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Additive and Subtractive Color Mixing
The world is full of colors. Some researchers report that humans can distinguish about 16 million different colors. But what's more interesting is that most of the colors we see around us and all the colors we see on a TV or computer monitor can be created from just three different colored lights. How are all the colors made from just three different colors? Simply by combining the light in different ratios. That's it. Adjusting the brightness of three colors in different ways creates all the colors you see in this graphic:
Colored lights are mixed using additive color properties. Light colors are combining two or more additive colors together which creates a lighter color that is closer to white. Examples of additive color sources include computers and televisions.
The additive primary colors are red, green and blue (RGB). Combining one of these additive primary colors with equal amounts of another one results in the additive secondary colors of cyan, magenta and yellow. Combining all three additive primary colors in equal amounts will produce the color white. Remember combing additive colors creates lighter colors, so adding all three primary colors results in a color so "light" it's actually seen as white. Although that may seem strange, if you think of the absence of all light equaling black, it begins to make sense that adding different colors creates white.
By changing the brightness of each of the three primary colors by varying degrees, you can make a wide range of colors.
Computer Monitors and Televisions
Computer monitors and televisions are an application of additive color. These devices use a mosaic of red, green and blue dots. Our eyes do not distinguish the dots. Rather, the dots stimulate the color receptors of our retina (called cones) by adding or blending the light together creating a composite color.
Animated RGB Color Cube
Here is an animated RGB color cube. Notice how the colors get lighter as they move toward the closest corner.
Another Way to Make Colors
Combining lights in different ratios creates additive colors and works great for TVs and computers, but how do you make a color photograph when your only source of light is the white light above your head? In this case, you'll use something called subtractive or pigment colors. The distinction between additive and subtractive colors is based on whether the image is derived from a light source, like a TV that uses glowing phosphorus, or reflected natural light, as from a book, photograph, wall or any other object.
Subtractive Color Mixing
Before TVs and computer monitors, printers and publishers wondered if they could print color pictures using just three colors of ink. Yes, it is possible, but you have to work in reverse of the process of mixing light colors! We see light colors by the process of emission from the source. We see pigment colors by the process of reflection (light reflected off an object). The colors which are not reflected are absorbed (subtracted).
The subtractive primary colors are cyan, magenta and yellow (CMY). These are the three colors used in printer ink cartridges.
When the source of color is pigment or dye, the result of combining colors is different from when the source of color is light. Subtractive color mixing occurs when light is reflected off a surface or is filtered through a translucent object. For example, a red pigment or filter only appears red because it absorbs (subtracts) all of the light that is not red and only reflects or allows the red light. A green pigment only reflects green light and a green filter only passes green light.
We know we can make any color from red, green and blue lights, but what happens if we try to paint with a mix of red, green and blue pigments? It doesn't work. Perhaps the easiest way to think about it is to realize that the red pigment absorbs green and blue, the blue pigment absorbs red and green, and the green pigment absorbs red and blue. In theory, the result should be completely black, but it is a bit more mud colored in reality.
However, this problem is easily corrected if we switch our thinking to consider the colors we want absorbed.
Let's say, for example, we want to absorb the color blue. From the additive color chart above (Additive Colors Combined in Equal Parts), we know we get a yellow light when we combine the two non-blue light primaries, green and red. Therefore, wherever we paint yellow on the paper, we absorb (subtract) blue. Combining the other primary light colors results in the following table showing the subtractive primaries:
So, when working with color pigments, you'll end up using Cyan, Magenta and Yellow as the primary colors.
But how do we print something that's red?
In order to print something that is red, we need to absorb both blue and green. (Remember, we're working in reverse.) To absorb the blue, we'll print yellow. To absorb green, we'll print magenta. So, by combinging both yellow and magenta pigments, we're left with red!
If we wanted to print the color yellow, we would need to combine the red and green pigments. This yellow pigment reflects both red and green, and absorbs blue. Likewise, combining green and blue creates cyan, and absorbs red. Combining red and blue creates magenta, and absorbs green.
If we wanted to print a blueish green, we again would need to work in reverse. A blueish green color has no red and just a little green. Therefore, we would need to print a strong pattern of cyan to absorb all of the red, and a lesser amount of magenta to absorb some, but not all of the green.
Combining pigment colors creates darker colors.
If we mix yellow, cyan and magenta pigments we get the following results.
Blackness of Black
As you can see, by working with subtractive pigments, combining all three yields black. In practice, however, the combination of all three does not yield nearly as true of a black color as printing with black directly, so most color printing is done with four ink colors, cyan, magenta, yellow and black, or CMYK for short. A "K" is used instead of a "B" to avoid confusion with blue. In the case of ink jet printers, it's also much cheaper to print with black ink.
Subtractive Color Filters
The same process of subtractive color mixing applies to mixing color filters. Instead of various colors being absorbed into the paint, the colors are absorbed into the filter.
Combining the Two
The following graphic of the color cube shows how the two color systems are related.
As you can see, the subtractive primary colors (cyan, magenta and yellow) connect at the top with white, the point where you don't add any pigment. Each of the single pigment legs branch out from white.
The light color branches are emanating from the black point at the opposite corner of the cube from white. They end in the additive primary colors (red, green and blue).
Speed of Light
Additive and Subtractive Colors
CIE 1931 Color Space
Spinning Color Top
Glossary of Color Terms
History of Color Science
Motion After Image
Munsell Color System
Color Optical Illusions
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