Additive Color Model
The RGB color model is an additive color model. In this case red, green and blue light are added together in various combinations to reproduce a wide spectrum of colors. The primary purpose of the RGB color model is for the display of images in electronic systems, such as on television screens and computer monitors and it’s also used in digital photography. Cathode ray tube, LCD, plasma and LED displays all utilize the RGB model.
In order to create a color with RGB, three colored light beams (one red, one green, and one blue) must be superimposed. With no intensity,each of the three colors is perceived as black, while full intensity leads to a perception of seeing white. Differing intensities produce the hue of a color, while the difference between the most and least intense of the colors make the resulting color more or less saturated. Note the white centers that appear in the two color charts above.
For web-page design the colors used are commonly specified using RGB. Today, with the predominance of 24-bit displays, it enables most users to see 16.7 million colors of HTML RGB code. In web page design, there are 216 so-called ‘web-safe’ RGB colors represented by hexidecimal values. Quite simply, the web-safe color palette consists of the 216 combinations of red, green and blue.
Subtractive Color Model
The CMYK color model (four-color process) is a subtractive color model. Primarily used in printing, CMYK works by partially or completely masking colors on a white background. The printed ink reduces the light that would otherwise be reflected. That’s why this model is called subtractive because inks ‘subtract’ brightness from a white background from four colors: cyan, magenta, yellow and black.
It is frequently suggested that the ‘K’ in CMYK comes from the last letter in ‘black’ and was chosen because B already refers to blue. However, this explanation is incorrect. The ‘K’ in CMYK stands for ‘key’ since in four-color printing cyan, magenta, and yellow printing plates are carefully keyed or aligned with the key of the black key plate. Black is used because the combination of the three primary colors (CMY) doesn’t produce a fully saturated black. This is evident in the central black color created by the overlapping circles in the color chart above.
CMYK is able to produce the entire spectrum of visible colors due to the process of half-toning. In this process, each color is assigned a saturation level and miniscule dots of each of the three colors are printed in tiny patterns. This enables the human eye to perceive a specific color made from the combination. In order to improve print quality and reduce moiré patterns, the screen for each color is set at a different angle.