OpenGL Programming Guide: The Official Guide to Learning OpenGL, Version 4.3, Eighth Edition

Dithering

On systems with a small number of color bitplanes, you can improve the color resolution at the expense of spatial resolution by dithering the color in the image. Dithering is like half-toning in newspapers. Although The New York Times has only two colors—black and white—it can show photographs by representing the shades of gray with combinations of black and white dots. Comparing a newspaper image of a photo (having no shades of gray) with the original photo (with grayscale) makes the loss of spatial resolution obvious. Similarly, systems with a small number of color bitplanes may dither values of red, green, and blue on neighboring pixels for the appearance of a wider range of colors.

The dithering operation that takes place is hardware-dependent; ...