HEAD UP DISPLAY WITH NIGHT VISION
FIELD OF THE INVENTION 5
This invention relates to a night vision enhancement system for motor vehicles and particularly to such a system incorporating head up display technology.
BACKGROUND OF THE INVENTION 10
It has often been proposed to use infrared cameras to produce images of a roadway revealing warm objects such as humans, animals or other sources of infrared radiation. This has the advantage of detecting such objects at night particularly if they are beyond the range of vehicle lights. Such systems have typically used a video monitor or the like to display the detected objects. A traditional monitor is bulky and difficult to locate in a convenient place for viewing, and requires 2Q the operator to look away from the roadway to observe the infrared image. The image would be quite small relative to the real roadway scene so that there could be some difficulty in accurately judging the distances of the objects being displayed. Thus if an object is not 25 visible in the real scene, it is hard to determine its location.
It is also known to employ head up display techniques to project instrument images or vehicle parameter data onto the vehicle windshield or other combiner so that 30 the display is in or immediately adjacent to the operator's line of sight. Such displays have been quite small relative to the roadway scene due to the limited space available for the required image source and projection mirrors. 35
SUMMARY OF THE INVENTION
It is therefore an object of the invention to enhance night vision by infrared imaging in the line of sight of a vehicle operator. Another object is to display object 49 images from an infrared source which have a one to one ratio with real objects observed by the operator.
The invention is carried out by an infrared sensor or camera mounted on a vehicle to view the roadway in front of the vehicle and generate a video signal repre- 45 senting the thermal image of the roadway, a video processor for improving characteristics of the video signal, and a head up display (HUD) having a video display responsive to the video signal, and an aspheric mirror for reflecting the display image onto the vehicle wind- 50 shield or other combiner so that the vehicle operator can view a virtual image of the display image which appears to be in front of the vehicle. The optical parameters of the camera and of the HUD are chosen to provide a 1:1 ratio of the image and the real scene observed 55 by the operator.
By placing the image directly in the operator's field of view the image can be superimposed on the real scene. Then the warm objects in front of the vehicle will be highlighted if they are illuminated by the head- 60 light beam, and they will be displayed in proper relationship to illuminated objects even if they are beyond the range of the lights. Alternatively, the image is directed a few degrees below the primary field of view so that the infrared image appears just below the real 65 scene. The latter approach is easier since no image registration is necessary as it is for the superimposed images. Still, by virtue of the 1:1 image ratio, the real
position of a warm object shown in the HUD display is readily determined.
In the infrared camera, due to the high cost of lenses suitable for infrared, focusing mirrors are used for the camera optics, and these tend to introduce image distortion. In one design, for example, otherwise horizontal lines tend to droop at both ends to produce a "frown effect". The aspheric mirror is designed to correct for that distortion. The aspheric mirror has previously been used to compensate for distortion due to windshield curvature, each style of windshield requiring a custom designed mirror. In this system, the aspheric mirror design must take into account the camera distortion as well as the windshield distortion.
The video processor can be set to an "object detect" mode, if desired, to select only the signals from the warmest objects so that those objects will be displayed and other background objects will be suppressed. This will attract the operator's attention to the warmest objects which are generally the most important ones to be made aware By operator selection, however, a full contrast mode can be employed to display all the infrared information.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other advantages of the invention will become more apparent from the following description taken in conjunction with the accompanying drawings wherein like references refer to like parts and wherein:
FIG. 1 is a schematic view of a night vision enhancement system mounted in a vehicle according to the invention;
FIG. 2 is the display portion of the system of FIG. 1;
FIG. 3 is a top view of a roadway scene showing an infrared camera view of the scene;
FIGS. 4 and 5 are illustrations of operator views of night vision enhancement display for two different display configurations;
FIG. 6 is a block diagram of a camera and display portion of the system according to the invention; and
FIG. 7 is a graph of video signals according to selectable modes of operation.
DESCRIPTION OF THE INVENTION
Referring to FIGS. 1 and 2, a vehicle 10 is equipped with night vision apparatus comprising a front-mounted infrared camera 12 or sensor which has a standard RS170 video output signal, a video processor 14 connected to the camera 12 output, and a head up display (HUD) system 16 including an image source or display 18 connected to the video processor output, and an aspheric mirror 20 which reflects the display image to the vehicle windshield 22, creating a virtual image 23 for viewing by the vehicle operator 24. The display 18 recreates the image in shades of gray. A separate combiner may be used instead of the windshield. The HUD 16 is installed beneath the vehicle dash 26 which has an upper opening for light passage to the windshield.
The infrared camera 12 preferably has a field of view of about 12 degrees or more horizontally and a smaller vertical field in the range of 6-9 degrees. While a camera having a wider angle may be used, only the image portion within the prescribed angle should be displayed for optimum effect. The horizontal view of the camera is illustrated in FIG. 3 which depicts the vehicle on a two lane roadway. The limit of the headlight range is indicated by the dashed line 28. A first person 30 is shown in the lane of the vehicle within the headlight