DIGITAL COLOR: THEORY AND PRACTICE

Color is a powerful, subtle and sometimes fickle tool. Add a little too much red to your blue, and suddenly you're looking at something entirely different than what you started with. How does color work, and what can be done to keep it consistent through digital and mechanical processes?

Digital retouching and manipulation. Final output through a 300dpi Xerox Electrostatic printer. 60" x 80". Click to see larger images.

The human visual system reads color. Light enters the eye, strikes the retina, and is absorbed by cone cells. The light is then transmitted to the brain via the optic nerve, where it is interpreted. An important lesson to draw from this model is that an observer may not actually see the true color of an object--the observer's cones may not respond to the exact wavelength. Furthermore, the brain interprets the signal received from the cones, and that interpretation could be misleading, hence optical illusions. the three types of cones: long, medium and short. Long cones are sensitive to red colors (which have long wavelengths), medium cones are sensitive to green, and short cones are sensitive to the shortest visible wavelengths, blue colors.

Cone cells are found mostly at the center of the eye and are unevenly distributed. Blue cones are rarer than red and green. Rod cells, which are not sensitive to color, are located around the periphery of the eye, and are responsible for night vision. Rods and cones usually do not function at the same time. The eye has a blind spot where the optic nerve meets the retina. However, this blind spot is seldom noticed since our eyes are continuously scanning the world and integrating between snapshots.

People are capable of detecting millions of colors--more than desktop printers, monitors, projectors and printing presses are capable of producing. To complicate matters, different devices produce different ranges of colors. Monitors mix light and printers mix ink, and results often vary. For example, your monitor might be capable of displaying a color like fire engine red, but to your printer it looks more like dry rust red. To combat the problem of accurate color reproduction, sets of device-independent standards have been created. One such standard was created by the International Color Consortium (ICC) and has been widely accepted. The ICC standard is based on experiments conducted by the Commission Internationale de l'Eclairage (CIE), which tested how people perceive color. Once a standard color space like ICC is agreed upon, devices can convert their colors to colors within the space. Problems arise when a device's colors are exotic flavors of the standard set. These color mismatches are resolved in a process called gamut mapping, which uses algorithms to convert extreme colors to standard colors. When everything works, what you see on your monitor is what you get in print