GDI halftoning produces a quality color-scale or gray-scale image for printing devices or display devices that do not already have a built-in color or gray scale. Color halftoning provides:
·Highest quality color and gray-scale reproduction possible on a given device.
·Increased visual resolution with a limited set of intensity levels.
·Improved color correlation between the different output devices.
Traditional analog halftoning is a cellular process that uses a halftoning screen. The halftoning screen is composed of cells of equal sizes, with fixed-cell spacing center-to-center. The fixed-cell spacing accommodates the thickness of the ink, while the size of a dot within each cell can vary to produce the impression of a continuous tone.
On a computer, most printing or screen shading also uses a fixed-cell pixel size. To simulate the variable dot size, a combination of cluster pixels simulates the halftone screen. In Windows NT, GDI includes halftoning default parameters that provide a good first approximation. Additional device-specific information can be added to the system to improve output.