User manual

11 • Modifying an image
ColorQuartet 5.0 Pro
114
The LCH color model
Color spaces vary
A color space or color gamut is the range of colors that can be produced by a given color repro-
duction process, including scanners, monitors, printers, proofing systems, and printing presses.
Because of variations in mechanical and electronic components, printing inks, etc., no two out-
put units reproduce colors exactly alike; each has its own slightly different color gamut. In addi-
tion, the human eye can perceive many more nuances of color than can be reproduced by
technical means. A color transparency has a smaller color gamut than the eye, and the four-
color printing process has a considerably smaller color gamut than a transparency.
Digital color requires standardization
Digital color handling often involves transferring color data among different devices. So meth-
ods for ensuring the color integrity of images have become very important. Based on a global
color space defined by the Commission Internationale de l’Eclairage (CIE) in 1931, the “LCH”
(or “Lab”) color model was developed in the 1970’s and is now used as a standard device-inde-
pendent reference for color management.
LCH is the solution
The LCH model is based on human color perception and can describe any perceivable color by
a set of coordinates. Because it is larger than the color space of any prepress device, the color
profile of any input or output device can be mathematically compared and converted to LCH
values as a neutral reference. This, in turn, makes it possible to compare and convert color data
from any two devices to each other.
The LCH color space is a three-dimensional model. The vertical axis is called the “L” axis, which
refers to lightness or luminance – how bright a color is. It varies from maximum lightness or
white (L = 100) at the top of the color space to minimum lightness or black (L = 0) at the bottom.
The horizontal axis is called “C” or chroma, meaning color intensity (saturation). It varies from
minimum intensity (C = 0) at the center of the color space to maximum intensity at the edge.
Hue or “H” varies around the circumference of the color space, moving through the visible
spectrum of color values. H values are expressed as angles, starting with 0° at red and moving
counterclockwise through yellow, green/cyan and blue back to red.