Film Separations

• Film screens have been used in printing since long before digital prepress and printing. Line screens determine the resolution of the final printed piece. The line screens in FilmGate separations are slightly higher than precomputerized film separations made with physical screens; 145 to 200 line screens are the norm.
  
  

The Stencil

• The stencil is central to the digital processing of FilmGate and its ColorGate software process. One stencil is the carrier of the printing information; the print stencil is the final developed form in the frame. Round stencils are used for rotation machines, while ink-jet systems print directly on the mesh. Other types of print presses may vary in their stencil requirements. 
  
  

Thread Geometry

• Thread geometry is a film separation consideration unique to digital prepress and FilmGate.
  When the user selects the screen angle, he must consider the thread geometry to avoid moiré. The mesh, stencil and colors used must meet specific requirements to ensure a desired-quality printing result. Typical line screens for screen-printing applications are 24 to 48 lines per inch, with mesh counts up to 200 threads per inch.
  
  

Screening Angles in Screen Printing

• Different screen angles ensure there's no moiré pattern to the final print. A moiré pattern is created by interference between two sets of fine pattern grids, for example, when an image created by a line screen is subjected to a new line screen; the screens don't exactly match. In creating FilmGate screen prints, moiré is avoided by varying the screening angles in each of the CMYK screens — for example, C equals 75 degrees, M equals 15 degrees, Y equals 0 degrees and K equals 45 equals. Moiré is prevented as long as there's at least a 30-degree difference in screen angles.