Click on the titles below to learn all about color quality.
Color Models/Color Spaces (Lab, RGB, CMYK)
A color space is a range of colors in the visible spectrum, and is synonymous with color profiles as used in color management. A model of a color space is usually depicted as a 3D graphic, where the top of the graphic represents light hues, and the bottom represents dark hues. The peripheral area represents pure colors and the center represents gray.
LAB, RGB, and CMYK are all color spaces. Here is a brief breakdown of each, followed by more detailed descriptions:
The LAB color space is what people see and is comprised of more colors than either RGB or CMYK. RGB is the color space used by cameras, scanners and color monitors. CMYK is what most printers lay on paper. LAB is the largest color space, and CMYK is usually the smallest of these three. Some colors as seen on a monitor (RGB) cannot be reproduced in print (CMYK). And some colors in print cannot be viewed on a monitor. Those specific colors are called "out of gamut".
The most universally accepted system for color measurement is the CIE system, developed in 1931 by the International Commission on Illumination - abbreviated CIE from its French title Commission Internationale de l'Eclairage. In an effort to better refine color measurement, CIELAB was developed in 1976. The CIELAB model is primarily used for reflective color. Properly designated L*A*B*, this color space is used to define color values mathematically. L* represents lightness. The A* value represents the position on a magenta-green axis. The B* value is the position on a yellow-blue axis. CIELAB encompasses the entire visible spectrum, and is called "Lab Color" in Photoshop.
The RGB color model is a projected color space, and is the type produced by computer monitors and TVs. This color space is device dependent - meaning the same signal or image can look different on different devices. Images are created using the Additive Color Primaries, Red, Green, and Blue. RGB is additive because when these primary colors are combined at a value of 100% for each, they produce white light. When they are combined at different values millions of colors can be produced, but they cannot be used to define the entire visible spectrum.
The CMYK color model is a reflected color space and is created when light bounces off printed material. Reflected color is produced using the Subtractive Primaries, Cyan, Magenta, and Yellow. CMY primaries are subtractive because they absorb light. The colors we do not see are absorbed by the inks and subtracted from the visible spectrum. The colors that are not absorbed and reflected back are the colors we see. Combining these Primaries at different percentages will produce many of the colors in the visible spectrum.
Why the K in CMYK?
When the Additive RGB Primaries are absent, black is the result. When the Subtractive CMY Primaries are combined, black should be produced, but due to ink limitations, the result is a muddy brown. Black ink is added to ensure that a true black is possible. Black ink also ensures that enough definition will be maintained in the printed image.