Abstract:
The present invention is an infrared imaging system that comprises a far-infrared camera disposed at the front end of a vehicle adapted for detecting thermal radiation in the 7 to 14 micron wavelength band and producing an image signal indicative of the temperature of the surrounding objects. A digital signal processor receives the image signal and selectively enhances the temperature resolution based upon the relative temperature distribution of the image signal, which is proportional to the temperature of objects emitting in the infrared region. In accordance with the present invention, the digital signal processor enhances temperature ranges having high concentrations and contracts temperature ranges having low concentrations. The digital signal processor selects between high and low concentrations based upon a predetermined threshold concentration value. A display apparatus receives a display signal that is temperature-enhanced and displays that signal to the driver.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Technical Field of the Invention  
           [0002]    The present invention relates to an imaging system for a motor vehicle, and in particular to an imaging system in which detected infrared radiation is processed by a digital signal processor in order to visually enhance road conditions based upon temperature.  
           [0003]    2. Description of the Prior Art  
           [0004]    Poor visibility at night results from a number of causes that have conspired to make traveling after dark a potentially troublesome situation. A typical driver uses low beam head lamps in most driving conditions after dark. Low beams, however, have a limited range and can illuminate a relatively small portion of the road ahead. Moreover, most drivers have experienced the temporary blinding effect caused by the head lamps of oncoming vehicles. The scattering of light is worsened in wet conditions due to the reflective surface of the roads. Rain, snow, fog and other types of inclement weather further limit visibility at night.  
           [0005]    As a result of reduced visibility at night, engineers turned to other means of visualization that involved detecting radiation that is otherwise invisible to the human eye. All objects are, to a greater or lesser extent, both emitters and reflectors of radiation. There is a correlation between the temperature of an object and the wavelength of radiation emitted by that object, a principle known as blackbody radiation. For objects having a temperature between 0° and 50° C., as is most common in everyday experience, the radiation emitted is in the infrared band of the spectrum. Even though an object is not reflecting visible light that same object is likely emitting infrared light. Scientists and engineers created a means of detecting infrared radiation thereby permitting the visualization of otherwise invisible objects—a night vision system.  
           [0006]    One such night vision system is known as thermal imaging. Developed by the military, thermal imaging was once thought to be too expensive and cumbersome for use in the consumer vehicle market. However, recent advances in electronics and infrared detectors have made the use of night vision in consumer vehicles more tenable, and at least one manufacturer recently incorporated thermal imaging system into a vehicle.  
           [0007]    Both passive and active imaging systems exist. A passive system is not unlike the human-eye in that it primarily detects radiation that is emitted from objects. On the other hand, an active system projects radiation and then primarily detects the reflection of that radiation off of objects. Passive systems have several advantages over their active counterparts. Most importantly, passive systems do not project any kind of radiation from the vehicle, and thus will not interfere with the surrounding environment or with the imaging systems of other vehicles. A far infrared camera is an example of a passive system, and it is the infrared camera utilized in the present invention.  
           [0008]    In general, a far-infrared camera detects radiation in the 7 to 14 micron wavelength band. This wavelength band corresponds to a temperature range of approximately −20° to 50° C. that covers all objects that are of interest to automotive engineers. The human body, for example, has a peak emission at approximately 9.3 microns, which corresponds to the human body temperature of about 37° C.  
           [0009]    A consumer vehicle thermal imaging system is typified by the Cadillac DeVille Thermal Imaging Night Vision System by General Motors. The Cadillac system consists of a thermal imaging camera, a heads-up display, and image controls. As in other thermal imaging systems, the Cadillac system uses a camera to capture infrared data, the camera electronics to process the data, and a heads-up display to present the information to the driver.  
           [0010]    Despite the Cadillac system improving night driving conditions, there remains a persistent problem in the resolution and contrasting of the infrared image. Although a standard far-infrared camera can detect incremental temperature ranges over a wide range of temperatures, the image presented to the driver does not adequately reflect subtle distinctions between objects. Most importantly, existing imaging systems cannot distinguish the road boundary from the road, nor can they distinguish the lane markers that separate traffic from the road.  
           [0011]    Thus, there is a need for a far-infrared imaging system for use in a vehicle that enhances the relative temperature distinctions between objects such that a driver will be presented with a complete representation of the road conditions, including the road boundaries and lane markers.  
         SUMMARY OF THE INVENTION  
         [0012]    The present invention is an infrared imaging system that comprises a far-infrared camera disposed at the front end of a vehicle adapted for detecting thermal radiation in the 7 to 14 micron wavelength band and producing an image signal indicative of the temperature of the surrounding objects. A digital signal processor receives the image signal and selectively enhances the temperature resolution based upon the relative temperature distribution of the image signal, which is proportional to the temperature of objects emitting in the infrared region. A display apparatus receives a display signal that is temperature enhanced, or temperature warped, and displays that signal to the driver.  
           [0013]    The far-infrared camera detects thermal radiation and produces an image signal indicative of the temperature of the objects, the image signal having selected temperature concentrations depending on the wavelength of the radiation emitted. A digital signal processor receives the image signal, calculates the temperature distribution of the signal, and selectively discriminates between temperature concentrations based upon the temperature distribution such that large temperature concentrations are mapped from the image signal to a display signal in which the resolution and differences in temperature are more evident to the driver. The display apparatus is disposed within the vehicle such that the vehicle operator is informed of the driving conditions ahead.  
           [0014]    The present invention also provides a method for enhancing the thermal imaging resolution of an infrared camera for a vehicle. The method comprises receiving thermal radiation and producing an image signal in response thereto, calculating the concentrations of radiation, and mapping the high concentrations of radiation into a display signal thereby thermally enhancing the display signal. The display signal is then displayed to the vehicle operator such that the vehicle operator can visually detect subtle distinctions in the road features, including the road boundary and lane markers as well as pedestrians.  
           [0015]    Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a perspective view of a motor vehicle equipped with the infrared imaging system of the present invention.  
         [0017]    [0017]FIG. 2 is a block of the primary components of the infrared imaging system of the present invention.  
         [0018]    [0018]FIG. 3 is a flow chart depicting the process by which a typical infrared image is thermally enhanced in accordance with the present invention.  
         [0019]    [0019]FIGS. 4 a  and  4   b  are graphical representations of the thermal enhancement of a typical infrared image and the thermally-enhanced infrared image in accordance with the present invention.  
         [0020]    [0020]FIG. 5 a  is a schematic view from the perspective of a vehicle driver depicting a typical image rendered by an infrared imaging system.  
         [0021]    [0021]FIG. 5 b  is a schematic view from the perspective of a vehicle driver depicting a thermally-enhanced image rendered by the infrared imaging system of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]    Illustrative of the preferred embodiment of the present invention, FIG. 1 shows a perspective view of a vehicle  10  disposed between a pair of lane markers  16   a  and  16   b  upon a road  22 . The road  22  is bounded on one side by a boundary  18 , which generally consists of a curb, a sidewalk, or simply bare ground. A peripheral space  20  is located adjacent to the boundary  18 . The peripheral space  20  generally consists of grass, dirt, or some other surface not suitable for driving and which a vehicle operator (not shown) would preferably avoid.  
         [0023]    The vehicle  10  is equipped with the infrared imaging system of the present invention, including a far-infrared camera (FIR camera)  14  and a display  12 . A digital signal processor  24  that is coupled to both the FIR camera  14  and the display  12  is not shown, but may be located within the vehicle  10  at any convenient position. As shown, the display  12  is of the type known as a head-up display, which may be located above a steering wheel  8  inside a passenger compartment  6  of the vehicle. In the head-up embodiment, the display  12  is disposed directly along the vehicle operator&#39;s line of sight so as to provide little interruption or distraction during driving. Alternatively, the display  12  may include a video monitor or other suitable device for communicating visual data to the vehicle operator.  
         [0024]    [0024]FIG. 2 is a block diagram of the primary components of the infrared imaging system of the present invention. The FIR camera  14  is coupled to the digital signal processor  24 . The digital signal processor  24  is coupled to the display  12 . The digital signal processor  24  functions to receive an image signal from the FIR camera  14 , process the image signal, and then transmit a display signal to the display  12  for viewing by the vehicle operator.  
         [0025]    The process of thermal enhancement is depicted in the flow chart of FIG. 3. In step S 101 , the FIR camera  14  detects radiation emitted from objects within its field of view. In a preferred embodiment, the FIR camera  14  is adapted to far infrared radiation in the range of 7 to 14 microns. The preferred field of view of the FIR camera is greater than 11 degrees over a range of approximately 400 meters. The FIR camera  14  typically detects radiation using a Vanadium Oxide Bolometer (not shown) or other infrared light-sensing means, which produces an electronic signal in response to irradiation from photons of a particular wavelength. The light sensing means will typically correlate emitted thermal energy from an area in the camera&#39;s field of view with a cell in the detection plane of the radiation detector (not shown). Each cell is designated by a row number &lt;i&gt; and a column number &lt;j&gt;, such that the radiation detected at any point in the plane can be designated as P i,j . Thus, the data gathered by the light-sensing means consists of an array of values assigned to a spatial coordinate that corresponds to an image received by the FIR camera  14 .  
         [0026]    The preferred FIR camera  14  is adapted to assemble the electronic data into an image signal which is indicative of the radiation incident upon the light-sensing means. Typically, the image signal will consist of the radiation values at each point P i,j , as detected by the light-sensing means.  
         [0027]    In step S 102 , the image signal is transmitted from the FIR camera  14  to the digital signal processor  24 .  
         [0028]    In step S 103 , the digital signal processor  24  correlates the image signal into a set of points in which the radiation values for each point, P i,j , are assigned a temperature value, T i,j , based upon the known relationships between the thermal radiation emitted by an object and its temperature. Thus, the digital signal processor  24  assembles a set of values T i,j  that are indicative of the temperature at each point in the image received by the FIR camera  14 .  
         [0029]    In step S 104 , the digital signal processor  24  calculates a temperature distribution function, N=f(T), also referred to as a temperature histogram. The temperature distribution function is a relationship between the temperature at a point, T i,j , and the number of points P i,j , that have that temperature, as shown in FIG. 4 a . The temperature distribution function is thus a mathematical relationship describing the concentration of temperatures within an image signal.  
         [0030]    In step S 105 , the digital signal processor  24  searches temperature distribution function for large concentrations of temperature values, as shown in FIG. 5 a . In the decision block of step S 106 , the digital signal processor  24  compares each temperature distribution value f(T) with a threshold concentration value f o  indicative of a particular concentration N. The threshold concentration value is predetermined, and in alternative embodiments, may be constant or variable depending upon the driving environment of vehicle  10 .  
         [0031]    The digital signal processor  24  calculates a maximum value of the temperature distribution f(T), from T=−20° C. to T=50° C. If the maximum value of the temperature distribution is greater than the threshold value, f o , then the digital signal processor  24  proceeds to step S 107 . Conversely, if the maximum value of the temperature distribution is less than the threshold value, f o , then the digital signal processor  24  proceeds to step S 108 .  
         [0032]    In step S 108 , for each point (i,j), T i,j  is assigned a corresponding value V i,j , which is adapted for receipt and display by the display  12 . That is, the as the display signal V i,j  is the same as the image signal T i,j .  
         [0033]    Conversely, in step S 107 , the digital signal processor  24  enhances the temperature dependence of the temperature distribution, f(T). The digital signal processor  24  enhances the temperature dependence of the temperature distribution by implementing the following mathematical transform:  
                 U   ij     =     g        (     T   ij     )         ,   where           (   1   )                   g        (   T   )       =     ∫            U          T               T           ,     and                 further                 where             (   2   )                        U          T       =       f        (   T   )       +   constant       ,   and           (   3   )                               
 
           F ( U )= f ( g   −1 ( U   ij )).   (4)  
         [0034]    Equation (1) defines the enhanced temperature, U ij . Equation (2), g(T), is a the temperature transform function. Equation (4) defines the new distribution of the enhanced temperature, F(U).  
         [0035]    By implementing equation (2), the digital signal processor  24  creates an enhanced temperature distribution given by equation (4). Thus, in step S 107  the appropriate temperature transform function is determined. In step S 109 , the temperature T i,j  is transformed to the enhanced temperature, denoted U i,j .  
         [0036]    The thermal enhancement of steps S 107  and S 109  is represented graphically in FIGS. 4 a  and  4   b . FIG. 4 a  depicts a temperature distribution function as calculated by the digital signal processor  24 . There are two peak concentrations in temperature regions. A first concentration  30  about 10° C. is likely inanimate and indicative of the road and the surrounding environment. Note that the first concentration  30  has a local peak  31  at approximately 12° C. The first concentration  30  is greater than the threshold value, f o , and all of the points (i,i) are temperature enhanced in accordance with steps S 107  and S 109 .  
         [0037]    [0037]FIG. 4 b  represents the temperature distribution function after the enhancement of steps S 107  and S 109 . The first concentration  30  and the second concentration  33  have been expanded relative to the central regions of low concentration  32 . Regions of low concentration, between 17° and 33° C. are contracted, emphasizing the distinction between the local peak  31  and the first concentration  30 .  
         [0038]    Returning to FIG. 3, in step S 109 , the digital signal processor assembles a complete set of points for a display signal consisting of the U i,j  by utilizing the temperature transform function of step S 107 . The display signal of step S 109  is transmitted to display  12  where it is displayed for viewing by the vehicle operator.  
         [0039]    In step S 110  of FIG. 3, the display  12  displays the display signal as an image which the vehicle operator may readily view while driving.  
         [0040]    [0040]FIGS. 5 a  and  5   b  are representative illustrations of the beneficial effects of the temperature enhancement process of steps S 107  and S 109 . FIG. 5 a  is a schematic perspective view of the display  12  as seen by the vehicle operator. The road  22  is bounded by the lane markers  16   a  and  16   b  and bounded further by the boundary  18 . Adjacent to the boundary  18  is the peripheral space  20  which, as noted above, is not suitable for driving. Additionally, a pedestrian  50  is shown crossing road  22 .  
         [0041]    [0041]FIG. 5 a  is a representative image from a typical infrared imaging system that does not possess the temperature enhancement of the present invention. As shown, the road  22  is not readily distinguishable from the lane markers  16   a  and  16   b . Moreover, the boundary  18  is not readily distinguishable from the peripheral space  20 . Thus, although the vehicle operator can see the pedestrian  50 , the vehicle operator cannot distinguish the features and boundaries of the road  22  without undue hesitation and concentration.  
         [0042]    In contrast, FIG. 5 b  is a representative image from the infrared imaging system that has been temperature enhanced in accordance with the present invention. As shown, the pedestrian  50  is still clearly visible. Moreover, the road  22  and its features and boundaries are more readily distinguishable. The lane markers  16   a  and  16   b , due to their thermal properties, are distinguished from the road  22 . The road boundary  18  is also visible without undue concentration. The peripheral area  20 , which the vehicle operator wishes to avoid, can be distinguished from the road  22  as well. The visibility of the pedestrian  50  is not degraded.  
         [0043]    The temperature enhancement of FIG. 5 b  is illustrative of how the digital signal processor  24  finds a high concentration of temperatures and enhances that concentration. For example, in general the road  22 , the lane markers  16   a ,  16   b , the road boundary  18 , and the peripheral area  22  will be approximately of the same temperature, i.e. within a certain range corresponding to the first concentration  30  of FIG. 4 a . The process of temperature enhancement magnifies the first concentration  30  such that formerly unnoticeable subtleties are more apparent. Therefore, as shown in FIG. 5 b , the road  22  is distinguishable from the lane markers  16   a  and  16   b  as well as the road boundary  18  and peripheral area  20  in spite of the close relative temperatures of each of the foregoing. The visibility of the pedestrian  50  is not degraded.  
         [0044]    The present invention as described in its preferred embodiment thus improves the image quality of infrared imaging systems by enhancing temperature distinctions for highly concentrated temperature ranges. It should be apparent to those skilled in the art that the above-described embodiment is merely illustrative of but a few of the many possible specific embodiments of the present invention. Numerous and various other arrangements can be readily devised by those skilled in the art without departing from the spirit and scope of the invention as defined in the following claims.