Color Models

RGB Model

A large percentage of the visible spectrum can be represented by mixing three basic components of colored light in various proportions and intensities. These components are known as the primary colors: Red, Green, and Blue. When these three primary colors overlap, they create the secondary colors: cyan, magenta, and yellow.

When the primary colors are combined white is created and so called additive colors. Adding all the colors together creates white, that is, all the light is reflected back to the eye. Additive colors are used for lighting, video, film recorders, and monitors. Your monitor, for example, creates color by emitting light through red, green, and blue phosphors to reproduce up to 16.7 million colors on-screen.
RGB contains three channels of color each with 256 values producing the 16.7 million colors on your screen. One channel each for red, green, and blue. Each channel contains eight bits of data to represent a pixel on a computer monitor. In other terms, 24 (8 x 3) bits per pixel. Computer monitors and televisions screens display colors using the RGB model.

CYMK Model

While the RGB model depends on a light source to create color, the CMYK model is based on the light-absorbing quality of ink printed on paper. As white light strikes translucent inks, a portion of the spectrum is absorbed. Color that is not absorbed is reflected back to your eye. In theory, pure cyan (C), magenta (M), and yellow (Y) pigments should combine to absorb all color and produce black; for this reason they are also called subtractive colors.

Because all printing inks contain some impurities, these three inks actually produce a muddy brown and must be combined with black (K) ink to produce a true black. (The letter K is used to avoid confusion, because B might also stand for blue. Combining these inks to reproduce color is called four-color process printing. The additive and subtractive colors are complementary colors. Each pair of subtractive colors creates an additive color.

CMYK contains four channels of color. One channel each for cyan, magenta, yellow and black. Each channel contains eight bits of data to represent a pixel on a computer monitor. In other terms, 32 (8 x 4) bits per pixel. CMYK color looks differently on computer monitors and televisions screens than on print because the display of colors on the monitor uses the RGB model.

HSB Model

The HSB (Hue, Saturation, and Brightness) model is based on the human perception of color. In the HSB model, all colors are described in terms of three fundamental characteristics. A color with an H value of 0°, an S value of 96%, and a B value of 90% would create a very bright red color. Let’s take a closer look.

Hue

Hue is the wavelength of light reflected from or transmitted through an object. More commonly, hue is identified by the name of the color such as red, orange, or green. Hue is measured as a location on the standard color wheel. Color is expressed as a degree between 0° and 360° where 0°/360° is red, 45° yellow, 135° is green and so on.

Saturation

Saturation, sometimes called chroma, is the strength or purity of the color. Saturation represents the amount of gray in proportion to the hue and is measured as a percentage from 0% (grey) to 100% (fully saturated). On the standard color wheel, saturation increases as one approaches the edge of the wheel; saturation decreases as one approaches the center.

Brightness

Brightness is the relative lightness or darkness of the color and is usually measured as a percentage from 0% (black) to 100% (white).

Grayscale

Grayscale uses up to 256 shades of gray to represent an image. The values between 0 and 255 correspond to points on the grayscale spectrum. Grayscale values can also be measured as percentages of black ink coverage (0% is equal to white and 100% is equal to black). Images with black and white or grayscale scanners are typically displayed in grayscale mode.