Night-vision drives back the dark

While less than a third of driving is done at night, just over half of all accidents occur in the dark. The night hides hazards, induces eye sensitivity to glare from oncoming headlights, and reduces visual acuity in drivers older than 40. And reduced visibility in precipitation is often accompanied by slick road conditions.

Penetrating such vision cloaks "is now past the technical feasibility," according to a design engineering manager at one of the companies developing night-vision systems. He adds, "The technology is proven. The next step is to commercialize it." Cost, human factors, and marketing may dictate when and in what form night vision is on your next car, with the turn of the century most often mentioned for availability.

Continental drift. European designers have taken the lead in night-vision development. Impetus comes from the Program for European Traffic with Highest Efficiency and Unprecedented Safety (PROMETHEUS) fostered by the European Union (EU). Driven by the relaxation of border regulations within the EU, which will increase traffic, the program seeks improvements in traffic flow "harmonization," safety, and transportation management. Night vision comes under safety and hinges on four key technologies: sensors, processing, displays, and illuminators. Sensors not only include vision enhancements but radar and electro-optics for collision avoidance and blind-spot warning; processing goes beyond image processing and includes object recognition by contrast or edge enhancement.

While sensors are the key to night vision, image processing must efficiently present objects to a driver in a recognizable form. For example, a sensor with 256 gray-scale levels might drive a display limited to 20 to 30 levels--data compression must maintain object definition.

Jaguar's Night Vision System (NVS) functions in the near IR (NIR) using conventional high-beam lamps, suitably filtered, for illumination. A 680 (500-pixel charge-coupled device (CCD) monochrome digital camera from the European subsidiary of Raytheon TI Systems, formerly Texas Instruments (Dallas, TX), mounted over the driver's head furnishes a nearly drivers-eye view ahead. Pilkington Optronics (Glasgow, Scotland) used its military head-up display (HUD) experience to produce the car's display on the windshield, superimposed over the driver's field of view. The image is focused just in front of the vehicle to minimize eye refocusing. Cranfield University (Cranfield, England) provides signal processing.

With roughly half of the lamp's available energy invisible to the eye, sufficient near-IR lighting allows the camera to form an image. The CCD-camera circuitry prevents "blooming" (spilling of energy from brightly illuminated pixels onto neighboring cells for a glare effect)--important for compatibility with oncoming NVS-equipped vehicles. There is also a "motion-smear" subtraction feature. Intuitive to operate, the system furnishes the driver's primary view of the road with backup provided by normal vehicle headlights. Trials have shown detection of pedestrians at two to four times the normal range, depending on the driver.

Jaguar’s night-vision system uses a camera within the passenger cabin to produce an infrared-illuminated eye-level view of the road, which is superimposed over the driver’s field of view on the windshield. A signal processor controlling the illumination lamps and CCD camera helps optimize the display image.

The digital signal processor (DSP) image-enhancement function analyzes the image intensity and ambient lighting to optimize the picture presented to the driver. Speed of this computation along with frame update rate are important for creating a system that feels natural to the driver. "DSP allows more complex and robust weighted functions to be used," compared to a microcontroller, says Paul Mulvanny a principal technical specialist with Jaguar, Coventry, England. Operations also include feature extraction so that road markers and edges, vehicles, and other objects are sufficiently distinct.

Delco Electronics' (Kokomo, IN) safety, security, and communications (SSC) concept-demonstrator vehicle features the Nightdriver^TM night-vision system developed jointly by the company and Raytheon TI Systems European operation. The former furnished the wide-angle Eyecue^TM HUD, and the latter provided the thermal imager and systems integration. Working in the far-IR, the system is passive, sensing temperature differences between objects in its view, eliminating separate illuminators. Because the system detects only heat, ambient light or oncoming headlights do not induce glare in the image. Nightdriver wavelengths also penetrate dust, fog, and precipitation to some extent. Effectiveness of the system was born out last November when off-road racer Rod Hall's team won the Baja 1000 using Nightdriver units to see not only in the dark but through natural and competitors' dust as well. Hall says the system allowed his son Chad's Hummer to "follow the course landmarks while maintaining his speed of 90 miles per hour."

Initial versions of the Delco Electronics EyeCueTM head-up display provide symbolic and digital vehicle information below the driver’s line of sight on the windshields of some Buick and Pontiac models. A wider-angle version was required to display images for the SSC vehicle’s NightdriverTM thermal night-vision system.

Delco sees the system as a driver aid and not the primary means of looking ahead. The image is projected on the windshield below the driver's line of sight where it can be glanced at to identify objects ahead. On the SSC, the camera is in the grill, along the driver's centerline. Such alignment is needed, according to Ross Olney, former Delco SSC program manager, to present an instinctive image for driver interpretation. "You wouldn't want the camera on the right and the driver on the left. In the vertical it's not as critical," he says, which can also be adjusted to the optimal viewing position via a tiltable mirror in the HUD. Physics precluded an in-the-cabin installation--the far-IR wavelengths don't penetrate auto glass. But the camera's pricy IR-transparent germanium lens could be a roadblock to commercialization.

HUDs up. Developing a large-diameter HUD (for the necessary viewing angles) and stuffing it into the dash panel was a design challenge according to both Delco and Jaguar. "It's pretty busy on the centerline," says Delco's Olney, who's proud of fitting in "the largest viewing-angle HUD for night-vision use." The EyeCue HUD can also display digital or symbolic information that, due to LCD image generation, can be reconfigured by the driver as needed, rather than use set icons in fixed positions.

A HUD keeps a driver's night scan out the windshield; more of a daytime pattern is obtained. A large "eye-box" HUD permits viewing over a wide range of natural head movements, giving a comfortable, natural feel. Use of LCDs rather than CRTs, injection-molded rather than optical-glass aspheric lenses, holographic narrow-band reflective optics, and enhanced optical coatings have large HUD cost and size.

While automobile night vision is poised for the mass market, it remains to be seen if initial use in luxury models can spur wider driver interest leading to increased production and lower prices. "It is envisaged the initial price will equate to that of a good quality in-car audio system," says Jaguar's Mulvanny. One factor not usually present in acceptance of new technology: peak interest is coming from numerous, and more affluent, older drivers whose night vision would reap the greatest benefit.

What night-vision means to you:

Enhancement of fleet, industrial, and commercial driving applications.

• Emergency response for search-and-rescue and brush-fire detection.

• Law enforcement surveillance and border patrol uses.

Get me on your wavelength

Several wavebands outside the visible spectrum of 400 to 700 nm are potentially useable for night vision, with object detection often hinging on illumination levels and atmospheric conditions. "A vision-enhancement sensor must produce an output which ultimately allows a driver to recognize objects with minimal or no [training] experience," according Jaguar's Paul Mulvanny. Thus radar would not be suitable--a high degree of data processing would be needed to present a pseudo-visual display. And image intensification (high amplification of minute amounts of light) is subject to blooming when viewing an intense light source.

"The responsibility for determining an object type, range, and bearing must remain the task of the driver. It is for this reason that wavebands close to the visible have been chosen," says Mulvanny. Using the UV band (below 400 nm) produces photoluminescence where visible light is emitted when an object is "painted" by UV light--no image detector, other than the Mk. 1 eyeball, is required, and other drivers would see the objects as well. But ultraviolet headlights are needed, which must be filtered to cut out harmful UV as well as visible red emissions, and not all objects are photoluminescent. And while UV is low-cost for individual vehicles, appropriate road signs and markings would be needed for maximum benefit.

Jaguar's night-vision system works in the near-IR (800 to 1,000 nm or 1µm) and requires an illuminator and camera for detection. Fortunately, the spectral response of a typical charge-coupled device (CCD) camera and the output of a tungsten headlight suitably filtered match quite well around 800 nm. The filtered high-beam lamp used in Jaguar's night vision provides a detection range somewhat farther than high-beam lighting (while not blinding oncoming drivers) with good object resolution and depth perception. Precipitation can cut down on range, much like visible wavelengths, but enhanced contrast remains for object recognition.

Thermal imagers in the mid- and far-IR (3 to 5 µm and 8 to 13 µm, respectively) need no illumination because they detect heat given off by objects and can see to longer ranges than near-IR devices. Mid-IR is better suited to hotter objects such as engine exhaust temperatures, whereas longer-wavelength far-IR emissions are common to objects in the everyday (or everynight) environment, particularly pedestrians. The latter is the basis of the system Delco Electronics has developed in its experimental SSC vehicle for GM. Temperature differences within a scene govern object resolution and depend on time since sunset, object emissivity, atmospheric water content, and whether weather wets the scene.