Color Correction and Restoration - Beginning Photo Retouching and Restoration Using GIMP - page 79

Color Essentials
Before moving on to the tutorials, there are a few essentials that must be covered. In this section, you'll learn
about additive and s ubtractiv e color models and using the Color Picker tool to sample and determine color
values. We'll also look briefly at the RGB color channels.
Additive Color
The color we see on a computer monitor is composed of light, which is additive color . The most common
color model is the RGB (which stands for red, green, and blue light), and is GIMP's default mode for
working with images. The RGB color mode can produce a little over 16.7 million colors. Full intensity of red,
green, and blue light results in white (Figure 4-1 ), while zero intensity of each results in black. When the
percentages of each are equal, it produces a shade of gray between black and white (as we saw in Chapter 3),
but when the percentages differ, the result is a colorized hue.
Figure 4-1. The RGB (additive) color model
Subtractive Color
Subtractive color is based on the absorption and reflection of light from printed pigments, dyes, and inks.
Colors that are absorbed by a particular ink, pigment, or dye are being subtracted. For example, red ink
reflects a red wavelength of light, but all other color wavelengths are absorbed. Black ink absorbs all color
wavelengths, resulting in an absence of any color.
The CMYK color model is widely used in the offset printing industry. CMYK refers to the ink colors cyan,
magenta, yellow, and black (the K is assigned to black, because it means “key” in the printing industry).
Theoretically, equal combinations of cyan, magenta, and yellow ink produce black (Figure 4-2 ), but in actual
practice, the result is a dark brown. This necessitates black as a fourth color, for accurate reproduction of grays
and black in print.