In 1983, Bill Atkinson (yes, that Bill Atkinson - HyperCard creator and digital photography pioneer) published a variation on error diffusion dithering that would become the default choice for Macintosh image processing. His algorithm differs from Floyd-Steinberg in one crucial way: it only distributes 6/8 of the error instead of all of it. This seemingly small change produces dramatically different results.
The Atkinson Difference
Floyd-Steinberg distributes error to four neighbors in a carefully balanced way. Atkinson spreads error to six neighbors, but reduces the total proportion. Each of the six neighboring pixels receives 1/8 of the error, meaning only 6/8 (75%) of the total error is propagated. The remaining 25% is discarded.
Why Discard Error?
By intentionally throwing away 1/4 of the quantization error, Atkinson creates sharper, crisper edges between color regions. Instead of a smooth gradient of error diffusion, the image develops more pronounced boundaries. This creates a look that's somewhere between Floyd-Steinberg's smoothness and Ordered dithering's structure.
The tradeoff: You lose some color gradation, but you gain clarity and reduced visual noise. For photographs with strong lines and high contrast, Atkinson often looks better.
Other Dithering Algorithms in the Family
Floyd-Steinberg and Atkinson aren't alone. The research community developed many variations:
Stucki Dithering (1981): Uses a larger error distribution (more distant neighbors), creating smoother gradations than Floyd-Steinberg. Great for photographs.
Burkes Dithering (1988): A compromise between Floyd-Steinberg and Stucki, with good speed and quality.
Jarvis-Judice-Ninke (1976): An earlier alternative that distributes error to a wide neighborhood. Produces very smooth results but requires more computation.
Sierra Lite (1989): Bill Sierra's simplified version, using only three neighbors. Fast and produces acceptable results.
So Which Is Best?
There's no universal answer. It depends on your content:
- Floyd-Steinberg: General-purpose, balanced quality and speed. Best default.
- Atkinson: Sharp edges, crisp lines, good for graphics and illustrations.
- Stucki/Burkes: Smooth gradations, best for natural photographs.
- Jarvis: Maximum smoothness if computation time isn't a concern.
Modern tools often let you choose, because what looks "best" is subjective and content-dependent.
The Cultural Impact
Atkinson's choice for early Macintosh made it the default dithering algorithm for a generation of designers. Many designers grew up with Atkinson dithering and still find it more aesthetically pleasing. It became iconic in Apple's design culture.
Ready to try it? Open GlitchArt Studio and experiment with this effect.