Digital Halftoning

Compared to the multimedia information displayed on screens in daily life (including images and videos, for example, in RGB color space, a single pixel has 8 bits of pixel depth on each color plane, expressing 2^8 colors), the representation of images printed in newspapers and magazines cannot be as colorful due to the limitation of the number of shades that the display/output device can express (a printer only has 1-bit pixel depth, meaning it can only express 2 colors - ink or no ink).

To overcome the limitation of the number of shades displayed, digital halftoning technology is used to create a visual illusion of multiple colors using a small number of colors. Using error diffusion (ED), one of the many well-known digital halftoning techniques, the corresponding image generated is shown on the right in the example image below, while the original grayscale image (with 256 different colors) is shown on the left. The significant difference in shades between the two images is visible upon inspection. However, as the viewing distance increases, the difference perceived by the human eye will decrease due to the low-pass characteristics of the human visual system (HVS) exploited by halftoning technology.

The original grayscale image.

The halftone image generated from the above image.