Abstract:
A vehicular display system having a camera for producing a video signal and a display device for displaying the video signal. The display device includes an integrity check to detect a defective video signal and alert the driver if a defective video signal has been detected.

Description:
[0001]    This application claims the benefits of U.S. Provisional Application Ser. No. 61/361,465, filed Jul. 5, 2010, which is hereby incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to the art of vehicular rear view cameras. 
       BACKGROUND OF THE INVENTION 
       [0003]    Vehicular rear view cameras are commercially deployed on numerous vehicular platforms. Such cameras are typically mounted in or adjacent to the rear bumper of a vehicle and have a rearward facing field of view. The cameras are typically connected to a display monitor in the vehicle to allow the driver to see what is behind the vehicle, particularly when the vehicle is shifted into reverse. The display monitor may be mounted in the center console, embedded or incorporated into the interior rear view mirror, or placed in some other location in the cabin visible to the driver. 
         [0004]    The vehicular rear view display system provides many safety benefits as it allows the driver a good field of view to see what is behind the vehicle and thus avoid tragic accidents such as running over children when backing out of one&#39;s driveway. 
         [0005]    The vehicular rear view display system has been so useful that it has now become ubiquitous and often the primary source of information for drivers when reversing. For example, many drivers rely solely on the rear view camera to squeeze into a tight parking spot or check to see if there are any children, toys or other objects behind the vehicle. 
         [0006]    Therein lies a problem. 
       SUMMARY OF THE INVENTION 
       [0007]    More specifically, because the vehicular rear view display system is often the primary source of information for the driver backing up, any error in the display system such as a frozen screen could result in calamity. In order to reduce the risk of such an event, the invention provides a life check subsystem to ensure that the video information provided to the display is not compromised. 
         [0008]    According to one aspect of the invention, a vehicular display system is provided which includes a camera for producing a video signal and a display device for displaying the video signal. The display device includes an integrity check to detect a defective video signal and alert the driver if a defective video signal has been detected. 
         [0009]    According to another aspect of the invention, a vehicular display system is provided which includes a display monitor; a camera for mounting on the vehicle to generate a video signal; and a video decoder receiving the video signal and providing pixel data for view on the display monitor. An integrity check circuit receives at least one of the video signal and the pixel data, and vehicle speed data. The integrity check circuit reviews at least one of the video signal and pixel data in order to ascertain a change therein beyond a threshold when the vehicle speed is not zero. In the event insufficient change is detected the integrity check circuit initiates an error indication intended for the driver for view on the display. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The foregoing and other aspects of the invention will be more readily appreciated having reference to the drawings, wherein: 
           [0011]      FIG. 1  is a system block diagram of a vehicular rear view display system according to one embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]      FIG. 1  shows a vehicular rear view display system  10  having a rear view camera  12  preferably mounted to the rear bumper of a vehicle, although other locations at the rear of the vehicle may be utilized as alternative attachment points. In the embodiment described herein, the rear view camera  12  includes a lens assembly and an imager that provides an analog video signal  14  to a head unit  16  that is preferably mounted in a protected location in the vehicle. The head unit  16  includes a video decoder  18 , such as an NTSC or PAL decoder, as known in the art per se, which intercepts the analog video signal  14  and provides pixel data on output line(s)  20 . In alternative embodiments, the camera imager may provide digital pixel data directly, omitting a separate video decoder (in which case video decoder can be considered to be integrated with the camera imager). Alternatively, the digital pixel data may be in the form of a compressed bit stream where not all pixels are directly represented in which case the video decoder  18  in the head unit  16  decompresses the bit stream to provide the pixel data. 
         [0013]    The pixel data line  20  is received by an integrity check functional block or circuit  24 . The purpose of block  24  is to ensure that the pixel data provided by the rear view camera  12  and video decoder  18  is “valid” data, suitable for display. If so, then the pixel data received on line  20  is output via one or more lines  26  connected to a display monitor  28  viewable by the driver. If the pixel data received on line  20  is invalid, then the integrity check block  24  provides an appropriate output on line  26 , such as a blacked out screen, or access and display a warning graphic (e.g., STOP, or ERROR) as may be retrieved by a graphic overlay memory  32 . In this manner, it is possible to reduce the danger of inaccurate data from being displayed on the display monitor  30 , such as a frozen screen. 
         [0014]    The integrity check block  24  may perform one or more validity checks. 
         [0015]    First, the integrity check block  24  preferably measures the impedance of the line carrying video signal  14 . If the measured impedance of the video signal line varies beyond a certain a range, the integrity check block  24  will assume that the line has a break in it or is otherwise compromised. A suitable error message may be displayed on the display monitor  28 , or an error code may be provided to the vehicular central control unit (not shown) via the vehicular local area network  30  such as CAN or LIN. 
         [0016]    Utilizing the input provided by the vehicular local area network  30 , the integrity check block  24  preferably receives a signal from the vehicular central control unit indicating when the vehicle transmission is placed in reverse and the speed of the vehicle. When the vehicle is in motion, the view received by the rear view camera  12  is expected to change, and hence the pixel data is expected to change. Accordingly, when the vehicle speed is greater than zero the integrity check block  24  looks for an absence in change in the pixel data received on line  20 . More particularly, the integrity check block  24  may examine one or more diagonal lines of pixels to ascertain if a minimum of a predetermined number of pixels have changed over the course of time. Additionally or alternatively, one or more horizontal lines, vertical lines or one or more sub-regions (such as areas closest to the vehicle) may be tested for change in the corresponding pixels. The magnitude of the change may also be a factor, and chrominance and luminance information may be separately considered to ensure that one or more of these quantities change a sufficient amount so as to avoid false alarm situations resulting from thermal, electromagnetic or other noise. Likewise, the rate of change in the pixel may also be a factor in ascertaining the validity of the pixel data based on the speed of the vehicle, as the greater the speed of the vehicle, the greater the expected change. 
         [0017]    Change of a pixel may be calculated by subtracting the pixel value of a previous frame n−1 from the value of the same pixel of current frame n. Change may also be detected by comparing a histogram of a previous frame n−1 with the histogram of current frame n. To qualify a video stream as being valid the amount of change between any two images may have to exceed a minimum threshold. The minimum threshold may be selected as a static value. Beneficially, the minimum threshold may also be variably selected based on the vehicle speed, so that a video stream with low change from frame to frame is classified as valid while the vehicle is stopped, however larger frame to frame change is necessary to indicate a valid video stream while the vehicle is moving. 
         [0018]    The integrity check block  24  may also communicate with one or more of the video decoder  18  and the display via  30  via control lines  34   a  or  34   b.  In particular, the integrity check block  24  may institute a heartbeat check, where for example, the integrity check block  24  periodically sends out a signal with a counter to the video decoder  18  and/or display  28  and the component(s) sends back a signal incrementing the counter. The failure to receive the incremented signal within a predetermined period of time may indicate a failure of the component, prompting a suitable response such as blanking out the display  28  or generating an error message. 
         [0019]    In some embodiments the display  28  may operate off of a pixel memory, where the display periodically provides a pixel output corresponding to the contents of the corresponding pixel memory location. In such systems a risk exists that the display will display the contents of the pixel memory, even where there has been no change in quite some time. The pixel memory may be located in the video decoder  18 , in the display unit  28  itself, or in some other location. The integrity check block  24  may communicate directly with the pixel memory via the control lines  34   a  or  34   b  to conduct memory checks as may be provided by the memory circuits as known in the art per se. 
         [0020]    For redundancy purposes, a second integrity check block (not shown) may be provided in the display system  10  which receives the same inputs as the primary integrity check block  24  and provides parallel outputs. The second integrity check block may monitor the inputs and responses of the primary integrity check block  24  and signal a message to the central vehicle controller in the event the primary integrity check block  24  malfunctions. 
         [0021]    Those skilled in the art will understand that the video decoder  18 , integrity check block  24  and graphic overlay memory  32  may be provided on a single integrated circuit, for example, in a “system on chip” microcontroller, or provided utilizing multiple integrated circuits. In such embodiments integrity check block  24  may be a software routine running on the microcontroller. Similarly, those skilled in the art will appreciate that the integrity check circuit may operate directly on the analog or digital video signal prior to it being converted to pixel data by the video decoder. 
         [0022]    While the foregoing has described a particular embodiment(s) of the invention, it will be appreciated that modifications and variations may be made to the detailed embodiment(s) described herein without departing from the spirit of the invention.