Who Says "Purple" Doesn't Exist?!!

[ameerat42]

This bloke does.

OK, so it's actually MAGENTA.

If NOTHING ELSE, this proves that the scary monsters called
PURPLE PEOPLE EATERS don't exist

[Mary Anne]

I am surprised you did not put a link on to the song Am

[ameerat42]

Hmm! Definitely a case of a missing link, M A

[Steve Axford]

Great explanation. Colour is a very useful concept, even if it doesn't quite respresent reality.
One of the results is that we use a colour wheel when clearly there is no "colour wheel" in nature.

[arthurking83]

What he's saying, in effect, is that Humans are defective .. at least in terms of eyesight!

colours get all mixed up in nature and adhere to specific laws of physics, but we don't really like all those colours(or lack of specific colours) so our brains invent some arcane colour to keep us happy.

[ameerat42]

OTOH, he's saying that humans are clever for inventing "cullers"
(Don't wurry about the spilling)

[ricktas]

Interestingly.. in the not to dark past, there was an issue present on all camera sensors that there was a particular range of purple that the RGB sensors could not deal with and rendered it a lovely blue shade. I recall a time when it was treated as fun to go out and try and find something purple that you could not photograph cause it came out blue in any photos.

Since then, sensors have improved and it has been rectified.

If you type "camera turns purple flower to blue" into google you can find a myriad of old forum posts and articles about the issue. Most back in the early to mid 2000s.

[jim]

What he's saying, in effect, is that Humans are defective .. at least in terms of eyesight!

colours get all mixed up in nature and adhere to specific laws of physics, but we don't really like all those colours(or lack of specific colours) so our brains invent some arcane colour to keep us happy.

Not really defective. The purpose of eyesight isn't so much to give a perfect description of reality, as merely to help you navigate!

[Steve Axford]

Spot on Jim. 3 fuzzy measures of wavelength can provide quite a bit of useful info. Imagine the problems with trying to measure every possible wavelength?

[ameerat42]

...as merely to help you navigate!...

Off-course Er! - Of course!

[Hamster]

Interesting. Although the concept of magenta not existing is a little philosophical given that anything is only as real as your brain tells you it is. As such, it exists as strongly as any other colour, no matter how that occurs....or "doesn't". The brain is an amazing thing. For anyone who hasn't watched The Brain, with David Eagleman, I thoroughly recommend it.

[Steve Axford]

Purple is seen as the addition of blue light and red light, just as yellow is often the addition of red light and blue light, or green is the addition of blue and yellow. The only difference is that yellow can also be just yellow light and green can be just green light while purple can only be the addition of red and blue. This doesn't mean it doesn't exist, just that it doesn't exist as a discreet wavelength. There are very few things in nature that are discreet wavelengths.

While purple isn't a spectral colour, violet is and we do see that. It isn't between red and blue. It is outside blue tending towards ultraviolet. The reason that we can see this is https://www.physicsforums.com/thread...ectrum.509416/

[Steve Axford]

This thread prompted me to try to fully understand what we mean by colour and what some scientists mean by colour. We, in this case, means we who think of colour as what we see.

We see colour because of the stimulation of 3 cone types in eyes. Red, green and blue. We "see" different colours as these three cone types are stimulated. We see red when it is mostly the red, yellow when it is partly the red and partly the green and magenta (purple) when it is partly the red and partly the blue. Pure wavelengths of visible light always stimulate one or more cone types in exactly the same ways that mixtures of different wavelengths can do (except magenta like colours). Our eyes have no way of distinguishing a pure green wavelength (extremely rare in nature), from white light with blue and red removed (green leaves).

Some scientists talk of colour as being a wavelength of light. For example, green light is a pure wavelength of light at about 545nm. The colour of leaves is defined as a mix of all colours (white light) with an absorbtion gap at around red (575nm) and blue (545nm). It is not green because they would not define colours as being a mix of wavelengths. Mixes of wavelengths are just that - mixes of wavelengths.

Since we cannot tell the difference between pure wavelengths and mixes of wavelengths, we can call them by the same names. This doesn't make them wrong. Just different, and it is important to understand the difference. Science sees colour as wavelength defined bu a number (in nanometres) and it has infinite variation within the limits of the wavelength of light (not quite infinite as the smallest difference in wavelength will be defined by quantum mechanics). Mixes of wavelength are defined by the addition of all the present wavelengths and their intensity. None of these numbers is quite infinite, but bloody close too it and for us it is effectively infinite.

On the other hand we can see a mere 7 million different colours, so we have to group things together. Since almost all "colours" in nature are mixes of wavelength colour, it makes sense to be able to distinguish them. Is it imperfect? You betcha, but it is also incredible useful. The imperfections make most of those curious optical illusions possible and also account for most of the camouflage in nature.