Science Friday
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At what point does the resolution on a TV display outpace what human eyes can actually see? Researchers investigated.
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I'm Flora Lichtman and you're listening to Science Friday.
Today in the show, a close look at the biology of vision. We'll get the big picture.
Yes, there is an upper limit for an average observer to how many pixels they can resolve. If we add any pixels beyond that, then the human eye is not able to perceive that extra resolution.
As Black Friday approaches, you're probably being inundated with ads for bigger, better televisions, 4K, 8K, super duper mega crystal, QLED, UHD plus. But how good is good enough? Are there limits to what our eyes can even make out? And just how similar is my visual experience to yours? Today, we are talking about how we see the world with two experts. Dr. Malia Ashraf is a postdoc at the University of Cambridge in the UK, and she's the lead author on a new study about display resolution, published in the journal Nature Communications. And Dr. Brian Jones is a retinal neuroscientist and professor of ophthalmology at the University of Pittsburgh. Welcome to you both to Science Friday.
Thank you.
Thank you so much.
Malia, your team studied what resolution people can actually see. Is there a point at which more pixels don't matter?
Yes, so that's exactly what we measured. In quantitative terms, it's 94 pixels per degree. So in each angle of your field of vision, you can see up to 94 pixels. If your stimulus or the content that you're seeing was black and white, find lines. And in terms of technology, if we translate that, then yes, there is an upper limit for an average observer to how many pixels they can resolve. If we add any pixels beyond that. Then the human eye is not able to perceive that extra resolution. And so it's computationally a waste.
I'm trying to picture how you did this research and I'm kind of imagining, you know, an eye test from the ophthalmologist's office on a sliding track, like moving closer and further away and at different angles. How far off base am I with that?
Yeah, so we didn't use the traditional eye chart that you see in an optician's office. Instead, we used a normal 4K 27-inch monitor and we mounted it on a rig, which can move back and forth. And the purpose of this was we controlled the viewing distance between the observer and the screen. And this change of viewing distance effectively changes the resolution or how many pixels are which are falling on one degree of your retina.
It seems like one of the take homes here is that the resolution that your eye can make out is related to the size of the screen, the distance you are away, and then how good your eye's personal resolution is. And so what I gathered was that the farther you are away from the screen, the less resolution matters. Does that sound right?
Yes, that's correct. So the further you are, the higher the pixel density will appear. So in terms of 4K screens, let's say. So you hear the word 4K very often, right? So that simply means that there are about 4,000 pixels in a row or in the width of the screen. Now that 4K or 4,000 pixels can be on a 14-inch screen or they could be on an 18-inch screen. So the number of pixels is the same, but because the size of the screen is different, that means that the how closely packed the pixels are is different. So the pixel density is different. So for the same number of pixels,
you will have different effective resolution depending on the size of the screen. And then similarly, you can watch the screen. From a meter or two meter, right? But the further you are, the less you can resolve the details because more pixels will fall on less area of your retina.
So listeners, if you want to nerd out on this in advance of your personal entertainment system upgrades, we have this calculator on our website at sciencefriday.com/display. And Malia, I mean, in what scenario would you even be able to tell you're watching an 8K TV versus a 4K TV? Do you need to be sitting like a couple of feet away to even make that difference meaningful?
Yes, so again, depend on the size of your TV and the resolution of the TV and your viewing distance. It can matter. So for example, if it was a 40 inch TV and you were watching it from a distance of one meter, then you might be able to see a difference between an 8K and a 4K. So this, this distance is close enough and the screen size is small enough that, that the higher resolution might make a difference.
But one meter is like three feet away. Like, most people aren't watching their TV. Well, my children are, but besides, besides children, many people are not watching that close, right?
Yeah. So that, so that's TV, right? But you have other applications, like right now I'm watching my screen from, I don't know, 40 centimeter.
Yes, true.
Yep. And if you're playing games for an office worker. So there are, there are viewing distances which, which might fall into that range. And also our research was not focused on TVs. We wanted to get just a general resolution limit in terms of pixels. And now pixels can be anything, on your phones, on tablets, on VR, AR headsets.
Right.
We just use TVs because that's a bit easier to explain. But anything which uses pixels, you can apply this resolution calculator and find out if your setup is below or above the human resolution.
We got to take a break, but don't go away. When we come back, is color just a mass-shared illusion?
The biology of vision is actually a lot more complicated than a lot of people understand.
Stay with us.
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Brian, let's take a step back. Is our ability to make out resolution the same as how well we score on a vision test? I mean, how is it related to having 20/20 vision, or nearsightedness, or farsightedness?
So, most of what we're talking about is something called acuity, our ability to resolve differences in contrast at some defined distance. For the standard eye test that most of us are familiar with, you know, that sort of defines normal vision of what people can readily resolve at 20 feet. And the biology is interesting. So, you have light coming in. There's a cornea, the clear part at the front of your eye. That's what surgeons operate on when they do, like, Lasik or radiocortisotomy, to change the refractive properties of lights that falls on the photoreceptors
of your retina at the back of your eye in the right way. If you can see things up close and not things at distance, you're myopic. If you can see things far but not up close, you're farsighted. And there are ways of correcting that so that you can improve the acuity of your optical system by operating on the cornea.
There's also the lens. The lens is behind that, sort of behind the pupil. The pupil sort of constricts or dilates depending upon the amount of light that's available. And pupil size also sort of factors into acuity. The tighter your pupil, the higher the acuity. And the more dilated your pupil, so like if you go to the doctor and you get eye drops and it dilates your eyes so that you can get a good view of the back of the eye, then everything is a little less sharp. And then the lens also shapes the light falling on the back of your retina as well. And as we get older, our lenses get a little less flexible.
The muscles that control the shape of the lens get a little less able to do their job. And so we, you know, start having trouble accommodating or changing the acuity of light that falls on the photoreceptors of the backs of our eyes. And then there are other issues that, you know, cataracts and things like that that can, that can also impact that.
Does that mean skip the 8K TV if you're getting up there?
Yeah, so basically as, as we get older, the visual performance of our eyes drops. And, you know, I mean, in terms of televisions, a lot of this argument was, I think, more important a few years ago when, when screen sizes were smaller. And it's like when, when Apple first came up, when Steve Jobs was up there on the stage and he was talking about a retina display, you know, a lot of us in retinal science were like, oh, come on. And then we actually did the calculations and yeah, it's, you know, at, at the standard distance of a screen, you know, it really was, quote, "retinal resolution." You could not distinguish the pixels at that density.
Televisions have gotten so big now and you're sitting far enough away that, you know, a lot of this argument really doesn't nodder. But where it's coming back into play now is where we've got VR devices.
Right, because they're right on your face.
They're right on our face. And we've got these displays very much closer and resolution for those devices is going to come back into play again, absolutely.
Are some people's retinas more sensitive than other people's?
So, uh, yes and no. The biology of vision is actually a lot more complicated, uh, in some ways than, than a lot of people understand. Um, there are certainly, there's, there's variation in, in what people perceive in terms of acuity. That's what we've been talking about. That's, that's for, for sure. In terms of retinas, there are retinal conditions which affect how many colors, um, some people can see. So, you know, 3% of males are red, green colorblind. So they have trouble distinguishing reds and greens. There are some other rarer forms of
color blindness. There are some genetic women who can, uh, distinguish four colors. They're tetrachromats, whereas most humans are trichromats.
That's a cool fun fact.
That, that is a cool fun fact. Uh, so, so that the gene for, for opsins, uh, in our cone photoreceptors that determine color is carried on the X chromosome. And you can have mutations in that gene. And, uh, if you're a male and you have a mutation in that, you know, you're sort of out of luck. But if you're a female, you have a backup copy. So females that have mutations can still see in trichromacy, but some of the mutations result in a shift in sensitivity that allows them to see a slightly wider chromatic range. So, so they're tetrachromats.
Hmm.
And there are other species of animals that can see far richer worlds than we can, uh, in, in terms of color and actually even acuity.
Really?
Uh, avians, a lot of bird species have much better acuity. They can see better than we can in terms of resolution. They can see better than we can in terms of speed, the speed at which they can see things. Um, and they can see more colors.
Did I read right that turtles can see more colors than we can?
Turtles can see, so most trichromatic humans, um, see a world with a mix of red, greens and blues. Um, so three colors. Turtles see nominally in seven spectral channels and maybe even more because they have additional oil droplets at the ends of their photoreceptors that may act as additional spectral filters. So yeah, it's an interesting biological world out there.
Brian, you call color a mass shared illusion. Tell me about this.
Yeah, so a lot of people think of retinas as cameras. But the way that they process information is more sophisticated than that. So the retina is like this multi-laminar structure. You've got photoreceptors at the back, so like a sensor array at the back. And then in front of that sensor array is a computer array. And that sort of breaks the visual scene down into color and contrast and luminance and vector and velocity and starts calculating all the primitives, all the sort of mathematical primitives, if you will, that form the algorithms that we see with and then sends those to brain.
Some of those primitives are channels of information that just do color. Others calculate edges. Others calculate edge movement over time and gives us velocity. And then it sends those data back to different places in our brains for processing. Color is funny. In general, trichromatic humans tend to agree on what color is, on what shade of red is the same shade of red, on what shade of green or blue is the same shade or brightness or luminance or what have you.
So like if I see a blue and my neighbor sees a blue, we probably interpret that blue the same way. In our brain, we see the same color.
Yes. And so the thinking was that humans would have the same ratios of red, green and blue photoreceptors across all humans. And it turns out we don't. We have wildly different ratios of red photoreceptors versus green photoreceptors, you know. But we still tend to agree on what the color is. So neural systems are difference engines. They're good at saying, this is similar to this and this is different from this. And in some ways, it doesn't matter what the stimulus is. But to get back to your original question, there is no color.
Photons, the things that fall in and stimulate our photoreceptors have a wavelength. But there's no color associated with that wavelength.
The color is a biological percept that we have and we perceive as a difference in color. And we communicate that and coming back to the social construct. It's an agreed upon social construct of what that color is. But you know, in terms of color in the universe, you could make an argument that there is no color.
Yeah, that's fascinating because it makes you wonder, you know, what are the other biological percepts that I'm creating in my brain? Malia, what about for acuity? Do we have the same acuity in color as we have in black and white?
We don't. So one of the lowest level tasks that the retina does is divide the content into three main channels, which is achromatic, red, green and blue violet, roughly. And without getting too technical, the achromatic channel is the one which encodes the spatial information of what the structure looks like. So what the outlines are, what the edges are, or the shape and form.
The black and white channel.
We won't call it black and white, more like achromatic, because it just strips off the color information and only works in terms of luminance differences, or how bright or how dark the different areas of the image are. And then the red, green and yellow violet are the color encoding channel, which strip off all the luminance information and just work on pure color signal. So most of the heavy lifting of our perception is done by the achromatic channel. But color channel adds information on top of it. So in terms of spatial discrimination, or such as visual acuity tasks, the achromatic channel has definitely way more acuity or resolving power.
And the color channels require less detail. So they add more like. Bigger or blobular information, I guess, rather than very, very high detail. So if you had very high detail in pure color, then they would not be able to perceive it as well.
Dr. Malia Ashraf is a postdoc at the University of Cambridge in the UK, and Dr. Brian Jones is a professor of ophthalmology at the University of Pittsburgh. Thank you to you both for joining me today.
And if you want to calculate your perfect screen size, we have a link to Dr. Ashraf's display calculator on our website at sciencefriday.com/display.
Today's episode was produced by Charles Burquist. I'm Flora Lichtman. Thanks for listening.
Page updated October 31, 2026 · transcript and summary are machine-generated