Additive color refers to a color model where colors are produced by combining light of the primary colors red, green, and blue. When you combine light of these three primary colors, you can create a wide range of other colors. This is the principle behind how screens like TVs, computer monitors, and smartphones create color.
Additive color is based on the trichromatic theory developed by Thomas Young in the early 1800s. Young proposed that the human eye contains three types of color receptors that respond to red, green, and blue light. By mixing different amounts of these three primary colors, we can perceive the full spectrum of colors.
Some key points about additive color:
– It involves combining colored light, rather than pigments or dyes.
– The primary colors are red, green, and blue. Combining all three in equal amounts produces white.
– It is used for colors displayed on electronic screens like televisions and computer monitors.
– The more light that is added, the brighter the color becomes. Adding full intensity red, green and blue makes white.
– The absence of all light is black.
So in summary, additive color starts with darkness and adds different combinations of red, green and blue light to create the colors we see on screens. The brighter the lights, the closer to white the final color is.
How Additive Color Works
The reason red, green and blue are the primary colors of additive color is due to the way our eyes detect color. The retina at the back of our eyes contains two types of light-sensitive cells: rods and cones.
The rods are sensitive to brightness, but do not detect color. The cones are specialized into three types that are sensitive to different wavelengths of light:
– Short wavelength cones that primarily detect blue light
– Medium wavelength cones that are sensitive to green light
– Long wavelength cones that respond best to red light
By combining signals from these three cone types in different ratios, our visual system can perceive the full range of colors. This is known as trichromatic color vision.
So when all three types of cones are stimulated equally, we see white light. With no stimulation, there is no light detected, so we see black. Varying the amount of red, green and blue light causes different cones to be stimulated, allowing us to see all the colors of the rainbow.
| Primary Color | Cone Type |
|---|---|
| Red | Long wavelength |
| Green | Medium wavelength |
| Blue | Short wavelength |
This trichromatic theory was later verified experimentally by measuring the absorption spectra of the cone cells. The peak sensitivities matched up with red, green and blue light.
So in displays like TV and computer screens, tiny dots of phosphors are used to produce pure red, green and blue light. By adjusting the intensity of these three colors, any color can be approximated by additive mixing. For example:
– Equal amounts of red, green and blue make white
– More red and green creates yellow
– Red and blue mixed make magenta
– Blue and green produces cyan
The more saturated the primary colors used are, the wider the gamut, or range, of colors that can be reproduced.
Comparison to Subtractive Color
Additive color differs from subtractive color, like that used with paints, dyes and inks. Subtractive color starts with a surface illuminated by white light, which contains the full spectrum of wavelengths. Pigments and dyes then subtract certain wavelengths, leaving only the desired colors to be reflected.
For example, a red paint absorbs all wavelengths except red, which is reflected back to our eyes. Combining cyan, magenta and yellow pigments absorbs all wavelengths except red, green and blue, producing a black surface.
The primary colors of subtractive color are cyan, magenta and yellow, as these can be combined to absorb all wavelengths and create black. In contrast, additive primaries can be combined to create white by emitting all wavelengths.
Additive and subtractive color represent opposite processes – adding light versus removing light. But they both allow a full gamut of colors to be created based on mixing primary hues.
Color Mixing with Light
We can demonstrate the principles of additive color using flashlights or theater gels of the primary colors. By overlapping and blending the beams, we can create secondary and tertiary colors.
Some examples of color mixing with light:
| Colors Combined | Resulting Color |
|---|---|
| Red + Green | Yellow |
| Red + Blue | Magenta |
| Green + Blue | Cyan |
| Red + Green + Blue | White |
Overlapping two primary colors creates the secondary colors yellow, cyan and magenta. Combining all three primaries results in white light.
You can try this yourself by shining separate flashlights with red, green and blue gels overlapping on a white surface. Add more lights to make the color get brighter and closer to white.
Computer and TV screens use the same principle of combining tiny red, green and blue light sources to create images in a wide spectrum of colors. Digital image formats store brightness values for each primary, which allows the additive color mix to be reproduced.
Color Gamut with RGB
The range of colors that can be created by mixing red, green and blue light is known as the RGB color gamut. This represents the colors that can be displayed on a computer monitor, television or other electronic display.
However, the RGB gamut does not encompass all visible colors that humans can perceive. There are certain highly saturated yellows, cyans, greens and violets that fall outside the standard RGB gamut.
This is because real-world red, green and blue primaries are not perfectly saturated or spectrally pure. There is some overlap and spillover into nearby wavelengths.
To represent the full visible color spectrum, we need an expanded color space. Two common wide gamut color spaces are Adobe RGB and ProPhoto RGB, which use more pure primary colors. This extends the range of displayable colors closer to human vision.
Even the best RGB displays are limited compared to print, however. While combining colored light adds wavelengths, printed CMYK inks work by subtracting wavelengths. This allows very pure, saturated colors to be produced on paper that are outside any RGB gamut.
So while additive RGB is limited, it is ideal for electronic devices. The gamut covers most colors adequately, and RGB pixels match how our eyes detect colors with three types of cones. This makes it a simple and efficient model for displays.
Advantages of the Additive Color Model
Some key benefits of the additive RGB color model include:
Compatible with human vision – RGB aligns with the three types of cones in our eyes, allowing displays to effectively stimulate color vision.
Efficient use of light – Combining emitted wavelengths is an efficient way to produce a range of colors from just three primaries.
Applicable to many display technologies – RGB can be implemented in CRT, LCD, LED/OLED, plasma displays, projectors and more.
Straightforward to digitalize and store – RGB color is easily represented digitally with brightness values for each primary.
Capable of producing millions of colors – Over 16 million color combinations are possible by varying levels of R, G and B.
Allows color adjustments – Digital RGB values can be changed to adjust hue, saturation, lightness, etc.
While limited compared to the human eye or reflective printing, additive RGB offers an effective and convenient model for producing color on electronic displays and devices.
Applications of Additive Color
Some common applications of the additive RGB color model include:
Television and Computer Monitors – All display technologies from CRT to LED use red, green and blue pixels to create images.
Smartphone and Tablet Screens – Mobile touchscreens are LCD displays illuminated with RGB pixels.
Digital Projectors – Video projectors use micro display panels or LEDs to generate RGB light.
LED Lighting and Signs – Additive color mixing is used to create colorful effects.
Electronic Billboards and Store Signs – Large LED panels allow vibrant outdoor advertisements.
Stage and Theater Lighting – RGB LEDs can produce millions of colors for performances.
Color Photography – Digital cameras capture RGB values to represent color pixels.
Color Printing – While printed with CMYK ink, designs use RGB for on-screen display.
Color Scanners – Scanned images are digitized to RGB data for computer storage.
So while invented centuries ago, additive color remains integral to most modern color technologies, displays and imaging. It offers an efficient model aligned with human vision.
Conclusion
Additive color is a key principle underlying most digital color technologies today. By combining the primary hues of red, green and blue light, a wide gamut of colors can be created that matches the three types of cones in our eyes.
While limited compared to the full spectrum humans can perceive, the additive RGB model offers an effective way to produce color from light. It enabled the development of color television, digital imaging, LED signage, projectors and more.
Understanding additive color helps explain how computer and phone screens create color. By mixing tiny red, green and blue pixels of varying intensities, these displays can stimulate our trichromatic visual system to see millions of different hues and shades.
So next time you look at a digital screen, you can think about how the color you are seeing is produced by the additive mixing of just three primary lights – red, green and blue.
