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.
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 presbyopia, and 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 I can’t, but Dr. Jay Pratt, who specializes in perception and visual cognition and is a professor at the University of Toronto, can.
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:
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
…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.
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:
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.
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.
There’s more to it, though; it’s not just an issue of focal distance, as screens have other factors in play:
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:
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.
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.
I dunno, I’m not all that bright.
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.
I will be passing on it now
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.
I miss it.
(and I’m almost 50.)
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.
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]
