An additive color system is a way of mixing colored light to create other colors. In an additive system, the primary colors are red, green and blue (RGB). When you combine these colors in different proportions, you can produce a wide range of colors. Additive color systems are used for lighting, video displays, photography, and other applications that involve emitted light.
How Additive Color Mixing Works
The additive color system is based on the way our eyes perceive color. The retina of the human eye contains three types of color receptors called cone cells. These cone cells respond to red, green and blue light. When you look at an object, the cone cells are stimulated in varying degrees by the wavelengths of light the object reflects or emits. The combination of stimulations produces the perception of different colors.
With additive color mixing, the more light that is added, the brighter and lighter the color becomes. Starting with darkness, as you increase the intensity of red, green and blue light, the end result will become white. This is because white light contains an even mixture of all colors in the visible spectrum.
The primary colors in an additive system are red, green and blue because these correspond to the peak sensitivities of the three types of cone cells in our eyes. By mixing varying levels of these three colors, we can stimulate the eye to perceive any color.
Additive vs. Subtractive Color Systems
There are two main types of color models: additive and subtractive. Both involve the mixing of a limited set of primary colors to create a range of colors. However, they work in complementary ways.
In a subtractive system like painting, ink or dye, the primaries are cyan, magenta and yellow. These are the complementary colors (opposites) of red, green and blue. Subtractive color starts with white light and selectively absorbs (subtracts) certain wavelengths, reflecting the remaining light as color. As more colors are mixed together, more of the white light is absorbed, so the color becomes darker and murkier.
In contrast, additive color starts with darkness and adds light wavelengths together to form color. Additive mixing involves light emitted directly from a source. Subtractive mixing involves light reflected off a surface.
| Additive Color | Subtractive Color |
|---|---|
| Starts with darkness | Starts with white light |
| Adds light together | Subtracts light by selective absorption |
| Light gets brighter/lighter as more color is added | Color gets darker/muddier as more color is added |
| RGB are the primary colors | CMY are the primary colors |
| Used for light sources and displays | Used for reflective surfaces and printing |
So while the principles of color mixing apply to both models, additive and subtractive color work in opposite directions starting from different points.
Additive Primary Colors
The primary colors in an additive RGB color model are red, green and blue. By combining these three colors in different proportions, all other hues can be created.
Red (R) – Red light stimulates the red cones in our eyes most strongly, without stimulating the green or blue cones much. In the visible spectrum, red light has the longest wavelength.
Green (G) – Green light activates the green cones selectively, with relatively little stimulation of the red or blue cones. In the spectrum, green is mid-way between red and blue in wavelength.
Blue (B) – Blue light triggers a strong response in the blue cones only, without much activation of the red or green cones. Of the three primaries, blue has the shortest wavelength in the visible spectrum.
Red, green and blue are primary because they cannot be created by mixing other colors in an additive system. All other colors can be formed by combining red, green and blue light.
Secondary Colors
When you mix two of the primary additive colors together in equal amounts, you get a secondary color. The secondary colors in an RGB model are cyan, magenta and yellow.
Cyan (G + B) – Cyan is an even combination of green and blue light. Since green stimulates the green cones and blue stimulates the blue cones, cyan stimulates both cones evenly to produce the perception of cyan.
Magenta (R + B) – When you mix red and blue light, the result is magenta. This color strongly stimulates the red and blue retinal cones while minimally activating the green cones.
Yellow (R + G) – Mixing red and green light produces the color yellow. This additively stimulates the red and green cones to generate the sensation of yellow, without much blue cone stimulation.
The secondary colors have wavelengths between the primaries. Cyan is between blue and green, magenta is between red and blue, and yellow is between red and green.
Tertiary Colors
By mixing a primary color with an adjacent secondary color, you get the tertiary colors. These include orange, chartreuse, spring green, azure, violet and rose.
For example:
Orange – Mixing red with yellow produces orange, which is between red and yellow.
Chartreuse – Adding green to yellow makes chartreuse, a yellowish green hue.
Spring Green – Combining green and cyan creates spring green, a bright, vibrant green.
Azure – Mixing blue and cyan results in azure, a light blueish cyan.
Violet – Red plus magenta makes violet, between red and magenta.
Rose – Adding red to magenta creates rose, a soft reddish tone.
By varying the proportions of the primary mixtures, many gradations of these tertiary hues can be produced.
Combining Additive Primaries
When you combine all three primary RGB colors in an additive system, the colors mix to produce white light. This is because white light contains roughly equal parts of all visible wavelengths.
For example, on a computer or TV screen displaying white, the red, green and blue sub-pixels are lit up at maximum intensity, merging additively to white light. Turning off all three sub-pixels yields black, which is the total absence of light.
By adjusting the intensity of the individual RGB primaries, any color can be reproduced on a screen. If you turn red fully on with green and blue off, you get pure red. With only green on, you see green. And blue by itself yields blue. Equal parts red, green and produce shades of gray from black to white.
Computer monitors and televisions have their colors calibrated so that mixing varying RGB values generates accurate hues. Digital images and video store color information as combinations of red, green and blue data. This data is then rendered on displays to reproduce those colors.
Perceptual Color Mixing
The way colors mix additively to produce different hues in an RGB model aligns with how we perceive color through our retina’s cone cells. The primaries correspond to the peak sensitivities of the three cone types. Mixing lights of these colors stimulates combinations of the cones to generate all other colors.
However, additive color mixing perception is more complex than simply triggering the cone cells. Our visual systems adapt to the overall level and type of stimulation. The surrounding colors also influence how a color is perceived. So the same RGB values can be perceived slightly differently depending on context.
Despite these factors, additive RGB color models effectively approximate human color vision. This makes them the basis for color video cameras, photography, TVs, computer monitors, scanners and other devices that capture or reproduce color visually.
Uses of the Additive Color System
The additive RGB color model is used extensively for any application where colors will be emitted rather than reflected. Here are some of the main uses of additive color:
- Television and Video Displays – All color TVs and computer monitors mix red, green and blue light to create the colors on screen. Patterns of RGB pixels make up the images.
- Digital Image Processing – Digital image formats like JPEG, PNG, GIF and BMP use RGB data to encode color. Digital image editing involves adjusting RGB values.
- Digital Video – Digital video encoding schemas like MP4 compress and store color video as RGB information. Mixing primary colors reconstitutes the video when played back.
- Smartphone/Tablet Displays – The LCD and LED displays on most smartphones, tablets and laptops are also based on RGB pixels emitting light.
- LED Lighting – Some LED lighting systems can mix red, green and blue LEDs to produce a wide gamut of colors for displays or ambient lighting.
- Stage/Event Lighting – Rock concerts, theater performances, and other staged events often use RGB LED lighting for vibrant, colorful illumination.
- Photography – Digital cameras have RGB image sensors that measure color via red, green and blue filtered photosites.
So from capturing images to displaying them, many color-based technologies rely on additive RGB color mixing. Any application where the color originates directly from a light source requires an additive system. Our eyes integrate the combined red, green and blue light to perceive full-spectrum color.
Conclusion
The additive color model uses red, green and blue light to create a wide range of hues. By varying the intensity of the primaries, different receptors in our eyes are stimulated to produce color vision. All modern color display and imaging devices use RGB color to encode color. Additive mixing also aligns with physics, since light can be treated as a spectrum of wavelengths or photons. Combining RGB lights essentially merges their spectra. This makes additive color an intuitive as well as technical way to generate color from light sources. While more complex than this summary, the additive system provides a fundamental model for color based on the physiology of human vision.
