Hue is what people usually mean when they say “color”.
Hue is simply the frequency of the electromagnetic light wave energy. Frequency is “waves per second” flowing past the viewer. The term for frequency is “Hertz” and it's abbreviated as “Hz”.
The reciprocal (the inverted viewpoint) of frequency is wavelength. That is, if the distance between wave crests is shorter, then more waves are packed into the same space and so more waves will arrive per second, even though the speed is fixed by the speed of light. So, shorter wavelengths are higher frequencies and longer wavelengths are lower frequencies. For example, the longest sound wavelength most people can hear is about 56 feet (17.1 m) long. And the shortest is about 3/4 of an inch (1.9 cm).
Red is the lowest visible light frequency and Violet is the highest which people can see. Birds have 4 light sensing pigments in their eyes instead of the 3 we have - so we can't even imagine all the colors birds perceive. Just below the light frequencies we humans can see is the Infra-Red range, which some animals can sense in a vision-like way, and which we can sense as heat. Just above human vision is the Ultraviolet range of frequencies.
Is color purity - that is, not having other Hues mixed in. People think of Saturation as the color's intensity.
The brightness, independent of Hue or Saturation, is the color's Value. You can see the Value of a color even in a black and white photo. Artists sometimes use the word “Tone” to refer to Value.
In the Additive (light mixing) color notation system the Primaries are Red, Green and Blue. “Primary” means that any other color can be created by mixing only these three. In systems using Additive color the term "RGB" is often used to mean "Red/Green/Blue".
Something that people find hard to believe is that equal amounts of red and green light is what we perceive as “yellow”. This may be because many people are used to thinking only in terms of the “Subtractive” (absorption by pigments) color notation system. See more about the Additive and Subtractive color systems below.
I think the Color Wheel should be called a “Hue Compass”, because it's useful to think of the Hues as measured by degrees around a circle. This can help in calculating colors mathematically too.
A Color Wheel is a useful tool, but it shows only 1 of the 3 color attributes (Hue). A Color Tree maps each of the 3 color attributes to one of the color tree's 3 dimensions, width, depth and height. Hue is displayed around the color tree as a compass-like radial dimension, Value is shown as the vertical dimension and Saturation is the horizontal distance from the center.
The color tree concept was developed by Albert Munsell and is also known as the “Munsell Color Tree”.
Here is a 3D computer model I made of a color tree.
Learn more...
Above is an accurate simulation of what actually happens when you shine 3 saturated (pure) light sources of a red, a green and a blue hue, of equal brightness, onto a white screen. For example you could do this with 3 light projectors or spotlights, if their hues are pure. This mixing of colored light is described by the “Additive Color” notation system - as used for photography, television, stage lighting and computer graphics - or wherever light sources of different hues are mixed.
Where 2 primary colors overlap, we see the Additive Secondary colors, Yellow, Cyan and Magenta.
This additive image also shows black and white (but I made the black area gray, to indicate the physical white screen). Black is where no light falls and white is where all 3 of the "RGB" (Red/Green/Blue) primaries overlap with equal values.
Why the order R-G-B? This is the order of decreasing wavelength (increasing frequency) of the tiny portion of the electromagnetic energy visible to we humans as "light". The most widely separated waves (longest wavelength) of the Additive Primaries are the Red (just above Infra-Red) and the most closely spaced (shortest wavelength) are the Blue (just below Ultra-Violet).
When pigments absorb some colors out of the visible light spectrum and reflect others, we call that ‘'Subtractive Color”’. This Subtractive Color notation system is used where paints, pigments, dyes or printing inks are involved. Some hues are subtracted from the white light illuminating the object, by the pigments of that object (white light is a mix of all visible hues). Those hues which are not absorbed are reflected to our eyes, giving the object its perceived ‘‘color”. Selectively absorbing certain hues (frequencies) is what pigments do for a living.
What happens to the light energy that's absorbed? The pigments convert it to a small amount of heat energy. In green plants, that energy is also used to make food for the plant. This is called “Photosynthesis”). As a byproduct of photosynthesis, the plants produce the oxygen we breathe and they also absorb CO2 from the air.
Did you know that you are a “living microwave receiver”? Yes, light is Electromagnetic Radiation, exactly the same as radio, television or radar, but way up in the higher microwave frequencies. That is, visible light starts up in the Terahertz frequency range (Trillions of waves per second, each shorter than about 100 millionths of a meter or about 39 thousandths of an inch).
Don't let that word radiation scare you. Most “radiation” isn't that dangerous type called Atomic Ionizing Radiation.
Anything that propagates through space is properly said to be “radiating”. It just means “spreading out”. For example, when you speak, you are radiating sound waves. A pebble thrown into a pool of water causes water waves to radiate.
Because our U.S. education system has become so poor at teaching science, many people don't realize that all “radiation” isn't the harmful type called “ionizing radiation”. Ionizing radiation is electromagnetic radiation of a very, very high frequency - way far above what you can see. Given a long enough exposure time to build up sufficient energy, it can modify some atoms, including the atoms you are made of, by “ionizing” them. That is, by knocking free some of their outer electrons.
Some people are even afraid of their microwave ovens, which have absolutely nothing to do with ionizing radiation, but simply vibrate water molecules to heat them up. I guess that word "nuclear" in "nuclear magnetic resonance" (using microwaves tuned to the exact frequency of water molecules to vibrate the water in food and heat it) scares them. Actually, there is no difference between vibrating the molecules in food, to cook it, by holding it over a flame or by using microwaves to vibrate the water in the food, except that microwaves do it more efficiently. Of course animals have lots of water molecules in them, so you'd best not dry your poodle in the microwave - even though your poodle will not become ionized.
Light waves visible to people are not powerful enough to affect most atoms - no matter how long the exposure time. But a few very special molecules are made in such a way that they are ultra-sensitive to visible light's feeble energy - such as the molecules of photographic film, solid state light sensors, photo-multiplier tubes, the light-sensing pigments inside our eyes and the light-using parts of plant leaves.
Think about it. Let's say that some fairly high electromagnetic energy, like the invisible high frequency ultraviolet energy in sunlight, is hitting you with x number of waves per second (frequency). If an even higher frequency of electromagnetic energy started to hit you later, say with 1,000 times as many waves per second, you would be absorbing a lot more energy per second. At some point, either by waiting long enough or by further increasing the frequency, you're going to start getting burned, even though each individual wave has very little energy.
Harmful ionizing electromagnetic energy delivery starts at the upper end of the frequency range of Ultraviolet light (given a long enough exposure time). Dangerous exposure time gets shorter as frequency increases, way up into the quite dangerous X-rays, even stronger gamma rays, and whatever may be beyond.
Electromagnetic energy, like radio, television, radar or light waves has both an electric part and a magnetic part, just as the name suggests. These 2 parts or “fields” travel at right angles to each other.
We can think of a single wave, or a "spectrum" (a whole set of waves of different frequencies), from the point of view of frequency (waves per second) or from the point of view of time (wavelength).
Below we see how this works for a single wave. For a set of waves of different frequencies (a spectrum), we would see a line on the frequency scale for each wavelength and a wave shape on the time scale for each.
These two different ways to view and think about waves are called “domains” - the “Frequency Domain” or "Spectrum" and the “Time Domain”.
The Frequency Domain is analyzed using an instrument called a “Spectrum Analyzer”.
This is an example of a software Spectrum Analyzer for audio frequencies
(The favorite instrument of Audio/Acoustics/Vibration engineers and other nerds - me too)
From Art Head Start by jim coe
Traditionally, the Time Domain is measured using an electronic Oscilloscope, although many modern Spectrum Analyzers can also display the Time Domain.
A traditional electronic Oscilloscope
(Yep, I had one just like this in my home lab)
From Art Head Start by jim coe
~ End ~
Wishing you a creative future!
_jim coe
