Atkinson dithering is a variant of Floyd–Steinberg dithering designed by Bill Atkinson at Apple Computer, and used in the original Macintosh computer.
The algorithm achieves dithering using error diffusion, meaning it pushes (adds) the residual quantization error of a pixel onto its neighboring pixels, to be dealt with later.
It spreads the debt out according to the distribution (shown as a map of the neighboring pixels):
The algorithm scans the image from left to right, top to bottom, quantizing pixel values one by one.
Unlike Floyd–Steinberg dithering, only 3⁄4 of the error is diffused outward.
This leads to a more localized dither, at the cost of lower performance on near-white and near-black areas, but the increase in contrast on those areas may be regarded as more visually desirable for some purposes.