This filter simulates the dot patterns of color haltone printing. It's not actually very accurate and is intended as a special effect rather than for actual printing use. You can specify the radius of the dots and the angles of the cyan, magenta and yellow screens. If you set the screens to the same angle and use a grayscale image you can get a monochrome effect which can sometimes be useful for creating textures.

Color Halftone Screen Color Halftone Screen
Color Halftone