We’ve all been taught since age 5 that “yellow and blue make green”. We all know that yellow, blue, and red are primaries. OTOH! The primary colors of LIGHT are different and mix differently! Ultimately, it is light which governs ALL the colors our eyes perceive. So, how is it possible that there are two different sets of primary colors which have different rules about mixing?
Can someone shed some light here?
Well, the two sets use different mediums-one set of primaries deal with light, and the other deals with pigments. (I believe the former are called additive primaries and the latter subtractive primaries.) As far as the pigments go, it’s the chemicals in them that determine what wavelengths of light they’re going to reflect. With the lights, you can pick which color you’re going to emit. When you mix the pigments, you’ve got to deal with the mixing of the chemicals and the resulting pigment; you’re at the mercy of the pigment.
Wow. It’s early, it’s been three years since my layout class, and I don’t know if this made any sense.
He weathered a firestorm of agony and did not break.
And while Yori raged against his unbending
courage, we took Kyuden Hiruma back.
His loss is great, but so is the gift his suffering brought.
-Yakamo’s Funeral
Flypsyde’s got it right. Our eyes have, essentially, red, blue and green receptors. These are the “true” primary colors.
When we’re dealing with direct input to our eyes, from a computer monitor, for example, we directly control the intensity of the red, blue and green light. When we’re dealing with reflected light, from a painting, for example, we control the intensity through pigments which absorb the unwanted colors.
Printers frequently use cyan, magenta, and yellow as primaries because these selectively absorb red, green and blue, respectively. In elementary school we used red, yellow and blue because these approximate cyan, magenta and yellow.
A further test of whether you’re dealing with additive or subtractive primaries is to mix them. Mixing additive primaries produces white. Mixing subtractive primaries produces black. In practice the subtractive primaries generally produce an ugly gray, so printers almost always use a black pigment as well.
That’ll do, pig. That’ll do.
I understand about the pigment, but I argue that we see yellow paint as “yellow” because the pigment absorbs all bands of white light except in the “yellow” range of the spectrum which is reflected back to the eye. Likewise, with blue pigment and “blue”.
Thus, one might expect the reflected light to follow the rules of light. I suppose, on the microscopic scale, the yellow pigment is superimposed on the blue pigment. The combined pigments act together to somehow become reflective in the “green” band of the spectrum.
It just seems paradoxical since the incident light governs how colors appear to us. The best example is objects under UV light. But, even under a red light source, for example, “normal” colors are skewed by the source lighting.
The scary thing is that 90% of the people think they’re above average! - unknown
Here’s what Cecil had to say:
http://www.straightdope.com/classics/a3_344.html
Not necessarily. Edwin Land (of Polaroid fame) did some interesting research on this topic. His work showed that the color of the incident light is not all that important in determining the colors we perceive.
In the extreme case it’s still true. If the incident light is monochrome we don’t see any colors at all and objects them same color as the light appear white. A red apple viewed in red light, or through a red filter, looks white. But for broad spectrum illumination the color of the light doesn’t prevent us from determining an object’s color.
Land would show subjects a gray patch and they would agree that it was gray. He would measure the spectral intensity of the reflected light from the patch and then show them a colored patch with the incident lighting adjusted so that the same spectral intensity was reflected – the colored patch had the same rgb value, if you will. The subjects could still properly identify the color, but only if there were other colored patches nearby. Without other colors to refer to the subjects thought they were seeing the same old gray.
He deduced that we automatically make adjustment for the incident light by comparison with surrounding colors. Since the adjustment processing presumably takes place in the cerebral cortex he called this the “retinex” theory, combining “retina” with “cortex”. He reasoned that color vision was an important survival skill and that we had to be able to correctly determine an object’s color in sunshine or shadow, midday or dusk, so our brains evolved to assist our eyes.
Interesting stuff, IMO. Scientific American had an article about it, oh, twenty-five years ago.
That’ll do, pig. That’ll do.
Here’s something I never really understood very well…
Red is at the low frequency end of the visible spectrum, and blue is near the high end. Violet is higher frequency than blue. Why, when I mix red and blue paint, does it become purple, which to me is basically the same as violet? Are violet and purple two different colors, even though they look alike? (and does that question even make sense? :))
Is it just the brain’s way of categorizing colors? Do the red and blue receptors both pick up violet frequencies?
It is too clear, and so it is hard to see.
WAG: violet light is very nearly an octave (twice the frequency, half the wavelength) of red light. So violet light will primarily stimulate the blue receptors in our eyes, but also stimulate the red receptors some by resonance. So violet light appears to us to be blue with a bit of red in it.
Most of this is educated guess but FWIW…
Basically your surmises are correct.
The light spectrum has a beginning and an end but our internal color spectrum is conceptually circular red -> orange -> yellow -> green -> blue -> violet -> red -> orange, etc., so we make a conceptual connection where no physical connection exists. If you can find a color map online or in a book it illustrates this point pretty well.
Spectral violet falls outside the range of the red receptors but the color we call violet has red and blue components. It might be more accurate to call it “unsaturated magenta”. Again, reference to a color map will help.
I can see I’m continually referring to a color map – I’ll see if I can find one online.
As far as the name of the color, purple or violet, I think that is largely a cultural thing. I always called it purple. When I was a kid I thought violet was just a hoity-toity word for purple. I guess technically purple is more reddish and violet is more blue. And I never knew what color indigo was (the I of ROYGBIV) until I found out years later that my “blue” jeans were dyed with indigo.
For an interesting discussion on categorization and color names check out Women, Fire and Dangerous Things by … um, I forgot the author. He references an interesting study on color names by a couple of other guys whose names I’ve forgotten. Isn’t that useful information.
I’ll go find that map and look up these guys names and get back to you.
That’ll do, pig. That’ll do.
The author of the book is George Lakoff. Still looking for the map…
Well, that was harder than I thought. The phrases “color map” and “color chart” have taken on new meaning in the HTML world.
It’s called a “CIE Chromaticity Diagram”. Here’s a reference: http://www.yorku.ca/faculty/academic/pkaiser/eye/ciediag1.htm
It’s impossible to render it accurately on a computer monitor. See the caveats associated with the diagram.
While we’re at it here are some links for Land’s retinex theory: http://www.livhope.ac.uk/lat/wwwlinks/psychokm/CAT5.HTM
Wow! I’m impressed by the complexity of my initial question! There’s always more to the story than meets the eye - so to speak!
Pluto, I’ve always heard it called a color wheel, and I never gave it much thought until now. I have seen detailed color wheels (maps). It’s almost a globe-like shape map where color varies longitudinally and shade and tin vary laterally, as I recall.
Thanks to everyone for their input!
The scary thing is that 90% of the people think they’re above average! - unknown
pluto can probably correct me if I get this wrong, but…
The normal color map you see is a hue/saturation or hue/value map, where the hue (color) varies around the circle, and either the saturation (“purity” of the color) or value (“brightness” of the color) decreases toward the center, making the center either white, or black, respectively.
This is more useful to artists than the CIEXYZ color map that pluto gave a link to, because it helps to know what color is opposite a give color, or 120 degrees away from a given color, etc. so you can easily find complementary colors.
There are a few problems with the color wheel, but probably the most significant one is that the arrangement is based on subjective measurements, but the CIEXYZ scale uses standard illumination, and standard functions to simulate the response of our retinas.
Oh, and more cool stuff about the retinex theory: It very nicely explains why we percieve light to be white both outside in the sun, and inside with florescent lights (unlike cameras, where outdoor film makes everything under florescents look horrid). The theory is that if the lights are bright enough, and almost white, we take the brightest spot in our visual field, call it white, and compare everything to that.