Dithering

In an image using a limited color palette, dithering can provide an illusion of a continuous gradient, or a field of color not in the palette. Using colors that are close to the target color, the technique applies a granular pattern of varying sizes and spacing of solid, single-color dots or lines. The human eye then interpolates between the colors at a larger scale.

Some techniques (like halftones) predate modern digital technologies because of their usefulness in traditional printmaking and engraving processes. There are even relevant techniques in the fields of painting and drawing; see stippling and pointillism! In digital imaging, modern palettes are usually comprehensive enough to reach a satisfactory visual fidelity for general purposes, but limits are still often reached in professional contexts.

Dithering is useful for realizing grayscale images with various digital fabrication equipment like laser cutters, pen plotters, CNC routers/mills, and more.

Types of dithering:

• Random
• Patterned
• Ordered
  • Halftone ⭐
  • Bayer matrix
  • Blue noise matrix
• Error-diffusion
  • Floyd-Steinberg ⭐
  • Minimized average error
  • Stucki
  • Burkes
  • Sierra
  • Two-row Sierra
  • Filter Lite
  • Atkinson
  • Gradient-based error-diffusion

Articles:

• Dither on Wikipedia

Code projects:

• Atkinson Dithering, Live in Processing by Windell Oskay of Evil Mad Scientist Laboratories
• Coding Challenge #90: Floyd-Steinberg Dithering by Daniel Shiffman (Github repo with source code for p5.js and Processing)
• Color Quantization and Dithering reference page for ImageMagick v6
• Digital Halftoning by C. A. Bouman
• #dithering-algorithms on Github
• Tramage (source) by Pierre Commenge - utility to dither small images and prepare machine knitting files. (p5.js and Processing)