1351: "Metamaterials"

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1351: "Metamaterials"

Postby dalcde » Fri Apr 04, 2014 4:07 am UTC

Image
Title text: "If I developed a hue-shifting metamaterial, I would photobomb people's Instagram pics with a sheet of material that precisely undid the filter they were using."

Took me a while to get the comic. I suppose it's that the box (made of metamaterial) covering the rose and the violet modifies the wavelength of the light getting through it?

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Re: 1351: "Metamaterials"

Postby Jiffy » Fri Apr 04, 2014 4:24 am UTC

Oooh! Colors!

I think it's been a while since there was any color in xkcd comics.

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Re: 1351: "Metamaterials"

Postby Mighty Jalapeno » Fri Apr 04, 2014 4:37 am UTC

"Violets are red"...

And it took you a while to get the comic? What color is purple normally?

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Re: 1351: "Metamaterials"

Postby chris_poulton » Fri Apr 04, 2014 5:45 am UTC

Um, much as I like the idea of blue-shifting a rose, this is not what metamaterials actually do, even in theory. The general idea of a metamaterial is that by controlling both the electric and magnetic response of a material at the microscale you can get some weird effects. Usually this involves making the refractive index negative (which results in some strange optical effects, like the refracted image of a straw in a glass bending "the wrong way") or some crazy out-there effects like bending light around an object completely, resulting in an invisibility cloak [patent pending]. However all these effects don't change the frequency of the light - the colours may be bent around in some odd ways but the red will still remain red and blue will remain blue.

ok, pedantic-nitpicking over. time for the weekend.
Last edited by chris_poulton on Fri Apr 04, 2014 5:52 am UTC, edited 1 time in total.

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Re: 1351: "Metamaterials"

Postby dalcde » Fri Apr 04, 2014 5:46 am UTC

Mighty Jalapeno wrote:And it took you a while to get the comic? What color is purple normally?

The last two panels. I thought the roses became blue and the violets became red :)

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Re: 1351: "Metamaterials"

Postby orthogon » Fri Apr 04, 2014 8:07 am UTC

Violets are violet, presumably by definition. Violet is also the name traditionally given in English to the colour of monochromatic light of the shortest visible wavelength. Spectral violet is interesting, though, because it's visible partly as a result of a recovery in the response of the red cone, which is why it looks similar to purple/magenta. Magenta, as you know, is an equal mixture of red and blue, and although the apparent amount of red "in" violet isn't as much as in magenta, there's kind of an argument that violets are a bit red. (I have a feeling I've talked about violet on this forum before. Sorry if it's getting boring.) Roses, of course, come in all colours, including violet, thanks to artificial selection.
xtifr wrote:... and orthogon merely sounds undecided.

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Re: 1351: "Metamaterials"

Postby dalcde » Fri Apr 04, 2014 8:17 am UTC

chris_poulton wrote:Um, much as I like the idea of blue-shifting a rose, this is not what metamaterials actually do, even in theory. The general idea of a metamaterial is that by controlling both the electric and magnetic response of a material at the microscale you can get some weird effects. Usually this involves making the refractive index negative (which results in some strange optical effects, like the refracted image of a straw in a glass bending "the wrong way") or some crazy out-there effects like bending light around an object completely, resulting in an invisibility cloak [patent pending]. However all these effects don't change the frequency of the light - the colours may be bent around in some odd ways but the red will still remain red and blue will remain blue.

ok, pedantic-nitpicking over. time for the weekend.


Well, according to Wikipedia,
Wikipedia wrote:Metamaterials are artificial materials engineered to have properties that may not be found in nature

So they are allowed to do any crazy thing they like (as long as it is crazy enough to be not natural). It just happens that most metamaterials are those that have negative refractive index.

Nevertheless, it is a bit weird that the wavelength of red light gets shorter while that of blue light gets longer.

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Re: 1351: "Metamaterials"

Postby JustDoug » Fri Apr 04, 2014 8:32 am UTC

I'll just drop in to say that the pun, "Strange matter theoreticians can truthfully say, 'I never metamaterial I didn't like'," went unused. This time.

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Re: 1351: "Metamaterials"

Postby da Doctah » Fri Apr 04, 2014 8:49 am UTC

Roses are tan,
Violets are gray.
I'm protanopic,
What more can I say?

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Re: 1351: "Metamaterials"

Postby Pfhorrest » Fri Apr 04, 2014 9:06 am UTC

Roses are red,
Grasses are green,
I'm deuteranopic,
if you know what I mean.
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Re: 1351: "Metamaterials"

Postby Jamaican Castle » Fri Apr 04, 2014 10:02 am UTC

Pfhorrest wrote:Roses are red,
Grasses are green,
I'm deuteranopic,
if you know what I mean.


If I don't know what you mean, does your problem clear up?

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Re: 1351: "Metamaterials"

Postby cellocgw » Fri Apr 04, 2014 11:19 am UTC

I didn't originate this one; some respiratory physician did.

Roses are red,
Violets are blue,
if you lungs didn't work,
your blood would be, too.
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Re: 1351: "Metamaterials"

Postby orthogon » Fri Apr 04, 2014 12:38 pm UTC

dalcde wrote:Well, according to Wikipedia,
Wikipedia wrote:Metamaterials are artificial materials engineered to have properties that may not be found in nature

So they are allowed to do any crazy thing they like (as long as it is crazy enough to be not natural).

... and as long as it's allowed by the laws of physics.

Most of the Wikipedia page talks about linear metamaterials; if they mean "linear" in the sense that I understand it then it would not be possible for such a material to change the frequency of a wave, though it could exhibit selectivity in what wavelengths it transmitted and in what directions. But there is a section and separate page on non-linear metamaterials. I guess in principle a nonlinear material could generate harmonics of the input frequency, so that red could be converted to violet.

Conversion of short wavelengths to longer wavelengths is what happens in fluorescence - does the reverse ever happen? I guess it would require two photons of just the right energies to be absorbed and one higher energy photon to be emitted.
xtifr wrote:... and orthogon merely sounds undecided.

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Re: 1351: "Metamaterials"

Postby cellocgw » Fri Apr 04, 2014 1:23 pm UTC

orthogon wrote:
Conversion of short wavelengths to longer wavelengths is what happens in fluorescence - does the reverse ever happen? I guess it would require two photons of just the right energies to be absorbed and one higher energy photon to be emitted.


Yes it does -- see '4-wave mixing', 'nonlinear crystals," for example. KDP, potassium di-deuterium phosphate is a well-known frequency doubling crystal which converts some of the incoming light to half the wavelength (typically used to convert Nd-YAG 1.06 micron light into 532, aka green, light). It works by having an asymmetric response, which if you do all the Fourier work, leads to the frequency doubling.
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Re: 1351: "Metamaterials"

Postby stickler » Fri Apr 04, 2014 2:10 pm UTC

cellocgw wrote:I didn't originate this one; some respiratory physician did.

Roses are red,
Violets are blue,
if you lungs didn't work,
your blood would be, too.

I'm pretty sure your blood would not actually turn blue, so I would want that physician anywhere near my body. Perhaps I am too literal.

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Re: 1351: "Metamaterials"

Postby PinkShinyRose » Fri Apr 04, 2014 2:29 pm UTC

A rose :D.
orthogon wrote:Roses, of course, come in all colours, including violet, thanks to artificial selection.

Except that roses don't naturally make any violet/blue pigments so blue roses cannot be bred by artificial selection alone. There is an artificially mutated variety though, albeit a slightly reddish one.

stickler wrote:
cellocgw wrote:I didn't originate this one; some respiratory physician did.

Roses are red,
Violets are blue,
if you lungs didn't work,
your blood would be, too.

I'm pretty sure your blood would not actually turn blue, so I would want that physician anywhere near my body. Perhaps I am too literal.

Maybe he was referring to the roses and forgot he mentioned the violets. Maybe he meant that lung diseases are common among the nobility (I know haemophilia is common amongst European royalty (they're all one family really), but I never heart something like that).

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Re: 1351: "Metamaterials"

Postby Moose Anus » Fri Apr 04, 2014 2:35 pm UTC

stickler wrote:I'm pretty sure your blood would not actually turn blue, so I would want that physician anywhere near my body. Perhaps I am too literal.
Perhaps you're not literal enough.
Lemonade? ...Aww, ok.

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Re: 1351: "Metamaterials"

Postby orthogon » Fri Apr 04, 2014 2:41 pm UTC

cellocgw wrote:
orthogon wrote:
Conversion of short wavelengths to longer wavelengths is what happens in fluorescence - does the reverse ever happen? I guess it would require two photons of just the right energies to be absorbed and one higher energy photon to be emitted.


Yes it does -- see '4-wave mixing', 'nonlinear crystals," for example. KDP, potassium di-deuterium phosphate is a well-known frequency doubling crystal which converts some of the incoming light to half the wavelength (typically used to convert Nd-YAG 1.06 micron light into 532, aka green, light). It works by having an asymmetric response, which if you do all the Fourier work, leads to the frequency doubling.

Cool, thanks.
On the one hand I can see a material as a medium that has a particular effect on electromagnetic fields, and how nonlinearity (e.g. asymmetry) can cause harmonics (e.g. frequency doubling); on the other hand there's this view of photons exciting electrons to higher energy levels etc. Are these somehow different ways of looking at the same thing because of the wave/particle duality, or are they completely different types of phenomena?

PinkShinyRose wrote:A rose :D.
orthogon wrote:Roses, of course, come in all colours, including violet, thanks to artificial selection.

Except that roses don't naturally make any violet/blue pigments so blue roses cannot be bred by artificial selection alone. There is an artificially mutated variety though, albeit a slightly reddish one.

Thanks for putting me straight - to be honest I just assumed you could get all colours, based on having seen some pretty crazy coloured roses recently. (Maybe the ones in our dining room are genetically modified mutants. I must keep an eye on them and lock the door at night.)
xtifr wrote:... and orthogon merely sounds undecided.

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Re: 1351: "Metamaterials"

Postby ahammel » Fri Apr 04, 2014 2:43 pm UTC

orthogon wrote:Violets are violet, presumably by definition.

Nope.
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Re: 1351: "Metamaterials"

Postby karhell » Fri Apr 04, 2014 2:49 pm UTC

ahammel wrote:
orthogon wrote:Violets are violet, presumably by definition.

Nope.

then let's correct that : violets are usually violet ^^
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Re: 1351: "Metamaterials"

Postby Introbulus » Fri Apr 04, 2014 2:50 pm UTC

Roses are grey
Violets are grey
The whole world is grey
I am a dog

ignoring the fact that dogs are actually only red/green colorblind.
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Re: 1351: "Metamaterials"

Postby San Fran Sam » Fri Apr 04, 2014 3:16 pm UTC

Okay, so where is pink in the light spectrum?


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Re: 1351: "Metamaterials"

Postby rmsgrey » Fri Apr 04, 2014 3:18 pm UTC

Introbulus wrote:Roses are grey
Violets are grey
The whole world is grey
I am a dog

ignoring the fact that dogs are actually only red/green colorblind.


And also that scent is a major sense for canines so the colour-blind canines would distinguish roses and violets primarily by odour rather than hue

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Re: 1351: "Metamaterials"

Postby rmsgrey » Fri Apr 04, 2014 3:23 pm UTC

San Fran Sam wrote:Okay, so where is pink in the light spectrum?



Human perception of colour is (mostly) 3-dimensional so many colours don't lie on a simple spectrum...

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Re: 1351: "Metamaterials"

Postby Whizbang » Fri Apr 04, 2014 3:24 pm UTC

Roses are loud
Violets can sing
I can taste the rainbow
I have synesthesia

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Re: 1351: "Metamaterials"

Postby Adam H » Fri Apr 04, 2014 3:29 pm UTC

Roses are green
Violets are green
Wait a second
They are just upside down
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Re: 1351: "Metamaterials"

Postby Splarka » Fri Apr 04, 2014 4:25 pm UTC

rmsgrey wrote:
Introbulus wrote:Roses are grey
Violets are grey
The whole world is grey
I am a dog

ignoring the fact that dogs are actually only red/green colorblind.


And also that scent is a major sense for canines so the colour-blind canines would distinguish roses and violets primarily by odour rather than hue


Are cats and dogs really color-blind? (tl;dr: Deuteranopes)

cellocgw wrote:
orthogon wrote:
Conversion of short wavelengths to longer wavelengths is what happens in fluorescence - does the reverse ever happen? I guess it would require two photons of just the right energies to be absorbed and one higher energy photon to be emitted.


Yes it does -- see '4-wave mixing', 'nonlinear crystals," for example. KDP, potassium di-deuterium phosphate is a well-known frequency doubling crystal which converts some of the incoming light to half the wavelength (typically used to convert Nd-YAG 1.06 micron light into 532, aka green, light). It works by having an asymmetric response, which if you do all the Fourier work, leads to the frequency doubling.


Also, this weird-ass stuff (don't move that hyphen), reverse fluorescence: IRUCG, IRUCB, IRUCR, IRSPG Up-Conversion Phosphors

It would be extremely difficult to have a passive metamaterial swap the spectrum as illustrated in the comic. But not impossible I guess. My money would be on it only working on direct-contact surfaces, as it would be even more difficult to make optically clear at the same time.
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Re: 1351: "Metamaterials"

Postby mathmannix » Fri Apr 04, 2014 4:32 pm UTC

Adam H wrote:Roses are green
Violets are green
Wait a second
They are just upside down

or they haven't bloomed yet, it's been a long winter.
I hear velociraptor tastes like chicken.

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Re: 1351: "Metamaterials"

Postby PinkShinyRose » Fri Apr 04, 2014 4:40 pm UTC


So I'm really MinusGreenShinyRose? Oh well, I don't think I can change my username anyway.

orthogon wrote:Thanks for putting me straight - to be honest I just assumed you could get all colours, based on having seen some pretty crazy coloured roses recently. (Maybe the ones in our dining room are genetically modified mutants. I must keep an eye on them and lock the door at night.)

I think they just regularly come in white, yellow, magenta and anything in-between on a subtraction set. Some people paint them though.

Anyway, I'm surprised no-one is marketing fluorescent or luminescent roses yet.

EDIT:
Jiffy wrote:I think it's been a while since there was any color in xkcd comics.

Since Tuesday, I guess, if you got to the dinosaur.

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Re: 1351: "Metamaterials"

Postby orthogon » Fri Apr 04, 2014 5:01 pm UTC

rmsgrey wrote:
San Fran Sam wrote:Okay, so where is pink in the light spectrum?



Human perception of colour is (mostly) 3-dimensional so many colours don't lie on a simple spectrum...

One of the most natural set of co-ordinates to use is Hue, Saturation and Brightness, where you start more or less with a pure spectral colour, add a certain amount of white (the more white, the less saturated) and then adjust the brightness of the whole thing. In this scheme, pink is desaturated red, i.e. red mixed with white, and brown is just dark red.

Something I hadn't thought about until today is that the recovery of the red cone at violet wavelengths means that there are spectral colours that excite the eye in the same way as a mixture of red and blue (without green) like magenta. If the three cones had single-peak responses, it wouldn't be possible to get that response from any pure spectral light, because any wavelength in between the peaks would also excite the green cone (which is more sensitive anyway). This means that mixtures of red and blue primaries, like magenta, give a similar impression to violet, whereas without the second peak, magenta would be subjectively unlike anything in the spectrum, and the spectrum (e.g. a rainbow) would appear to contain only a subset of the (100% saturated) colours that are available. "All the colours of the rainbow" would have a completely different meaning. As it is there are of course colours that aren't in the rainbow, but they can mainly be expressed as desaturated ("pastel", if you like) or darker versions of the pure rainbow colours.
xtifr wrote:... and orthogon merely sounds undecided.

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Re: 1351: "Metamaterials"

Postby cellocgw » Fri Apr 04, 2014 5:26 pm UTC

PinkShinyRose wrote:Anyway, I'm surprised no-one is marketing fluorescent or luminescent roses yet.


Be a nice match for those glow-in-the-dark plants, and I thought someone made some light-up mice, too. :o
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Re: 1351: "Metamaterials"

Postby gmalivuk » Fri Apr 04, 2014 5:48 pm UTC

Splarka wrote:
rmsgrey wrote:
Introbulus wrote:Roses are grey
Violets are grey
The whole world is grey
I am a dog

ignoring the fact that dogs are actually only red/green colorblind.


And also that scent is a major sense for canines so the colour-blind canines would distinguish roses and violets primarily by odour rather than hue


Are cats and dogs really color-blind? (tl;dr: Deuteranopes)
Yeah, I'm pretty sure most (all?) mammals naturally have multiple types of photoreceptor, and so aren't truly completely colorblind.
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Re: 1351: "Metamaterials"

Postby Pfhorrest » Fri Apr 04, 2014 5:49 pm UTC

orthogon wrote:One of the most natural set of co-ordinates to use is Hue, Saturation and Brightness, where you start more or less with a pure spectral colour, add a certain amount of white (the more white, the less saturated) and then adjust the brightness of the whole thing. In this scheme, pink is desaturated red, i.e. red mixed with white, and brown is just dark red.

That's what I would mean by "pink", but in that MinutePhysics video he seems to mean "magenta". Really, "purple" would work better, because the line of purples is the usual term for the colors between red and blue.

My girlfriend however insists that "pink" and "light red" are different colors, so that combined with this video makes me think there are some people for whom "pink" means the less-blue hues of purples, i.e. magenta more or less. And yeah, those are pink of a sort... "hot pink" is a common term for magenta, anyway.

I think maybe a pie-slice out of the color wheel deserve the name: those hues from 300 until 0, and saturations from 100 to 0, and brightnesses from 100 to 0, with how much it counts as "pink" fading as it gets closer to (0,100,100) [red], (*,0,100) [white], or (*,*,0) [black]. Making magenta (300,100,100) the only corner of that "pink space" which is definitely solidly pink, but counting "light reds" (and dim shades of all of these) as pinks too.

As it is there are of course colours that aren't in the rainbow, but they can mainly be expressed as desaturated ("pastel", if you like) or darker versions of the pure rainbow colours.

Not really... see magenta again. Magenta isn't just a desaturated violet. It's a redder violet, fully saturated. Violets look subjectively similar to hues approaching 270 (half way between blue and magenta), as you say because of the red cones' recovering response curve there. But that recovery cuts off well before there's ever a spectral color that stimulates the red and blue cones equally as magenta does.

Also I'm pretty sure we can artificially produce cyans more intense than any of those in the rainbow. You can definitely do it via a sort of optical illusion trick: stare at a blank red screen (here's one, mostly) for a few minutes, then stare at a white screen (click the white swatch there in the middle to get one) and bam, a more electrifying cyan than you've ever seen in nature.
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Re: 1351: "Metamaterials"

Postby da Doctah » Fri Apr 04, 2014 6:53 pm UTC

Adam H wrote:Roses are green
Violets are green
Wait a second
They are just upside down


Roses are brown,
Violets are brown,
Screw it,
Who has time for gardening anyway?

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Re: 1351: "Metamaterials"

Postby Introbulus » Fri Apr 04, 2014 7:08 pm UTC

gmalivuk wrote:
Splarka wrote:
rmsgrey wrote:
Introbulus wrote:Roses are grey
Violets are grey
The whole world is grey
I am a dog

ignoring the fact that dogs are actually only red/green colorblind.


And also that scent is a major sense for canines so the colour-blind canines would distinguish roses and violets primarily by odour rather than hue


Are cats and dogs really color-blind? (tl;dr: Deuteranopes)
Yeah, I'm pretty sure most (all?) mammals naturally have multiple types of photoreceptor, and so aren't truly completely colorblind.


Looks like at least two people didn't bother to read the fine print on my first post. :P

or just didn't realize that this is really tiny text
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Re: 1351: "Metamaterials"

Postby speising » Fri Apr 04, 2014 7:15 pm UTC

Pfhorrest wrote:
orthogon wrote:One of the most natural set of co-ordinates to use is Hue, Saturation and Brightness, where you start more or less with a pure spectral colour, add a certain amount of white (the more white, the less saturated) and then adjust the brightness of the whole thing. In this scheme, pink is desaturated red, i.e. red mixed with white, and brown is just dark red.

That's what I would mean by "pink", but in that MinutePhysics video he seems to mean "magenta". Really, "purple" would work better, because the line of purples is the usual term for the colors between red and blue.

My girlfriend however insists that "pink" and "light red" are different colors, so that combined with this video makes me think there are some people for whom "pink" means the less-blue hues of purples, i.e. magenta more or less. And yeah, those are pink of a sort... "hot pink" is a common term for magenta, anyway.

I think maybe a pie-slice out of the color wheel deserve the name: those hues from 300 until 0, and saturations from 100 to 0, and brightnesses from 100 to 0, with how much it counts as "pink" fading as it gets closer to (0,100,100) [red], (*,0,100) [white], or (*,*,0) [black]. Making magenta (300,100,100) the only corner of that "pink space" which is definitely solidly pink, but counting "light reds" (and dim shades of all of these) as pinks too.

As it is there are of course colours that aren't in the rainbow, but they can mainly be expressed as desaturated ("pastel", if you like) or darker versions of the pure rainbow colours.

Not really... see magenta again. Magenta isn't just a desaturated violet. It's a redder violet, fully saturated. Violets look subjectively similar to hues approaching 270 (half way between blue and magenta), as you say because of the red cones' recovering response curve there. But that recovery cuts off well before there's ever a spectral color that stimulates the red and blue cones equally as magenta does.

Also I'm pretty sure we can artificially produce cyans more intense than any of those in the rainbow. You can definitely do it via a sort of optical illusion trick: stare at a blank red screen (here's one, mostly) for a few minutes, then stare at a white screen (click the white swatch there in the middle to get one) and bam, a more electrifying cyan than you've ever seen in nature.

for the definitive discussion of colour shades, may i refer to the blag?

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Re: 1351: "Metamaterials"

Postby gmalivuk » Fri Apr 04, 2014 7:23 pm UTC

Introbulus wrote:
gmalivuk wrote:
Splarka wrote:
rmsgrey wrote:
Introbulus wrote:Roses are grey
Violets are grey
The whole world is grey
I am a dog

ignoring the fact that dogs are actually only red/green colorblind.


And also that scent is a major sense for canines so the colour-blind canines would distinguish roses and violets primarily by odour rather than hue


Are cats and dogs really color-blind? (tl;dr: Deuteranopes)
Yeah, I'm pretty sure most (all?) mammals naturally have multiple types of photoreceptor, and so aren't truly completely colorblind.


Looks like at least two people didn't bother to read the fine print on my first post. :P

or just didn't realize that this is really tiny text
Adding tiny text to your post and then acting smug when people don't notice it is not cleverness.
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Re: 1351: "Metamaterials"

Postby orthogon » Fri Apr 04, 2014 7:35 pm UTC

@Pfhorrest, I basically agree with you. I maybe overstated my point, which is really that the spectral colours cover a wider range of hues than might have been the case. So magenta itself is outside the range of my system (wavelength, saturation, brightness).

It seems that whatever coordinates you choose, you either get colours that are outside the space or illegal colours in the space. A colleague of mine working on video compression many years ago once told me that his algorithms sometimes generated illegal colours, e.g. with negative rgb values or saturation exceeding 100%. He claimed that he'd learned to recognise these colours on the display by their eerie unnaturalness. I never saw what he meant but liked to think of parts of the picture glowing octarine.
xtifr wrote:... and orthogon merely sounds undecided.

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Re: 1351: "Metamaterials"

Postby Klear » Fri Apr 04, 2014 10:32 pm UTC

gmalivuk wrote:Adding tiny text to your post and then acting smug when people don't notice it is not cleverness.


Are there such people? I always though that making text tiny is drawing attention to it.

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Re: 1351: "Metamaterials"

Postby gmalivuk » Fri Apr 04, 2014 10:44 pm UTC

Klear wrote:
gmalivuk wrote:Adding tiny text to your post and then acting smug when people don't notice it is not cleverness.
Are there such people? I always though that making text tiny is drawing attention to it.
Adding size=1 text to your post is drawing the wrath of the Large Text Baron to it, which is trouble you've not known.

Unless you've had your small text previously embiggened by the LTB, I suppose.
Unless stated otherwise, I do not care whether a statement, by itself, constitutes a persuasive political argument. I care whether it's true.
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