I don't disagree with it but the colors shown in the article aren't violet, they are all shades of purple. Spectral violet is outside the gamut of most RGB color spaces, including sRGB, Adobe RGB, Pantone, CIELAB, etc. Monitors also wouldn't be able to reproduce it anyway.
The CIE 1931 curve showing a bump in red inside the blue is misleading I think. It does not represent how the cones react (the article says so in small print). The L cones aren't excited at all when pure blue or indigo or violet light hits them. The graph was built to find the best RGB primaries to use in order to best "emulate" how we interpret colors, so I think it actually already encodes our bias and general lack of skill at distinguishing violet from purple.
Similarly many people don't really make a distinction for cyan and just call it blue or green when they see it.
What people are calling “spectral violet”, as in, a particular range of wavelengths of light, is not a “color”. Color is a perceptual phenomenon which happens in people’s brains, and is several steps removed from light spectra, involving several types of adaptation and varying from person to person and context to context.
“Violet” is a type of purple or purple–blue flower. People use the color term “violet” to mean a hue between blue and purple, without specific reference to the spectrum. People get confused about this because Newton stuck the label violet on a diagram of a color wheel one time.
> The “red” signal path has an interesting additional property. As you can see above, it has a small bump of activation around the short-wavelength (violet) end of the visible spectrum
No this is bunk. That bump is an artifact of the process used for defining the XYZ color matching functions in the 1930s before anyone could measure cone cells directly, and the author is grossly misinterpreting what it means. On a linear scale the cone responses look like this https://upload.wikimedia.org/wikipedia/commons/thumb/1/1e/Co...
* * *
While we’re at it, “cyan” is a terrible generic name for a blue–green hue. Stick to “teal”.
“Cyan” is just the Greek word for “blue”, and is a technical term for the type of greenish blue ink used in 4-color printing.
Also it’s a crying shame that the RGB display color made of mixing yellowish green and purplish blue is called “cyan”, since it bears almost no resemblance to the printing color.
> On a linear scale the cone responses look like this
Regardless of whether or not the article's description of the specific mechanism is correct, it's true that humans perceive violet (~400nm) light in a way that can be simulated on a monitor using a mixture of red and blue light.
Using "violet" and "purple" interchangeably in a lot of contexts is probably fine, but it's extremely frustrating when someone uses "violet" to mean "purple" (or vice-versa) in a technical context. E.g. if I buy a "violet" photo filter, I will be extremely disappointed if it turns out to be dark magenta/purple.
> “Cyan” is just the Greek word for “blue”, and is a technical term for the type of greenish blue ink used in 4-color printing.
My understanding is that hundreds of years ago, "blue" was used to refer to what we would now think of as "cyan", and "indigo" was used to refer to what we would now think of as "blue" (0x0000FF on a computer monitor).
> Also it’s a crying shame that the RGB display color made of mixing yellowish green and purplish blue is called “cyan”, since it bears almost no resemblance to the printing color.
The colour people typically refer to as "cyan" in RGB colourspace (0x00FFFF) is the same colour referred to as "cyan" in the CMYK colourspace used for printing. I have several cyan glass photo filters (intended to cut out all longer wavelengths like red, but let shorter wavelengths pass), and they also look the same.
If you perceive 0x00FF00 on a computer monitor as "yellowish green" and 0x0000FF as "purplish blue", and especially if 0x00FFFF doesn't look like cyan printing ink to you, have you considered having the spectral sensitivity of your eyes tested? It sounds like either that's different than usual, or you grew up with a different set of perceptual colour definitions than most people.
> extremely frustrating when someone uses "violet" to mean "purple" (or vice-versa) in a technical context. E.g. if I buy a "violet" photo filter, I will be extremely disappointed if it turns out to be dark magenta/purple.
If you are buying a photo filter you should look for a chart showing what specific wavelengths of light it absorbs.
Neither “purple” nor “violet” is a technical term.
> hundreds of years ago, "blue" was used to refer to what we would now think of as "cyan", and "indigo" was used to refer to what we would now think of as "blue" (0x0000FF on a computer monitor).
0x0000FF on your computer display is not anything like “unique blue” (some blue color a typical observer would say is neutral between green and red). Arguably calling computer-display primaries “blue” is a huge mistake.
Reasonable unambiguous human-comprehensible names for the RGB primaries would be something like “orangish red” (or even “reddish orange” if you take the ISCC–NBS color category name), “yellowish green”, and “purplish blue”.
> The colour people typically refer to as "cyan" in RGB colourspace (0x00FFFF) is the same colour referred to as "cyan" in the CMYK colourspace used for printing.
The +, ◻, and × are printer’s “cyan”, (the ISCC–NBS named category for this is “greenish blue”) and the triangle shows the mixture of sRGB B and G (right at the edge of the ISCC–NBS category “bluish green”).
In a similar way, printer’s magenta is a purplish red color, whereas the 0xFF00FF on a computer display is very slightly reddish purple. The two are not remotely similar.
Notice that diagram also shows dotted lines for the NCS “unique hues” of red, yellow, green, blue, and also shows round dots for the world color survey’s color category foci.
> have you considered having the spectral sensitivity of your eyes tested?
Yes, I have normal color vision, can perfectly pass a Farnsworth-Munsell 100 hue test, etc.
OK, I acknowledge that I was in error here about RGB full-saturation green + blue being equivalent to printer's cyan, and apologize for the error. However, they are still both (in my mind) firmly in the category of "colours in the sky on a cloudless day".
I think we're going to have to agree to disagree on the rest, but thank you for teaching me some new things today.
> “Violet” is a type of purple or purple–blue flower. People use the color term “violet” to mean a hue between blue and purple, without specific reference to the spectrum. People get confused about this because Newton stuck the label violet on a diagram of a color wheel one time.
If violet is between blue and purple, and indigo is between blue and violet, what are we doing here?
But yeah, color is a weirdly cultural-specific thing. For instance, "orange" used to just be considered a shade of red. (Not sure whether it's an urban legend or not, but supposedly the term "orange" to refer to a color originates from the Dutch royal house of Orange.)
I'd heard previously that the fruit used to be called "a naranj", and through linguistic evolution that transformed into 'an aranj', and a light bit of google for 'a naranj' returns the following: https://en.wikipedia.org/wiki/Orange_(word).
>> The word ultimately derives from a Dravidian language — possibly Tamil நாரம் nāram or Telugu నారింజ nāriṃja or Malayalam നാരങ്ങ nāraŋŋa — via Sanskrit नारङ्ग nāraṅgaḥ "orange tree". From there the word entered Persian نارنگ nārang and then Arabic نارنج nāranj.[2] The initial n was lost through rebracketing in Italian and French, though some varieties of Arabic lost the n earlier.[2]
Teal is in the vicinity of #0AA, while cyan is around #5FF; there's almost as much difference between cyan and teal as between cyan and (light) blue or green.
Printer’s cyan is a color in the vicinity of #00A2CC, which is not at all close to #55FFFF.
Using the name “cyan” for the latter is very confusing. I would strongly advise against it.
If you want you can use names like “bluish green”, “greenish blue”, or “blue–green” to stay out of trouble.
If you have a blue–green color, maybe slightly on the greenish side, “teal” is a pretty safe name: people won’t misinterpret what you mean. The name “teal” can represent a quite large generic range of colors.
> Color is a perceptual phenomenon which happens in people’s brains, and is several steps removed from light spectra, involving several types of adaptation and varying from person to person and context to context.
That's one way it's commonly used. But in some contexts color is also used to mean spectral distribution.
That's the whole issue.
It's the same as "If a tree falls in a forest and no one is around to hear it, does it make a sound?". The whole conundrum only arises due to overloaded meanings in many languages.
The photopigment absorption curve [1] shows that the red (L) cones have a slight rise at 400nm (violet wavelength). Also, Wikipedia's image shows it [2].
That's why cameras also have a bump at 400mn, as shown on this manufacturer's page (under the relative sensitivity tab) [3]. Cameras must have it so that they can capture light at 400nm the same way our eyes do. Otherwise those colors would look wrong in pictures.
That is also how computer monitors can display a color that we see as violet. They output a bit of red and lots of blue, which excites our red and blue cones and give the same stimulus as violet at 400nm wavelength. So, monitors can't output violet, but they can trick our eyes to think that there is violet.
The same happens for yellow. Monitors can't output yellow wavelength (590nm), but they output red and green, which excites our red and green cones and we think we see yellow. So, you could also say that when you see yellow on web pages, it isn't really yellow. It is just a mix of red and green.
You can make a camera out of any invertible linear combination of human cone cell responses and you will end up recording basically the same information as far as an idealized human observer is concerned (that’s the basic idea of the CIE system of colorimetry).
The specific choice of computer display primaries has to do with maximizing the possible gamut (as well as other technical and economic criteria), not precisely targeting specific cone cells.
> when you see yellow on web pages, it isn't really yellow
You are using a non-standard definition of “yellow” not accepted by color scientists or color measurement experts.
Have you considered the possibility that human vision might have a more-or-less logarithmic response, and that this is why so many graphs related to it use a log scale?[1][2][3]
Human vision is non-linear, but it is not logarithmic. What it does have is several different mechanisms of adaptation which allow it to respond to very dim or very bright contexts. Some of these adaptations take 30 minutes or more.
But what we are talking about here is the wavelength-responses of a particular type of cone cell. Individual cone cells are activated when some photon excites a little protein and causes a chemical reaction. You can read about the details here https://en.wikipedia.org/wiki/Opsin
The spectral sensitivity charts we are talking about here show more or less a summary of how likely that signaling process is to happen for a particular type of cone cell for light coming in at a particular wavelength. To figure out the eye’s overall cone response to some particular light source, you can more or less take the spectrum of the light source, multiply by the spectral sensitivity of the type of cone cell, and then integrate. Notice that that part of our process is linear in terms of the charts we are talking about.
The non-linear part has to do with various types of adaptation which attenuate or discount those cone sensitivities more or less uniformly across wavelengths (for each cone). This doesn’t suddenly make the left part of the long-wavelength cone response more relevant.
Let's assume you're correct, and that the more-or-less logarithmic aspect to human vision is inconsequential here, and also that the hump in absorption around 410nm by the red cones is also irrelevant. How would you explain the human perception of violet light as a purple colour, then?
In normal circumstances (say, daylight surroundings), a moderate amount of light at very short wavelengths won’t look like much of anything at all, bluish–black, because the cone cells (especially L and M cones which determine red–green response) will be getting much more stimulus from other wavelengths.
If you go to a completely dark room, let your eyes adapt, and look at a blacklight, then you are right that you are at that point going to see it looking purplish because the L cones are stimulated a bit more than the M cones for those wavelengths, and other wavelengths are entirely absent. But this is a really weird edge case for vision.
Because the light that blacklights emit is on the longer end of the possible UV wavelengths. This is what the UV-A means. There are also UV-B and UV-C with shorter wavelengths.
Your second link is on a log scale. The left tail of that long-wavelength cone cell response is not related to the bump in the X of the XYZ color matching functions.
> The CIE 1931 curve showing a bump in red inside the blue is misleading I think.
The CIE color space isn't intended to represent the cone responses, though. The goal was to have a set of reasonably orthogonal, positive-definite functions with which to represent all visible colors as linear combinations of primitives. The "green" Y coordinate was chosen not for its color at all but because it matched the experimentally derived "brightness" function. X and Z are only kinda associated with red and blue.
But because CIE can represent all colors, you can use it to define other color spaces like sRGB which do correspond closely to retinal cell responses. There are also refined versions like LUV and LAB which are (sometimes nonlinear) transformations from XYZ and are intended to better represent perceptual "distance" linearly.
XYZ is just the basic language all these things are defined in, which was its purpose.
> sRGB which do correspond closely to retinal cell responses
What does this even mean? sRGB primaries are chosen to maximize the gamut of a 3-primary additive computer display. They do not “correspond closely to retinal cell responses”.
It means that the colors chosen for those primaries are "red", "green" and "blue" for precisely the reason that those match our cones and are easy to reason about, which (I assume) is the quality you are desiring in XYZ because of the "bump" you're complaining about.
I get that you're trying to be pedantic on this, and that's fine. But the fact that you're complaining about XYZ the way you are shows that... you've sorta missed a few steps. The pedantry goes much deeper, and XYZ is the way it is for some very good reasons.
[edit: shortened this comment] I’m not trying to be “pedantic”, just not grossly misleading / confused, the way the article and most of the comments here are, including the one at top of this thread. Frankly this nonsensical article should be flagged off the front page, as it is going to lead people who read it to be misinformed.
RGB display primaries are only related to the CIE system insofar as people use the CIE system for characterizing and describing them. But it doesn’t constrain the choice of primaries. The primaries are chosen (more or less) to maximize the display gamut under the constraint that there will be 3 of them. They don’t match human cone cells per se (obviously there is some relationship between cone cell responses and maximizing the gamut, but it is not a simple one).
We're in the weeds and I've lost you. You said "The CIE 1931 curve showing a bump in red inside the blue is misleading I think. It does not represent how the cones react"
Which I took to be a complaint that XYZ doesn't represent cone response well.
And I responded that that's silly, because (1) XYZ wasn't designed to represent cone responses and (2) the bump is there deliberately to produce a more mathemetically orthogonal basis.
If you go back to all those books you've read over that decade you spent building your expertise, I'm sure you'll find the same info.
OK, makes sense. You're still being sorta oddly pedantic about this. sRGB was for sure designed to reflect a phosphor set based on red, green, and blue primaries that absolutely were chosen for their correspondence to what most people reason about as primary colors, and the reason for that is that we have three cone pigments in our retina and those three tickle them more or less orthogonally.
So I don't get your criticism. Poster above wanted a set of primaries that corresponds to how the cones react. The closest you can get to that is an RGB space like... sRGB.
Arguing about which design point (phosphor correspondence or cone correspondence) is "real" or "derived" is IMHO meaningless pedantry at this level.
> so I think it actually already encodes our bias and general lack of skill at distinguishing violet from purple.
> Similarly many people don't really make a distinction for cyan and just call it blue or green when they see it.
Isn’t there a difference here between poverty of naming and physiologic limitation? Most people call cyan something else because they don’t have a name for it, but they can be trained to distinguish blue or green and cyan. OTOH, the point here is that certain violets and purples are metamers and although they have different spectra they cannot be physiologically distinguished.
Either a UV laser/lamp, or you need a broadband light source, like sunlight, and a filter/monochromator of some kind (either using a prism or a diffraction grating, or a bandpass filter). You could find something that only reflected UV, yes, but only if you had a source that emitted UV in the first place. Odds are most people don't want UV emitters in a screen they look at 6 hours a day.
The point is that you need a source which contains the wavelength of interest. Monitor leds are red/green/blue and don't emit violet photons. 405nm is usually somewhat visible, if a bit blurry. Blue leds are usually Gallium Nitride based which produces more like 450nm.
I see "spectral violet" and "UV" in two different comments. I have the understanding that "ultraviolet" is past violet and outside the visible spectrum. So now I have questions...
Do spectral violet and ultraviolet differ? In what way? If something isn't visible, why does it matter?
A UV lamp will emit a range of frequencies, and one the lower frequency side of that distribution will be some spectral violet, along with a bunch of UV you can't see.
Spectral violet and ultraviolet are just two ranges on the continuous frequency spectrum, so they differ in frequency.
Yes, ultraviolet is technically outside the visible range (ultra meaning too short a wavelength). In the same way that infrared wavelengths are too long for us to see. In optics, basically anything beyond blue is referred to as UV until you get to other stuff like X-ray. The reason is partly laziness and partly that there aren't many functional uses for violet light, whereas UV is used for all sorts of things.
There are several different classes of UV light, just like there's many shades of blue or classes of infrared (near, long-wave, mid-wave, etc).
The reason that you can see light from "UV" lamps is because they're usually emitting over a range of wavelengths and some of that falls in the visible spectrum. And on the other end, some infrared LEDs emit a little bit of red light which is visible.
If something isn't visible it matters for safety. Most of your eyes' defense mechanisms rely on limiting the amount of light entering your pupils, so they need to be able to perceive how bright a light is. Strong UV is particularly dangerous because it's high energy (think sunburn) and you can't see it so you won't reflexively blink and your pupils won't close. Infrared can also be dangerous, but it's a lower wavelength so you need more of it to do damage.
>Do spectral violet and ultraviolet differ? In what way?
It's ultra because it isn't within the visible spectrum. Violet is a spectral color, which means it's evoked by a single wavelength of light. So the term spectral violet refers to all the shades of violet.
Ultraviolet refers to wavelengths of light which are just a little bit outside the range which humans can perceive. It is not visible.
Some fluorescent materials can be lit with UV light, because they will fluoresce at wavelengths we can see. Otherwise, UV lamps also emit visible wavelengths.
This is a bit of a nitpick, but most people (especially children) can see at least a bit into UV. With my contacts in, I can see down to about 400-410nm. With them out, I can see to about 390nm, because the plastic in the contacts blocks shorter wavelengths. I tested this using a spectrophotometer.
People who have had cornea-replacement surgery and opted for the UV-transparent corneas can see further into the UV.[1] A child (with young corneas that haven't yellowed at all) almost certainly can too.
Slighly off topic, but UV visibility is important in other species. See this link for photos of flowers showing how they appear to bees or birds.
The CIE charts don’t really consider how to interpret or recolor data outside the color space, for example the UV reflection from flowers or astronomy photos in the UV/X-ray spectrum.
Yes, sunlight plus a good prism, inside a box with a pinhole, projecting on white paper. Or a room with a window that faces the sun, covered except for a pinhole, projecting on a whitewashed wall. Which is what Newton did, or so I've read.
Anyway, when I do that, my moderate red-green color blindness is obvious. Because there's a gap in the spectrum. But on a good computer display, there's far less of a gap, because colors aren't spectral, just mixed. For example: https://www.deviantart.com/0bsidianfire/art/Sanguine-4676007...
Paint pigment gamuts are no better than display filters. Get a UV "black light", the color you see from the tube (not the fluorescence from other stuff) is basically what this article is calling "violet".
Look for an LED UV torch/flashlight with a wavelength of 400nm.
You could also use a diffraction grating, prism, or spectroscope, but you'll need to make sure the light source going into it actually contains violet light. i.e. if you use one of those with a CFL or LED bulb, you'll most likely not get much (if any) actual violet.
> I don't disagree with it but the colors shown in the article aren't violet, they are all shades of purple. Spectral violet is outside the gamut of most RGB color spaces, including sRGB, Adobe RGB, Pantone, CIELAB, etc. Monitors also wouldn't be able to reproduce it anyway.
Monitors can display a colour with the same hue as spectral violet, just less saturated (i.e. spectal violet + grey). I think it makes sense to call this colour a kind of violet.
Monitors produce a mixture of blue and red. This is the definition of purple. Our monitors are not capable of producing violet. There is no "kind of" violet to discuss.
The article deceptively passes off purple for violet, and shows magenta for contrast. It is wrong.
I'm using a definition of colour under which two lights are the same colour if they look the same to a typical human, whereas you're using a definition where two lights are only the same colour if they have exactly the same spectrum.
Can we at least agree that computers can produce a colour that looks the same as a spectral violet light reflected off grey paper?
Colors are not purely spectral. Pink and brown are colors that must be mixtures. Black is no color. Normally I wouldn't care, but the point of article is the difference between mixtures and wavelength. The point of the post is semantics.
Some child just learning the colors gets a free pass, but if you put up a website to explain something and its wrong, I think its reasonable to "aggressively" say so.
I suspect they meant "in the spectral color space".
Claiming that it is no color in general is actually a pet peeve of mine: You're right, of course black is a color, in the right context. Colors are not singularly defined as some point across the spectral scale, where there is indeed no black and white, but can be interpreted through many other common, reasonable, and useful definitions as well.
For example, it is perfectly reasonable to define "color" as a point in a 3-dimensional space, for example as RGB or HSV triples, which are very popular and useful definitions in many contexts. Black, then, is (0,0,0).
You can also define color as an element of a particular set of available colors. If you had a "black" car, and someone asks you what color your car is, would they seriously answer with "my car does not have a color, it is black"? (Even ignoring the fact that that would most likely be a lie according to the physical definition, since the car is most certainly not perfectly black in the physical sense, but then what would you call it?)
Fascinating. I've often thought about how purple relates to violet, but never really figured it out.
There are of course colours we call violet that we make by mixing red and blue. For example, the colours in this very article, which use RGB colours to mix red, green and blue light to create violet. So the violet in this article isn't "true" violet at all; it's just a faded bluish purple.
So are there real world paints that are actually violet? Or is the violet from the rainbow something we cannot truly reproduce, and only fake by mixing red and blue?
White light contains light of all frequencies, so a violet paint that only reflected a single frequency would look very dark since it would only be reflecting a tiny proportion of the light that hit it. Even if it reflected a range of frequencies around violet it would still look very dark unless the range was large enough to also contain a lot of blue.
If you wanted to see "true" violet, your best bet would be to find a monochromatic violet light source. A Blu-ray laser would do the trick. But it won't look any different from the RGB imitation aside from being brighter.
EDIT: Please do not shine a Blu-ray laser directly into your eye.
How about a blacklight? The frequency of light you can see leaking through the filter is 404nm, so that should be a relatively safe way to see what "spectral violet" looks like, right?
If your white light source has a flat spectrum, then the violet paint wouldn't be any dimmer than any other color. The reason red or blue paint looks bright enough to see is because, as you said, they do reflect a range. So the violet paint could reflect the same bandwidth range as the traditional visible spectrum paints, and it would have the same power density.
Unless you mean appearance, in which case, yeah, our eyes don't detect violet very well.
I'm surprised this doesn't mention the Sapir-Whorf hypothesis and the work done by Paul Kay & Willett Kemptom to test this with color labels. Basically it found that the presence of labels on colors influenced the decisions speakers of different languages, with different lexical entries for colors, made when categorizing colors in the presence of labels. However, absent labels, the decisions made became more "absolute" with respect to the color spectrum and less subjective, and different language speakers' decisions began to match each other. [0]
Good one, but the part where we as a society collectively define what 'violet' and 'purple' means is lacking. It's all been covered in a wonderful book called Through the Language Glass, by Guy Deutsch.
"So, purple is more reddish and saturated, while violet is more bluish and less saturated."
I'm slightly colorblind and this sentence made me WTF out loud. Purple in that picture looks way more bluish than violet.
"If you take a look at the distance between violet and blue in the picture of the spectrum above, it is about the same as the distance between green and orange."
Since I can easily mistake the colours in any of such pairs I assume that colorblindness works by "muddying the lines" of spectral representation of colour? Would that make it a neurological problem rather than an optical one?
As others are pointing out, it's worth remembering our monitors aren't necessarily even capable of producing true violet. And I'd add that monitors vary widely in quality themselves. This one I'm typing on doesn't yell to me "piece of crap", because I mostly do coding-type activities on it and it's plenty fine to do syntax highlighting, but sometimes when the rotating desktop background shows the same one on this monitor and the built-in Macbook monitor, it's like, huh, there's a lot of difference there. It really wouldn't be a great monitor to watch media on routinely.
We aren't even all looking at the same colors in the first place.
Yeah I get the same impression, it's just that I don't think I could recognise those as Purple and Violet even in non-oversaturated form, to me it's all just different nameless hues of blue.
I'm not so sure about that. The left side appears _overwhelmingly_ purple, and the right side looks _very_ blue. Have you tried something like the Farnsworth-Munsell 100 hue test?
Thanks, that was an interesting test. I guess my feeling of "I'm slightly colourblind" is correct. I don't seem to have that many problems with blue though.
Does anyone know what colourblindness really is? My guess would be that it's one (or more) of the cones either not working properly, or working differently, creating a very different colour experience.
For example, looking at the graph in the article, I'd expect that if your green cones don't work, you'd see no real difference between green and red. If your blue cones don't work, blue would look slightly red. If red cones don't work, again red and green are roughly the same, but violet would look blue.
But that's entirely my uneducated guess as a complete layman on the subject.
As for the purple and violet in the picture, that violet can never be true violet because it mixed by your computer screen from RGB colours, so it's really created by mixing more blue with red, and probably a bit more green, since it's a lighter colour (adding more of the least represented colour moves it closer to white I think).
So if that looks more red to you than the equally mixed purple, the only explanation I can think of is that it might come from the added green, which your eyes might register as potentially red if it's your red cones that don't work properly.
We know exactly how colour blindness works. Usually, the cones all work, but the range of wavelengths they can detect is slightly shifted from normal. Red-green/green-red colour blindness is the most common, and in that case the range of wavelengths that the red and green cones can detect overlaps more than they usually do.
That's not true, actually. Tetrachromats see the same range of electromagnetic wavelengths as everyone else—there's just an extra cone in there that's mostly useless. There's a great video on YouTube called Tetrachromats Don't Have Superpowers that explains it quite well: https://youtu.be/fDoAs0qN7lU
Violet in the article is not a real violet. A computer screen shows violet as a mix of red, green and blue as all colors. So the violet in the article is really a blueish purple. Also many file formats encode them as such. That's only an approximation.
My understanding of color blindness has always been that it's typically a problem with the actual eye cones for color sensing--at least for non-pathological cases of color blindness.
There is no hump in the red detectors. The hump exists only in curves we use to translate light into RGB, and is there precisely to help translate that violet into purple.
The mean absorbance for the red cones was higher from about 400nm to about 430nm than it was for the green cones in at least one published paper.[1]
For some reason that's not clear to me, the graph below the data table doesn't extend the red cone curve far enough to the left to illustrate the hump.
Thanks for pointing this out, thought I was going crazy. So the article's explanation of why violet and purple look similar even though they are completely unrelated in spectrum is bogus (the article claims it's due to this secondary peak in the red cone). So what's the real reason?
Quoting the legend of said picture in the article:
"""Note that this chart does not show the spectral properties of the cones themselves (but they look similar). It represents the CIE 1931 colour space, which, simply put, corresponds to the signals after they have been processed by the brain."""
"""The reason why purple and violet look similar to us is because they stimulate our cones in a similar way, but most other animals don’t share the same types of cones and “post-processing”. This means that to other animals, purple and violet may look completely different!"""
Emphasis theirs. This is the part I'm calling out. Stimulation of the cones is not relevant!
(Of course the cones are relevant but the difference is very much larger and of a different nature than they make it out to be. Most mammals have only two color cones.)
I'd expect so. It's simultaneously easy and hard to test. Easy because you need to show something violet on a similar purple background, and hard because we're not good at producing violet: computer screens and regular printers won't work.
Of the seven traditional named spectral colors, indigo and violet seem to be the least distinct pair. Newton may have included it mainly to have seven named colors, as a parallel to the seven notes of the western major scale in music. He admitted that his ability to distinguish colors was not acute, and, after he had selected his seven, he asked others to mark them off on a spectrum projected on a wall. This is different, of course, then asking them how many distinct colors they thought best characterized the visible spectrum.
Which almost exactly corresponds to the ‘rainbow colors’ as used in Russian (and probably other Cyrillic languages). The color swatches in the linked article are precisely Russian ‘blue’ for Newton's indigo and ‘lightblue’ for blue.
People use words differently. Indigo is somewhere below blue in the spectrum, and violet is below indigo. Some people call a mix of red and blue "violet" but they should use the word purple instead. The French word "pourpre" is often used as a translation for purple, but actually refers to a color with more deep red mixed in.
Very interesting! All my life I've wondered why sometimes we say "violet" and sometimes "purple", with a vague sense that they are not exactly synonyms.
Here is a related question that got a very knowledgeable and helpful answer: https://news.ycombinator.com/item?id=17507968 (Why is there a color "wheel" when frequencies are linear?) HN is amazing!
> Purple objects are "red and blue at the same time," whereas violet objects are . . . just violet.
Not on RGB screens. If I take a color picker to the page's image of a color spectrum, said to contain pure violet, it is still a mix of red and blue.
I admit that it is odd that the left end of the spectrum seems to have color from the right end. It's as if the spectrum wraps around, in our mind's eye at least.
Had an art teacher tell me that "purple" was not a "color" but rather the name of a dye used hundreds of years ago. She said "violet" is the name of that "color" you are referring to as purple.
It is interesting to me that if there would be a way to stimulate red and blue cones, without stimulating green, you would see a color never seen before. As there is no wavelength that accomplishes that.
You've heard of super-tasters? There's a genetic variation that creates a kind of fourth color receptor in some people, apparently giving them the ability to perceive colors others can't!
> One study suggested that 2–3% of the world's women might have the type of fourth cone whose sensitivity peak is between the standard red and green cones, giving, theoretically, a significant increase in color differentiation.
To me, most of these discussions about color come off as, “Weird flex but okay.” And I don’t care if you know how the human eye perceives color.
There is a distinct difference between how we talk about color and how we perceive it, and while it’s helpful to understand both (especially if you need to for your profession), I don’t find it helpful to act like you’re smart for knowing this. Or similarly, to act like other people are stupid and it’s a “pet peeve” of yours that they use the word “violet” to describe a color instead of spectral light. Words can have multiple meanings, and the violet ship has sailed.
I don't disagree with it but the colors shown in the article aren't violet, they are all shades of purple. Spectral violet is outside the gamut of most RGB color spaces, including sRGB, Adobe RGB, Pantone, CIELAB, etc. Monitors also wouldn't be able to reproduce it anyway.
The CIE 1931 curve showing a bump in red inside the blue is misleading I think. It does not represent how the cones react (the article says so in small print). The L cones aren't excited at all when pure blue or indigo or violet light hits them. The graph was built to find the best RGB primaries to use in order to best "emulate" how we interpret colors, so I think it actually already encodes our bias and general lack of skill at distinguishing violet from purple.
Similarly many people don't really make a distinction for cyan and just call it blue or green when they see it.