The Free On-line Dictionary of Computing (30 December 2018):

rasterising
rasterizing

    A transformation that can be applied to an image
   to prepare it for printing.  Rasterising reduces resolution by
   a factor of typically four to eight.  It also reduces
   sensitivity to paper properties.  Rasterising can be combined
   with dithering.

   [How does it work?]

   (2003-07-20)