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What is a screening module

Halftone screens trick the human eye into perceiving the continuous tones of photographs, artwork and other images.  In traditional graphic arts, screening was generally done using a screen-like pattern etched into a glass plate.  A camera operator had several of these plates, each with a different pattern.  The image to be reproduced was projected through a chosen screen onto film and the resulting image looked like the original except that it was broken into a lot of little dots.

A LF-DCP creates an electronic version of the traditional halftone screen.  Screening software in the RIP applies an electronic dot pattern to the electronic image.

The RIP creates halftone screens using screen frequencies measured in lines per inch (lpi) - a grid is used to represent the screen frequency.  Each square in this grid is a halftone cell, capable of holding one halftone dot.  Think of each halftone screen as a grid that is superimposed on the image recorder resolution grid.  To convert a photograph into a halftone, the halftone grid is superimposed on an image.  Each halftone cell is assigned a different sized dot to represent the image data for the cell.  When looked at together, the dots resemble the original image.

Most RIP manufacturers supply proprietary screening modules and algorithms which have been based around the traditional:

  • error diffusion
  • FM screening
  • standard halftoning


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