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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?
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    $\begingroup$ Go to a car dealer and look at the price difference between a car with rear-view cameras and one without. That's a large part of your answer. Also, go to any less-developed nation and have a look at their cars. They can barely afford to fuel the cars, let alone replace a costly camera system when it fails. Mirrors are cheap and they work. $\endgroup$
    – grfrazee
    Mar 16, 2016 at 13:10
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    $\begingroup$ My first thought is fault tolerance. Every machine breaks eventually. What if a camera goes out while you're driving? What if the screen goes out? $\endgroup$
    – Devsman
    Mar 16, 2016 at 13:40
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    $\begingroup$ For starters, If I need to see just a hair further left when trying to assess my blind spot then I can just adjust my butt and and gain that additional sight. I am quite sure that it would be slightly more time-consuming to adjust a camera; odds are that car designers will be silly enough to actually implement the camera controls into the touchscreen interface of the car thus eliminating any level of tactile feedback. Also, with a normal mirror, if my kids are misbehaving in the back seat then I can adjust the mirror quickly to scold them. $\endgroup$
    – MonkeyZeus
    Mar 16, 2016 at 15:44
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    $\begingroup$ I work at Gentex, who has the majority market share in LCD (and other fancy) mirrors. I don't have the reputation to post an answer, but most of what you want to know can be found at Gentex.com - and there's the promo video at youtube.com/watch?v=CHSr0J_l8EY $\endgroup$
    – RoadieRich
    Mar 17, 2016 at 3:12
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    $\begingroup$ Car manufacturers are already trying this technology. However, traffic laws in about every country dictate that side and rear view mirrors should use mirrors. There's also the fear that adding technology increases the risk of something failing. I remember some car manufacturer, cannot remember the name, fixed this by using the typical mirroring glass you see in interrogation rooms. As long as the screen displays something, the glass lets it through, when the screen goes dark for some reason, it reflects like a side mirror would normally do. $\endgroup$
    – BlueCacti
    Mar 18, 2016 at 15:56

9 Answers 9

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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).

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    $\begingroup$ How is checking a camera display any different from checking your instrument cluster? You already need to change focus to verify speed/RPM/etc. For that matter, some cars these days actually have heads-up displays, a camera system instead of mirrors would integrate well with that. $\endgroup$
    – JAB
    Mar 16, 2016 at 13:48
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    $\begingroup$ (Hi Carl) I joined this community just to upvote this answer. Cameras see differently from eyes. Regarding focus, when a human is looking through a mirror, they can choose different objects to focus on in the field of view. A camera cannot read a driver's mind and focus on different objects as needed. Also, humans can move their heads around and extend the useful field of view in a mirror of a given size. When you look at a screen, all you get is what's on the screen. Backup cameras have a very distorted image to increase FoV. You just can't see as well with a camera for so many reasons. $\endgroup$
    – Todd Wilcox
    Mar 16, 2016 at 14:10
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    $\begingroup$ @JAB It's very different because you barely ever need to check the instrument cluster as you can easily guesstimate speed/RPMs based on other factors and you have a choice when to make such a reading - which you often don't when checking side mirrors. Furthermore, because you DO want to sometimes get that information without getting distracted, this is only more of an argument to keep gauges analog in presentation since they don't require nearly as much concentration to read off as compared to digitally presented info. $\endgroup$
    – A.S.
    Mar 16, 2016 at 15:03
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    $\begingroup$ @JAB: besides things like cruise control, you don't check speed as often as other traffic since you should be able to fairly well approximate the speed difference since the last time you checked. Also the information provided by the needle is usually small enough over a big fov that you barely have to adjust focus to see it well enough $\endgroup$
    – PlasmaHH
    Mar 16, 2016 at 18:41
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    $\begingroup$ Just a minor technical nitpick: your optical infinity is 15 metres plus, not 5. $\endgroup$
    – ArtOfCode
    Mar 16, 2016 at 22:56
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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.

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    $\begingroup$ Note that, especially in low-light conditions, very few cameras can achieve contrast ratios anywhere near that of the human eye. $\endgroup$
    – Dan Henderson
    Mar 17, 2016 at 17:30
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    $\begingroup$ On the other hand mirros have to be located where they can see both the driver and the subject of interest. Center mirrors require a clear path to the back of the vehicle to work which is not always available. Wing mirrors are easilly damaged and increase the effective width of the vehicle.. $\endgroup$
    – Peter Green
    Mar 17, 2016 at 21:59
  • $\begingroup$ @Peter Green: Is there something in your comment that I didn't cover in the answer? $\endgroup$
    – Adrian McCarthy
    Mar 17, 2016 at 22:33
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    $\begingroup$ @AdrianMcCarthy I don't see that your answer explicitly addresses either of the points Peter is making. You could reasonably expand your answer to incorporate the line-of-sight and vehicle footprint issues. $\endgroup$
    – Air
    Mar 18, 2016 at 17:43
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    $\begingroup$ @AdrianMcCarthy To an extent. I'd also join Peter and Air in arguing that line-of-sight and obstructed-view issues aren't the same as blind spots. A mirror will often have blind spots even when it has a clear sight line, while even full-coverage mirrors with no blind spots are useless if something obstructs the sightline. A camera view's sightlines consist entirely of eyeball-screen + camera-objects, which can be a major win especially over the center-mount rear view mirror's long, cluttered sightlines. $\endgroup$
    – FeRD
    Mar 21, 2016 at 14:32
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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.

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    $\begingroup$ I strongly disagree that these are the primary reasons. I'd really be surprised if mirrors are replaced, rather than augmented, by cameras. $\endgroup$
    – Carl Witthoft
    Mar 16, 2016 at 12:15
  • $\begingroup$ I would still regard the second point as a primary reason. Finding a proper replacement / augmentation for such a simple yet effecitve device is a major challenge in my opinion. And adressing your point regarding the focal distance. Isn't your typical mirror roughly the same distance away as a well placed display would be and you'd still have to change focus? Also you could place the display, HUD, whatever in the peripheral field of vision too. $\endgroup$
    – idkfa
    Mar 16, 2016 at 13:12
  • $\begingroup$ @idkfa thanks for the great explanation. I think we certainly can rely on electronics and cameras. We already are using so much electronics in the car and we trust it. This will be another piece of electronics which will be added. $\endgroup$
    – parag
    Mar 16, 2016 at 14:03
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    $\begingroup$ @idkfa Do not make the mistake of assuming that a mirror is a flat plane that you must focus on. A mirror reflects light. Think of it more as a window than a display. A mirror 3 feet from your face displaying a car 17 from the mirror actually requires your eyes to focus 20 feet away. $\endgroup$
    – Ogre Psalm33
    Mar 16, 2016 at 14:45
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    $\begingroup$ @OgrePsalm33: An important corrollary to the fact that a mirror's virtual image is behind the mirror (and the curvature of the mirror does result in a distance different than that of the real object) is that depth perception also works for the observer with stereo vision. This is perhaps more important than the eyestrain associated with focal length. $\endgroup$
    – Ben Voigt
    Mar 16, 2016 at 19:01
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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.

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    $\begingroup$ CRTs have the same problem. In fact, they have a much higher latency, due to the fact that their frames are much longer - a typical LCD is around 60 Hz, while a typical CRT is 24 Hz interlaced (half of the picture is refreshed every 1/12 of a second). This is easily seen when you aim the camera at your TV (though today it might be tricky finding an analog camera to use with an analog TV :)). LCD doesn't imply a digital connection, and a digital connection doesn't need to imply a higher latency compared to analog - you're still pushing a 2D image through a 1D line. $\endgroup$
    – Luaan
    Mar 16, 2016 at 16:56
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    $\begingroup$ Actually, it's mostly the opposite. An interlaced CRT has a field rate that's double the nominal frame rate (60 fields/second vs 30 frames/second, or 50 fields/second vs 25 frames/second). FILM traditionally has a framerate of 24FPS (though some TV shows from the 1990s... before affordable HD cameras existed, though everyone knew HD was coming... shot film at 30FPS or 25FPS. Star Trek: TNG and Friends are good examples of this). In theory, a LCD wouldn't have to have any more latency than a CRT... but in the real world, LCDs with common controllers add at least 1 or 2 frames of latency. $\endgroup$
    – Bitbang3r
    Mar 16, 2016 at 17:46
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    $\begingroup$ @Luaan, tell that to my 160 Hz CRT computer monitor. $\endgroup$
    – Mark
    Mar 16, 2016 at 21:56
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    $\begingroup$ Also, if someone is approaching you at your speed + 60mph, it will be damn hard to estimate the distance with 1m precision even through a regular mirror. $\endgroup$
    – Dmitry Grigoryev
    Mar 17, 2016 at 9:44
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    $\begingroup$ @Luaan First, the warning is actually the opposite of what you say: objects in the mirror are closer than they appear. And second, that warning is there exactly because car mirrors are not flat. How would a flat mirror make object appear further away? $\endgroup$
    – Dmitry Grigoryev
    Mar 17, 2016 at 9:48
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Cameras are used as rear-view mirrors, simply not in mainstream passenger cars. For example, here's how rear-view is done in tramways: enter image description here

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.

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    $\begingroup$ I remember that one time I was driving a tram and had to abruptly change lanes... $\endgroup$
    – A.S.
    Mar 17, 2016 at 15:19
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    $\begingroup$ @A.S. Do you remember the time when you were about to close the doors and saw a kid sticking his head out? $\endgroup$
    – Dmitry Grigoryev
    Mar 17, 2016 at 15:21
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    $\begingroup$ Good example, but it only underscores fundamental differences in how mirrors are used in cars vs trams. I see cameras instead of mirrors being advantageous for trams, but not for cars. $\endgroup$
    – A.S.
    Mar 17, 2016 at 15:26
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    $\begingroup$ @ Yep, I totally agree. Cars don't really need IR vision, and trams' price isn't affected by extra couple of thousands anyway. $\endgroup$
    – Dmitry Grigoryev
    Mar 17, 2016 at 15:40
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    $\begingroup$ @a.s. agreed. this does highlight some differences between cars and trams, but the question asks specifically about cars. trams are a completely different use case with their own sets of requirements and shouldn't really be compared to cars... it is not very feasible/practical to put a chain of (potentially articulating) mirrors to try to see out the back... I would downvote this answer if I could simply because it is off-topic $\endgroup$
    – agent provocateur
    Mar 17, 2016 at 20:13
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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.

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  • $\begingroup$ The link provided by @idkfa will provide great information than other incorrect answers which are unnecessarily upvoted. $\endgroup$
    – parag
    Mar 16, 2016 at 17:25
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    $\begingroup$ @parag personally i dont like that article because it states nothing concrete. just states how certain manufacturers would like to change the laws, but theres no timeline or state of progress or likelihood. What is concrete is the law and the reasons for making the law the way it is, which is mainly determined by safety factors. Safety comes first, THEN optional nice to haves (like being able to use a camera and display). $\endgroup$
    – agent provocateur
    Mar 16, 2016 at 18:52
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    $\begingroup$ I would expect that the law will change to no longer require physical mirrors, conditional upon the car being driven by a computer. $\endgroup$
    – gerrit
    Mar 16, 2016 at 19:55
  • $\begingroup$ @gerrit thats if "being driven by a computer" is safety tested and approved over years of testing. once (if) that happens, that will open the "gate" to many potential electronically controlled upgrades such as cameras/displays etc. since a computer driven car is much more advanced and most likely has many more modes of failure, i personally feel that if we even get close to approving computer driven cars, we will most likely already have the other things, like camera/display replacements, approved (or close to being approved). $\endgroup$
    – agent provocateur
    Mar 16, 2016 at 20:15
  • $\begingroup$ Your assertion that the driver can always control the car "in the event of any failure in the system controls or electronic components" is wrong. For example, there is a failure mode for the ABS/ESC system where the computer can command the valves to isolate all brakes from the master brake cylinder and possibly even release all pressure from the brakes. This results in a "hard" braking pedal and total loss of control over the brakes. $\endgroup$
    – dasdingonesin
    Apr 1, 2016 at 8:43
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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.

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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.

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

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