William Henry Talbot developed the original technique for halftoning in 1852. Known as amplitude modulated (AM) screening, this structure of halftoning uses a regulated patterning of dots to create an image. Roy Lichtenstein employed and exaggerated this technique in his paintings of comic strip panels. In AM screening, larger black dots create areas of darkness and shadow. However, many light areas of an image may still contain dots. Printing presses create dots so small that the naked eye cannot identify individual ones. They collectively appear as a very light shade of gray.
Stochastic screening is a more recent technique of halftone printing that increases or decreases the frequency of equally sized dots. They are not patterned systematically like in the AM structure. Instead, the density of dots affects the shading in an image. For that reason, this type of halftone printing is also referred to as "frequency modulated" (FM) screening. Stochastic printing may be useful for increasing image detail, especially in color reproductions because the dots are very small.
In many circumstances, halftoning works successfully when the viewer does not perceive it. The purpose is to make the best possible reproduction of the original image. However, graphic designers also may exaggerate halftoning to stylize their work. This method can be an excellent way of disguising pixelation in low-resolution images. Most simply, filters in Adobe Photoshop or Sapphire for After Effects allow the user to generate a halftone image instantly. Not only may you create AM patterns, but options exist to use other computer-generated structures such as lines or even circles. Further, tutorials for more sophisticated methods of digital halftoning are available.
AM and FM halftone structures have their own pros and cons. AM is good for smooth shading of midtones but FM reproduces highlights and shadows better. Hybrid printing allows synthesis of both halftone structures. In Hybrid FM printing, the dot may be elongated or reshaped. Hybrid AM printing selectively removes individual dots from the regulated pattern in lighter areas of an image.