Define the default halftone processing method for monochrome prints.

‍From Wikipedia:
Halftone is the reprographic technique that simulates continuous-tone imagery through the use of dots, varying either in size or in spacing, thus generating a gradient-like effect.

Section	Variable
features	halftone

Values:

none
ordered
fls
jjn

Value: none

Method: Simple threshhold

This method has no grey scale emulation at all. Pixels below a fixed threshhold are printed, pixels above this threshold aren't.

For simple black text or graphics to print, this method might be sufficient. But for coloured text or grey scale graphics it might skip complete content and the printed result isn't what you expect (at least most of the time).

Left: original, right binary halftone

Value: ordered

Method: Bayer Pattern

Left: original, right ordered halftone

Value: fls

Method: Floyd and Steinberg

This is a so called "error diffusion" halftone method and the most popular one. Its result is very good for text and graphics and it has less visible artefacts on large areas with the same grey scale.

Left: original, right FLS halftone

Value: jjn

Method: Jarvis, Judice, and Ninke

This is a so called "error diffusion" method and similar to the fls one. Its result is very good for text and graphic, but it has visible artefacts on large areas with the same grey scale.

Left: original, right JJN halftone

Note: If no halftone processing method is defined, Floyd and Steinberg is used as the default.

Attention: This halftone processing method is used only, if the document format's rasterizer doesn't support monochrome raster. In this case libcapsdriver pre-processes the raster data with halftone method selected here.
If the corresponding rasterizer supports monochrome raster, it selects its own halftone method, which can differ from the one selected here.