a collective image of a scene or an object. In particular, the disclosure expands on previous work described in U.S Patent Publication 2007/0188653 published on Aug. 16, 2007 which is incorporated herein by reference. Improved cameras replace the plurality of cameras of the image capture system providing an improved image capture system. The improved image capture system simultaneously provides a projected area scene and a scene spectrum with an improved binary dynamic range greater than 1000 to 1. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0003]    The disclosure can be better understood with reference to the following drawings. The elements of the drawings are not necessarily to scale relative to each other, emphasis instead being placed upon clearly illustrating the principles of the disclosure. Furthermore, like reference numerals designate corresponding parts throughout the several views. 
           [0004]      FIG. 1  depicts a conventional camera having a lens and a detector panel. 
           [0005]      FIG. 2  depicts an embodiment of a camera in accordance with the present disclosure. 
           [0006]      FIG. 3  depicts an embodiment of a detector with multiple sensors for the camera of  FIG. 2 . 
           [0007]      FIG. 4  depicts an embodiment of a camera having a solid-state modulator in accordance with the present disclosure. 
           [0008]      FIG. 5  depicts an embodiment of a lenslet of the solid-state modulator for the camera of  FIG. 4 . 
           [0009]      FIG. 6  depicts an embodiment of a camera with a baffle system in accordance with the present disclosure. 
           [0010]      FIG. 7  depicts an embodiment for the baffle system depicted in  FIG. 6 . 
           [0011]      FIG. 8  depicts a cross sectional view of a baffle for the baffle system of  FIG. 7 . 
           [0012]      FIG. 9  depicts an exemplary method for processing optical information for the camera of  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    An image capture system comprises one or more cameras mounted to a camera mount, such as described in U.S Patent Publication 2007/0188653 published on Aug. 16, 2007, which is incorporated herein by reference. Such an image capture system may be used to observe various items, such as people, terrain and associated items from commercial facilities, a moving platform, a vehicle, an aircraft or a satellite. The characteristic of each camera of the one or more cameras is a factor in determining the characteristics, such as size and quality, of a collective image of the image capture system. It would be understood by those persons skilled in image capturing technology that the quality of optical information of the collective image is partially dependent on the quality of the image from each camera of the image capture system. Embodiments of an improved camera of the present disclosure provide both quality spatial information and spectral information, thereby improving the quality of the collective image. In general, digital cameras are used as elements of such image capture systems. Such digital cameras focus light energy from radiant sources of a viewed object or scene on a detection panel having an array of detectors. The detection panel converts, via its detectors, the light energy into electrical signals that are communicated to a processing element. The processing element converts the electrical signals into image information that may be viewed on a display device, such as a digital monitor. Viewable images from multiple cameras may be combined, e.g., stitched together, to form a composite image of the object or scene provided by cameras of the image capture system. 
         [0014]    An embodiment of a camera of the present disclosure comprises a lens, a spatial-phase modulator, a baffle system and a detection panel having detectors with multiple sensors. Light energy from radiant sources enters the camera via an aperture in a frame of the camera and the spatial-phase modulator modulates the light energy so that the dynamic range of the camera is extended. Modulated light energy from the modulator is received by a lens, wherein the lens focuses the modulated light energy on a detection panel having an array of detectors and whose detection surface is aligned with the focal plane of the lens. The detectors have multiple sensors that convert the modulated light into electrical signals that are communicated to a processing element. The processer processes the electrical signals to provide image information in response to the energy from the radiant sources. The baffle system comprises multiple baffles positioned to reduce the amount of unwanted light energy that is received by detectors of the detection panel. 
         [0015]      FIG. 1  depicts a conventional camera  10  having a lens  30  that focuses light energy from a radiant source  22  on a detection panel  50 . Although only one radiant source  22  is depicted, it would be understood by those skilled in the area of optics, that a scene in a field of view  36  of camera  10  at a distance  170  from the lens  30  has multiple radiant sources  22  at multiple distances  170  that represent the scene. Detectors on a detection surface  51  of detection panel  50  convert the focused light energy into electrical signals and such signals are communicated to processing element  60  via communication link  62 . Processing element  60  converts the electrical signals into optical information that may be viewed on a display device, such as, for example, a digital monitor. Components of the camera  10 , such as lens  30  and detector panel  50 , are mounted within a frame  12  of the camera  10 . The frame  12  has a substantially tubular shape with a light absorbing inner surface  14  and an aperture  20  of fixed dimensions. The fixed dimensions are an image of the specific lens edge  35 . The aperture  20  limits the amount of light energy entering the interior of frame  12  from radiant source  30 . The other end of the frame  12  has a surface substantially perpendicular to the longitudinal axis  55  of the frame  12  and in alignment with the focal plane  34  of the lens. 
         [0016]    Note that the processing element  60  may be implemented in hardware, software, firmware, or any combination thereof. In one embodiment, the processing element  60  is implemented via a digital signal processor (DSP) that executes software in order to provide the functionality of the processing element  60  described herein. However, other configurations of the processing element  60  are possible in other embodiments. 
         [0017]    Although lens  30  is depicted in  FIG. 1  as a single lens, lens  30  may comprise multiple lenses and/or mirrors in a variety of arrangements that are typically used in a camera or other optical devices. Further, lens  30  may be replaced by a sequence of apertures that focus light energy on detector panel  50 . The focal length  32  of the lens  30  as depicted in  FIG. 1  is the distance from lens  30 &#39;s edge  35  to a focal plane  34 . The focal length  32  may also be referred to as the effective focal length (efl) of the lens. The lens  30  has a center  31  defined as a point produced by the intersection of the longitudinal axis  55  and a vertical line (the y-direction) that extends upward through the lens  30  as shown in  FIG. 1 . A detection surface  51  of detection panel  50  is aligned, i.e., it is coplanar, with focal plane  34 . The detection surface  51  comprises an array of m by n detectors, such as, for example, a million or more, that may be arranged in a rectangular pattern. Each detector, a pixel, is an independent bitmap of the image of a scene viewed by the camera. The detectors convert the light energy from multiple radiant sources of a scene into electrical signals that are coupled to processing element  60  via the communication link  62 . An optical output signal of the processing element  60  is pixel information that may be stored in memory and/or may be available as an input to an optical display device. Light energy received by the detectors comprises both desired light energy that represents the scene or an object and unwanted light energy from within the scene other sources that is referred to as optical noise. Unwanted light energy reduces the quality of an image provided by the camera. The ratio of the desired light energy to the unwanted light energy is expressed as an optical signal-to-noise ratio for the camera, an ensemble of components. The quality of an image provided by the detection panel  50  improves as the signal-to-noise ratio increases. 
         [0018]      FIG. 2  depicts an exemplary embodiment of a camera  100  of the present disclosure. Camera  100  comprises a spatial-phase modulator  120 , hereafter referred to as modulator  120  that modulates light energy from the radiant source  22  that enters the camera  100  via aperture  20 . Lens  30  receives the modulated light energy and focuses that modulated light energy on detector panel  150 . Detector panel  150  has an m by n array of detectors  152  on detector surface  151 . Each detector  152  of detector panel  150  comprises multiple sensors  1 - 4  as shown in  FIG. 3 , a view seen looking in the z-direction from lens  30  towards the detector surface  151 . Modulator  120  is configured to steer a light ray, representing the light energy, to periodically excite sensors  1 - 4  at a modulation frequency of the modulator  120 . 
         [0019]    An exemplary embodiment of modulator  120  comprises wedges  122  and  123  positioned as depicted in  FIG. 2 . The wedges  122 - 123 , made of material having a selected index of refraction, are shown in a side view and generally have a round shape when viewed in the z direction from aperture  20 . The wedges  122 - 123  each have a narrow edge  124  and a wide edge  125 . If the wedges  122 - 123  are positioned as shown in  FIG. 2 , light energy going in the z-direction passes through the same thickness wedge material. However, if one of wedges  122 - 123  is rotated about the longitudinal axis  55 , for example by 90 degrees, then light energy from radiant source  30  goes through material of various thicknesses resulting in a phase change of the light energy received by a detector  152  of detector panel  150 . A modulator with rotating elements, such as modulator  120 , is often referred to as a photo-mechanical device. In an exemplary embodiment, wedges  122 - 123  rotate (the rotational mechanism is not shown) in opposite directions about longitudinal axis  55  causing a continuous variation in the phase of light energy received by the detector panel  150 . In one embodiment wedges  122 - 123  are configured to sequentially excite each sensor  1 - 4  of detector  152  at a modulation frequency of modulator  120 . Each sensor  1 - 4  of detector  152  is a transducer that converts light energy into electrical energy. The dimensions of the wedges  122 - 123  and the index of refraction of the wedge material are selected so that a detector centered on an un-modulated light ray does not substantially extended outside the boundaries of the detector  152  as modulation occurs. 
         [0020]    Modulator  120  as depicted in  FIG. 2  operates similarly to a Risley prism device that is well known to those in field of optics. Such a Risley prism device is used to steer lasers and other light beams upon receiving position information from a device controller having vectoring information. The light energy from radiant source  22  destined for a particular detector  152  is modulated by modulator  120  in such a way that light energy is steered to periodically excite each sensor  1 - 4  of detector  152 . 
         [0021]    As indicated above, each detector  152  of the detector panel  150  comprises multiple sensors, for example, four such sensors  1 - 4  are positioned in a checkerboard arrangement as depicted in  FIG. 3 . For one exemplary embodiment there are m by n such detectors  152  arranged in a rectangular shape. In other embodiments other numbers of detectors and sensors arranged in different shapes are possible. Each sensor  1 - 4  of detector  152  provides an electrical signal in response to the modulated light energy that is received by that sensor. The sensors  1 - 4  communicate their respective electrical signals via communication link  62  to processing element  60 . The processing element  60  combines the electrical signals to provide optical information related to the scene viewed by the camera  100 . An optical output signal of the processing element  60  is pixel information that may be stored in memory and/or may be available as an input to an optical display device. Because each sensor  1 - 4  of detector  152  continuously provides an electrical signal, due to modulated light energy, the energy of signals from each detector  152  is greater than the energy from a detector having only one sensor. The signals of greater energy are received by the processing element  60  and provide an improvement in camera sensitivity. 
         [0022]    Another embodiment of a modulator for camera  100  that distributes light energy to sensors  1 - 4  of detector  152  via a modulation action is depicted in  FIG. 4 . Modulator  155 , a solid-state phase modulator, provides modulated light energy to detector  152 . An exemplary embodiment of modulator  155  comprises an array of lenslets  153 , wherein a lenslet is a small lens. The lenslet  153  is placed next to and in front of a respective detector  152  of the detector panel  150 . In such an arrangement, the number of lenslets  153  and number of detectors  152  is substantially equal. In other embodiments, other numbers of lenslets and detectors are possible. For example, one lenslet may be used to modulate light energy for multiple detectors. 
         [0023]    In one exemplary embodiment lenslet  153 , sometimes referred to as a quantum-mechanical device, is an electro-optic modulator made of materials that change their optical properties, such as their index of refraction, when subjected to an electric field. The electric field for modulating the light energy is provided by a control voltage  154  that is applied to edges of the lenslet  153  as depicted in  FIG. 5 . The control voltage  154  generally has a magnitude and a phase that causes a light ray to periodically and continuously excite each sensor  1 - 4  of detector  152 . The lenslet  153  is configured to modulate the light energy destined for its respective detector  152  at a modulation frequency consistent with the operation other components of camera  100 . Each of the sensors  1 - 4  of the detector  152  provides an electrical signal in response to the modulated light energy that reaches detector  152 . The sensors  1 - 4  communicate their respective electrical signals via communication link  62  to the processing element  60 . The processing element  60  combines the electrical signals to provide optical information that may be viewed as an image and/or stored in memory of the processing element. Because each of the sensors  1 - 4  of detector  152  provides an electrical signal, periodic signal strength received by the processing element  60  due to such intrinsic light modulation action results in an improvement in camera sensitivity. The processor  60  is configured to processes the electrical signals from the detectors  152  in such a way that both spatial information and as spectral information are available. As with the embodiment of  FIG. 2  unwanted light energy received by detector  152  also generates electrical signals that appear as optical noise to processing element  60 . It is desirable to limit the amount of unwanted light received by the detectors  152  so as to increase the signal-to-noise ratio of camera  100 . 
         [0024]    In general, desirable light rays that enter a camera are generally parallel to the longitudinal axis  55  of the camera  100  and fit within a boundary such as defined by lines  134 - 135  of  FIG. 7 . Light energy entering aperture  20  from areas outside the boundary is considered undesirable since such light rays are not in the field of view  36  of the scene. When such undesired light energy reaches detector panel  150 , the quality of an image of the scene is often degraded. Further, desirable light rays entering the camera from the field of view may bounce from the detector panel and/or from other surfaces within the camera frame and also appear as an additional source of noise. Specific baffles are used to reduce the amount unwanted light received by detectors  152  of detector panel  150 . Such baffles form optical shields that block, deflect and attenuate unwanted light that might otherwise strike detectors  152 . So when baffles reduce the amount of unwanted light energy reaching detector panel  150  without an equivalent reduction in amount of desired light energy reaching the detector panel  150 , then the signal-to-noise ratio of the camera is increased. Although baffles and the interior of the camera frame are coated with black light-absorbing material, it is known that no object, such as a baffle or other optical element is a perfect absorber or a perfect reflector. 
         [0025]    An embodiment of a baffle system  200  in accordance with the present disclosure is depicted in  FIG. 6 . Baffle system  200  comprises one or more baffles  202  located between lens  30  and focal plane  34  of the camera  100 . In other embodiments it is possible to have baffles located on both sides of lens  30 . When frame  12  has a round tubular shape with a circular inside surface, baffles  202  are generally disk shaped, i.e., round and flat, with an outside diameter such that the outside edges of the baffle  202  fit snuggly within the inside surface  14  of the frame  12  and are coupled thereto. The baffles  202  may be coupled to the inside surface  14  of the frame  12  using any attachment techniques known to those in the field of optical devices and instruments. Further, each baffle  202  has an aperture, formed by edges of the baffle  202 , centered within the disk shape of the baffle so that desired light energy from the radiant source  22  reaches detector panel  150  with a minimum attenuation. The shape of the aperture of each baffle  202  is round with a selected inside diameter as will be described herein below. The size and shape of the aperture for each baffle  202  may be different in other embodiments. However, for exemplary embodiment of  FIG. 7  the baffles  202  of baffle system  200  are configured to substantially reduce the amount of unwanted light that reaches detector panel  150  and appear as noise to the camera  100 . 
         [0026]    An exemplary embodiment of baffle system  200  in accordance with the present disclosure is depicted in more detail in  FIG. 7 , wherein some camera components are removed so as to better show baffle system  200 . As depicted in  FIG. 7 , there are four baffles  202  extending towards the longitudinal axis  55  of the camera  100  from the inner surface  14  of the frame  12 . In other embodiments other numbers of baffles are possible. In the embodiment of  FIG. 7  the baffles  202  are positioned between the detector panel  150  and the lens  30 . The baffles  202  have a disk shape and the surfaces of baffles  202  are coated with light absorbent black material to reduce the amount of light that might otherwise be reflected within the camera frame  12 . Each of the baffles  202  has a circular aperture substantially centered about the center of the corresponding disk shape of the respective baffle  202 . The diameter  205  of the aperture of baffle  202  is depicted in  FIG. 8 . As depicted in  FIG. 7 , the size of each baffle aperture varies, wherein the baffle  202  closest to lens  30  has the largest aperture and the baffle  202  closest to the detection panel  150  has the smallest aperture. The height of the baffle  203 , the distance it extends from the inner surface  14  of frame  12  is defined by template  210 . When the longitudinal location (the z direction) of a baffle  202  is determined, then the height of baffle  203  is equal to the distance from the inner surface  14  of frame  12  to a boundary defined by lines  212  and  214 . Boundary line  212  is a line extending from lens edge  35  to panel center  154 . Boundary line  214  is a line extending from the center of the lens  31  to the panel edge  156 . As depicted in the  FIG. 7  boundary line  212  and boundary line  214  intersect forming point  216 . For the baffle system  200  of  FIG. 7  the diameter  205  of each aperture of a baffle decreases when going from the lens  30  towards the detector panel  150 . An unobstructed view of the template  210  is provided in  FIG. 7  to more clearly view the shape of template. 
         [0027]    A cross section view of baffle  202  is depicted in  FIG. 8  as seen looking towards the detector panel  150  from a location between the lens  30  and the baffle nearest the lens. The outside diameter each baffle  202  is selected so that the baffle  202  fits within the inside surface  14  of frame  12  as depicted in  FIG. 8 . As indicated above, the aperture size of each baffle  202  decreases when moving from the lens  30  towards the detector panel  150 . Hence, the diameter  205  of the aperture of the baffle closest to the lens  30  is the relatively largest and the diameter  205  of the aperture of the baffle closest to the detector panel  150  is the relatively smallest. Each diameter or shape is relative to a real or virtual lens edge  35  in  FIG. 7 . In other embodiments other aperture diameters and other aperture shapes are possible. For example, when a baffle  202  located at intersection point  216 , then that baffle would be the baffle with smallest aperture diameter. As would be appreciated by those skilled in the design of cameras, the boundaries of the template  210  of embodiment of baffle system  200  depend on the panel size, the focal length  32  of lens  30 , and the lens edge  35  of lens  30 . The exemplary embodiment of baffle system  200  of  FIG. 7  has four baffles separated by approximately equal distances. In other embodiments other numbers of baffles with other separation distances are possible. 
         [0028]      FIG. 7  depicts an embodiment of camera  100  with baffle system  200  for reducing the amount of unwanted light that reaches the detector panel  150 . As indicated above, each baffle  202  has a height  203  and the baffles are separated by a baffle spacing  204 . In order to better understand camera geometry and the lines  212 ,  214  that define template  210  and the allowable height of each baffle  202  it is necessary to determine the view angle, δ, of the camera. The view angle, as will be seen below, is dependent of the focal length  32  or effective focal length (efl) of the lens and the panel height  157  of detector panel  150 . 
         [0029]    Assume that the panel height  157  of the detector panel  150  is known and that the plane of detector panel  150  is co-planar with the focal plane  34 . In one embodiment the panel height  157  is equal to the length of a diagonal of a rectangular shaped array of detectors. In other embodiments the panel height  157  may have multiple values depending on the shape of the array of detectors and the angular position about the longitudinal axis  55 . The lens  30  is located at a distance from the panel equal to the focal length  32  of lens  30 . Extend a line, shown as line  132 , from the top edge (located in the y-direction from the center of the detector panel) of detector panel  150  through lens center  31 . In addition, extend a line, shown as line  133 , from the bottom edge of the detector panel  150  through the lens center  31 . The angle between line  132  and line  133  is the view angle, θ, for camera  100 . Note that the view angle depends on the focal length  32  of the lens  30  and the panel height  157  of the detector panel  150 . When a distance to a scene  170  is known, the radius of a scene area viewed by the camera is approximately equal the tangent of θ/2 times the distance to the scene  170 . To determine an area that radiates desired light energy extend a line from the bottom of the field of view  36  through the bottom of the camera aperture  20  shown as line  134 . Further, extend a line from the top of the field of view  36  through the top of the camera aperture  20  shown as line  135 . Light energy that falls within the area between lines  134 - 135  represent a scene and is considered a source of desired light. Light energy from below line  134  or above line  135  that passes through camera aperture  20  is considered a source of undesired light energy. 
         [0030]    An exemplary method embodiment for processing the electrical signals from sensors  1 - 4  of detectors  152  is depicted in  FIG. 9 . The electrical signals S 1 -S 4  provided by the respective sensors  1 - 4  of each detector  152  are processed by the processing element  60 . The spectral information  915  of the camera  100 , having a panel of m by n detectors, is determined by combining S 1 -S 4  for each of the detectors, via a summer and a subtractor that provides an output, Δ. The output, Δ shown in  FIG. 9 , is processed using well-known optical processing techniques including the taking the Laplace transform the Δ of each detector  152  of detector panel  150 . Spatial information  925  is determined by summing the outputs S 1 -S 4  of each detector of the m by n detectors with a summer and dividing the resulting sum by Δ with a divider. A Hartley transform corrects the Δ sum, an off-set relative to zero the signal. The spatial information  925  and the spectral information  915  may be viewed on an image on optical viewer, such as a digital display device. Operations and actions for method embodiment are provided by logic within processing element  60  of camera  100 .