Why we're blind to the color blue | Hacker News Reader

Why we're blind to the color blue

calebkruse.com

575 pointsgoodway211 comments

I don't believe the blurred images at the end have anything to do with eye focus, as the author suggests.

After all, chromatic aberration is blurring of only a very, very small amount.

The demonstrated seemingly negligible perceptual effect of blurring blue to a huge degree in a multicolor image doesn't seem to have anything to do with that, but rather the fact that we perceive primary blue as a much darker color than primary red or green, and we perceive differences in lighter colors much more easily.

If the author were correct that we have big problems focusing on blue, then we'd see that blue text against a black background would be massively blurry -- but it's simply not. It's comparatively low-contrast (because blue is a dark color), but it's nearly indistinguishably as sharp as red and green.

Right, I picked the "blurred blue" and "blurred green" pictures, converted them to grayscale using luminance and "blurred blue" still looks sharp and "blurred green" still looks blurry.

If it really was the effect of blue light, the effect should have disappeared by converting to grayscale.

It is well known that luminance matters much more than color when it comes to perceived sharpness. Digital and analog video exploit that by encoding color at a lower resolution (chroma subsampling). And blue only accounts for less that 10% of luminance while green is around 70%. You may find different values because color spaces are a mess but that's the general idea.

That’s not an apples to apples test because of how greyscale is computed. Try swapping the blue and green channels rather than converting to greyscale.

I think for a proper comparison, you would need to swap them by perceived brightness (luminance), not just the RGB value. You can't do that here because the green channel in this image is out of the possible range of luminance you can achieve with blue (in any standard color space, probably).

Which really illustrates why TFA doesn't make any sense- our eyes are less sensitive to blue, so the contrast provided by max RGB value blue is going to be completely drowned out by red and green if the source of your contrast is white on black.

Here's what it looks like with all channels shifted to have the same luminance: https://i.imgur.com/AnKNdfX.jpg - note it is perhaps a little softer as the peak brightness is closer to black.

Now here's what each channel looks like blurred by 2.5px: https://i.imgur.com/XzVWeZg.jpg https://i.imgur.com/LB5JArJ.jpg https://i.imgur.com/jf4ntth.jpg

They're all clearly fuzzy in comparison to the un-blurred image. The answer to "why we're blind to the color blue" is not chromatic aberration (although it could be a contributing factor, maybe even why we have less blue receptors), it's that we're less sensitive to blue and therefore contrast is usually defined by red and green.

Perceived brightness is very tricky as our vision naturally adjusts to normalize perceived colors. https://en.wikipedia.org/wiki/The_dress

Personally I don’t see each image as equally blurred, but YMMV.

There's a difficulty with testing perceived color by using a computer display, which is that the "blue" is the spectrum of the blue pixels, whereas the "blue" receptors in your eye may have a different spectral response.

Where I've noticed weird things with blue are with blue sources that have fairly short wavelengths, such as some of the blue LEDs used in Xmas tree lights, and the old blue lights that were on police call boxes. Both of those are very hard for me to focus on.

>such as some of the blue LEDs used in Xmas tree lights, and the old blue lights that were on police call boxes. Both of those are very hard for me to focus on

This happens to me as well and I though I was becoming blind (to blue light) because of my heavy use of monitors/"white" light, etc...

This article is false. Tried this out Photoshop and not even close.

Here are my results, with a 22px Gaussian Blur on the Channels

https://imgur.com/a/AS0LAyk

IMO The only reason the blue appears a little less blurry is that most of that color is in the water & clouds.

Not in the land masses, with the sharp borders

See the very low coefficients for the blue channel when converting (gamma-compressed) RGB to luma. E.g. the common Rec. 709 standard assigns only 0.0722 weight to blue.

  Y' = 0.2126R' + 0.7152G' + 0.0722B'

Indeed, green contributes more. Example of the Y channel after blurring r/g/b: https://imgur.com/a/3p15Qe1

And colured versions: https://imgur.com/a/Knq2Ue3

(image source: https://en.wikipedia.org/wiki/Flower#/media/File:Flower_post...)

More, as in 10 times more for green, and 3 times more for red. So it's true that we're pretty blind to blue, just the "focusing" explanation is not correct...

Except that our perception of brightness, like loudness, is logarithmic, not linear.

So even if blue is 1/10th or 1/3rd as strong as another color, it's not really a big deal in terms of sensitivity.

I think you're imagining something like a logarithm for each channel, log(R/3) + log(G) + log(B/10). But that's not how it works.

Instead it's like log(R/3 + G + B/10). So when G and B are about the same size, the effect of B will be negligible. It's only when R and G are small that the logarithm will kick in and let you see detail using the blue.

So for seeing detail in a normal picture, blurring the green will have a much larger effect than blurring the blue. But entirely removing the green would let it still look sharp, because we could see the detail using the red (or if we removed that, then blue). If we just blur the green it overwhelms the blue and red to make the picture look blurry even if the blue and red were enough to provide sharp detail if the green wasn't there.

To be honest I need to rethink the arguments of the linked article - if we just use coloured filters in front of our eyes which exclude each channel, the image (I think) remains sharp (or at least that happens with red/cyan anaglyph glasses).

This is basically the same as the Y component used in JPEG, right? Could the phenomenon described in the article be caused by the fact that they used JPEG images? I.e. would we observe the same thing happen with raw/uncompressed images?

No, it's not an encoding artifact.

Did you mean to respond to another comment in this thread where they were talking about YUV? Your comment does not make much sense to me here but would make more sense to me there.

Luma is an approximation of perceived brightness. All the conversion formulae weigh blue substantially less than the other primaries. This supports crazygringo's assertion that "we perceive primary blue as a much darker color than primary red or green".

It makes sense to me here - GP discusses how we see perceive blue as a dark color, and parent comment corroborates that with a low luma coefficient for blue.

I dunno, but when I look at glowing blue signs and blue Christmas lights at night, they look significantly more fuzzy than other color lights.

Yes! I have difficulty with some blue signage and especially with certain intense blue LED lights as they seem to vibrate to my eyes. I also find it hard for me to read the text in blue on the small, scrolling LED signs common in storefronts.

> At long last, we can see why the human eye can't focus on blue light

At long last indeed. For decades I wondered why blue lights are disturbingly blurry at night, to the point I'd rather not look at them. I always thought it was just me since other people didn't seem to care as much.

I’ve found my people! I have similar issues and nobody I’ve ever spoken to about it seems to have the same experience.

Two similar issues I’ve had, and I’ve wondered if they’re related, are:

- at conferences with very large overhead projection sometimes the setup produces an effect where each time I blink it’s like it separates the RGB elements. It’s like a combination of being able to see the refresh rate (like when a CRT was filmed out of sync) and the colours being projected out of alignment. - a stadium near me as those digital display advertising signs around the sidelines. If I’m not looking directly at them they appear to flicker. Which actually makes watching a game at that venue not enjoyable as watching the action means I have a permanent shimmering right on the periphery.

Does anybody know what’s happening with either of these?

That's most certainly the display sequentially flashing red, green and blue sequentially in time to approximate shades and hues. When you stare right at it, your eye averages the photons with a time constant of 1/30th of a second or so, and so you don't perceive the flicker. When you move your eye or blink, though, individual portions of your eye are exposed to only relatively narrow time slices, and so re only exposed to the red, green or blue photons.

Cheaper DLP projectors use a single light source and mechanically spin a color wheel with alternating red, green and blue filters. They look great when staring at it, but if you move your head or wave your hand in front of it, you can easily see the three color channels.

Perhaps those stadium displays are DLP projectors based, or maybe they're RGB LED and are simply PWMed at a relatively slow rate. Most LEDs can be switched very fast, at say 10Khz, but maybe there's electrical limitations of building such a large high brightness display. If it's only PWMing at 100-200Hz, you'd see similar effects. In particular, each color channel will be on for different duty cycle durations, and LEDs are very fast to turn on and off. So, when you move your eyes or blink, you'll once again get separation of the channels in your vision.

You can do a similar trick with your smartphone camera. Record video, and point it at the display then wiggle the phone up and down and side to side. The phone most certainly has a "rolling shutter" which means it captures an image sequentially in lines either horizontally or vertically. It does it quickly, but slow enough that different lines should be able to pick up colors. You may not even need to shake the camera up and down to see a funky image. It's the same reason why CRT monitors and TVs look funky on video but not film.

Thanks for the explanation!

I can certainly perceive all those flickering effects when moving the eyes. Slow PWM is hell, but some stuff like colour separation can be cool too.

My favourite trick is making a digital clock's numbers "slide" over the clock's surface, in a sort of parallax way. I guess that's due to low refresh rates, so for a very brief moment there's a disconnect between the clock's physical position and the last know position of the digits.

I totally know that digital clock effect you're talking about. It's caused by something else though. It's actually a physiological hallucination due to high power ultrasonic waves coming out of those types of clocks. Rather than smoothly turning a small crank at 60rpm like in an analog clock, the clockwork gnomes inside digital clocks have to frantically push and pull a lever at 32.768KHz, and their stiff little pointy silk hats make perfect tweeter elements. It's also why those clocks get so warm, and why the snooze button is so unreliable; the gnome gets a well deserved nap, but is so exhausted he sleeps through his own alarm...

Oh... What? Hallucinations from a 32kHz RTC? Can't tell if your entire comment is a joke or just the last half... Couldn't find a thing after a quick search but now I'm curious.

None of it was serious. :-) Although I have indeed noticed that particular optical illusion of the clock digits moving relative to the clock.

I hated blue christmas lights because of this. Also, I couldn't read the time on the stove from any reasonable distance since it used blue LEDs.

After LASEK, though, I can see blue LEDs nearly as clearly as everything else. My eye surgery gave me nearly 20/10 vision and the greatest thing I got from it was the ability to read the stove clock from across the room. Lol.

I had a car with blue and red illumination in the dashboard. It always felt like I couldn’t see it properly - like it was blurred.

While I like the colour combination, my next car had orange displays, which always look sharp.

Also the blue LED on a PS3. Those always looked blurry to me. It’s especially obvious because of the adjacent green LED.

You are so right! I always assumed it was the LED's problem until I started reading all these comments. I think I remember the PS2 having the same thing.

Does this only affect people with Blue eyes ? As someone with utterly black eyes, I don't have a problem looking at glowing blue signs and don't find them fuzzy either.

Eye color doesn't matter in vision, it's not part of the optical path, its role is the same as an aperture on a camera lens.

Ok it seemed to me that that the stroma of blue eyes scatters back more light: https://medium.com/@ptvan/structural-eye-color-is-amazing-24...

Yes, scatters it back out — that light does not enter the pupil or contribute to what that person sees (save probably a vanishingly small amount that is re-scattered in the cornea, which is totally de minimus).

I have mostly brown eyes, so no?

It's true that we don't focus well on blue light sources, but it's also true that this web page does not demonstrate that fact in the slightest.

It also matters a bit that the blue channel is only 2% of all color-sensitive cones in the retina. That has a lot more to do with poor spatial resolution int the blue channel than the optics.

http://hyperphysics.phy-astr.gsu.edu/hbase/vision/rodcone.ht...

Chromatic aberration may be a contributing factor, but I am surprised the author didn’t mention that S cones (which we use to perceive blue) are only 2% of the cones in the retina [1]. Additionally S cones are distributed randomly when compared the regular lattice of M and L cones. The distribution of the different cone types alone may be sufficient to explain why our acuity for blues is impoverished relative to reds and greens.

[1] https://en.m.wikipedia.org/wiki/Cone_cell

This lower resolution of blue is pretty well known in recent image compression work (XYB space of JPEG-XL and guetzil), and number of S cones is the only explanation I have seen on that.

Also, S cones are mostly found outside the fovea.

I'm not sure you're right. At night both I and my wife have reported difficulty reading glowing blue signs compared to glowing red/green signs at the same font size, brightness, and distance.

I'm also not sure that the author is correct; the wrong-focal-distance explanation seems rather weak simply because our focal length is adjustable.

You have astigmatism. I have a similar issue with blue when not wearing my glasses. I have 20/20 vision, but my astigmatism makes it difficult to focus on certain things. A computer being a big one. Blue light blockers help, but with proper astigmatism correction I don’t need them.

20/10 vision in one eye, 20/13 in another, no astigmatism.

Blue LEDs in clocks when viewed at night look completely fucked up.

I’ve never met anyone without some astigmatism; especially, people with other vision impairment. Astigmatism is the number one cause of night blindness which is what you described.

HN is so funny. 'I have no astigmatism.' -- 'Sure you do!'

It's right up there with 'I've been clinically diagnosed with ADHD by a qualified psychiatrist and this medication has improved my life tremendously' -- 'There's no such thing, the medication doesn't do anything and you just need to mediate more, have you tried mindfulness?'

There were three people involved in that exchange, not two, assuming nobody's using multiple aliases...

crdrost described their vision problems, jbluepolarbear said "you have astigmatism", techrat popped in and said "[I have] no astigmatism" and jbluepolarbear made a more general statement that most people do.

I'd assume techrat doesn't know anything about crdrost's vision either.

Because nearly every person has some amount of astigmatism.

Sure, but presumably the parent has been checked by their eye doctor and indeed, not everyone has it.

Signed, a dude with very slight astigmatism :)

pro tip: don't tell other people about their own experiences unless they ask you, and you're a professional.

Pro tip: nope

You're precious. Why don't you tell me what else my eye doctor has never diagnosed me with?

9 in 10 people have some affliction of astigmatism. Astigmatism is just that your eye isn’t perfectly spherical. What does your eye prescription say in the cyl and axis fields, that’s your astigmatism correction.

20/10 and 20/13 means much better than average good vision. It would be bad if they were e.g. 20/30. Funny that you're LARPing an eye doctor without knowing this.

You can still have 20/10 vision with Astigmatism. I guess my years of research into astigmatism because of my own affliction and years of optics study visual effects means I’m larping. Never said I was a doctor, I’m just intimately familiar with how corneal distortion.

'eye prescription'?

Bruh. Read the comment of mine you replied to. 20/10 and 20/13 vision. I don't need prescriptions.

Aren't those numbers about your ability to focus on distance objects, though?

I could totally believe the someone might have "perfect" vision that doesn't require correction, but still have a slight astigmatism that impacts their vision under certain specific scenarios such as when viewing blue LEDs in low light.

I'm not necessarily saying that's what you have, but more just that to the extent your eyes have been evaluated, it was likely "yeah they look great as far as your ability to perceive the brightly lit eye chart, no need to do the more detailed analysis where we figure out the other parameters that will never be used because you're fine, bye."

That's like saying you can run a 3 minute mile so you don't have a shoe size.

This whole thread is silly.

Shoe size is an inherent byproduct of having feet of a certain dimension. A prescription has to be prescribed.

If we're doing dumb analogies, it's like you're trying to insist a homeless man must have an address.

...Actually, that's a real problem in the financial services sector. You can't satisfy KYC requirements without an address of record.

Off topic, but I'm jumping around a bit tonight.

i'm imagining a homeless man receiving his begging money via a bitcoin QR code on his phone.. i hope he has a bitcoin atm nearby.

I think more than one person has confused you with the person a couple levels up thread, i.e. https://news.ycombinator.com/item?id=27859324

> About one in three people has some degree of astigmatism.

https://my.clevelandclinic.org/health/diseases/8576-astigmat...

> about 9 in 10 people have some degree of Astigmatism

https://patient.info/eye-care/astigmatism

I wonder why there's such a big degree in difference between the two claims.

The 30-60% is most likely for those affected by their astigmatism. Astigmatism is when the eye isn’t a perfect sphere. Many people have very slight astigmatism and don’t require correction.

> In Europe and Asia, astigmatism affects between 30 and 60% of adults.

https://en.wikipedia.org/wiki/Astigmatism

I can’t actually verify that number presented in that paper. I’ve looked and that stat is attributed to that paper, but there’s no evidence that the paper said that. Plus the paper is pay walled so unverified.

Considering the obvious inability for anyone to reliably know the astigmatism status of everyone they meet, not only is your anecdata unverifiable it's completely absurd.

I don't think it's night blindness. I have the same problem, with and without glasses (I have astigmatism).

Astigmatism is easy to self-detect, and it's quite different from the light focusing to the wrong plane. Astigmatism will noticeably warp the entire shape of the distant point object, rather than just make it "fuzzy" in an isotropic manner.

Source? Astigmatism can blur and distort.

https://patient.info/eye-care/astigmatism

for me, it's mainly the difference in looking up and down compared to looking left and right.

You're not alone. I normally have excellent night vision but seeing things in glowing blue, such as the clock on the coffee maker or the microwave, causes the digits to split like double vision and become blurry while everything else remains the same.

I have the exact same thing. It always makes me wonder why companies choose to have blue neon lights on their buildings because it's nearly impossible to read them when it's a thin font.

I mostly agree with you, but would add that blurring the blue is affecting the sharpness of the ocean, which has little detail in that image; blurring red or green affects details on the land, which are very noticeable. One might think the cloud-ocean edges would be blurred by the blurring of blue, but the clouds are so much brighter than the ocean (red & green channels), that you can barely notice any difference.

I agree. Further, almost all of the blue channel in this image is from the white clouds or nearly black water. There's no other major source of blue.

What would be the result if you flipped the colors, so that the sharp elements are blue and the ocean is red or green?

That's an interesting thought but unfortunately I'm travelling.

One thing is that the ocean is hardly blue. Not sure why my eyes register it as such, but it's mostly very close to black with nearly equal parts of red and green, at least the parts I sampled. I think a certain amount of this article's claim is predicated on the reader erroneously believing the ocean should become blurry.

I think that the title is a massive oversimplification because chromatic aberration by itself is not enough for us to be blind to the color blue. We do have cones that can detect blue for one.

We are however, less sensitive to it so maybe the eye doesn't focus based on that channel(?).

I wanna point out that LCA cannot be responsible for e.g. blue displays being basically impossible to read. Why? Because they are still impossible to read when they're the only thing that's around, and blue LEDs are very monochromatic. So the eye would have to focus on the blue light, which would make LCA go away.

I suspect that a plausible cause could be that there just aren't a lot of blue receptors in the retina, as the eye is pretty insensitive to blue overall.

I’d love to see the same comparison across a range of images.

Exactly. In the real life I find very difficult to focus on violet signs against the black night background, but it’s a completely different effect from the one in this article and it’s exacerbated by the bigger pupil diameter in the night that increases the aberration.

I agree, in that it was pretty easy to dismiss effects on the example image. Doing this with shapes and a variety of hues and luminances would be a better way to prove the point if it bears out.

Maybe the (evolutional) reason that we perceive blue as darker is exactly that it would otherwise reduce the sharpness of what we see.

It has a whole lot to do with our eyes having far fewer blue receptors.

I'm sure you could find an image where blurring blue ruins it, and blurring red and green have no impact. This feels like cherrypicking especially given how trivial it would be to just show a bunch of examples.

The author is correct. Lighting designers sometimes use the effect deliberately to create blue spotlights that viewers can't focus on.

That description doesn't do it justice - you have to experience it to appreciate it. It's very striking and slightly surreal.

They might be correct about chromatic aberration and the difficultly of focusing on pure blue, but the conclusion from their experiment is completely wrong.

One of my favourite series in art is Yves Klein's blue work. For anyone unfamiliar, he found a blue that he considered the bluest possible blue [1], and went on a journey painting everything in that blue. I loved that he did this, and then eventually managed to get to an exhibition of his work at the Tate Modern and was absolutely blown away by it - it really needs to be seen in the flesh to appreciate it. There's something about his blue, that when painted on to a sculpture, almost makes the 3D disappear and the sculpture looks 2 dimensional. Extremely beautiful.

As a side note, some (many?) cultures around the world have no word for blue, blue is just other shades of green.

[1] https://en.wikipedia.org/wiki/International_Klein_Blue

Yes!! The lack of green-blue distinction is prevalent enough in linguistics that the term "grue" has entered the lexicon.

Paul and Kay (1969) argue for a linguistic universal which posits that the set of which colors a language has is a function of how many colors it has. (Stealing from https://en.wikipedia.org/wiki/Linguistic_relativity_and_the_...):

1. All languages contain terms for black and white. 2. If a language contains three terms, then it contains a term for red. 3. If a language contains four terms, then it contains a term for either green or yellow (but not both). 4. If a language contains five terms, then it contains terms for both green and yellow. 5. If a language contains six terms, then it contains a term for blue. 6. If a language contains seven terms, then it contains a term for brown. 7. If a language contains eight or more terms, then it contains terms for purple, pink, orange or gray.

The opposite of the grue phenomenon exists too, i.e. languages which subdivide the "blue" part of the spectrum into separate lexemes. In Russian, for instance, goluboy = light blue, whereas siniy = blue to dark blue. This morning I was reading the Wikipedia entry for color revolution, and there's a quote from Belarusian President Lukashenko, "They [the West] think that Belarus is ready for some 'orange' or, what is a rather frightening option, 'blue' or 'cornflower blue' revolution." I had to chuckle about that - it sounds so goofy in the English translation, but that's only because we don't have a lexical distinction there. (Now I would have personally translated it to light blue, but that's another matter.)

Fantastic post, thank you!

And I thought grues were the furry adventurer-eating dungeon-dwelling horrors!

As someone who hasn't seen it in the flesh yet, and doesn't "get" modern art unless someone explicitly spells it out for me, could you elaborate more on why it's so spectacular?

For example, Blue Monochrome [1] seems to my uneducated eye to be just a layer of pure blue that every wall painter recreates every time they paint a wall blue. Why is the Blue Monochrome piece more than just a wall painted blue?

[1] https://www.moma.org/collection/works/80103

Klein blue is outside the color gamut that can be represented on normal monitors, so it's physically impossible to get the full impact of it through a picture. It just looks .. deeper.

There are a few flowers that have this property; fuscias, and others with strong UV fluorescence.

Consider the time period and the historical context. It's modern times, Cold War is occurring, and WW1 and WW2 left scars across Western Europe and caused major changes in the art world, including being a boon to abstraction and fragmenting styles into many eclectic directions.

Chemistry has DRASTICALLY altered painting from the Renaissance to the World War era. New pigments have been constantly highlighted and displayed in artwork. Finally, an insanely blue blue has been invented, bluer than any other blue paint in the past.

The artist highlighted above attempts to showcase the new technology in its purest form. Though, despite this strive for purity of blue, the application is inherently uneven. If you look into the painted canvas up close, you will see imperfections and patterns in "just a wall". It's also a statement, it may cause reactions and cause viewers to question the boundary between art and not-art.

It's not my cup of tea compared to masterworks of Van Gogh or Homer or any of the legendary painters, but art goes through many phases and is used to express many different ideas. What I do think is bonkers is that modern artists (who are well-connected) may be paid millions of dollars for these works, which to me don't showcase skill and talent, but which reward creative ideation and concepts.

> Finally, an insanely blue blue has been invented, bluer than any other blue paint in the past. The artist highlighted above attempts to showcase the new technology in its purest form.

I was thinking something along these lines. Based on the first Wiki article, Klein was involved in developing this pigment. If so, the work stands on the merits of that achievement alone. He was, for that moment, literally the only person in the world that could have created that painting.

There’s a really great short story by Alistair Reynolds about an artist that’s obsessed with a certain Zima blue (name of the story) which is essentially an extended meditation on the above, I think you might like it. :)

It was an awesome short as part of Love Death and Robots https://www.imdb.com/title/tt9788510/

There's some great answers to your question below, but I'll add mine anyway. Because of the way our eyes see blue (as highlighted in the OP), and especially Yves Klein blue, it has some slightly magical properties in art. The flat blue canvases are absolutely uninspiring at first glance, but stand in front of it for 30 seconds and it starts to recede - it becomes hard to tell how far away the canvas actually is. You're unable to make out texture on the surface because the brain is struggling to actually work it out. It's most striking on the sculptures though, they almost entirely lose their depth and become a flat thing that changes shape as you moved around it. Imagine a 3d rendering of a gallery scene where there's one model that is untextured and unlit - it's like a brilliant blue silhouette.

I took my then 5 year old daughter to the Tate for the exhibition and it had the same effect on her, while almost everything else on show had no effect at all. The only other thing she loved was Bridget Riley, and I think Yves Klein's blue work is somewhere in the same realm - the art is in defining something that makes the viewer's brain do some of the work, that is going to be experienced slightly differently by everyone who sees it.

Don't know about Yves Klein specifically but remember seeing this video from Vox:

"Why these all-white paintings are in museums and mine aren't" [1]

[1] https://www.youtube.com/watch?v=9aGRHOpMRUg

I like to wander around art museums, and on one visit, I shared a gallery with what seemed like a private tour group.

One woman was conducting the tour for three people, when they stopped at one of these all-white paintings.

She was describing the potential meaning behind the work, and noted that sometimes the artist expresses textures, or covers some background work.

It's hard to describe, but I felt this sort of absurdist joy when I watched all four of them lean in very closely for half a minute, only to discover absolutely nothing unique about the work in its texture or color.

Maybe sometimes art isn't made for the observer, but the observer's observer.

That's the missing piece! Now I know how to spend my next rainy day!

As mentioned above, it just looks different in person, that picture does not do it justice by any means. It's kinda like when you see a 3D render with inaccurate physics, but this one is in the real world - it feels out of place. Or like catching a really pink sunset: you can look at it for as long as you want and the color never ceases to impress you.

Great anecdote!

Reminded me of the short story Zima Blue by Alastair Reynolds (which was adapted into an animation short on Netlifx's "Love, Death and Robots").

I found that episode very moving. It captured the feeling I suspect many of us experience, of having started out with simple, blissful naivety, before slowly accreting layers of grown up, professional bullshit until a craft loses its joy. The desire to strip it all away, not just the ways in which your work has changed over the years but also the ways in which it has changed you.

I had no idea Alastair Reynolds was behind the story, I’ve enjoyed his work quite separately.

Apparently more than one "Love, Death + Robots" episode was based on Alastair Reynolds' work. "Beyond the Aquila Rift", for example.

I also spotted references to other scifi authors. There's one episode from the first season that is almost 100% something Bradbury would have written (without me telling you which one, can you guess which episode I'm thinking of? Just to doublecheck my own perception), and of course "Pop Squad" from the second season is based on the short story of the same title by Paolo Bacigalupi (from "Pump Six and Other Stories").

And I'm sure I'm missing many more!

John Scalzi authored at least one episode in the first season, and I think another in the second.

I saw some of the same things you'd have seen in the MoMA (not actually called that) in Nice, France. Walking into the room of these insanely blue paintings and sculptures was almost a religious experience. It's the first time I experienced Stendhal Syndrome[0]. I just had to stand there and stare for a while.

Yves Klein's "Leap into the Void"[1] is another one of his works that really grabbed me when I first saw it. Can't quite explain it. Those are the best types of art experiences in my book.

[0]: https://en.wikipedia.org/wiki/Stendhal_syndrome

[1]: https://www.metmuseum.org/art/collection/search/266750

That's awesome. Looks like his hue is very, very close to YInMn blue, one of my favorite contemporary scientific discoveries:

https://en.wikipedia.org/wiki/YInMn_Blue

Amazing, thanks for the pointer to Yves Klein.

I’ve seen blue man group live and they have an otherworldly look in person, and I suspect it’s related to this phenomenon.

I really like his combination of blue and grey images.

funny how it's different when interpreted in biology limits

also how no art teacher ever told us about Klein's blue the way you did.. they simply used it as an authority figure

There's an optometry place in my neighborhood with a back-lit sign with big, blue block letters. And every time I walk by at night I note how fuzzy it looks.

I'm convinced this is an intentional troll. This optometrist knowingly picked a sign to make people momentarily question their vision.

This happens every wintertime for me as blue string lights are put up, and they always appear “fuzzy” compared to other colors.

Technology Connections did some videos on "Making Holiday Lights Less Garish", where instead of using narrowband colored LEDs he filtered white ones: https://www.youtube.com/watch?v=PBFPJ3_6ZWs

I got dry eyes some time ago. Dryness gone but now I see starburst at night in headlights, neon signs and stars. Being unable to see stars as flickering dots anymore hurts me the most. Neon signs in particular if blue are totally whacky and unreadable until I go too close. I went to optometrist recently and they didn't understand why blue in particular and recommended a color blindness test which I obviously passed.

Now I understand why blue in particular. Damage is done, I wish I could take it back.

Wait, stars are flickering dots for most people?

Yes, stars typically twinkle slightly.

Stars are unimaginably small point lights in the sky. They look like larger dots because of imperfect focus in our eyes [1]. But since they are in fact so tiny, it means very small atmospheric variation and obstruction—heat shimmer, floating dust, etc.—can significantly momentarily occlude the star. That causes its perceived brightness to vary over time.

[1]: https://en.wikipedia.org/wiki/Airy_disk

From atmospheric distortion they can appear to flicker, or “twinkle” as the song goes.

What are they for you?

May I ask how exactly your dry eyes led to degradation in vision? I've recently been struggling with mild corneal abrasions that leave me with something resembling a "starburst" in my night vision, and I'm suspecting it may be caused by dry eyes.

I think dryness did some damage on cornea. It's better some rare days (which feels like a beautiful dream) but mostly I see lights, moon, stars any bright light with dark background as starburst or multiples. Even moon :(

Do you also find that this effect is way more pronounced in recent years with LED string lights than colored lights many years ago? I think b/c LEDs are more monochromatic, I will notice a difference between my parent's extremely old string lights and newer sets.

Epic! Trolling or genius marketing while a bit misleading. At the same time if people can't clearly read the sign how do they know it's an optometry and that they need to go there?

The author is wrong, that experiment doesn’t show anything about focusing. The blue channel in RGB is simply much less bright than the green, which means it has much less contrast, which means that manipulating it in various ways has less of a noticeable effect on the image as a whole. This happens to be true for blurring it, but also adjusting the contrast, inverting it, pixelating it, offsetting it, averaging it completely, whatever manipulation you can think of.

There are also fewer blue cones in the retina, so we have lower resolution in blue.

Blue LEDs and black lights show this effect very clearly. This is e.g. described much more succinctly in the top comment here: https://www.reddit.com/r/askscience/comments/3c1qsg/why_do_b...

> 2 reasons: 1) You don't have the nearly as many short wavelength detecting blue cones as you do red and green in your fovea. 2) The angle of refraction is dependent on wavelength and short wavelengths get refracted more than relatively longer ones by your eye and therefore focus in front of your retina if you are myopic (nearsighted). The black lights are throwing off a ton of very short wavelength light and when coupled with the larger pupil you have in the dark it sets your eye up for a bunch of chromatic aberration. They should look clearer if you are hyperope or overcorrected in your myopic prescription, or if you view them at a closer distance.

Interesting demo, but I think the retina resolution has more effect on this.

Also note that blue neurons are also much less dense, and our eye blue channel has natively much lower resolution.

This is why in old Windows installers, blue color was used for gradient, when colors were 16 or 256 -- blue and black dots were blurred in the eyes, while the same combo of green dots was very visible.

A windows setup with blue background: https://guidebookgallery.org/pics/gui/installation/copying/w... (Don't have a green one, but one may try photoshopping this one.)

I would guess the deeper reason is that the sky is blue. That makes it more useful to have good vision in red and green.

If we needed good resolution everywhere, we might have had eyes optimizing for different colors, four eyes, etc.

Also, it isn’t as simple as this article describes. The human eye can vary its focal distance (https://en.wikipedia.org/wiki/Accommodation_(eye)) over a larger range than the effect of color aberration, so the eye _could_ optimize for having optimal focus for blue light or vary that over time.

(https://www.osapublishing.org/josa/abstract.cfm?uri=josa-68-... indicates humans can learn to do that in the lab)

One theory I've heard is that hunting for fruit was probably a major driving factor in human color vision, as well as that of other primates. Good red/green vision would've helped our ancestors search for ripe fruit (usually red) by being able to easily distinguish it from foliage and unripe fruit (usually green).

What's funny is that most mammals can't distinguish between red & green.

For example: the reason why tigers have red camouflage is that their prey cannot distinguish them from the background green of the forest, combined with the fact that mammals cannot create green pigment for their fur (yet).

The second to last demonstration blows my mind. I can't help but feel like I'm being duped, the result is so sharp.

i guess with red you get a similar effect. The green channel is the one that affects most the perceived intensity. If you blur the green everything becomes blurred.

Interesting article and discussion.

I always wondered how the focusing actually works. It happens „automatically“, but what is involved? Are all cone types used for the focusing, or mostly the green-type ones? Or are there even special, dedicated cells for the focusing only? Does the control ober the muscle controlling the lens shape goes via the brain, or is there a more direct mechanism?

Is there an expert around to explain or give some links to explanations?

(as a side comment: as a teenager I learned to control the focus point to a certain degree. There were these pattern-3D images, „Magic Eye“, and since the perceived depth does not correspond to the actual distance of the image, they eye needs to correct. I guess the same applies to 3D cinema, and may well cause the eye strain reported by many)

This is amazing to see. We should use this for image optimization. When we compress channels, we should compress the blue channel to like 30% while keeping others at fairly large 80% and it might appear better than a 60% compressed image.

As triclops200 says, lossy image compression algorithms have long taken advantage of this. You might be interested in this page, Your Eyes Suck at Blue, which shows an image with the blue channel increasingly compressed:

https://gamesx.com/misctech/visual.htm

edit See also this counterpoint: https://news.ycombinator.com/item?id=573593

We already do and have done historically. The most obvious example I know of is that 8bit color uses 3 bits for green and red and 2 for blue.

For some time many graphics cards had a 16 bit "hi-color" mode with 5:6:5 bits for RGB (SVGA, etc.). Most graphics card modes that used only 8 bits per pixel used that value as an index into an 256x(8x3) bit color palette (MCGA, VGA, etc.).

That's chroma subsampling, most commonly 4:4:4 4:2:2 and 4:2:0 where this principle is used

I guess we can call it lossy compression ;)

That’s exactly why images tend to be compressed in a YUV colour space instead of an RGB one.

It's no big surprise given that the fovea, which is responsible for detailed vision, contains no blue cones.

[0] http://hyperphysics.phy-astr.gsu.edu/hbase/vision/rodcone.ht...

I'd like to see what happens when the red channel is blurred. Digital images like JPGs seem to blur the red channel more than the blue and green channels.

JPEG transforms the color into YUV channels. Y is the luminance, equal to R+G+B or something like that. The U&V channels (color) are often downsampled.

Y is basically "mostly green, a bit of red and hardly any blue" rather than a flat R+G+B. So blurring the green channel (as TFA does) is nearly equivalent to blurring the Y channel.

I guess that will teach me for saying "or something like that" rather than going into detail.

The Himba tribe of Namibia cannot see the color blue (same tribe that Nike studied about running long distances). They are an isolated tribe that can't see blue ... The study included presenting a chart with 10 boxes where 9 boxes were green and 1 was blue but all boxes had the same hue (reasonable value that we can easily differentiate); and the entire village couldn't identify 'the one box that was different from the others'. They relocated an orphan newborn to another tribe and the child easily identified the color blue proving it wasn't genetic. It's weird how all the videos about it have been deleted. It was presented on a TED Talk and an unrelated National Geographic episode. A linguist on TED Talks did a whole talk on how vocabulary defines what we see. I wonder if this was a correction and hence, the removal.

I guess this is the updated understanding: https://www.youtube.com/watch?v=mgxyfqHRPoE

They cant see the color blue and we cant see hue in green

>This is one of many examples of our brains being much more powerful than our eyes. Too often we think of our eyes as perfect cameras. However, it is the brain that is able to accomodate [sic] for all of the optical shortcomings in order to resolve the world.

While this is a description of the human brain and human eye it's interesting to me that it is a very accurate description of the progression of camera technology in the last few years as we shift from the supremacy of Big Glass to the amazing results from computational photography being applied to cell-phone sized lenses

I'm surprised the author doesn't mention the fact that only 2%-5% of the cone cells in our eyes can perceive blue. That's a huge factor in how well we process colors with blue light.

Citation please.

Not exactly the same thing, but we have practically no blue receptors in our foveas:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2715890/

Wikipedia and many websites claim 2%, this pdf claims 4%-5% but only on 2 individuals

http://haegerstromportnoy.vision.berkeley.edu/Pubs/ROORDA.PD...

Alternate source showing something similar: https://gamesx.com/misctech/visual.htm

This is incredible on two grounds.

First, personal. I always thought something was wrong with my eyes because I couldn't focus on blue LEDs at night. I always thought either the LEDs have done irreversible damage to my eyes since some are so bright or that my eye is damaged some other way.

Second. This means we're missing so much about the world that we're not seeing. To be exact 33% or maybe even more if Earth has more blue than red and green, which I suspect it does last time I looked up.

Lots of doubt in the discussion here. I found this, and it’s not quite as elegant an explanation, but it seems to agree that it is due to chromatic aberration and the eye being tuned to focus on red and green light.

https://www.thenakedscientists.com/articles/questions/why-ar...

This would seem to explain why when you go to the optician, he's got a lot of red/green tests but never blue one as far as I can tell. The critical graph is the one with the blue peak to the left and the red and green near each other on the right.

Also it seems to hint that there's a fourth receptor that humans don't have in the gap region. Tetra-chromatic creatures do exist IIRC.

Even tetra-chromatic humans exist, although it's pretty rare. The fourth cone tends to peak between green and red though.

That explains beautifully why I always feel like I've lost my contact lenses when I'm at a concert and the lighting goes all blue.

That was my first thought when reading this. On numerous times I've been watching a stage show and can see everything great. Then the lights turn blue and it's just a blue blur.

Doesn't hurt that there's hardly any blue in that image and it's dialed down almost to black.

Alas, this situation is even worse if you have an astigmatism, which blurs the blue more than the other colors. I had an astigmatism my whole life (although my near/far vision was otherwise fine), and the invention/popularization of blue LEDs has been a constant source of irritation.

Unfortunately, this effect is even worse if you wear glasses (as described in the article), which I have done for about two decades now.

And even more unfortunately, it is even worse with the shift to progressive lenses (due to age-related presbyopia) in my experience. It has gotten to the point where all my computers are configured to use blue sparingly, and almost never in pure blue color. For example, there is no blue in my IDE color schemes anymore, and any mostly blue color is made magentaer or cyaner.

Interestingly, many ancient text sources do not speak of blue color at all, using other expressions.

https://en.wikipedia.org/wiki/Wine-dark_sea_(Homer)

There's a fascinating Radiolab episode that expands on this topic, asking the question about whether 'blue' is a feature of nature or a cultural invention & transmission:

https://www.wnycstudios.org/podcasts/radiolab/segments/21121...

(Non-rhetorical question). I don't understand why the article writes off κυάνεος / κύανος as "later stages of Greek", when it's already present in Herodotus [0]. Just how a big of a sample size do they have between Homer and Herodotus, that they can interpret the evolution of such a minor, infrequent word? Isn't Homer basically "before written literature" Greek anyway?

edit: Also, wasn't Homer supposed to be a blind dude?

[0] https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext...

https://en.wikipedia.org/wiki/Ecbatana#Historical_descriptio...

>"The battlements of the first circle are white, of the second black, of the third circle purple, of the fourth blue [κυάνεοι], and of the fifth orange:"

If you like this, you'll very much enjoy this exploration of color and chroma keying in cinematography: https://www.youtube.com/watch?v=aO3JgPUJ6iQ

Could this be a factor in why we didn’t evolve to see a wider range of wavelengths?

Is the visual spectrum just barely within the range that our brains can correct for the diverging focal lengths without needing additional lenses or modifications to the eye?

Water is relatively opaque at wavelengths above and below the visible spectrum. Air is also much more absorptive outside of the visible range. These two effects compliment eachother - water has a very sharp increase in opacity in the ultraviolet, while air has a sharp increase in the infrared. Our eyes are full of water and we look at things through air. Coincidentally, the visible spectrum matches the peak output from the sun. While you can go a little further into the infrared and ultraviolet ranges, there simply isn't much more to see, it would be as if we were looking through muddy water and dimly lit fog. Any mutation allowing you to see these wavelengths would convey no advantage.

I think our brain would have evolved some sort of post-processing algorithm to deblur the signals from blue cones, if blue was so necessary.

But blue comes mostly as diffused light from the sky. And the effect is especially pronounced in dusk, when blue color floods everything and reduces contrast. That's why yellow glasses help to increase it back and are used in sports and in driving.

It appears to be somewhat hereditary. My daughter and I have it but my son does not. When I look at color blue and purple, I see a smudge so when there letters such as store names far away, I absolutely can’t read it. It appears like all the letters are smudged. I recently bought a InstaPot cooker which has blue color led lights. The previous mode had red. I can’t read it from far. I have to get close to read the blue led lights.

Edit: edited for clarity.

The use of "blind" in the title is problematic in several serious ways, not least, for being obviously false for any conventional interpretation.

Idle comment: were divergent focal point such a significant issue for visual perception, IMO we could anticipate it would be widely applied by evolution, and we would see many prey species hiding inside blue blurs. There are innumerable reasons this is not the case; but that it isn't is one more problem with the conjecture.

I wonder if this is the reason for the recent Ontario license plate fiasco. The new design for license plates had a blue background but they were very difficult to read.

https://toronto.ctvnews.ca/premier-doug-ford-to-hold-first-n...

https://biology.stackexchange.com/a/49067

This effect can often be seen with stage lighting: Metallic/shiny objects, like the stands for the drum set, which are illuminated with both (deep) blue and red, will typically appear as a red line with a blue halo around it.

I'm tempted to experiment. If I take a blue LED and a green LED in the dark, when I focus on one the other should appear blurred.

Blue LED clocks (like on 'high end' microwaves or appliances) are one of my biggest pet peeve. I'm not an old fart by any stretch -- my eyes are fine -- but the blue blur when looking at the clock at night is a real thing.

Fun fact: this phenomenon is similar to why older cars had yellow-tinged fog lights. It's partly light scattering in suspended water droplets (fog), it's partly the perception factors talked about in the article, but basically reds and yellows have lowest "light scatter". You're not gonna build a red foglight for red-is-danger reasons, so yellow foglights are the next best thing.

Yep, exactly. Scattering of light is proportional to the fourth power of the frequency (or, equivalently, inversely proportional to the fourth power of the wavelength).

I've been telling this to my kids whenever I got the inevitable "why is the sky blue" line. :)

Major pet peeve of mine too.... Blue leds on appliances are an instant deal breaker for me. Green looks cheap. Fortunately starting to see some white led displays on appliances, but hard to come across still.

My experience is that in the dark, I can't focus on a blue LED at all. It will just look a bit blurry.

This article is false. Try this out Photoshop and not even close.

Here are my results, with a 22px Gaussian Blur on the Channels

https://imgur.com/a/AS0LAyk

IMO The only reason the blue appears a little less blurry is that most of that color is in the water & clouds.

Not in the land masses, with the sharp borders

Nah, the one where blue is blurred still looks the sharpest. And you blurred them all very little so no surprise they look less different.

Blurred red and blue look similar but blurred green is absolutely blurred to me.

I think this is why one of the older analog video formats, I can't remember if it was VHS or NTSC, used less bandwidth for blue color than for the other colors. This was not noticeable unless blue letters were recorded, which always looked more blurry than letters in other colors.

What happens in monochrome light, say if you are in a darkroom with a monochrome blue light source, would you be able to focus on objects? Would they appear blurry? Or this "out of focus blue" only happens when other colors are present?

Is this why I can't focus my eye on a blue LED while focusing on the surrounding area?

As mentioned in other threads, it also has to do with low percentage of blue cones in the eyes.

TBH I was totally in the dark about this. With the article having put this in focus for me, I now feel a little blue about the whole affair, though in a diffuse kind of way.

easy physics question here: if the light converges in one focal point after passing through the lens, as pointed in the 2nd animation, that means that the outer light beams reach that point latter in time than the inner ones, right? My point is that at the same speed, they are traveling longer distances, and the animation does not show that, but that they get to at the same time.

So if you're looking for ways to hide data in an image, making slight adjustments to the blue channel isn't the worst idea.

The animations are really nice. Does anyone have a guess what tool they're made with (based on font or other hints)?

Thanks! These were all done by hand in Procreate on an iPad since I wanted to give them more of a chalkboard feel.

Nice style of the videos. Also the content, of course, but it's nice seeing them so chalkboard-like.

Does someone know, if this phenomenon is this also related to our bad visual capabilities at night?

You know what's funny about this?

The most common color of Call To Action buttons on websites is blue.

For me discerning dark blue from black on white backdrops/screens is so difficult

Oh, so that's why I can't read blue lettering at night. Always wondered.

Blue is my favorite color. Has my whole life been a lie?

Blue is my favorite color and it seems like whenever I call something blue somebody tells me it’s green. I don’t like green.

I have no idea what to make of that.

Maybe it's the lighting?[0]

[0]https://en.wikipedia.org/wiki/The_dress#/media/File:Wikipe-t...

If you can’t find a way to teal with it, try cyan turquoise?

the blue channel in this image is not as filled as the green, the levels are lower.

the conclusions here are a stretch.

I’ve always found blue LED or cold cathode signs absolutely illegible at night - just an amorphous blur. I always thought it was just me.

This was offensive? Seriously? Christ, you lot are weird.

As other comments have pointed out, this article is inaccurate — particularly about root causes. It's frustrating in part because it is so easy to tell it's not true: look at anything "blue" and notice that it's not blurred. There are a few operating principles here that explain why this observation is functionally incorrect, but also how it's adjacent to the truth.

The first is metamerism, or more generally the fact that we don't observe wavelength directly. Many of the blue colors we can perceive in the real world have a lot of "green" and "red" wavelengths in them too; the cones that detect green and red will still fire for those collections of wavelengths, but the blue-detecting cones will fire faster. We perceive "blue" through higher level processing of those signals; furthermore, it's not a 1:1 mapping.

More importantly: most light we see isn't spectrally pure, so chromatic aberration is not as significant as those charts seem to indicate; rather than multiple distinct planes of good focus, you really have a general region that has a minimum spot size. For most human eyes that spot size is pretty small; errors in the human eye are going to be a larger factor than chromatic aberration for most people.

Also significant: most chromatic aberration people talk about in lenses is lateral chromatic aberration, which can be significant in biological eyes — it's supposedly why herbivores with wide fields of view have horizontal irises! — but for human color vision, most of our acuity is in the foveal region, for which LCA is vanishingly small. The magnitude of LCA is a function of angular distance from the chief ray (~foveal). Axial chromatic aberration has a much smaller effect and generally only affects your minimum spot size, but as mentioned before biological eyes are not accurate enough for this effect to dominate.

Now, what the article nearly gets right: there are examples of light you can't focus on: short wavelength light that is spectrally pure (and sufficiently distant) could be 'unfocusable' for certain eyes. I can report with high confidence this is true for my eyes, and likely for a lot of other people. You can see this with blue laser light, some violet-hued LEDs (not red + blue mixed), or even the visible spectrum from mostly-UV sources. I find that the light itself will appear to have a halo and not be particularly sharp; for me, the perceptual effect is not quite like it being blurry, because the shape of the 'blur' is affected by my eye's aberrations, so it tends to have a 'spiky' bokeh. YMMV.

Finally, there is a truth about human color vision that the tests here seem to get close to: we mostly perceive sharpness or acuity in images as a function of luminance, not chrominance. (Modern image and video formats exploit this extensively.) In fact, the equation to derive luminance from chrominance values models this explicitly; it varies based on color space, but here's the equation for sRGB:

Y = 0.2126R + 0.71522G + 0.0722B

Where Y is luminance, and R, G, and B are the individual color channel values (source: https://en.wikipedia.org/wiki/Relative_luminance). Note the coefficient for blue suggests that only ~7% of our brightness perception derives from the blue channel. This is the source of chroma-based data compression, where we throw away data in the chrominance channels but maintain it in luminance (see YCrCb coding), which is also the reason why blue seems to matter less when doing per-channel blurring: it simply contributes less to the perceived luminance value due to the mechanics of human color perception.

The is interesting!

Snell's work on optics would later be overshadowed by the GNU alternative, Fresnel.

I can't believe this awesome joke is getting downvotes. It's like pearls before swine, but I'm leaving it up so you can find out which amongst you are objectively bad people.

Explain the joke?

Presumably “Snell” > “FreeSnell” > “Fresnel”.

And its BSD fork, Libresnel

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