Halftone is the printing technique that simulates continuous tone imagery through the use of dots, varying either in size or in spacing.
In contrast to continuous tone imagery (such as the traditional silver-halide photographic process) which contains an infinite range of colors or grays, the halftone process reduces visual reproductions to a binary image that is printed with only one color of ink. This binary reproduction relies on a basic optical illusion—that these tiny halftone dots are blended into smooth tones by the human eye.
Just as color photography evolved with the addition of filters and film layers, color printing is made possible by repeating the halftone process for each subtractive color—most commonly using the CMYK color model. The semi-opaque property of ink allows halftone dots of different colors to create another optical effect: full-color imagery.