Why do cars have mirrors for rear view rather than cameras?

Question

Despite having so much technological advancement, I wonder why cars still uses mirrors (right and left side of the driver) for the rear view. These mirrors can be easily replaced by cameras and monitors (display for the driver). I noticed such technology exists but it is restricted to only when you take the car in the reverse direction. If we use this technology while driving the car (i.e. in forward direction), I believe it will be helpful for the driver since multiple cameras installed on the rear side of the car will give consolidated view to the driver. Also it will save the hassle of monitoring both the mirrors while driving. I think this will have two benefits:

1. Since the mirrors will be replaced by cameras, it will reduce the wind resistance for car.

2. Weight of the car will be reduced negligibly assuming electronic circuits will be lighter than mirrors.

   So, my questions are

   1. Why cameras (and obviously displays) are not used instead of mirrors?
   2. Does such technology exist? If it exists then why it is not widely used?

Answer 1

This is another case of fancy new (SHINY!!!) technology being A Bad Idea(TM) . When you're driving, your eyes are focussed roughly at infinity, i.e. looking at objects more than 5 m away. When you look at a rear view mirror, you are still looking at distant objects.

But when you look at a camera display, you're focussing on the image screen, which is probably 30 cm away. This means you need to constantly change focus to be able to look ahead and check the rear view monitor. Not only is this physically exhausting for your eyes, it leads to a significant time period when you're not focussed on either area.

Cameras for backing up, which (I hope) happens only at very slow speeds, may be helpful. Blind spot coverage is generally an assistive system which does not provide direct view (just warning lights or sounds).

Answer 2

We still use mirrors because:

• A mirror is cheap, simple, passive technology that works. Pretty much the only failure mode is it breaking on impact. (Though I have had a center rearview mirror fall once because the adhesive that held it to the windshield failed.) Camera and screens are more expensive, more complex, active devices. There are many more failure modes.

• A mirror allows you to observe with binocular vision, preserving 3D clues, like parallax. A camera projects a single-viewpoint onto a screen giving a 2D projection.

• A mirror allows you to see more by slightly shifting your viewing position.

• A mirror has much better contrast, color, and resolution than any camera and screen combo.

• A mirror has effectively zero latency. A camera and screen has a lag on the order of tens of milliseconds, which could conceivably make a difference in an emergency situation.

Camera and screens (with good processing) could give many advantages:

• They could completely eliminate the glare of headlights or a low sun while still preserving contrast.

• They could improve the aerodynamics of the car.

• They could improve night vision by shifting infra-red spectrum into the visible range.

• They could completely eliminate blind spots, even while allowing for radically different car shapes that might prove more aerodynamic or cheaper to manufacture.

ETA: Backup cameras haven't stopped drivers from backing into stuff. This is only tangentially relevant because backup cameras are for backing up but mirrors serve many other purposes.

Answer 3

The industry is already going down that path for the exact reasons you mentioned. There is an article that provides information about that.

In summary the main reasons why we don't have it yet are

1. State laws require mirrors and would have to change first
2. Conventional mirrors are basically fail safe, imagine the camera system turning off on the motor way. The new systems have to match a mirror in terms of reliability and safety. Electronics can be manipulated, have a latency etc.
3. Price point, conventional mirrors are pretty cheap and cars with cameras are not the basic configuration. Many people simply can't afford cars with expensive extras.

Mercedes Benz for example has some really nice safety features that use cameras already. 360 ° bird's eye parking assistance. Collision detection features that check your dead angle and if it is unsafe to change lanes a little red triangle lights up in your side mirror. Followed by acoustic warnings if you still try to change lanes up to point where the car brakes on side to put you back in your original lane. You even have active lane tracking already.

Technology is there already, we only adapt slowly to the change. It's the same with everything else, it takes years before new technology really reaches the rank and file.

Answer 4

Digital camera systems with LCD screens impose latency of at least a frame on the images. Fine for slow moving parking cameras, maybe a problem at speed. An object moving at 60mph shown through a 30fps camera with a latency of 1 frame is 1m away from where it appears to be.

(CRT screens with analog TV cameras that have no digital in the signal path are pretty much the only way to avoid this, which would be an absurdly bulky system.)

Getting the screen brightness right could be a problem when driving at night. The brightness and contrast needs to be roughly the same as ambient, otherwise having a bright rearview mirror would be a distraction. Whereas a mirror shows the same ambient illumination level as looking forwards through the windscreen.

FoV and distortion could also be a problem. Objects would appear differently. This has a potential benefit - the elimination of the blind spot - but would require relearning.

Note on focusing: when you focus on an object in a mirror, you're focusing at the apparent distance, not the distance of the mirror. So for a mirror 1m away from your eyes looking at a car 20m behind the mirror, you're focusing at 21m. This is not true for screens.

Answer 5

Cameras are used as rear-view mirrors, simply not in mainstream passenger cars. For example, here's how rear-view is done in tramways:

Aside from improved wind resistance which you mentioned, cameras allow to cut maintenance costs. Vehicles without external mirrors can be easily washed by automated washing stations. On older tramways with mirrors, the cabin often has to be washed manually.

Another important aspect is the IR sensitivity, which allows to use cameras in the dark, where mirrors would be inefficient.

To sum it up, it is indeed possible to replace car mirrors with cameras, but this is not done for practical reasons.

Answer 6

All the points mentioned by others are factors, but the true answer (i believe) is:

Why cameras (and obviously displays) are not used instead of mirrors?

The law (regulations on street automobiles) states that you need mirrors.

The law will most likely not change to exclude physical mirrors because:
like power brakes and power steering systems, it is a requirement that a physical connection is always available to actuate the brakes and steering in the case of any electronic or component failure for safety reasons. It must be a power "assist", in that it can only "assist" the existing mechanical connection to make it easier on the driver to actuate, not replace it completely.
In the event of any failure in the system controls or electronic components, the driver still has the ability to actuate the brakes and steering (albeit requiring much more effort than before).

So basically: the cameras and display are the electronic "assist" and the mirrors are the fail-safe physical devices.

When it comes to law, safety always comes first, then the optional nice-to-haves can have consideration like cameras and displays or power assisted systems.

Does such technology exist? If it exists then why it is not widely used?

Technology definitely exists but durability and reliability (at consumer-level cost effectiveness) is where we are still struggling. Especially for automotive use, which means day-to-day relatively harsh conditions. It takes years to test new systems and approve them for use on automobiles.
Usually when human lives are at risk, we have double or triple redundant systems depending on severity. The physical mirror serves as a (manual) redundant system.

Answer 7

Replacing all car mirrors with cameras is not a good idea. All it does is add unnecessary cost to a vehicle, and the cameras would actually not be quite as good as a standard mirror.

The existing automobile mirrors do their jobs quite well. They require zero electricity to operate, and they work when the vehicle is completely powered off. Mirrors are also very resistant to normal wear and tear. They don't break down, display erroneous images, and they even work somewhat when they are broken.

On the other hand, cameras and their corresponding screens are far more inferior to a standard mirror. They are much more easily subjected to damage. In a vehicle, the sensitive electronics can fail over time due to stresses such as constant vibrations. Connections can come loose, etc. Using cameras can be somewhat disorienting. The screens would not typically be in a convenient, or logical place. It could be hazardous because the driver would be looking at a screen in the cockpit instead of looking around the car, and get a false sense of security. Anyone that has a backup camera knows that the camera becomes useless if it is at all obstructed. A small speck of dirt is all it takes to effectively block the view. The biggest drawback of cameras is that they do not operate at all when the vehicle is powered off. When a vehicle is parked in a city, typically the driver checks their mirror to make sure it is safe to exit the vehicle. If the vehicle is parked, and turned off, then they would lose the ability to check for traffic and could result in injury or the loss of life.

Cameras are great for certain purposes. The backup camera is very useful because it allows you to see objects which are not visible from standard mirrors. It lets you see how much room is behind you and is very useful when parking, and also attaching trailers. I could see other uses for cameras on vehicles such as on big trucks. Tractor trailers especially, have very large blind spots. The biggest blind spot is on the passenger side which is sometimes called the "no zone". When vehicles pass trucks on the right, usually the driver cannot see where they are. The addition of cameras would help to greatly reduce the number of blind spots, and could result in the reduction of accidents.

Answer 8

To put it simply the use of camera's will work for 99% of the time but they can still fail in certain scenarios (i.e. extreme weather, malfunction, object blocking/obstructing camera, etc) whereas mirrors can be used in any situation furthermore they reduce the level of distraction.

Answer 9

Aside from other good reasons already mentionned : Because the eye & brain have a better dynamic range than most mainstream cameras