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 arm's 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.