Type Default Value Read Only Static Description
String "" No No Default halftone type and options.

Set this property when converting continuous-tone colors to a number of discrete colors, for example when converting gray tones to black and white pixels.

The halftone type can be:

  • Spot
  • ErrorDiffusion
  • OrderedDither
  • Threshold

If the type is Spot then an angle in degrees, frequency and spot function can also be specified. These should be separated by commas with no extraneous spaces. For example: "Spot, 30, 100, CosineDot". This is also the default when no value is set in this property.

The spot functions available are:

  • SimpleDot
  • InvertedSimpleDot
  • DoubleDot
  • InvertedDoubleDot
  • CosineDot
  • Double
  • InvertedDouble
  • Line
  • LineX
  • LineY
  • Round
  • Ellipse
  • EllipseA
  • InvertedEllipseA
  • EllipseB
  • EllipseC
  • InvertedEllipseC
  • Square
  • Cross
  • Rhomboid
  • Diamond

If the type is Threshold you should specify a value - for example "'threshold=60". This is used when calculating the value of a black and white pixel. If the grey level l is greater than the threshold the pixel will be black otherwise it will be white.

For full details of how Halftones work you should see the Adobe PDF Specification available from the Adobe web site.