[General Battuta]

Clue: Magenta is a product of our minds, literally.

Not really. It can be pretty well quantified, even if it isn't a spectral colour.

What's the wavelength of white?

The important thing to grasp is that there are multiple ways to arrive at each color, which means there is no 1:1 mapping between color and wavelength. You can't look at a given color and know what wavelength of light produced it.

This makes color a good tendentious signal but still a construct.

So, to dissect one of your examples

The fact that our brain does signal processing doesn't mean it invents all the qualities in the image we see. A rectangle is a rectangle in reality, and if it reflects red light and absorbs others (or even emits red light in otherwise dark room) then its colour is red.

You've constructed a false 1:1 mapping here. It could be reflecting any type of light that sums to red on the CIE chromaticity diagram.  There's a whole space of physical properties that rectangle could have which could lead it to reflect all sorts of different light but they would end up as red.

It's not some imaginary quantity that our brain just plasters on, it's a perceived property corresponding to physical property and I don't see how it's relevant to say that there's "no colour" in external world.

It's a perceived property corresponding to multiple physical properties and it could mean any one of them. Ergo, there is no color in the external world; color is a construct which can signal multiple things.

There is no color in the external world.

ed:

This statement is also factually false:

I can agree that perceived colour is a mix of not only the wavelength spread of the light but also the context in which it's seen, physical surface structure (diffuse, shiny, emitted or reflected light), environment's lighting (is the object in a shadow or direct light), but that just means our image processing facilities combine these features with each other to give us more information than just the spectral spread of light that an object emits or reflects.

because it implies a 1:1 mapping in which each combination of wavelength, physical surface structure, and environmental lighting produces a unique color (as you said, more information). This is untrue.

[Herra Tohtori]

I don't know if I'm formulating my arguments poorly, but I never suggested that one combination of physical attributes corresponded to only one perceived colour.

The fact that we can perceive different colours as the same doesn't mean that the external word doesn't have the attributes that make up the colour in our perception. And even if our brain can mix up a lot of stuff together and those things can alter our perception of what the colour appears as, that doesn't change the fact that the colours themselves do exist.

I don't understand the argument that they are just a product of some mental processing. Clearly they correspond to physical attributes of the objects we observe.


A rose by any other name...

[General Battuta]

I don't know if I'm formulating my arguments poorly, but I never suggested that one combination of physical attributes corresponded to only one perceived colour.

The fact that we can perceive different colours as the same doesn't mean that the external word doesn't have the attributes that make up the colour in our perception. And even if our brain can mix up a lot of stuff together and those things can alter our perception of what the colour appears as, that doesn't change the fact that the colours themselves do exist.

No, it doesn't - in fact you're defeating your own argument internally, right here in the sentence:

The fact that we can perceive different colours as the same

You can perceive different sets of the physical traits that determine color as the same color. You're talking about color as if it's something that exists outside the head but it's not. Saying 'that object is yellow' gives very little information about an object's physical properties - it simply places it in one area of the CIE diagram. It restricts its properties to a set with considerable variability.

And again, here:

even if our brain can mix up a lot of stuff together and those things can alter our perception of what the colour appears as

You speak of altering as if there were an objective color which is then altered or moved by the brain's perceptive filters. But there is no such thing. All that exists, objectively, are the traits which are used to generate color - and multiple sets of those traits can lead to the same color.

I don't understand the argument that they are just a product of some mental processing. Clearly they correspond to physical attributes of the objects we observe.

Color does not correspond in a 1:1 fashion. There is no clean bidirectional mapping.

Let's say we create the color 'hooligans'. Hooligan colored objects are objects which possess legs OR tentacles AND bone OR cartilage. A hooligan object could have legs and cartilage, or it could have tentacles and bone. But the definition of hooligan exists only in the rule we have established to define hooligan. You could not build a hooligan meter without first establishing that rule.

Similarly, a machine or alien could not understand our perception of color without being transmitted the rules we use to create color. It could, of course, objectively measure the physical properties that we use to construct color, but it would have no way to arrive at the concept of color from there unless it dissected a human mind, because the rules do not proceed from the physical properties in a trivially mappable fashion.

Ergo, color does not exist outside the human mind.

[Luis Dias]

"Colours themselves do exist".... do you see where I am getting at, Battuta, when I say that people are still deluded my metaphysical thinking?

[General Battuta]

"Colours themselves do exist".... do you see where I am getting at, Battuta, when I say that people are still deluded my metaphysical thinking?

No.

Colors do exist. They're an obvious, measurable property. They're just a property of the signal processing of the human mind, rather than the external world.

[Herra Tohtori]

Nah, I don't think that's right.

I agree that colour perception is largely an internal process. However, your claim that because several different mixes of attributes can appear as the same colour, colours somehow don't exist in reality is false. It's merely demonstrative of the limitations of our visual perception - we can't make a distinction between the two things so our brain dubs them the same colour, but that doesn't mean it's somehow an incorrect distinction.

I can see the value in your argumentation, but I think our definition of colour is a bit different.

Let's try this:



Here we have three dithered fields. Each field consists of blocks of four pixels, enlarged in the upper left corner for each picture.

These appear as the same grey colour. Why? Because on each image we have a situation where every other pixel has two sub-pixels lit up, and every other pixel only one.

On our display hardware, every square should render identically as far as the light intensity goes, and it should appear the same level of grey.

Now, our ability to see colours on computer screen hinges on dithering; our inability to distinguish sub-pixels as individual entities makes it possible to mix red, green and blue in varying quantities to produce a more or less wide gamut of colours.

However, the fact that our rendering displays render all three images similarly doesn't mean they are the same. Their individual properties are different, and each is made of completely different colours pixel-wise, as zooming in reveals.

Now if I were to compare the display to our visual perception, one could say that both arguments have value: All objects are grey in our display, but they don't have grey in reality - hence the greyness is an illusion caused by our display hardware.

The other argument says that each of the objects still have individual colours. One made of cyan and red, one made of green and magenta, and one made of yellow and blue. The fact that display renders them similarly doesn't mean the images themselves don't have these properties.


I don't know if this portrays what I'm trying to say: I'm saying that colour as a physical property does exist in various ways and we can identify them, but limitations in our perception sometimes make us identify various physical properties as the same colour.

You're saying that colour as a concept exists just inside our heads. In my opinion, this undermines the abilities of human visual perception quite a bit, because even though it is limited, it still can distinguish between quite a bit of clearly differently coloured objects.

You could say that my concept of colour is primarily involved in the physical side of things rather than psychological or neurological perception. Mixtures of properties aside, we can still identify spectral colours correctly within the visible spectrum...


TL;DR:

You say because we identify various properties as same colours, colours don't exist.

I say there are more colours than we can identify, and thus some identify as the same.

[General Battuta]

we can't make a distinction between the two things so our brain dubs them the same colour, but that doesn't mean it's somehow an incorrect distinction.

If you're still misunderstanding things this early in the process I ask that you please do some research on the topic before we continue this discussion.

If you can explain to me how an alien or machine would perceive color using only objective measurements perhaps you can make some headway.

[Herra Tohtori]

If you can explain to me how an alien or machine would perceive color using only objective measurements perhaps you can make some headway.

The measurements done by a digital camera's sensor seem pretty objective to me.

However, it obviously doesn't "perceive" the colours, it's a sensor and data storage instrument. To handle the data you would need to have some sort of processing unit that would analyze the image with some purpose.

For example, you could give a robot a task of identifying objects with some colour from the image to separate them from rest of the objects. That'd require a primitive way to perceive the image to distinguish objects in it in the first place...

You could do that by either giving them an RGB colour code with error bars to look for; most likely you wouldn't get very good results with just this method because the colour values on the image would depend on lighting, position of the object, angle of the surfaces etc... but with standardized lighting, you could get relatively good results in controlled conditions.


To make things more accurate and independent of environment, you would probably have to code something that would build a three-dimensional space of the image, separate differently coloured and contrasted parts from the image into individual objects, place them into the 3D space, read their shape, compensate for the lighting making upper parts of objects brighter and lower parts darker, check if the object has any specular glints disturbing the colour analysis, neutralize them based on the interpreted shape of the image, and THEN compare the compensated colour with the target colour to define if the surface of the objects themselves matches the desired colour parametres closely enough.


If I misunderstood what you're after, you'll need to define the word "perceive" for me...

[General Battuta]

If you can explain to me how an alien or machine would perceive color using only objective measurements perhaps you can make some headway.

The measurements done by a digital camera's sensor seem pretty objective to me.

I'm fairly sure there is no color in a digital camera image. There are recorded objective properties. Color is introduced by the human looking at the image.

For example, you could give a robot a task of identifying objects with some colour from the image to separate them from rest of the objects. That'd require a primitive way to perceive the image to distinguish objects in it in the first place...

You could do that by either giving them an RGB colour code with error bars to look for; most likely you wouldn't get very good results with just this method because the colour values on the image would depend on lighting, position of the object, angle of the surfaces etc... but with standardized lighting, you could get relatively good results in controlled conditions.

You're still not talking about color here. You're discussing properties like the wavelength of reflected light.

How would a machine or alien, using an objective sensor that detects the wavelength of light, perceive color?

Allow me to quote Wikipedia.

Two different light spectra that have the same effect on the three color receptors in the human eye will be perceived as the same color. This is exemplified by the white light emitted by fluorescent lamps, which typically has a spectrum of a few narrow bands, while daylight has a continuous spectrum. The human eye cannot tell the difference between such light spectra just by looking into the light source, although reflected colors from objects can look different

Simply measuring wavelengths, it is impossible to arrive at the perception of color the human eye and brain generates. The two different light spectra described in the quote would appear to an alien or machine as two different light spectra. They would have no reason to consider these the same colors, any more than an observer looking at two objects, one with cartilage tentacles and one with bone limbs, would have any reason to consider them both hooligans.

You need the definition of 'hooligan' in order to identify the group 'hooligan'. You need the definition of a color in order to identify the color. It does not exist without that coding.

[Herra Tohtori]

You need the definition of 'hooligan' in order to identify the group 'hooligan'. You need the definition of a color in order to identify the color. It does not exist without that coding.

If it exists, it doesn't need a definition from us to exist, just for us to perceive it.

You're essentially saying that because we identify several different things as the same colour, colour doesn't exist outside our definitions for them.

I say we don't have enough definitions for all the colours in the world, but they exist outside our definitions of them.


It seems we are at an intellectual impasse.

[General Battuta]

You need the definition of 'hooligan' in order to identify the group 'hooligan'. You need the definition of a color in order to identify the color. It does not exist without that coding.

If it exists, it doesn't need a definition from us to exist, just for us to perceive it.

You're essentially saying that because we identify several different things as the same colour, colour doesn't exist outside our definitions for them.

I say we don't have enough definitions for all the colours in the world, but they exist outside our definitions of them.

It seems we are at an intellectual impasse.

Far from it. You're trying to make a speculative argument about something that is quite grounded and measurable. The response curves of receptors in the eyes can be measured. The human visual system simply does not distinguish within a color; it treats all inputs that create the same response pattern as the same color.

You can break down all the possible wavelengths which create, say, magenta into subunits, and name each of those individually - but then you're simply not talking about color any more; you've moved on to something else, something not perceived by the human visual system.

If you want to discuss color, you need to discuss color. Color is, by definition, perceptual. You cannot make an argument that relies on the extraperceptual. We can measure what is perceived. And that measurement is quite clear.

[Herra Tohtori]

If you want to discuss color, you need to discuss color. Color is, by definition, perceptual. You cannot make an argument that relies on the extraperceptual. We can measure what is perceived. And that measurement is quite clear.

I disagree. To me, colour as a property of objects is something substantial, which we perceive in a limited fashion.

I don't agree with binding the definition of colour simply to our perception of it. Clearly the combinations of properties that make us identify them as a colour are quite real.

[General Battuta]

If you want to discuss color, you need to discuss color. Color is, by definition, perceptual. You cannot make an argument that relies on the extraperceptual. We can measure what is perceived. And that measurement is quite clear.

I disagree. To me, colour as a property of objects is something substantial, which we perceive in a limited fashion.

I don't agree with binding the definition of colour simply to our perception of it. Clearly the combinations of properties that make us identify them as a colour are quite real.

Now you're simply wrong - using the wrong words to discuss the wrong things. Color does not exist as a property of objects; we've already demonstrated this. You cannot find and point to a red object. You can find an object with the set of properties that generates the perception of red, but not all red objects will have these properties. 'Red' does not become meaningful until the eye and brain are introduced into the system.

Attempting to make a philosophical argument here is pointless; there is simply no room for philosophy to inject itself. You are free to come up with your own definition of the word color and ascribe whatever properties you like to it, of course, but it will remain orthogonal to any discussion of color in the sense of physics and psychophysics.

[General Battuta]

Define 'red' as a unitary group without using a single characteristic of the human eye or brain and maybe you'll convince me. That's your mission.

[Herra Tohtori]

Now you're simply wrong - using the wrong words to discuss the wrong things. Color does not exist as a property of objects; we've already demonstrated this. You cannot find and point to a red object. You can find an object with the set of properties that generates the perception of red, but not all red objects will have these properties. 'Red' does not become meaningful until the eye and brain are introduced into the system.

An object that emits 620 nm photons is a red light. I doubt there's any simpler way to describe redness. It's a good way to describe this property, albeit not quite as accurate as just calling it 620 nm monochromatic light.

Of course this simplicity is limited to spectral colours, which are an easy case, but the mixtures that make up additive colours are equally real combinations, and not calling them colours would just be an unnecessary complication.

So, I prefer to call them colours, and our perception of them is the perceived colour.

Attempting to make a philosophical argument here is pointless; there is simply no room for philosophy to inject itself. You are free to come up with your own definition of the word color and ascribe whatever properties you like to it, of course, but it will remain orthogonal to any discussion of color in the sense of physics and psychophysics.

I might be suggesting that coconuts migrate, but it doesn't really interest me to say that colour doesn't exist in world until we perceive it.

To me it's the same argument as whether there's a sound if there's no one to hear it, and I don't see the point in it. The physical qualities that cause us to detect a colour will be there regardless of our colour perception.

Our colour perception is just our way to label them, but because of the limitations of our sensory systems we can't label them all. The colours as properties of light would still exist just the same if we were all blind and used echolocation as our primary sense.

[Herra Tohtori]

Define 'red' as a unitary group without using a single characteristic of the human eye or brain and maybe you'll convince me. That's your mission.

Simplest definition for red would be light that activates the red receptors in retina, but not green and blue receptors.

[General Battuta]

An object that emits 620 nm photons is a red light. I doubt there's any simpler way to describe redness. It's a good way to describe this property, albeit not quite as accurate as just calling it 620 nm monochromatic light.

But a red light is not an object that emits 620nm photons; therefore this definition is incomplete. You give a better definition below which also proves my point.

So, I prefer to call them colours, and our perception of them is the perceived colour.

It's nice that you prefer this, but I can prefer to call neutrons protons and protons neutrons and it'd still have no place in a discussion of the topic.

Our colour perception is just our way to label them, but because of the limitations of our sensory systems we can't label them all. The colours as properties of light would still exist just the same if we were all blind and used echolocation as our primary sense.

No, they wouldn't, because the properties of light do not map to the colors and the colors do not exist without our senses. If you're talking about something you invented called 'colors as properties of light' which simply means 'properties of light', fine, but the whole point of this discussion is that that is not color.

Simplest definition for red would be light that activates the red receptors in retina, but not green and blue receptors.

Exactly. Now you've nailed it.

[MP-Ryan]

Whoa.  Maybe I can phrase this in a different way and reduce some confusion.

Wavelength is a property of light by which the quality of the light can be quantified.  All light has a wavelength associated with it.  Wavelengths are measurable in quite a number of ways.  It is an objective value associated with a physical property.

Colour is the rough approximation that all species with eyes attribute to particular wavelengths.  The wavelength(s) that define a particular colour are not universal to all species.  Colour is perception of a wavelength; wavelength is objectively measurable, whereas colour is not (as it requires interpretation).

Simplest definition for red would be light that activates the red receptors in retina, but not green and blue receptors.

Not entirely true.  For one, humans have four photoreceptor pigments.  Second, they have peak absorption wavelengths and absorption curves.  Third, those curves overlap.  Fourth, the curves don't actually correspond to any single colour that we perceive, as the receptor proteins absorb wavelength ranges that are quite specific to evolutionary fitness (human photopsins have peak absorptions of wavelengths that we perceive as yellow-green, green, and blue-violet; rhodopsin picks up green-blue light and allows for sight in low-light conditions)  This is part of what I was getting at by saying photoreceptors perceive rather than observe light - different light conditions are capable of triggering the same response patterns in photoreceptor cell groups.  Furthermore, colour perception requires at least two different types of photopsins to fire at once; the brain then interprets the different absorption curves to deduce colour from the wavelengths being absorbed.

Colour perception is an artificial construction of the brain to give meaning to wavelength and intensity.  Colour names are just handy ways of interpreting light conditions; different conditions can produce the same colour perception without loss of information because our brains don't actually need to be able to distinguish those conditions, evolutionarily-speaking.  Trichromatic vision evolved only in species that really need it; dichromatic species don't "see" an absence of a particular colour, because they have no perception of it.  Perception of the colour "red" came about evolutionarily later than the other colours (red requires the longwave photopsin that actually reads colours we see as yellow) presumably as a result of changes in diet; a species than can distinguish the light conditions that ripe fruits reflect is going to have a much easier time ensuring it can eat.  The yellow and yellow-green photopsins are quite genetically similar, leading to pretty solid hypothesis (that howler monkey species, some of which are dichromatic and some of which are trichromatic) seem to support.

[Luis Dias]

"Colours themselves do exist".... do you see where I am getting at, Battuta, when I say that people are still deluded my metaphysical thinking?

No.

Colors do exist. They're an obvious, measurable property. They're just a property of the signal processing of the human mind, rather than the external world.

Way to purposedly miss the point.

[watsisname]

I didn't get your point either.  What on earth was it?

MP:  Excellent post.  The mechanics and evolution of dichromatic and trichromatic vision are very interesting.