What Is The Resolution Of The Eye?


Hey, Vsauce. Michael here. I am at the White House, in America’s capital, Washington, D.C. America makes a lot of
feature films every year – Hollywood. But they don’t make the most
feature films every year. Nigeria makes more. But the country that makes the most
films every single year is India. Every two years, the country of India fills up enough film with unique
feature films that stretch all the way from this city,
Mumbai, to where I live, in London. That’s double what Hollywood
produces in two years. That is a lot of movies, but is real-life a movie? I’ve discussed the frame
rate of the human eye before but how does the resolution of the human eye compare to a camera or screen? VHS, LaserDisc, DVD, Blu-ray, IMAX. Numbers like these are
pixel dimensions. When multiplied they tell us the total number of picture
elements an image is made up of. A figure often used to describe digital
cameras. It might sound like more is better, but to be sure numbers
like 1920 by 1080 are not resolutions per se.
More pixels is only part of the equation. Resolution is about distinguishing fine details and that depends on a lot of other factors. For instance, the amount of light, the
size of the sensors, what the millions of pixels are actually
encoding and how close the subject is. I mean, up close Salvador Dali’s painting of his wife
looking at the Mediterranean can be resolved into boxes. But from a far, well, it’s Abraham Lincoln. For crying out
loud, on a small enough screen from far enough away, low and high,
so-called resolutions on screens, aren’t even resolved differently from one another by your eye. How different nearby pixels are from one
another also matters. This is called spatial resolution. For instance, if I go out-of-focus the number of pixels in the video frame
stays the same but you can’t resolve as much detail. Now, with all this in mind we can still compare human vision to a digital image,
by asking a better question. Assuming everything else is optimal, how
many pixels would you need to make an image on a screen large enough to fill
your entire field of view look like real life, without any
detectable pixelation? Now we are getting somewhere. Kind of. The analogy is still crudy because a camera snaps an entire frame
at once, whereas our eyes move around. The brain amalgamates their constant stream of information
into what we call vision – sight. In fact, the image created by the
eyeball alone during a single glance would hardly even be acceptable on a
broken TV screen. We think our eyes create images like this picture
Guy took of me with a camera. But for one thing, unlike a camera,
you’ve got some stuff in the way. For instance, you are always looking at your own nose, and maybe even
glasses, if you have them. Luckily, our brains
process those stimuli out because they don’t matter and they don’t change. But thinking those are
the only difference is a pitfall, literally, latinly. The fovea gets its name from the Latin for ‘pitfall’. The fovea is the pit on your
retina that receives light from the central two degrees of your field of view, about the area
covered by both your thumbs when held at arms length away. Optimal
colour vision and 20/20 acuity are only possible within that little area.
When it comes to these limitations XKCD[.com] has a brilliant illustration. It points out other problems, like blind spots – literal blank spaces in our vision where the optic nerve meets
up with the retina and no visual information is received. If you bought a camera that did this, you would return it. You can find your own blind spot by closing your right eye, fixating your left eye
on a point in front of you, extending your left thumb and then moving it left-of-center slightly slowly carefully
until it’s not there anymore. Crazy(!)
But, of course, we don’t see the world horribly, like
this, because our eyes are constantly moving, dragging foveal resolution wherever we need it. And our brains’ complex visual system fills in details, merges images from both eyes and makes a
lot of gueses. What we actually see is a processed image.
Not computer-generated imagery, but, well, meat-generated imagery.
The neon color spreading illusion is a great way to demonstrate this
difference. There is no blue circle in this picture. The white here is the same as the white here. A camera isn’t fooled, a screen isn’t fooled, only you and the fleeting gumbo of
ingredients you call perception is fooled. Our vision is not analogous to a camera. But our
reformulated question can still be answered because human anatomy allows us
to resolve, to differentiate certain angular distances. Famously, Roger N .Clark used a figure of 0.59 arcminutes
as the resolution of the human eye to calculate, based on the size of our total field of
view, how many of these distinct elements
could fit inside of it. The result was an approximation of
exactly what we want to know: how many individual picture elements –
pixels – our vision can appreciate. His answer? 576 megapixels. That many pixels, packed
inside a screen large enough to fill your entire field of view, regardless of proximity, would be close enough to be undetectable
by the average human eye. But we should factor in the fovea, because Clark’s calculation assumes
optimal acuity everywhere, it allows the eye to move around. But a single glance is more analogous to
a camera snap, and, as it turns out, only about 7 megapixels,
packed into the two degrees of optimal acuity the fovea covers during a fixed stare, are needed to be rendered undetectable.
It’s been roughly estimated that the rest of your field of view would only need about 1 megapixel more information. Now that might
sound low but keep in mind that there are plenty of modern technologies that
already use pixel densities better than we can differentiate.
As Bad Astronomer deftly showed, Apple’s Retina Displays truly do
contain pixels at a density average eyesight can’t differentiate from typical reading distances. But the fact that
there are screen sizes and pixel densities that can fool the human eye is not a sign that we see in any kind of megapixelly way. Human vision just isn’t that digital. I mean, sure, like a
camera sensor we only have a finite and discrete number of cells in our retina. But the brain adjusts our initial
sensations into a final perception that is a wishy-washy top-down processed blob of experience. It’s not made of pixels and furthermore, unlike a camera, it’s not
saved in memory with veracity like a digital camera file. Absolutely no evidence has ever been
found for the existence of a truly photographic memory. And what’s even
cooler is that not only do we not visually resolve the real world, like a movie camera, we also don’t narratively resolve
conflict and drama in our lives like most movie scripts. The point of
all of this, what I’m getting at, is an idea. An idea that initially drew me to this question. We play roles in the movie of life, but it’s a special kind of movie.
Cinematic victories and struggles are often discrete, resolved, like pixels, with
unbelievably perfect beginnings and endings, whereas the real world is all about ear resolution. I like how Jack Angstreich put it in ‘Cinemania’. In a movie, a character can make a
decision and then walk away from the camera across the street and have the credits
roll, freezing life in a perfect happily ever after. But in the real world, after you cross
the street, you have to go home. The world goes on. Life doesn’t appear in any particular pixel resolution or narrative resolution. Things are continuous. The world was running before
you came around and it will continue running after you are gone. Your life is a plot
only in so far as it begins and ends and occurs in medias res. Damerish opens illustration for
Charles McGrath’s endings without endings says it perfectly. In life, there rarely is the end. There is only the and. And as always, thanks for watching.

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