Raster image processor
Screening: In order to print, a continuous-tone bitmap is converted into a halftone (pattern of dots).  Two screening methods or types are Amplitude Modulation (AM) screening and stochastic or Frequency Modulation (FM) screening. In AM screening, dot size varies depending on object density -- tonal values; dots are placed in a fixed grid. In FM screening, dot size remains constant and dots are placed in random order to create darker or lighter areas of the image; dot placement is precisely controlled by sophisticated mathematical algorithms.