Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: artistic on 16/08/2006 16:02:31
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Is it possible that other colors are existant in the world, just that we cannot see them with this pair of eyes? Someone told me I think, that a bee's eyes can see other colors.
Don't make me angry, I have advanced "Green Technology".
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Yep, there's a whole spectrum that we can not perceive..but can detect it and display representations with sensitive equipment. Which is nice .
Men are the same as women, just inside out !
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Nope.
There are only 3 prmary colors: red[V], green[^], blue[:(].
All other colors combine from these 3.
The secondary colors are in between the primary 3.
Like yellow[:)]=red[V]+green[^], cyan=green+blue, violet=red+blue.
Then white=red+green+blue, and black=none.
Then all the rest,
eg orange=red+yellow =orange[;)]=2red[V][V]+1green[^]. etc...
Colors have distinct frequencies and we can 'see' every combination.
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oops..I stand corrected ....[:)]
Men are the same as women, just inside out !
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I don't think you stand corrected, Neil.
We humans speak of 3 primary colours. That is because we have three different colour receptors (cones) usualy indicated as S, M and L. See also wikipedia for details : http://en.wikipedia.org/wiki/Colour_perception
It has been suggested that other species may have other receptors, or receptors with different sensistivities.
Problem is that it is rather difficult to ask a bee or a bird of prey about colour perception.
It is quite possible that some animals sees colours that to us would be either in the infra-red or in the ultraviolet. And (because possible differences in sensibility), it is also possible that the mixture of cyan, magenta en yellow we use to render one of the colours of the spectrum, would be interpreted as another colour of the spectrum by some other species !
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AH HA!!! MY THEATRE EXPERIENCE FINALLY PAYS OFF!! YES there are probably colors we do not see! as a theatre student i have studied light, and color, and everything about it.. i love lighting the stage, and there is quite a lot of science involved....so.. there is a large spectrum of wavelengths, and since color is light reflecting off of an object, and that object absorbs some light and reflects other light .. the light we see is the light that is reflected back. for instance grass absorbs blue and red, and reflects green ... however, we can only see a VERY small portion of this spectrum of light (which is actually wavelenghts), so POTENTIALLY we are completely missing out on many other colors (besides red blue and green) mixing together because we cannot see in this type of wavelength :)
i have a great visual but its at home on my bookshelf :(
becca :)
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quote:
Originally posted by eric l
I don't think you stand corrected, Neil.
Thank you Eric. [:I]
Men are the same as women, just inside out !
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What we see colour wise is totally dependent on the ability and range of the colour receptors. There many colours outside our ability to see them.
What you do speaks so loudly that I cannot hear what you say.
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Say a bee can see colors we can't see, so if we extract the DNA that allows the bee to see those colors and put it in a test subject..[:0]
Don't make me angry, I have advanced "Green Technology".
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Well, Artistic, putting a bee's DNA (or the "usefull" part of it) in a test subject would require you to do it at the moment of conception !
What you would have to do is implant a bee's cones (or maybe complete retinas) into a subject's eyes and make sure they are connected to the brain.
The other possibility would be more like a mathematical model. Going back to the graph with the sensitivity of the different cones as shown in the wikipedia article (http://en.wikipedia.org/wiki/Colour_perception), imagine a Q-type cone with a similarly shaped sensitivity curve, but peaking in the orange. Check the response a certain wavelength would have, and check also the response the YellowMagentiaCyan mixture would have that a printer would use to render this colour.
Maybe there is someone around with sufficient expertise in computer simulation, I certainly am not.
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Color perception doesn't only depend on wavelenghts (to which peak wavelenght does brown color correspond? The same as red!); it also depends on brain physiological response and on brain psychological interpretation (example: the vision of colored shadows).
We perceive a specific color of a colored lamp, for example, even because that light, interacting with the retina, generate a specific combination of electrical signals that are sent to a precise area on the brain cortex. What would happen if we modified those signals with an electronic circuit before going to the brain cortex?
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I am not sure one can ask in any sensible way how the brain sees a colour, and whether one can modify the brain to see another colour.
The only questions that I think are meaningful is whether the brain can see the difference between two things (i.e. whether one red looks the same, or different, from another red; whether a red looks different from a blue; whether a red looks different from a black?
Once the brain/eye is able to distinguish two things, what label you apply to that thing is arbitrary. If someone looks to the sky, and is told that the colour he sees there is green, then to him the sky is green. The issue that matters is not whether the sky is blue or it is green, but whether one can distinguish between the colour of the sky and the colour of grass.
George
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quote:
Originally posted by another_someone
I am not sure one can ask in any sensible way how the brain sees a colour, and whether one can modify the brain to see another colour.
The only questions that I think are meaningful is whether the brain can see the difference between two things (i.e. whether one red looks the same, or different, from another red; whether a red looks different from a blue; whether a red looks different from a black?
Once the brain/eye is able to distinguish two things, what label you apply to that thing is arbitrary. If someone looks to the sky, and is told that the colour he sees there is green, then to him the sky is green. The issue that matters is not whether the sky is blue or it is green, but whether one can distinguish between the colour of the sky and the colour of grass.
George
You can modify the brain to see colored numbers or to perceive a smell instead of an image! This happens in some people, according to neurophysiology. I wouldn't be much surprised if we could also see different colors.
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quote:
Originally posted by lightarrow
You can modify the brain to see colored numbers or to perceive a smell instead of an image! This happens in some people, according to neurophysiology. I wouldn't be much surprised if we could also see different colors.
What you are talking about here is some people who can confuse colour and smell, or colour and words (i..e. The pathways for the two responses overlap, and so the same stimuli appears to originate from two different sources). This is totally consistent with what I was saying about not whether one can distinguish two different colours (i.e. two different stimuli creating the same response), but is nothing to do with a single isolated stimuli creating a discernibly different response.
Ofcourse, it is still for some people to see colours another can't, insofar as they can see a difference in colour where another can see no difference – but, as I said, it is all about difference. The brain does not care about what something is, it only cares about patterns, which ultimately means it only cares about differences.. If everything is the same, then it contains no useful information, and thus to extract information, one needs to see where things are different.
George
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Some related stories of interest.
http://www.abc.net.au/science/news/stories/s832476.htm
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Superior marsupial eyes see more colour
They might spring from an ancient lineage and produce babies that look like peanuts, but marsupials have eyesight that is even better than ours, reseachers have found.
The discovery by Dr Catherine Arrese from the University of Western Australia in Perth strikes another blow for those researchers challenging the view that marsupials, far from being primitive living fossils, are often superior placental mammals.
Using a combination of behavioural studies and tissue analysis, Arrese found that two types of marsupial - honey possums and dunnarts - can see colours from red right through to ultraviolet, a colour outside detection by humans and most animals. This enables the creatures to pursue a lifestyle which spans both day and night activities.
Arrese first suspected that sight is important to honey possums as she watched them scurry up banksia bushes to lap up the nectar of a particular flower. Banksia flowers turn from green to orange, and possums would always head for the brightest orange blossom - without being distracted by the fragrance coming from other flowers.
Using microspectrophotometry - a delicate technique where a fine beam of coloured light is shone through a single eye cell - Arrese found that marsupials had numerous cones of at least three different types, enabling them to see a wide colour spectrum.
Colour vision depends on cones - tiny cells in the retina which react to different wavelengths of light. Birds and reptiles have four types of cones in their eyes (ultraviolet, blue, green and red), while most placental mammals have only two (they've lost the blue and green), greatly limiting their colour vision.
Humans and apes have two types of cones, but one of the cone types, SWS1 has a huge variation in spectral sensitivity, allowing primates - including humans - to see a wide range of colours.
Some experts believe that placental mammals 'lost' the extra two cone types some time in their evolution, as they adapted to a nocturnal lifestyle. But primates re-acquired an extra cone type, enabling them to detect the reddish colour that fruit acquires as it ripens.
Arrese believes that marsupials have kept their full colour vision throughout evolution, and were only thought not to have colour vision because most people thought they were nocturnal, she said: "Far from being typically nocturnal … the honey possum is actually crepuscular [active at dawn and dusk]."
So far, three types of cones in dunnarts and honey possums have been found, but Arrese suspects a fourth type is also present in smaller concentrations.
http://abc.net.au/science/news/stories/s1028434.htm
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Primates swap smell for sight
Like all primates, humans can distinguish all seven colours of the rainbow. But international research says they may have developed this sense of sight at the expense of a superior sense of smell.
Dr Yoav Gilad and collegues at the Max Planck Institute for Evolutionary Anthropology in Germany and the Weizmann Institute of Science in Israel, showed that as primates evolved, so did the genes that controlled their senses.
With time, they lost functional genes that controlled their sense of smell but gained a type of retinal protein that allowed full colour vision.
The results appeared in the latest issue of the Public Library of Science Biology journal.
Researchers know that people who are deaf or blind often have greater sensitivity in their remaining senses. Now Gilad and his team have shown that this greater sensitivity may also develop as species evolved.
All 19 species of primates the researchers studied have about 1000 genes that control smell. These olfactory genes are the largest family of genes in mammals.
But not all olfactory genes help us smell. Some are pseudogenes, genes that are thought to have once worked but as species evolved they lost their function due to mutations.
The percentage of olfactory genes that are non-functional pseudogenes varies with each species. Primates with a greater proportion of pseudogenes genes can't smell so well.
By correlating the proportion of olfactory pseudogenes with the number of different types of retinal proteins, Gilad and his team showed that humans and our closest relatives, the apes, traded our olfactory ability for a full set of retinal proteins that are are crucial to see things in colour.
Common ancestors
Around 23 million year ago, humans and apes once shared a common ancestor with Old World monkeys, a group that includes the Rhesus monkey and the baboon. Old World monkeys, like apes, also have full colour vision and about 30% of their olfactory genes are the non-functioning pseudogenes. But they still out-sniff humans who have a greatly reduced sense of smell. Some 60% of humans' olfactory genes are pseudogenes.
Humans share less in common with New World monkeys, such as spider monkeys and marmosets, than they do with Old World monkeys. This also holds true for sight and smell. Most New World monkeys have only two types of retinal proteins meaning they have limited colour vision. The compensation may be that New World monkeys generally have a more superior sense of smell with only 17% of their olfactory genes being pseudogenes.
The exception is the howler monkey. Unlike other New World Monkeys, these have a full set of visual proteins, so can distinguish all colours in their environment. To achieve this full colour vision, the howler, like humans and apes, increased their proportion of olfactory pseudogenes and lost part of their keen sense of smell.
Howlers underwent this evolutionary split with other New World monkeys between 7 and 16 million years ago.
Gilad's research showed a swap in importance of sight and smell during primate evolution. Sight may have become more important than smell in finding food or the choosing a mate, the researchers said.
George
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Hello Boo,
Apparantly I share that theatre experience with you, with the important difference that I acted as an amateur (sound and)light technician for an amateur theatre group. But things were done rather on a trial and error base there, and praying tha no bulbs would burn out during the show was as imortant as perfect colour rendition.
I have learned about colours and colour perception mainly by expanding on my training in physical chemistry.
Are you still involved in lighing stages ?
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quote:
Originally posted by eric l
Hello Boo,
Apparantly I share that theatre experience with you, with the important difference that I acted as an amateur (sound and)light technician for an amateur theatre group. But things were done rather on a trial and error base there, and praying tha no bulbs would burn out during the show was as imortant as perfect colour rendition.
I have learned about colours and colour perception mainly by expanding on my training in physical chemistry.
Are you still involved in lighing stages ?
well... kinda.. at arizona state university there are only two lighting courses i could take and ive taken both already.. i have worked on lots of shows doing lights since high school but this semester i am taking a break and im stage manager for a mainstage performance but i love lights, i have a very visual memory and am a very visual person.. isnt it amazing how much science goes into things like theatre?
becca :)
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quote:
Originally posted by Boo
well... kinda.. at arizona state university there are only two lighting courses i could take and ive taken both already.. i have worked on lots of shows doing lights since high school but this semester i am taking a break and im stage manager for a mainstage performance but i love lights, i have a very visual memory and am a very visual person.. isnt it amazing how much science goes into things like theatre?
Here is a page on using UV-A lights (a.k.a. "black light") in the theatre.
http://www.theatrefx.com/funfacts2.html
Note: UV-A is not "harmless" as the "theatrefx" page states:-
" UV-A radiation causes us less harm compared to the shorter wavelengths. Although, it can cause sunburn and cataracts. UV-A radiation can benefit humans by synthesizing vitamin D in the body."
http://enhs.umn.edu/5103/uv/risk.html
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what gets me is that you perceive the same colors for monochromatic red as you do for red made of a combination of different wavelengths, and you can even see magenta, which has no monochromatic counterpart.
the subject of 'primary colors' is more biological than universally physical. defining them as red blue green or cyan magenta yellow or any three points 120 degrees apart on the color wheel will work the same. finding out which colors the cones in your eyes react to would be more limiting and valuable in determining the means of perception.
it is frustrating that the colored shadow phenomenon and things like tartini notes (sound) and so on exist to confound our senses and make observations more difficult.
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Actually all cones react to all wavelengths ! The difference is that the S-cones react more (not exclussvely)to shorter wavelengths, while M and L cones react more to longer wavelengths.
(See again http://en.wikipedia.org/wiki/Colour_perception)
The primary colors for absorption are not linked to a specific wavelenght. If you would measure the spectrum refelected by the yellow, cyan or yellow ink in your printer, you would actually see a graph with a maximum, but with a multitude of small peaks and valleys.
The so called primary colors are defined by centuries of experience from painters, printers, photographers... That is also the reason why the primary colours for your printer are not the same as the primary colours for your screen. The light emmited by the red, green and blue "guns" is closer to monochromatic light than the light reflected by a printed or painted surface with only one of the primary colors.
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quote:
Originally posted by eric l
Actually all cones react to all wavelengths ! The difference is that the S-cones react more (not exclussvely)to shorter wavelengths, while M and L cones react more to longer wavelengths.
(See again http://en.wikipedia.org/wiki/Colour_perception)
The primary colors for absorption are not linked to a specific wavelenght. If you would measure the spectrum refelected by the yellow, cyan or yellow ink in your printer, you would actually see a graph with a maximum, but with a multitude of small peaks and valleys.
The so called primary colors are defined by centuries of experience from painters, printers, photographers... That is also the reason why the primary colours for your printer are not the same as the primary colours for your screen. The light emmited by the red, green and blue "guns" is closer to monochromatic light than the light reflected by a printed or painted surface with only one of the primary colors.
Yes to everything, excepting to: "The so called primary colors are defined by centuries of experience from painters, printers, photographers... That is also the reason why the primary colours for your printer are not the same as the primary colours for your screen".
The main reason for this difference is that with ink or paint or pigments, you make the others colours by "subtractive synthesys", while with lights by "additive synthesys" (I hope I have correctly translated from italian).
It means that, mixing two pigments, white light hitting on this new pigment looses those wavelenghts absorbed by both pigments, so you subtract them from the white light; mixing to coloured beams of light (or putting close together two tiny coloured points, as in the monitor's screen) you have to add the wavelenghts.
Example: mixing red light and green light produces a yellow light. If you look at a brilliant yellow spot on your screen through a powerful lens, you can see it's actually made of red and green pixels.
Mixing red and green pigments gives a completely different colour (dark greenish or reddish brown). So you cannot obtain yellow colour mixing pigments of others colours.
Because of these two different ways to obtain colours, it was found that the entire visible spectrum is better reproduced (better doesn't mean perfect!), using only three lights, by mixing the (primary) colours: red, green, blue; while instead, mixing pigments, with the three (primary) colours: magenta, yellow, cyan.
In this way, every colour, made with lights or with pigments, is unambiguously determined by a three-components vector: (x,y,z) where each component represent the intensity of every primary colour.
This is very useful, e.g., in digital elaborations of photos and pictures in general, because every coloured point on the monitor's screen, or every coloured dot printed on (or read from) paper, is identified by a triplet of numbers, and so, easily elaborated mathematically by softwares.
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i beg to differ. you can start from any three colors 120 degrees apart on the color wheel and make any other color additively or subtractively, just as well. try it out if you don't believe me.
as far as the cones reacting to all wavelengths, this is not exactly clear. they do react to a range of wavelengths. obviously, they do not react to infrared or ultraviolet or anything beyond that. what i was referring to, was the maximum of each kind of cone. each one has a global maximum sensitivity correlated to a primary color. one of them (i forget which- violet, or maybe green) acts goofy with a couple of local maxima as well.
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quote:
Originally posted by bostjan
i beg to differ. you can start from any three colors 120 degrees apart on the color wheel and make any other color additively or subtractively, just as well. try it out if you don't believe me.
Please, try to make bright yellow subtractively, of course without using orange-yellow mixed with yellow-green! It would be cheating! And in this case, you won't be able to obtain all the other colours (but very unsaturated ones) if these two are two of the primaries. For example, with these two and blue, you can't obtain red, ecc.
About trying it out, don't worry, I have done it a lot of times.
quote:
...as far as the cones reacting to all wavelengths, this is not exactly clear. they do react to a range of wavelengths. obviously, they do not react to infrared or ultraviolet or anything beyond that. what i was referring to, was the maximum of each kind of cone. each one has a global maximum sensitivity correlated to a primary color. one of them (i forget which- violet, or maybe green) acts goofy with a couple of local maxima as well.
Yes but not completely exact. Yes because each retinal receptor (cone) has a sensitivity spectrum (curve) with a global maximum sensitivity correlated to a primary color. Anyway, those curves, even if with very low levels of sensitivity, have tails on the left and on the right, stretching in all the visible spectrum.
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You saying you cannot subtract to yield red?! You have not tried enough, then. Surely, Yellow and Magenta subtracted yield red. To get any very bright colors subtractively is difficult, but try pale green and tiny bit of red. If you got brown, mix in white to lighten it up.
There is nothing magical about any certain color, I assure you.
And I never said that the sensitivity curve did not span the visible range, merely that it did not span outside this range. I stated this quite clearly in the first and second sentences you quoted.
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what gets me is that you perceive the same colors for monochromatic red as you do for red made of a combination of different wavelengths, and you can even see magenta, which has no monochromatic counterpart.
the subject of 'primary colors' is more biological than universally physical. defining them as red blue green or cyan magenta yellow or any three points 120 degrees apart on the color wheel will work the same. finding out which colors the cones in your eyes react to would be more limiting and valuable in determining the means of perception.
it is frustrating that the colored shadow phenomenon and things like tartini notes (sound) and so on exist to confound our senses and make observations more difficult.
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Actually all cones react to all wavelengths ! The difference is that the S-cones react more (not exclussvely)to shorter wavelengths, while M and L cones react more to longer wavelengths.
(See again http://en.wikipedia.org/wiki/Colour_perception)
The primary colors for absorption are not linked to a specific wavelenght. If you would measure the spectrum refelected by the yellow, cyan or yellow ink in your printer, you would actually see a graph with a maximum, but with a multitude of small peaks and valleys.
The so called primary colors are defined by centuries of experience from painters, printers, photographers... That is also the reason why the primary colours for your printer are not the same as the primary colours for your screen. The light emmited by the red, green and blue "guns" is closer to monochromatic light than the light reflected by a printed or painted surface with only one of the primary colors.
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quote:
Originally posted by eric l
Actually all cones react to all wavelengths ! The difference is that the S-cones react more (not exclussvely)to shorter wavelengths, while M and L cones react more to longer wavelengths.
(See again http://en.wikipedia.org/wiki/Colour_perception)
The primary colors for absorption are not linked to a specific wavelenght. If you would measure the spectrum refelected by the yellow, cyan or yellow ink in your printer, you would actually see a graph with a maximum, but with a multitude of small peaks and valleys.
The so called primary colors are defined by centuries of experience from painters, printers, photographers... That is also the reason why the primary colours for your printer are not the same as the primary colours for your screen. The light emmited by the red, green and blue "guns" is closer to monochromatic light than the light reflected by a printed or painted surface with only one of the primary colors.
Yes to everything, excepting to: "The so called primary colors are defined by centuries of experience from painters, printers, photographers... That is also the reason why the primary colours for your printer are not the same as the primary colours for your screen".
The main reason for this difference is that with ink or paint or pigments, you make the others colours by "subtractive synthesys", while with lights by "additive synthesys" (I hope I have correctly translated from italian).
It means that, mixing two pigments, white light hitting on this new pigment looses those wavelenghts absorbed by both pigments, so you subtract them from the white light; mixing to coloured beams of light (or putting close together two tiny coloured points, as in the monitor's screen) you have to add the wavelenghts.
Example: mixing red light and green light produces a yellow light. If you look at a brilliant yellow spot on your screen through a powerful lens, you can see it's actually made of red and green pixels.
Mixing red and green pigments gives a completely different colour (dark greenish or reddish brown). So you cannot obtain yellow colour mixing pigments of others colours.
Because of these two different ways to obtain colours, it was found that the entire visible spectrum is better reproduced (better doesn't mean perfect!), using only three lights, by mixing the (primary) colours: red, green, blue; while instead, mixing pigments, with the three (primary) colours: magenta, yellow, cyan.
In this way, every colour, made with lights or with pigments, is unambiguously determined by a three-components vector: (x,y,z) where each component represent the intensity of every primary colour.
This is very useful, e.g., in digital elaborations of photos and pictures in general, because every coloured point on the monitor's screen, or every coloured dot printed on (or read from) paper, is identified by a triplet of numbers, and so, easily elaborated mathematically by softwares.
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i beg to differ. you can start from any three colors 120 degrees apart on the color wheel and make any other color additively or subtractively, just as well. try it out if you don't believe me.
as far as the cones reacting to all wavelengths, this is not exactly clear. they do react to a range of wavelengths. obviously, they do not react to infrared or ultraviolet or anything beyond that. what i was referring to, was the maximum of each kind of cone. each one has a global maximum sensitivity correlated to a primary color. one of them (i forget which- violet, or maybe green) acts goofy with a couple of local maxima as well.
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quote:
Originally posted by bostjan
i beg to differ. you can start from any three colors 120 degrees apart on the color wheel and make any other color additively or subtractively, just as well. try it out if you don't believe me.
Please, try to make bright yellow subtractively, of course without using orange-yellow mixed with yellow-green! It would be cheating! And in this case, you won't be able to obtain all the other colours (but very unsaturated ones) if these two are two of the primaries. For example, with these two and blue, you can't obtain red, ecc.
About trying it out, don't worry, I have done it a lot of times.
quote:
...as far as the cones reacting to all wavelengths, this is not exactly clear. they do react to a range of wavelengths. obviously, they do not react to infrared or ultraviolet or anything beyond that. what i was referring to, was the maximum of each kind of cone. each one has a global maximum sensitivity correlated to a primary color. one of them (i forget which- violet, or maybe green) acts goofy with a couple of local maxima as well.
Yes but not completely exact. Yes because each retinal receptor (cone) has a sensitivity spectrum (curve) with a global maximum sensitivity correlated to a primary color. Anyway, those curves, even if with very low levels of sensitivity, have tails on the left and on the right, stretching in all the visible spectrum.
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You saying you cannot subtract to yield red?! You have not tried enough, then. Surely, Yellow and Magenta subtracted yield red. To get any very bright colors subtractively is difficult, but try pale green and tiny bit of red. If you got brown, mix in white to lighten it up.
There is nothing magical about any certain color, I assure you.
And I never said that the sensitivity curve did not span the visible range, merely that it did not span outside this range. I stated this quite clearly in the first and second sentences you quoted.
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quote:
Originally posted by bostjan
You saying you cannot subtract to yield red?! You have not tried enough, then. Surely, Yellow and Magenta subtracted yield red. To get any very bright colors subtractively is difficult, but try pale green and tiny bit of red. If you got brown, mix in white to lighten it up.
There is nothing magical about any certain color, I assure you.
And I never said that the sensitivity curve did not span the visible range, merely that it did not span outside this range. I stated this quite clearly in the first and second sentences you quoted.
I said it's not possible to obtain saturated red with orange-yellow, yellow-green and blue as primaries.
Magenta and yellow, of course can make red subtractively! They are primary colours of subtractive synthesys! Otherwise, how could a printer make red as well as all the other colours?
About a brown (or dark) pigment or ink, if you add white, you obtain of course a lighter colour, but not saturated anylonger (I am assuming you know very well what "saturated" means).
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When I first joined the colour printing business the explanation I was given for subtractive colour generation was that white light passed through the printing ink removing some components, was reflected by the white paper and then passed out through the ink again and the normal additive process then took place
syhprum
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quote:
Originally posted by syhprum
When I first joined the colour printing business the explanation I was given for subtractive colour generation was that white light passed through the printing ink removing some components, was reflected by the white paper and then passed out through the ink again and the normal additive process then took place
Yes, but this happens only for those kinds of printing where pigment dots never overlaps one onto another. In that case it's the same as coloured light dots on the monitor's screen forming an image, and the syntesys is additive.
You can make this simple experiment: on a white paper, draw ~ 20 thin lines of red and green colour, alternatively, one by the other, without overlapping. You should do it with bright colours.
When you have finished, looking at this drawing from a short distance, you see a reticolus of red and green lines, but from some meters apart, you see a yellowish stain.