COLOR SPACE represents all the possible colors that can be produced by a particular output device, such as a monitor, color printer, photographic film or printing press. The definition of various color spaces arose from a need to standardize color descriptions. Try verbally describing a color to a friend and you’ll find it very difficult to be accurate.

In 1931, the Vienna-based Commission Internationale de l'Eclairage (CIE) developed the RGB model, which uses the three primary colors of transmitted light. The RGB standard is a ADDITIVE COLOR MODEL- that is, if you add red, green and blue light and you get white.

A second dominant color space model uses reflected light. This SUBTRACTIVE COLOR MODEL attains white by subtracting pigments that reflect cyan, magenta and yellow (CMY) light. Printing processes, the main subtractive users, add black to create the CMYK color space.

Aside from RGB and CMYK, there are many alternative color spaces; here are some of the most common:

BITMAP uses one of two colors (black and white) to represent the pixel (single point in a graphic image) in an image.

GRAYSCALE uses up to 256 shades of gray. Every pixel of a grayscale image has a brightness value ranging from 0 (black) to 255 (white). Grayscale values can also be measured as percentages of black ink coverage (0% is equal to white, 100% to black).

DUOTONE is used to increase the tonal range of a grayscale image. Although a grayscale reproduction can display up to 256 levels of gray, a printing press can reproduce only about 50 levels of gray per ink. This means that a grayscale image printed with only black ink can look significantly coarser than the same image printed with two, three, or four inks, each individual ink reproducing up to 50 levels of gray. Sometimes duotones are printed using a black ink and a gray ink--the black for shadows and the gray for midtones and highlights. More frequently, duotones are printed using a colored ink for the highlight color. This technique produces an image with a slight tint to it and significantly increases the image's dynamic range. Duotones are ideal for two-color print jobs with a spot color (such as a PANTONE ink) used for accent.

INDEXED uses, at most, 256 colors. By limiting the palette of colors, indexed color can reduce file size while maintaining visual quality. The .gif image format uses indexed color space; as such, .gif images cannot be anti-aliased unless they are first converted to RGB.

LAB COLOR (a.k.a. L*a*b and CIELAB) has a lightness component (L) that can range from 0 to 100, a green to red range from +120 to -120 and a blue to yellow range from +120 to -120. LAB is designed to be device independent and is used by such software as Photoshop as a intermediary step when coverting from one color space to another. LAB is based on the discovery that somewhere between the optical nerve and the brain, retinal color stimuli are translated into distinctions between light and dark, red and green, and blue and yellow.

MULTICHANNEL uses 256 levels of gray in each channel. A single Multichannel image can contain multiple color modes - e.g. CMYK colors and several spot colors - at the same time.

MONITOR RGB is the color space that reflects the current color profile of your computer monitor.

sRGB is a new RGB color space developed by Microsofft and Hewlett-Packard that attempts to create a single, international RGB color space standard for television, print, and digital technologies.

ADOBE RGB contains an extended gamut to make conversion to CMYK more accurate.

YUV (slang for Y’CbCr) is the standard for color television and video, where the image is split into luminance (i.e. brightness, represented by Y), and two color difference channels (i.e. blue and red, represented by U and V). The color space for televisions and computer monitors is inherently different and often causes problems with color calibration.

PANTONE is a color matching system maintained by Pantone, Inc., headquartered in Carlstadt, New Jersey. In 1963, Lawrence Herbert created the Pantone Matching System of identifying, matching and communicating colors to solve the problems associated with producing accurate color matches in the graphic arts community. Over the years, the Pantone system has expanded to include other color-critical industries, including digital technology, textiles and plastics.

When discussing color theory in general, particularly as it applies to digital technologies, there are several other important concepts:

HUE - The color reflected from, or transmitted through, an object. In common use, hue refers to the name of the color such as red, orange, or green.

SATURATION (referred to as CHROMINANCE when discussing video) - The strength or purity of a color. Saturation represents the amount of gray in proportion to the hue, measured as a percentage from 0% (gray) to 100% (fully saturated).

GAMUT - The total range of colors produced by a device. A color is said to be "out of gamut" when its position in one device's color space cannot be directly translated into another device's color space.

GAMMA - The values produced by a monitor from black to white are intentionally nonlinear because the human eye perceives such shifts in a logarithmic curve. Gamma defines the slope of that curve at the halfway between black and white.

BIT DEPTH - The number of bits (binary digits) used to define a pixel. For example, images that use 1 bit per pixel have two possible colors (2^1); 8 bit images contain a maximum of 256 colors (2^8); and 24 bit image can use any combination of 16.8 possible million different colors (2^24)

LOOK-UP TABLE (a.k.a. LUT) - When digital imagery, such as computer animation, is shot to motion picture film, it must be adjusted to look correct. Film stock relies on the SUBTRATCIVE COLOR MODEL since it uses CMY dyes, while the film recorder CRT tube (on which the images are played) relies on the ADDITIVE COLOR MODEL standard to television. The look-up table is the mathematical formula with controls this adjustment of lightness, saturation and hue.