Home » Digital Rearview Mirrors Are Garbage And I Can Explain Why With Science

Digital Rearview Mirrors Are Garbage And I Can Explain Why With Science

Mir Top

There are some things that sound great on paper, but in practice are awful, just awful. Things like, say, a popsicle made of chowder or a genetically-engineered flying chihuahua. When it comes to cars, I think one of the best examples of this concept is the inside rearview mirror that is actually an LCD screen connected to a camera. In principle, these should be terrific. But I hate using them. Why? What makes them so awful? To figure it out, I had to reach out to a scientist who studies visual cognition.

Are you familiar with these sorts of digital rearview mirrors? They’ve been around for a few years, and they seem to offer a lot of benefits: because the “mirror” (again, it’s not really a mirror at all, it’s a screen in the shape and location of a traditional inside mirror) is fed via a camera mounted at the rear of the car, nothing inside the car – passengers heads, luggage, pillars, errant balloons, whatever – can block your rear vision.

Also, the camera can provide a wider field of view, and prevents getting dazzled when someone has their brights on behind you. Here, I’ll let Toyota try and explain why these should be great:

I just tried one out myself in the 2023 Toyota Sequoia, and while the technology itself was impressive and well-executed, actually using the screen-mirror for its intended purpose was awful, almost literally unusable. It’s terrible.

(I should mention that while my examples here are from Toyota, this is not a Toyota-only thing. Other carmakers have these, and there’s aftermarket options as well.)

It’s terrible in an unusual way, too, in that there’s nothing actually wrong with the design or execution, it seems to be terrible in concept. I wasn’t exactly sure why, but I had some suspicions. I also wasn’t sure if maybe there was just something wrong with me, but I asked a couple other Toyota reps (whom I won’t name, of course) and got confirmation that I’m not alone in finding these digital mirrors unusable.

Mir 1

Part of what seemed to be going on had to do with my own particular vision situation. Ever since I made the decision to Become Old, which happened a few years ago in my late 40s, my once-perfect-vision eyeballs decided they’d help my more mature look by suddenly refusing to be able to see anything close to my head.

This is known as presbyopiaand happens to pretty much everybody, so all you beautiful, sexy young readers out there holding your phones inches from your gorgeous, clear, vivid eyes can just fuck right off, because it’ll happen to you, too, and then you’ll be having to get used to yourself in glasses just like I did.

Anyway, because this condition only really affects your close-up vision, I don’t wear glasses to drive, as my distance vision is fine, and I just deal with the fact that my dash instruments are a bit blurry. But, significantly, when I drive and look in my conventional rearview mirror, inches from my face, the images reflected in that mirror do not look blurry. They look as clear as any of the other distant cars through the windshield look.

But when I look at the digital rearview mirror’s screen, it’s blurry as hell. It’s the same distance as a normal mirror, so what’s going on, here? And, even with my glasses on, I can see the screen-mirror image clearly, but it still feels unsettlingly wrong compared to a normal mirror. How can I make sense of this?

Well, maybe can’t, but Dr. Jay Pratt, who specializes in perception and visual cognition and is a professor at the University of Toronto, can.Mir John

Of course, he did refer to me as “John” in all our correspondence, but I think he still knows what he’s talking about when it comes to this sort of visual puzzle.

Dr. Pratt gave some really interesting explanations for what I was experiencing, so I’ll let him explain. First, the issue of why the digital mirror image was blurry when a regular mirror, the same distance away, is not:

Issue #1: the mirror image is crisp but the LCD image is blurry.  I think this is an optics issue and probably due to your farsightedness.  The mirror is essentially reflecting light from distant objects plus the distance between your eyes the mirror (i.e., everything is distant viewing).  The LCD screen, however, is taking images from distant object, going through some processing, and then projecting it at the relatively short distance from your eyes (i.e., a relatively short viewing distance).  Depending on your correction, putting your reading glasses on might bring the LCD into focus – but you’d lose focus on the sideview mirrors.  Indeed, I wear progressive lenses; reading viewing at the bottom, distance viewing at the top.  This is good for driving because dashboards are down and windshields and mirrors are up.  But an LCD screen above my head would require me to tilt my head a lot to get my reading correction onto the screen.
Try this.  Stand a foot or two away from a mirror in a bright space.  Hold something with writing at the mirror; it’s probably fuzzy without your reading glasses.  At the same distance, now hold the object with writing beside your head and look at it through the mirror.  By doubling the viewing distance (object to mirror to you) the writing is probably crisper (albeit reversed).
Or think of it this way.  If you had a picture of a distant mountain on an LCD screen near your head, you would need glasses to see it clearly.  If it was a mirror at the same distance, with a mountain in the distance, you would not need your reading glasses.

This fits with something I was sensing intuitively, that I look into mirrors, but at screens. The image and light on a screen is generated and displayed right at the surface of the screen, but a mirror is actually bouncing light off the surface in such a way that

“A reflection appears to be the same distance from the “other side” of the mirror as the viewer’s eyes are from the mirror. Also, when light is reflected from a mirror, it bounces off at the same angle in the opposite direction from which it hit.”

…which just means that when I see a car in the rearview mirror behind me, to my eyes it’s the same as if I was looking directly at that car at a distance directly. I’m not looking at an image of the car on a flat plane four inches from my face, I’m actually looking at the car with my distance vision, because that’s how far the light actually traveled.Mir Mirrordiagram

Does that make sense? I don’t have to re-focus from distance vision to close vision because the mirror is distance vision.

Dr.Pratt elaborates on this a bit more:

Mirrors work differently because they are reflecting distant light.  Imagine you’re sitting at your desk looking at a computer monitor.  The monitor might be 2 feet away from you, and for that you need your glasses (well, maybe not now, but likely eventually).  If we replace the monitor with a mirror, it’s reflecting whatever is behind you, say that back wall of your office some 10 feet away.  So 10 feet between the mirror and back wall, plus another 2 feet between you and mirror, and your viewing distance is 12 feet.  At that distance, you don’t need glasses to see in the detail the back wall in the mirror.  It’s all a matter where the light information is coming from; a nearby screen or reflected from a more distant object.

Oh, here’s another way to think of it.  Suppose you have a mirror that has a sticker on it. You stand 5 feet from the mirror, looking straight at it.  Your image is 10 feet away; 5 from you to the mirror and 5 from the mirror back to you.  The sticker viewing distance is only 5 feet (from the mirror to you).  So depending on one’s eyesight, one might be in focus and one out of focus. The LCD is like a sticker on a mirror.

So, even if you have perfect vision, looking from the windshield to the LCD screen of the digital mirror will still require your eyes to re-focus, like they do when you look down at your dashboard, and that’s not nearly as seamless as you’d think. You notice it, partially because most drivers are used to having no need to re-focus going from windshield to mirror and back.

There’s more to it, though; it’s not just an issue of focal distance, as screens have other factors in play:

Issue #2: Transitions from LCD to windshield are hard. I’m guessing that the reverse transition, from windshield to LCD is much easier. This may be due to the attention capturing properties of the LCD.

LCD screens are very luminant with lots of light energy, and changes in luminance are very good at automatically capturing our attention. For another driving example, normal roadside billboards are pretty easy to ignore, but LCD billboards are much more distracting. Depending how much light energy the LCD is pumping out, being right near our focus of gaze (unlike the LCD center consoles with are away from where we should be looking), these things might be harder to disengage attention from that a mirror.

After all, the mirror is just reflecting light from outside the car; it’s the same luminance out the front and back windshields). Turning down the contrast of the LCD should equate luminance inside and outside, thus reducing the transition difficulties.

This is a big factor, too, at night more so, as the LCD screen is actually a light-generating source. And, if that’s not enough, there’s the issue of why the image is a bit disorienting from the digital mirror as well, even when you can see it clearly. The good doctor has an answer for this, too:

And yes, only a camera mounted on the rearview LCD monitor would give the same perspective as a rearview mirror.  A camera anywhere else would give a different perspective. Now that could be offset with some fancy processing of the images, but do to so would be a lot of computing power.  With enough practice, the new camera perspective would come to seem normal.

That one is a bit obvious – a camera on the back of the car has a different perspective and field of view than one mounted at the point of the mirror – but it’s definitely a factor in why using these digital mirrors feels so off.

Not having your view blocked by headrests or cargo is good, and having a wide field of view is good, but it’s still a view that’s discordant with where you are, as you drive, and that shift is a bit disorienting. This particular issue is likely the easiest one to get used to, but it’s still not great, and doesn’t feel as seamless or natural as a conventional rearview mirror.

It’s an interesting problem, why digital rearview mirrors suck so profoundly, and it’s not really the sort of problem that better technology can fix, because it’s an issue with the physics of light itself.

What complicates things even more is the fact that similar tech, rearview cameras used when reversing, don’t suffer from the same issues even though they’re essentially the same basic technology. The reason is that we don’t use them the same way. A back-up camera is focused on for the short period while reversing; it’s not glanced at with regularity over a long period of time like a rearview mirror is, so the transition issues just don’t come up.

Despite how great they sound when described or shown in a promotional video, I’d have to suggest that anyone, especially if you need reading glasses, should save their money and stick with good old cheap real rearview mirrors. Digital ones are just the wrong application of too much technology in a place where it doesn’t work.

I don’t know why or how these ever made it past the initial testing phase, though I suppose you could get used to them, and maybe in some cases the benefits could outweigh the negatives. But I’d encourage everyone even considering one to get in a car that has one and try it out, so you can actually feel what I’m talking about here, because words can’t really describe the suckiness properly.

Until Toyota or some other carmaker changes the fundamental nature of light, these overcomplicated non-solutions to the problem of poor rear visibility are best avoided.

Share on facebook
Share on whatsapp
Share on twitter
Share on linkedin
Share on reddit

116 Responses

  1. Wow. Hmmm. Everything you say does make sense, AND I do wear progressives prescrip glasses. However, I have a car with almost ZERO rear visibility 🙁 How can this be better than one of these digital video rear views ?
    Honestly, the reason I had been surfing around looking at these, was that “all I thought I needed” was a digital rear view. I already have a back up camera AND an aftermarket 3 way camera…. But they all try to include this stuff, which is useless to me.

  2. Good explanation of the issues. Definitely needs to be switchable to regular mirror for normal driving use. This from a retired (old) physicist.

  3. Random thought. Where is rear-facing camera mounted? Is it the same as the backup camera? Would any of this be mitigated if the camera were to be moved up to give a better “more natural” view?

    I dunno, I’m not all that bright.

    1. Dunno about ones like Cadillac, but on Toyota/Lexus it is a separate camera all the way at the top of the rear window (and also in a section the rear wiper covers)

  4. Another problem not addressed here is that a mirror reveals a slightly different view every time your head moves to a different position. The angle of view changes when your head moves in relation to the mirror.

    A digital rearview display shows the view from one stationary point on the rear of the car, from where the camera lens is mounted. No matter how much your head moves around, the image in a digital display comes from the same point.

    You are used to seeing the viewing angle change slightly as your position relative to the mirror changes, and a digital rearview cannot provide the same experience you’re accustomed to, so it is very disorienting until you get used to it.

      1. Been looking and waiting for someone to mention this factor. REAL eyes and brain can adjust to a mirror and compensate for any depth perception changes. Our brains/eyes are not hard wired to achieve such with a screen. Actually I wish any screens had never been incorporated into vehicle design. It feels like the manufacturing process does not give a damn about real human interface anymore. Screw that.

  5. I was thinking of getting one of these for my BMW 850, when I got it the rear view mirror was long gone. I have gotten used to driving without one. Helps a lot with the BroDozers and their landing light bright headlights.

    I will be passing on it now

  6. Rather than a problematic special skeumorphic viewscreen that flips to being a physical mirror with suboptimal, compromised reflectivity it would make more sense to have a plain mirror for regular use and a means of activating the backup camera on its’ dashboard screen while driving forward for edge cases when the camera’s wider, unobstructed view is helpful.

  7. So why can’t I just have the backup camera stay displayed at all times and have a normal mirror to have the best of both? On most cars it turns off as soon as you shift out of reverse. On some it’ll stay on until you reach a certain speed moving forward or some time delay. This is great when maneuvering a trailer back and forth. Why aren’t they all like that? It is a patent issue?

    1. I have a Nextbase 522GW Dash camera mounted right next to the mostly useless rearview mirror on the driver’s side in my MINI Coupe S. Additionally, I have a rear-facing camera (connected to the front dash cam) mounted at the top of the glass in the car’s hatch looking straight backward. The main dash camera’s settings allow you to choose to have its screen on at all times, or turn off after a short period. Additionally, you can choose to display the front camera or the rear camera’s view displayed on the screen. I have it set to stay on at all times when driving because the view out the back and over my left shoulder is practically non-existent in the Coupe. The reverse camera has just enough field of view that any car that approaches me from behind is visible the whole time until it passes me on either side, but then at that point I can see the vehicle in my side view mirrors, so there is a sort of unbroken overlap between the view of the reverse camera and my car’s side view mirrors. Though the dash camera has a relatively small screen, it’s good enough to spot movement, if not great detail, so it does what I want it to. I also have a license plate reverse camera that streams to my cell phone when I’m reversing. That license plate camera runs on a rechargeable battery, however, so I only use it when reversing. So with the two rear-facing cameras, my view out to the rear and sides has markedly improved in my case.

    2. Backup cameras are often angled slightly downward, so they don’t provide a sufficient viewing angle under normal operation. They point down so you can see what your car would hit at ground level.

  8. This runs against my dad’s advice, never forgotten, that your eyes should be pointing in the same direction your car is moving, at all times. Mirrors are for fancy-boys, drape your right arm over the passenger-side headrest and do it the way our forefathers did! I guess our forefathers never drove lifted trucks or cars without views around the C-pillar.

  9. I also must disagree. My wife recently got a Bolt EUV with one of these and she hates it but I dig it. I can see way more stuff in it than a regular mirror but I don’t have the near sighted thing going yet (although rapidly approaching the big five o). At first I noticed the refocus thing with my eyes but lately I got used to it and don’t even notice. Also my wife’s a foot shorter than me so instead of readjusting her rear view every time I drive ( which used to drive her nuts) I just flip the lever and go digital screen and everyone’s happy. Conclusion, I like this tech, sorry Torch.

  10. I like the mirror cam in my Chevy Bolt. Wider field of view and reduced glare at night. It also allows me to have the mirror as high as it will go so it doesn’t block my forward vision. (This is a problem on a lot of new cars. As the roof of cars slope more for aerodynamics the rear window gets shorter. To maintain line of sight out the back window the rearview mirror has to move down the windshield)

    The only point I’ll give Jason is that the traditional placement high on the windshield isn’t great for older drivers with bifocals (which Jason should be wearing while driving so he can see). Since a mirror cam does not need line-of-sight out the back it could be put into the top of the dash at the same height as the instrument cluster and therefore easier for people with bifocals to see it out of the bottom part of their bifocals.

  11. good article. I noticed that too (I’m 47 now), somehow all glass surfaces have become hard to focus on, especially when having reflections. I lost autofocus 🙂 on reflective glass, I always see the reflection first and I’ve been repositioning all reflective surfaces at home to not reflect too much. Even transitioned from normal TV to projector on screen for the same reason.
    It all makes sense now! Thanks again for articulating the reason and the explanations.

  12. This has also infuriated me, simply due to the need to refocus from the distant forward vision to the relatively close rearview display. Normally, a glance in the rearview mirror is just a glance, but it takes longer and strains your eyes when you need to refocus every time.

  13. FYI: I have contacts and your eye doctor can adjust the prescription so that one eye focuses long and one focuses short. You would think it is a problem, but your brain soon learns how to favor one vs another as needed. Works pretty well.

    1. YMMV. I tried that for a time and did I ever have eye pain. My eyes would never give up on trying to focus individually. After a few hours the pain would become unbearable as my eye that was blurry (the close up one if I was doing mostly outdoor distance viewing OR my distance eye when I tried to do my office work) tried to focus.

  14. Why is it that I can back up a trailer for a mile using mirrors, but can’t back up a few feet using my rear camera? I can’t be the only person this happens to.

  15. The way I ‘see’ it is that a standard mirror is better than a digital mirror, unless it’s a situation where you can’t see shit with a regular mirror because of something (cargo, a trailer) or someone (people sitting in the back) are blocking your view.

    So if a standard mirror works, stick with it.

    But for vehicles/situations where you can’t see out the back such as a moving van or when towing a trailer, a digital mirror can be a huge improvement even if it’s not ideal.

  16. PEOPLE! This has been solved. How do you think VR googles work! You can’t focus on something 1″ away even if you are JT’s unborn progeny. Yet they work.
    I’m sure it would adjust like the mini viewfinder on my digital SLR, you move the slider until it is in focus (now unfocused for the fully sighted) and voila. For the smarter car it would remember your focus setting like it does your seat, mirror and steering wheel position.

    1. Doesn’t VR use 2 separate lenses, one for each eye, to achieve that though? I’m not sure how you would account for such a parallax of not just different heights but the fact that your head isn’t always in the exact same place every time

  17. Old guy takes car to dealership.

    Old guy: Fix my rear view mirror, it’s all blurry!

    Service person: There’s nothing wrong with it. That’s your eyes.

    Old guy: Bah! My eyes are fine!

    Service person: OK … [sells him cheap stick-on mirror for $250]

  18. This could explain why I like the digital mirror in my RAV4, and my wife hates it. I like the wider field of view it provides, and don’t have an issue focusing on it.

Leave a Reply