gs-wts.ps

%!PS-Adobe-3.0
%%
%% This postcsript code snipplet switches on the Well-Tempered
%% Screening feature in Ghostcript 8.00+.
%%
%% Adapted from Raph Levien's WTS announcement.
%%
%
% UseWTS is ghostscript-specific

<< /UseWTS true >> setuserparams

% - The Half-tone dictionary syntax is defined in PLRM,
% Section 7.4.3: Halftone Dictionaries.
%
% - Table 7.3 defines the valid values for HalftoneType.
%
% - The Spot Function below is exactly as the example in
% Sectction 7.4.4: Spot Functions
%
% - { 180 mul cos exch 180 mul cos add 2 div}
% (cos(180 * x) + cos( 180 * y))/2
% where (x,y) is the co-ordinate of a pixel in [-1,1].
<<
  /AccurateScreens true
  /HalftoneType 1
  /HalftoneName (Round Dot Screen)
  /SpotFunction { 180 mul cos exch 180 mul cos add 2 div}
  /Frequency 137
  /Angle 37
>> sethalftone