I love the headline, but unfortunately both the headline and the explanation are wrong.
Better explanation:
The red, green and blue receptors in the eyes all respond to all wavelengths of light, they're just more sensitive at red, green and blue respectively.
When violet hits those receptors, it doesn't hit any of the receptors at their peak sensitivity point. All three receptors fire. However, the green receptor has much better sensitivity than the red receptor, so violet triggers the strongest response in blue and red. If the red receptor was more sensitive, we'd probably interpret violet as a shade of blueish-brown rather than of purple.
The headline:
Purple definitely exists. The eye & brain interpret purple and violet the same, but in the physical world they are different colors, and they both exist in the wild. Purple is a mixture of red & blue, violet is the highest visible frequency. A purple flower is a flower that absorbs green and reflects red & blue. A violet flower is a flower that absorbs red, green and blue and reflects violet.
Agreed. It's simply philosophically sloppy to suggest that purple, brown, and really any other colour don't exist without qualifying what one means by existing in this context, and why that definition of the word is used.
In this case, it seems the "what" is that for a colour to "exist", it has to be a distinct, isolated frequency of light, and (for some reason) it needs to appear in a logical place in the frequency space in relation to other colours. They don't answer the "why" question, and I think if they tried, they would find it difficult, because it's completely arbitrary and in conflict with reality.
Just because some colours do in fact correspond to frequencies of light, that doesn't mean all colours have to. There's a reason we have the terms primary and secondary colour. Some colours are emergent from mixing other colours together. Does that mean they can't appear in the natural world, being discriminated by sensory systems? No. Does purple cause things to happen? I'm sure you could find myriad examples of this in the natural world.
Ironically, the only thing here that only exists in our brains, is the notion that purple doesn't exist.
>All three receptors fire. However, the green receptor has much better sensitivity than the red receptor, so violet triggers the strongest response in blue and red.
I'm confused - it sounds like you're saying it's so off-peak for all of them that, even though it's more proximal to blue, it is effectively equally out-of-range for all three - except that the green receptor is more sensitive. But then that would mean it should look more green, rather than more red and blue, no?
I think you're misinterpreting color and wavelength. No color exists "in the wild". Colors only exist in the consciousness of beings that can capture photons. Wavelengths do exist in the wild I guess, or at least it's a human description of how electromagnetic waves move in the wild.
Purple is a measurement, but wavelength is a measurement too. Ultimately everything is a measurement to us as that is the only way we can experience "the wild".
I think you are misunderstanding the purpose of a headline. "Purple exists only in our brains" is a reasonable summary. Your last paragraph is not a headline.
Not true. Human tetrachromats have an extra kind of receptor somewhere between the blue and red receptors' sensitivity. This doesn't help with colors like violet that are outside of that range.
Also, purple (a non-spectral color) is easily distinguished from violet (a spectral color) if you see them side-by-side.
Exactly this, purple ≠ violet. They don't even look the same.
You won't see violet on a computer screen because it's a higher frequency than what blue LEDs produce. You won't see it on the output of consumer-grade printers for similar reasons regarding the color of the ink.
The easiest way to see actual true violet is to pass sunlight through a prism onto a white surface.
Purple on the other hand is a mixture of red and blue frequencies that stimulate both kinds of receptors in your eyes. It looks like a reddish blue that can't be produced by any one frequency of light.
True violet looks like a deep, deep blue without any red tint.
You usually can't see the really purple-y violet in a rainbow because it's quite dark -- it's easily absorbed by the atmosphere and our color cones aren't very sensitive to that wavelength. But it's there if you amplify it.
More than purple not existing, brown really doesn't exist. Brown is just reflected orange-y light in the right context. You can play around with it, by looking at a picture of say, earthy soil, color picking that pixel and painting it on a white canvas in a different way. Or by trying to shine an RGB light with that color code. It will look orange in a direct light.
Also the purple hallucination is because the same cone that mostly detects red also has a small peak futher along the spectrum next to blue. Since it slightly reacts to blue/violet light, you get that purple tickle.
I wonder if near-UV like 380nm starts exciting the red receptor at 760nm like a resonant frequency or harmonic. Would also explain why something that's deeply red enough doesn't start looking purple, because the lower-energy photons can't get the higher energy receptors to trigger, unlike the other way around for deep blue. Which would make the color purple a distinctly quantum phenomenon.
> brown really doesn't exist. Brown is just reflected orange-y light in the right context.
The Pirahã language only has two words for "color" – which more or less translate to "light" and "dark". Therefore red, green, blue, even orange don't really exist either. Except they do, because we've defined them to exist. Brown is no different.
Well.. no color “exists”, they are just wave like particles.. not even “reality” as we see it exists.. it’s just in our minds..
I think that what they really mean is that there is no wavelength for the purple we see
Except for colors that are combinations of different, disconnected, wavelengths. This is why there are red and blue stars, but no green or magenta stars.
That's not really the reason. Green is a spectral color, and in fact the sun peaks around the green part of the spectrum. But to see a star as green, it would need to exclusively emit green light.
The article says this (and pretty much all the other comments here).
It doesn't however mention James Clerk Maxwell who took a break from inventing equations to torture EE students forever to figure this stuff out, including making the first color photograph.
(Yes I know Heaviside actually came up with the equations we use)
The curved rim of the horseshoe is the spectral locus; that of the purest, single wavelength spectral colors.
Purples are what you get when you travel between the ends of the horseshoe, where no spectral color lies. This is what is meant when one says purple exists only in our brains; it is non-spectral.
Furthermore, our vision is such that objectively different spectra can look the same; cf. metamers. This follows from the fact that the process of projecting an infinite dimensional spectra into three dimensions (because color is 3D) is lossy. But our vision optimizes the dimension reduction for spectral discrimination in parts of the electromagnetic spectrum that are beneficial for evolution.
I forgot to add that in addition to being non-spectral, they are the most saturated colors of their hue. All colors inside the horseshoe are non-spectral; they are mixtures of spectral colors.
Fun fact: such "purples" exist for other species. There was a study that found that hummingbirds are more attracted to a color that is a mix of green and ultraviolet (imperceptible to humans, but similar to our concept of "purple"), than just green, violet, or ultraviolet.
I mean, all colors exist only in our brains. "Color" is a perceptual experience that may start as spectral power and cone excitation, but is then mapped to color sensation through a fantastically complex visual system in the brain. That's why color-based optical illusions work. That's why "The Dress" was controversial.
There's nothing that special about purple. The article makes a big deal about purple "connecting" two opposite ends of the spectrum, but this is just an artifact of humans seeing rainbows and realizing that pink-purple would connect the two ends, even if they're not present in the rainbow. It's just a human framework, not some kind of physical truth.
Put another way, there are a ton of colors that are not in the rainbow, because it's a 1D simplification of our color perception, which is 3D (three cones). Would you say brown "exists only in our brains?"
Well if we get on to hearing, our ears do a lot better than our eyes. From the source entering into hole on either side of our head we can split the sound into a myriad of frequencies and gather a lot of information from it.
In a similar situation from a single point of light out eyes would say "sort of blue-ish". Most visible frequency information is ignored.
It seems reasonable to me to say that soundwaves exist in the world, but music only exists in our brains. There is something added in our perception of the soundwaves that turns them into music.
Something exits in the world, it seems. Sound waves and music are merely our interpretation of it. Maybe what actually exists in the world is music, and sound waves are what our brain invents when the music is too complex for it to grasp?
Readit News
Better explanation:
The red, green and blue receptors in the eyes all respond to all wavelengths of light, they're just more sensitive at red, green and blue respectively.
When violet hits those receptors, it doesn't hit any of the receptors at their peak sensitivity point. All three receptors fire. However, the green receptor has much better sensitivity than the red receptor, so violet triggers the strongest response in blue and red. If the red receptor was more sensitive, we'd probably interpret violet as a shade of blueish-brown rather than of purple.
The headline:
Purple definitely exists. The eye & brain interpret purple and violet the same, but in the physical world they are different colors, and they both exist in the wild. Purple is a mixture of red & blue, violet is the highest visible frequency. A purple flower is a flower that absorbs green and reflects red & blue. A violet flower is a flower that absorbs red, green and blue and reflects violet.
In this case, it seems the "what" is that for a colour to "exist", it has to be a distinct, isolated frequency of light, and (for some reason) it needs to appear in a logical place in the frequency space in relation to other colours. They don't answer the "why" question, and I think if they tried, they would find it difficult, because it's completely arbitrary and in conflict with reality.
Just because some colours do in fact correspond to frequencies of light, that doesn't mean all colours have to. There's a reason we have the terms primary and secondary colour. Some colours are emergent from mixing other colours together. Does that mean they can't appear in the natural world, being discriminated by sensory systems? No. Does purple cause things to happen? I'm sure you could find myriad examples of this in the natural world. Ironically, the only thing here that only exists in our brains, is the notion that purple doesn't exist.
Can you think of any?
I'm confused - it sounds like you're saying it's so off-peak for all of them that, even though it's more proximal to blue, it is effectively equally out-of-range for all three - except that the green receptor is more sensitive. But then that would mean it should look more green, rather than more red and blue, no?
Also, purple (a non-spectral color) is easily distinguished from violet (a spectral color) if you see them side-by-side.
You won't see violet on a computer screen because it's a higher frequency than what blue LEDs produce. You won't see it on the output of consumer-grade printers for similar reasons regarding the color of the ink.
The easiest way to see actual true violet is to pass sunlight through a prism onto a white surface.
Purple on the other hand is a mixture of red and blue frequencies that stimulate both kinds of receptors in your eyes. It looks like a reddish blue that can't be produced by any one frequency of light.
True violet looks like a deep, deep blue without any red tint.
Also the purple hallucination is because the same cone that mostly detects red also has a small peak futher along the spectrum next to blue. Since it slightly reacts to blue/violet light, you get that purple tickle.
https://www.youtube.com/watch?v=wh4aWZRtTwU
[1]: https://physics.stackexchange.com/questions/673991/red-cones...
The Pirahã language only has two words for "color" – which more or less translate to "light" and "dark". Therefore red, green, blue, even orange don't really exist either. Except they do, because we've defined them to exist. Brown is no different.
https://www.youtube.com/watch?v=wh4aWZRtTwU&pp=0gcJCdgAo7VqN...
Not naming certain colours does not mean they cease to exist. They can be split, created, and we have the receptors to perceive them.
It doesn't however mention James Clerk Maxwell who took a break from inventing equations to torture EE students forever to figure this stuff out, including making the first color photograph.
(Yes I know Heaviside actually came up with the equations we use)
The curved rim of the horseshoe is the spectral locus; that of the purest, single wavelength spectral colors.
Purples are what you get when you travel between the ends of the horseshoe, where no spectral color lies. This is what is meant when one says purple exists only in our brains; it is non-spectral.
Furthermore, our vision is such that objectively different spectra can look the same; cf. metamers. This follows from the fact that the process of projecting an infinite dimensional spectra into three dimensions (because color is 3D) is lossy. But our vision optimizes the dimension reduction for spectral discrimination in parts of the electromagnetic spectrum that are beneficial for evolution.
https://en.wikipedia.org/wiki/CIE_1931_color_space#Chromatic...
That outer *bolded* edge is monochromatic light, as perceived by humans. The number labels are the wavelength in nanometers.
https://en.wikipedia.org/wiki/Line_of_purples
There's nothing that special about purple. The article makes a big deal about purple "connecting" two opposite ends of the spectrum, but this is just an artifact of humans seeing rainbows and realizing that pink-purple would connect the two ends, even if they're not present in the rainbow. It's just a human framework, not some kind of physical truth.
Put another way, there are a ton of colors that are not in the rainbow, because it's a 1D simplification of our color perception, which is 3D (three cones). Would you say brown "exists only in our brains?"
In a similar situation from a single point of light out eyes would say "sort of blue-ish". Most visible frequency information is ignored.