Epson Stylus Color 850 User Manual page 211

Process of color printing
A printer produces color images by printing tiny patterns of ink dots
using CMYK colors as mentioned in the previous section. Because most
ink jet printers are not able to print different gradations of the three
primary colors, they must use a halftoning method in order to represent
millions of colors or the gradation of colors as follows:
Dithering and error diffusion are the most commonly used halftoning
methods.
Dithering
Dithering uniformly aligns individual dots of different colored inks to
create the appearance of neutral colors. This method is suitable for
printing documents that contain large areas of solid color, such as bar
charts and graphs.
Error diffusion
Error diffusion blends individual colored dots with the colors of the
surrounding dots to create the appearance of natural colors. By blending
colored dots, the printer can achieve excellent colors and subtle color
gradation. This method is best suited for printing documents that contain
detailed graphics or photographic images.
B-4
Tips for Color Printing