A grayscale image is one that contains shades of gray instead of numerous other colors. This technique is often used to create bold, graphic images that are more economical in design and color usage. The advantage of grayscale images is that they can be reproduced on any type of media, not just print media like black and white pictures.
The human eye can see up to eleven million different shades, variations, and tones in a single color scheme; while the computer only recognizes 256 shades (8-bit). Illustrators use grayscale to get around this limitation by having multiple shades of gray that are blended together using dithering or halftoning techniques which produce a pattern that resembles the movement, shape, or distribution of ink on paper.