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Clustered and Dispersed Dot Screen
Screening is used to obtain tonal gradations in cases where output processes are only able to provide binary output. This slide shows a typical screen cell for a clustered dot screen on the left. The tonal value is produced by modulating the size of the dot; the frequency (i.e. distance) of screen dots is constant (and given by the cell size). These screens are also called AM (amplitude modulated) screens. An alternative approach to screening shown on the right is to vary the frequency and keep the dot size constant. The dots are dispersed throughout the cell. The higher the density of dots the higher the tonal value. These screens are also called FM (frequency modulated) screens.