Stochastic Printing Process Renders Larger CMYK Gamut
Conventional halftones, often referred to as AM screens (amplitude modulated), distribute ink over a grid of dots that increase in size for darker tones. Throughout the tone scale, the frequency of dots remains the same, but the size or amplitude increases. The ink and water requirements vary greatly throughout the tonal range, causing a basic lithographic instability for which there are no on press controls.
An alternative to traditional halftone printing is stochastic printing process. The ink water requirements are more evenly distributed throughout the tonal range thereby overcoming the inherent instability of the AM screen. Stochastic printing is referred to as FM screening (frequency modulated), because the number and frequency of dots changes with tonality. Note that the average size of dot structures remains relatively constant through the tone scale. The dots are positioned in a pseudo random pattern to avoid moiré and patterning problems.