Abstract:
An infrared video camera system having a plurality of interchangeable imaging lens units and optical filter units. Identifying information, used to modify the operation of the camera system based on the specific imaging lens unit and optical filter unit attached thereto, is stored in an Electrically Programmable Read Only Memory (EPROM) located in each imaging lens unit and optical filter unit.

Description:
FIELD OF THE INVENTION 
     The present invention relates in general to an infrared video camera system having a plurality of interchangeable imaging lens units and optical filter units. In particular, the present invention provides a method and apparatus for storing identifying information in each of the imaging lens units and optical filter units that is used to modify the operation of the infrared video camera system. 
     BACKGROUND OF THE INVENTION 
     Recent infrared (IR) video camera systems employing IR sensitive elements, e.g., a Charged Coupled Device (CCD) focal plane array, are generally provided with a plurality of detachably mounted imaging lens units. This allows a user to interchangeably mount one lens unit at a time to the body of the video camera system, based on the object scene to be captured. Each imaging lens unit is configured to image at least a portion of the object scene onto the focal plane array, depending upon the field of view of the imaging lens unit. For example, a telephoto-type imaging lens unit will generally provide a relatively narrow viewing field, while other types of imaging lens units will provide a wide angle or mid-range field of view. 
     Such infrared video camera systems may also include a plurality of interchangeable optical filter units which are configured to filter the energy of the object scene prior to capture by the IR sensitive element. Such optical filter units may include spectrally narrowing bandpass filters, e.g., for preventing non-IR wavelengths from reaching the IR sensitive element, or for simply narrowing the spectral range of viewing, neutral density filters for attenuating the luminous energy reaching the IR sensitive element, and the like. 
     In infrared video camera systems of this type, both the individual imaging lens units and the individual optical filter units are identified to a microprocessor contained within the body of the camera, and a characteristic data set, stored in a memory device in the camera body, is made available to characterize or tailor the response of the IR sensitive sensor element to an object scene image. A set of characteristic data is stored in the camera memory for each type of imaging lens unit and optical filter unit which may be installed on the infrared video camera system. A typical characteristic data set may include a bias voltage for the IR sensitive element, a sensor integration time, an equalization table of pixel by pixel gain and/or offset data, and absolute temperature calibration data. In each case, the characteristic data set stored in the camera memory is predetermined to modify the camera system for operation with a corresponding imaging lens unit or optical filter unit. 
     Imaging lens and filter unit identifiers have heretofore utilized Hall-effect sensors mounted to the camera body, and one or more permanent magnets mounted onto the imaging lens unit housing and optical filter unit housing, to identify the imaging lens unit and optical filter unit to the microprocessor of the camera system. When the imaging lens unit and optical filter unit are attached to the camera body, the permanent magnets on the imaging lens unit and optical filter unit are aligned with the Hall-effect sensors attached to the camera body. The microprocessor software determines the status of the Hall-effect sensors, identifies the lens and filter configuration of the imaging lens and optical filter units based on the status of the sensors, and selects the appropriate characteristic data set from the camera memory. 
     A major problem with this approach is that one Hall-effect sensor is required for each binary bit of information. For example, a combination of 16 separate identifiers requires 4 sensors, since 2 4 =16. Further, since the Hall-effect sensors require a relatively large amount of space, and one or more wires must be attached to each Hall-effect sensor, the number of sensors which can be used is limited by the space and wiring constraints of the camera system. Clearly, including more substantial identifying information, such as lens transmission data, serial number or date placed in service, is not practical because of the large number of sensors that would be required. 
     A further disadvantage associated with the use of Hall-effect sensors is their susceptibility to magnetic fields. Occasionally, when used in or near strong magnetic fields, the output of the Hall-effect sensors may be adversely affected, potentially resulting in the misidentification of an attached imaging lens unit or optical filter unit, and the use of an incorrect characteristic data set for the operation of the camera system. 
     SUMMARY OF THE INVENTION 
     The present invention obviates the disadvantages associated with the use of Hall-effect sensors in an infrared video camera system by storing identifying information in an electronic memory, e.g. an Electrically Programmable Read Only Memory (EPROM), housed in each imaging lens unit and each optical filter unit. 
     Each imaging lens unit and optical filter unit includes a single, dedicated, small EPROM having sufficient capacity to store all necessary identifying information. Preferably, the EPROM is of the single data wire type, wherein the stored data is read out serially through a single wire. 
     The use of this type of EPROM overcomes the above-described limitations associated with Hall-effect sensors. For example, the EPROM is very small, and only one wire per imaging lens unit or optical filter unit is required to access the stored data, thereby removing the severe space and wiring constraints associated with the use of Hall-effect sensors. In addition, the magnitude of the identifier is essentially unlimited. Advantageously, more substantial and/or detailed identifying information, such as lens transmission data, serial number, or date placed in service, may now be stored and accessed by the microprocessor of the camera system. Also, unlike Hall-effect sensors, the EPROM is not susceptible to magnetic fields. 
     Generally, the present invention provides an infrared camera system for capturing an infrared image of a scene, comprising: 
     a camera body for housing an image capturing system, the image capturing system including an infrared sensor for providing an image signal, and an image processor for modifying the image signal; 
     a plurality of image forming devices interchangeably attachable to the camera body for forming an image of the scene onto the infrared sensor, each image forming device including a memory for storing at least one identifying characteristic; 
     a plurality of filter devices interchangeably attachable to the camera body for filtering the image of the scene formed onto the focal plane array, each filter device including a memory for storing at least one identifying characteristic; 
     an interface for communicating the stored identifying characteristics of the image forming device and the filter device attached to the camera body to the image processor; and 
     a camera memory for storing a plurality of characteristic data sets; 
     wherein the image processor selects one of the plurality of characteristic data sets from the camera memory, and modifies the image signal using the selected characteristic data set, according to the identifying characteristics of the image forming device and the filter device attached to the camera body. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features of the present invention will best be understood from a detailed description of the invention and a preferred embodiment thereof selected for the purposes of illustration and shown in the accompanying drawing in which: 
     FIG. 1 illustrates an infrared video camera system in accordance with a preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now specifically to FIG. 1, there is illustrated an infrared video camera system, generally designated as  10 , in accordance with a preferred embodiment of the present invention. The infrared video camera system  10  includes a camera body  12  for housing an infrared sensor arrangement  14 , such as a CCD focal plane array, an analog to digital (A/D) converter  16  for converting the analog video output of the infrared sensor arrangement  14  into digital image signals, and an image processor, referred to generally by reference numeral  100 . The image processor  100  includes a digital image processor  18  for modifying the digital image signals and for preparing the digital image signals for video display, and a microprocessor  20  which directs the operation of the digital image processor  18 , as well as other operations of the video camera system. 
     An imaging lens unit  22 , for imaging at least a portion of an object scene onto the infrared sensor arrangement  14 , is detachably mounted onto the camera body  12 . Preferably, a plurality of different imaging lens units  22  may be interchangeably mounted onto the camera body  12 , depending upon the object scene to be captured, environmental conditions, and other factors. 
     Each imaging lens unit  22  is provided with a memory module  24  for storing identifying information corresponding to that imaging lens unit  22 . The identifying information for each imaging lens unit  22  may include, for example, the type of imaging lens unit (e.g., telephoto, wide-angle), spectral characteristics of the imaging lens unit optical system, lens transmission data, manufacturer, lens serial number, date placed in service and or date of repair or calibration, and the like. Of course, other types of identifying information may be stored in the memory module  24  without departing from the intended scope of the present invention. 
     The memory module  24  preferably comprises an EPROM or other type nonvolatile memory having sufficient capacity to store all required identifying information. In accordance with the preferred embodiment of the present invention, the memory module  24  is a single data wire type, such as the DS2502P 1 Kbit EPROM manufactured by Dallas Semiconductor. In this type of EPROM, control, address, data, power, and programming signals are communicated through a single wire connection. The EPROM also includes a ground connection which may be terminated within the lens or filter unit. The use of this type of memory module  24  reduces the wiring and interfacing requirements for accessing the identifying information stored in each imaging lens unit  22 . 
     An optical filter unit  26  may also be detachably mounted onto the camera body  12 . As illustrated in FIG. 1, the optical filter unit  26  is positioned between the imaging lens unit  22  and the camera body  12 . Alternately, the filter may be positioned between the imaging unit  22  and the object scene, or may be detachably mounted to the imaging lens unit  22 . The optical filter unit  26  selectively filters the energy of the object scene captured by the imaging lens unit  22  prior to imaging on the infrared sensor arrangement  14 . As with the imaging lens unit  22 , a plurality of different optical filter units  26  may be interchangeably mounted onto the camera body  12  or onto the imaging lens unit  22 . 
     Each optical filter unit  26  is provided with a memory module  28  for storing identifying information corresponding to that optical filter unit  26 . The identifying information stored in the memory module  28  may include, for example, filter type, spectral and or transmissive filtering characteristics, manufacturer, and other filter related information. The memory module  28  of the optical filter unit  26  preferably comprises the single data wire EPROM described above with reference to the memory module  24  of the imaging lens unit  22 . 
     Identifying information stored on the memory modules  24 ,  28  is accessed by the microprocessor  20  through an interface  30  when an imaging lens unit  22  and an optical filter unit  26  are attached to the camera body  12  as shown in FIG.  1 . Upon attachment of an imaging lens unit  22  and an optical filter unit  26  to the camera body  12 , the single data wires  32 ,  34  of the memory modules  24 ,  28  are connected to corresponding input leads  36 ,  38  of the interface  30  through suitable point to point contacts  40 . If the imaging lens unit  22  is used without an accompanying optical filter unit  26 , wire  32  is connected to lead  36  of the interface  30 , while lead  38  remains unconnected. If the filter unit  26  is detachably mounted to the imaging lens unit  22 , e.g. between the imaging lens and the object scene, a electrical path can be provided between the filter memory module  28  and the input lead  38  through the imaging lens unit  22  using suitable point to point contacts on either end of the imaging lens unit. 
     The microprocessor  20  analyzes the identifying information received from the memory modules  24 ,  28 , and instructs the digital image processor  18  to use a characteristic data set, stored in a memory module  42  in the camera body  12 , to modify the response and/or output of the infrared sensor arrangement  14 . A characteristic data set is stored in the memory module  42  for each type of imaging lens unit  22  and optical filter unit  26 , or combination thereof, which may be installed on the infrared video camera system  10 . 
     Preferably, the memory module  42  is a flash-type memory, thereby allowing the characteristic data sets stored therein to be easily deleted, updated, added, or otherwise modified as necessary. For example, a characteristic data set may need to be added to memory module  42  if a new type of imaging lens unit  22  or optical filter unit  26  becomes available for use with the infrared video camera system  10 . 
     Each characteristic data set stored in the memory module  42  may include, for example, data  44  regarding the required integration time and or bias voltage of the infrared sensor arrangement  14 , equalization data  46  for applying a pixel to pixel correction to the digital image data output by the A/D converter  16 , or data  48  which is used as a look up table by the microprocessor  20  to convert the pixel data of the frame buffer  52  to absolute temperature values, e.g. in degrees centigrade or Fahrenheit. Of course, other types of data for modifying the response/output of the infrared sensor arrangement  14  may be included in one or more of the characteristic data sets stored in the memory module  42  without departing from the intended scope of the present invention. 
     In operation, the image processor  100  uses the data  44 ,  46 ,  48  stored in the memory module  42  in various ways. The integration time and bias voltage data  44  is provided directly to the infrared sensor arrangement  14  to modify its infrared response in accordance with the particular imaging lens  22  or filter unit  26  mounted to the camera body  12  or camera system  10 . Since the infrared sensor provides an analog image signal, data  44  modifies the analog image signal. The analog image signal is converted to digital image data by the A/D converter  16 . The equalization data  46  is used by an equalization processor  50  to apply a pixel to pixel correction to the raw digital image data output by the A/D converter  16 . Such a correction may adjust individual pixel gains and or offsets to compensate for factors such as pixel to pixel variations. Again, the equalization data  46  is selected according to the particular imaging lens  22  or filter unit  26  mounted to the camera body  12  or camera system  10 . This corrected digital image data is subsequently stored in a frame buffer  52 . Thereafter, the digital image data stored in the frame buffer  52  may be used in conjunction with temperature calibration data  48  to provide absolute temperature values for individual pixels of the object scene image. Finally, the modified digital data is scaled by a scaling device  54  which may select the entire scene image or a portion of the scene image for display on a video display device and adjust resolution, brightness, contrast, or other video parameters, for displaying the infrared scene image on a monitor or other video display device. A video output driver  56  provides the infrared video scene image data in a format for video display. 
     It will also be recognized by those skilled in the art that, while the invention has been described above in terms of preferred embodiments, it is not limited thereto. Various features and aspects of the above described invention may be used individually or jointly. Further, although the invention has been described in the context of its implementation in a particular environment, and for particular applications, e.g. an infrared sensor assembly and an infrared video camera system, those skilled in the art will recognize that its usefulness is not limited thereto and that the present invention can be beneficially utilized in any number of environments and implementations. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the invention as disclosed herein.