How Rearview Cameras Work

Rearview cameras are like having eyes in the back of your head. These small devices, usually the size of a nickel, are mounted on the exterior of a vehicle and provide real-time video pictures of whatever is happening outside your car. Some rearview camera systems incorporate backup sensors, which aid in drivers' awareness of objects behind their vehicle.

Engineers designed the first rearview cameras to fight blind spots. As far back as the late 1970s, large construction vehicles such as dump trucks and heavy mining equipment including dozers and scrapers began placing cameras on the back of the equipment to help operators with rear vision. Because the tractors and dump trucks used on strip mines are so large, and the mines themselves are so vast of a work area, rear visibility is limited, so operators couldn't see behind them when they needed to back up. This was especially true for the dump trucks and large bulldozers, as they frequently needed to reverse direction during a typical work day. To combat the lack of rear visibility, mechanics installed tiny cameras and connected them to a small monitor. Since some of the vehicles used on strip mines had no rear visibility, the makeshift cameras proved a valuable safety measure.

Lester Lefkowitz/Getty Images
If that giant dump truck in the mining facility doesn't have a rearview camera, that little truck behind it is in trouble.

As the need to improve safety in the mining industry grew and more contractors began retrofitting aftermarket camera systems, companies like Caterpillar responded. The WAVS onboard rearview camera system found on Caterpillar tractors and off-highway trucks offers one or two cameras used for rear viewing. Take a 797B mining truck. Measuring 21.5 feet (6.5 meters) tall, 47 feet (14.3 meters) long and 32 feet (9.7 meters) wide, it would be virtually impossible to see a small pickup directly behind the vehicle. As a result, Caterpillar employs the single- or dual-camera system in place of a rearview mirror, which isn't feasible in such a large vehicle. These trucks have dump beds blocking all rear visibility, much as a camper shell obstructs the rear view in a pickup truck.

Auto manufacturers have followed the lead of construction and mining equipment companies and now offer rearview cameras similar to the one seen on the Infiniti EX35. While Infiniti's AVM system boasts a 360-degree view, most rearview cameras found in the auto industry display only what's behind the vehicle. Just about every manufacturer, from Lexus to Chevrolet to Dodge with the iconic Caravan, offers a rearview camera system on one or more of their vehicles.

Several other safety features complement rearview cameras, such as backup sensors, which sound off with proximity alarms. Have you ever been sitting at home and heard a truck beeping as it backed up? Those are backup alarms alerting people outside the vehicle. Similar technology has made its way into the cars we drive, and rearview cameras look to be gaining in popularity, especially as vehicles grow larger. Read on to learn more about Infiniti's 360-degree camera system and how the cameras on other vehicles produce the images we see in the car.

We started by briefly describing the full-view camera in the Infiniti EX35, so let's take a closer look at it. If you understand Infiniti's system, you should have a good idea of how similar technologies across various manufacturers operate.

First off, rearview cameras actually capture images that are the opposite of what you really see on the display. What you see is a mirrored image with the video feed reversed so you have the proper orientation when you look at the LCD display. If you were to back up your vehicle based on the raw images from a rearview camera, you would mistakenly turn left to avoid an obstacle on the right side.

Photo courtesy Nissan
The interior of the 2008 Infiniti EX

As mentioned earlier, the Infiniti uses four tiny cameras with fish-eye (or wide-angle) lenses. These devices are placed on all four sides of the car: One sits above the left side of the license plate, another inside the Infiniti logo on the front grill and the remaining two fit beneath each side mirror. The cameras record raw digital footage, and software electronically straightens the images through electronic interpolation or pixel enhancement. In the EX35, the result is a real-time overhead (or bird's-eye) view of the vehicle.

Cameras like the Infiniti's use fish-eye lenses because they can capture a wider field of view at a much closer proximity. The problems associated with fish-eye lenses are the characteristic bending or image distortion due to the curvature of the lens. Fortunately, CCD sensors create high-quality images, and digital-imaging software can manipulate and flip the images, so that what drivers see is a perfectly clear picture. To learn more about how CCD sensors transform what the camera sees into digitally displayed images, read How Digital Cameras Work.

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This image typifies what a rearview camera with a fish-eye lens might capture before the image distortion is corrected.

The majority of rearview cameras found on vehicles today are hardwired systems powered by the car's battery, and digital images travel through the cables to the LCD display. Virtually all rearview cameras and screens activate when the driver puts the car in reverse.

One of the coolest rearview cameras can be found in several Toyota models, including the 4Runner. Instead of using a large LCD screen in or around the dashboard, a small display is mounted in the rearview mirror itself and activates either when the vehicle is placed in reverse or when the driver turns it on manually. Cameras in vehicles with only a rearview system are typically located somewhere near the license plate.

Again, factory-installed rearview camera systems are hardwired and reliable, but not every one operates the same. Some aftermarket systems are wireless and can be installed quickly by you or an experienced installer. In the next section, we'll look at aftermarket rearview cameras and get an idea of what you could expect to pay for a decent one.

If you walk into any car dealer nowadays, more than likely you'd be able to outfit certain vehicles with a rearview camera system. For example, Chevrolet and Ford offer cameras on their larger vehicles such as the Suburban and Expedition. If you'd like to retrofit your vehicle with a rearview system, you have plenty of choices.

Several reputable organizations have tested various aftermarket rearview camera systems. Consumer Reports conducted a recent study and found nothing lived up to a factory-installed unit; however, some aftermarket models came close. For example, the Hitchcam VideoMirror retails for about $800 and resembles the rearview cameras found in the Toyota 4Runner. Instead of using a monitor, the Hitchcam is a replacement mirror with the display built in. Consumer Reports compared the Chevrolet Suburban camera system with Hitchcam's technology and found the following:

[­source: Consumer Reports]

What does that mean? If you stood 5 feet (1.5 meters) away from the center of the vehicle's rear bumper, the Chevy Suburban camera could see you and about 9 feet (2.7 meters) to the left of you and 9 feet to the right of you. It wouldn't be able to see all of you though, unless you stand less than 3.8 feet (1.1 meters) tall.

Now let's talk about that third measurement Consumer Reports includes. Think of an object about 6 inches (15.2 centimeters) tall, like a pen. If you drew a line down from the Suburban's rear bumper to the ground and then extended that line on the ground, 11.5 inches away from the bumper, that's when the Suburban camera could spot that pen if it were somehow standing up. These are some good measurements to keep in mind when evaluating rearview camera systems.

The Hitchcam isn't your only aftermarket option. The Visor View V-V-VCLP2 works the same way and uses a small LCD monitor that clips onto the sun visor. At a cost of $389, the Visor View system is less expensive than the first two models, but installation is pricey as only professional installation is recommended.

CNET reviewed another popular system on the market -- the VR3 VRBCS300W -- which uses 2.4 gigahertz wireless technology. The camera is mounted on the rear of the vehicle and transmits a wireless signal to the display. The VR3 is cost-effective at $150, and anyone can mount the lens and monitor, eliminating installation fees. However the wireless technology isn't stable, and the display can be choppy due to interference from closed circuit TV systems, wireless routers and other electrical equipment. Drivers may also have a hard time judging distance as the fish-eye lens doesn't have a processor to clean up the images like the Infiniti AVM system does.

These are but a few of the options on the market today. Backup sensors are a more cost-effective alternative and offer similar safety features as rearview cameras without the hefty price tag. While sensors don't show you what's behind your vehicle, they do help when parking or backing up. As we'll see in the next section, backup sensors can be very useful, especially in an area with lots of children. Aimed at trucks and SUVs, the Dolphin Sonarstep beeps a warning and visually catches the driver's attention with warning lights that flash as the vehicle approaches an object.

Perhaps shelling out several hundred or several thousands of dollars for a good rearview camera system is out of your range. It may just be a good idea to get a backup sensor, especially if you have a larger vehicle with blind spots. Either way, it may soon be something everyone must consider. Keep reading to find out why.

The U.S. National Highway Traffic Safety Administration estimates more than 180 fatalities occur each year as a result of back-over accidents, often with a parent or close relative behind the wheel. The majority of the deaths are children ages 12-23 months, prompting many activists to seek ways of limiting fatal accidents. In a one-month period alone during 2006, 15 recorded back-over fatalities occurred, with 12 coming at the hands of a relative [Kids and Cars].

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Rearview cameras may replace review mirrors in the U.S. if the Cameron Gulbransen Kids and Cars Safety Act passes.

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As a result, rearview cameras may soon become a staple on every vehicle. Prominent politicians such as Sen. Hillary Clinton (D-N.Y.) have lobbied heavily to mandate rearview cameras in all cars. Clinton, along with Sen. John Sununu (R-N.H.), introduced the Cameron Gulbransen Kids and Cars Safety Act, which would effectively mandate rearview cameras in cars by 2010, in 2005 and again in 2007. The bill has been shelved for later discussion.

The costs of installing such cameras may be more than consumers can bear. Depending on the manufacturer, backup and rearview camera systems can range from $455 on a 2008 Ford Expedition to $7,850 for the package on a Mercedes-Benz R350 [source: Wall Street Journal]. In the case of the R350, Mercedes-Benz adds a bundle of options and corners consumers into having to buy some things they may not desire just to get something they do.

To read more about rearview cameras and related topics, including a list of car manufacturers that offer them in their lineups, check out the links on the next page.