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Vanadium 50
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Coal? You had coal? When I was a kid your so-called coal was still dinosaurs.
A good point. You'd have to detect wave lengths over 1 micrometer to have temperature differences near room temperature be visible, and the chemical properties of surfaces would also affect the appearance at the same time.hutchphd said:I think the distinction between "night vision" (which is Near Infrared (NIR) often actively illuminated usually silicon detected devices) and thermal imaging FIR devices needs to be emphasized here. Only the thermal imaging devices will see the glowing enemy combatant in the dark field but these are very different from usual silicon optics or eyeballs.
I once had to explain this to a client who had already spent a fair sum of money trying to develop a silicon CCD-based imaging thermometer. Lack of understanding can be expensive, and I felt like the Grinch as I invoiced him for my services.
Well true, but Macaroni and Cheese was never that colour either...Vanadium 50 said:It is now "peach".
And no human being ever had skin that color.
The colour named Indigo is often placed well inside the CIE graph, rather than on the spectral locus. It's a pretty dodgy part of our colour perception range around there.DaveC426913 said:Well true, but Macaroni and Cheese was never that colou
No, actually there is cyan in all rainbows, as well as white light split by a prism. But there is no magenta.James Demers said:Fun fact: not all colors are found in the rainbow. There's no magenta, and no cyan.
The problem with that statement is that Cyan is a mix of blue and green primaries (It can also be considered as -Red but that system is based on primaries. Primaries are not spectral wavelengths and can only add together to produce resulting colours on a straight line on the CIE chart. That means it cannot actually lay on the (very much curved) Spectral locus. A rainbow is not actually a very pure spectrum; it's very de-saturated because there's a lot of white in there. Basically, a rainbow is not a very good example of the spectrum of sunlight. The colours can often look impressive and vivid but nothing like as good as what you get in a dark room with a prism.Anachronist said:No, actually there is cyan in all rainbows
Maybe on a monitor, but there's a frequency of light between blue and green that correlates with cyan (at least, allowing for saturation, as you say).sophiecentaur said:The problem with that statement is that Cyan is a mix of blue and green primaries.
Yeah I can’t really disagree. I was being mischievous but no colour you can make with primaries is actually spectral. Lowering the saturation involves adding a third primary.DaveC426913 said:Maybe on a monitor, but there's a frequency of light between blue and green that correlates with cyan (at least, allowing for saturation, as you say).
The problem with magenta is that there is no single frequency, since magenta is a perceived mix of red and blue. If you took the frequency between red and blue, you'd get a green.
There are a couple of ways to demonstrate why it might be seven.hutchphd said:After all we have only three distinct eye pigments and yet I swear there are seven colors when I look at the rainbow.
Very interesting. I was wandering down those same (3-bit) channels myself while staring at the CIE chart of colors (please note the compactness of the absent silent "u")Baluncore said:So that gives us seven named and identifiable colours in a rainbow.
Is gold an orthogonal colour ?hutchphd said:Very interesting.
If 000 is black, would not 111 be white, leaving 6 colours ? Which is what most people see.Baluncore said:There are a couple of ways to demonstrate why it might be seven.
We detect three different colours. Red, Green & Violet, that we sometimes call Blue.
That gives us a three bit binary number with 23 = 8 possible combinatorial states.
But black is zero, so only 23 - 1 = 7 colours remain.
If we are colour blind to one colour we see 22 - 1 = 3 colours.
If we had an extra detection pigment we would see 24 - 1 = 15 colours.
Yes. But the physiological cone detectors get weighed and balanced dynamically by the brain, so white is coloured. We then use rod detected brightness to determine the difference between dark and light.Merlin3189 said:If 000 is black, would not 111 be white, leaving 6 colours ?
JeffJo said:First, Newton separated the colors of the spectrum (not the rainbow) into seven categories of color (not discrete colors).
- The rainbow has different colors. The spectrum's are all single wavelengths of light, and the rainbow's are composites of one tight group of wavelengths that is very bright, and less dim contributions from all the others toward the red end of the spectrum. In fact, the rainbow continues all the way to its center as gray.
What part of the claim? There was a link to Newton's history, which is well known so I have to assume that isn't what you meant. So it must be the rainbows?hutchphd said:Please provide a reference for this claim. It does not comport with my understanding of either light or Newton.
Those are pretty much the categories Newton used. But what you call Cyan, he called Blue. What you call Blue, he called Indigo (as in "blue jeans" which are indigo). Only the border between them is unclear.Anachronist said:As others have noted, "indigo" generally isn't used nowadays. Instead of the 7-color spectrum ROYGBIV, I'd remove "I" (indigo) and add "C" (cyan) for ROYGCBV. Still seven.
That is indeed one way. It wasn't what Newton did.Anachronist said:It also makes more sense to break down the color categories into six groups, corresponding to each color receptor type in our eyes (red, green, blue) and the colors in between them (yellow=red+green, cyan=green+blue, magenta=blue+red). That's basically how we perceive colors. Violet or purple is basically magenta skewed a bit toward blue at lower luminance, and orange is basically yellow skewed toward the red.
When trying to 'regularise' colour, it's easy to paint oneself into a corner. Of your six colours, one (magenta) is not a spectral colour and you don't get it by choosing one section of the spectrum. The only 'magic number' involved is the three analysis curves that (so the tristimulus colour theory says) are used to give the gamut of colours we perceive. But there are no hard boundaries and those analysis curves all cover pretty much the whole of the visible spectrum. It's wide band analysis that allows three 'signals' to be obtained for all those colours in the CIE chromaticity chart.Anachronist said:It also makes more sense to break down the color categories into six groups, corresponding to each color receptor type in our eyes (red, green, blue) and the colors in between them (yellow=red+green, cyan=green+blue, magenta=blue+red).
Because red berries are poisonous and we needed to communicate or die.sophiecentaur said:Nothing that we perceive is quantised to why to quantise colour?
Berries come in a whole continuum of 'reds' which we have always needed to distinguish between. Also, the colour of another human's face can extends over a whole range of reds, pinks, light and dark browns and will be used to assess the other guy's health and emotional state. Look in your garden and you will see leaves with yellows, greens and blues (and browns).Baluncore said:Because red berries are poisonous and we needed to communicate or die.
Thanks. A few comments about the physics.JeffJo said:I showed you the picture of it. It came from here, one of the leading references on rainbows:
sophiecentaur said:I have no idea what is so attractive about choosing to quantify the colours - except to allow kids to learn, by rote, some names for the colours of the rainbow. Nothing that we perceive is quantised to why to quantise colour?
. . . and that the colours we see in a rainbow are highly desaturated.hutchphd said:As to effect on color perception one needs to always remember that the eye is very logarithmic in response
Hence PANTONE came into being. Not cheap but it's a standard that gives a pretty good match between identical colours on different materials and surface textures.DaveC426913 said:Millions of consumers all over the world recognize my brand and trademarked colours, so get it right.
No, it isn't; at least, not how it gets depicted. And rainbows aren't a prism-like effect. Nor did Newton characterize them.hutchphd said:But the raindrop is still just a (slightly bizarre focussing) prism.
In response to this remark:JeffJo said:I didn't say it wasn't a light-deflecting device. I said the way the effect is formed is not due to what people think of as the prism effect.
Your opening sentence was:hutchphd said:But the raindrop is still just a (slightly bizarre focussing) prism.
@hutchphd did not say that a raindrop was a "light deflecting device"; he said that it was a "(slightly bizarre focussing)" prism.JeffJo said:No, it isn't; at least, not how it gets depicted.