Color Modes and Models

HSB Model (hue, saturation, brightness).

Hue is the color reflected from or transmitted through an object. It is measured as a location on the standard color wheel, expressed as a degree between 0° and 360°. In common use, hue is identified by the name of the color such as red, orange, or green. Saturation, sometimes called chroma , is the strength or purity of the color. Saturation represents the amount of gray in proportion to the hue, measured as a percentage from 0% (gray) to 100% (fully saturated). On the standard color wheel, saturation increases from the center to the edge. Brightness  is the relative lightness or darkness of the color, usually measured as a percentage from 0% (black) to 100% (white). Although you can use the HSB model in Photoshop to define a color in the Color palette or Color Picker dialog box, there is no HSB mode available for creating and editing images.

RGB model (red, green, blue)

A large percentage of the visible spectrum can be represented by mixing red, green, and blue (RGB) colored light in various proportions and intensities. Where the colors overlap, they create cyan, magenta, yellow, and white. Photoshop’s RGB mode uses the RGB model, assigning an intensity value to each pixel ranging from 0 (black) to 255 (white) for each of the RGB components in a color image. For example, a bright red color might have an R value of 246, a G value of 20, and a B value of 50. When the values of all three components are equal, the result is a shade of neutral gray. When the value of all components is 255, the result is pure white; when the value is 0, pure black. Although RGB is a standard color model, the exact range of colors represented can vary, depending on the application or display device. Photoshop’s RGB mode varies according to the working space setting that you have specified in the Color Settings dialog box.

CMYK model (cyan, magenta, yellow, black)

The CMYK model is based on the light-absorbing quality of ink printed on paper. As white light strikes translucent inks, part of the spectrum is absorbed and part is reflected back to your eyes. In theory, pure cyan (C), magenta (M), and yellow (Y) pigments should combine to absorb all color and produce black. For this reason these colors are 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. (K is used instead of B to avoid confusion with blue.) Combining these inks to reproduce color is called four-color process printing. Although CMYK is a standard color model, the exact range of colors represented can vary, depending on the press and printing conditions. Photoshop’s CMYK mode varies according to the working space setting that you have specified in the Color Settings dialog box. 

L*a*b model

The L*a*b color model is based on the model proposed by the Commission Internationale d’Eclairage (CIE) in 1931 as an international standard for color measurement. In 1976, this model was refined and named CIE L*a*b. L*a*b color is designed to be  device independent, creating consistent color regardless of the device (such as a monitor, printer, computer, or scanner) used to create or output the image. L*a*b color consists of a  luminance or lightness

Component (L) and two chromatic components:

•  The  a component (from green to red)
•  The b component (from blue to yellow).