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Art a tonal value midway between highlight and dark shading
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005


(graphic arts)
An engraving used in printing to reproduce photographs and drawings that contain continuous tones, that is, grays (middle tones or halftones) in addition to black and white; preparation involves photographing the artwork through a screen.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


The reproducion of greyscale images using dots of a single shade but varying size to simulate the different shades of grey.

Laser printers that cannot print different sized dots, halftones are produced by varying the numbers of dots in a given area.

This process is also used to produce a black and white version of a colour original using shades of grey in place of colours.

See also device independent bitmap.
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In printing, the simulation of a continuous-tone image (shaded drawing, photograph) with dots. All printing processes, except for Cycolor, print dots. In photographically generated halftones, a camera shoots the image through a halftone screen, creating smaller dots for lighter areas and larger dots for darker areas. Digitally composed printing prints only one size of dot.

In order to simulate variable-sized halftone dots in computer printers, dithering is used, which creates clusters of dots in a "halftone cell." The more dots printed in the cell, the darker the gray. As the screen frequency gets higher (more cells per inch), there is less room for dots in the cell, reducing the number of shades of gray or color that can be generated.

In low-resolution printers, there is always a compromise between printer resolution (dpi) and screen frequency (lpi), which is the number of rows of halftone cells per inch. For example, in a 300 dpi printer, the 8x8 halftone cell required to create 64 shades of grays results in a very coarse 38 lines per inch of screen frequency (300 dpi divided by 8). However, a high-resolution, 2400 dpi imagesetter can easily handle 256 shades of gray at 150 lpi (2,400 / 16).

PRINTER RESOLUTION & MAXIMUM SCREEN FREQUENCYShades of     Gray or  --At printer resolutions--Cell  Colors  300 dpi  1200 dpi  2400 dpi4x4    16    150 lpi   300 lpi   600 lpi

  8x8    64     38 lpi   130 lpi   300 lpi

 16x16  256     19 lpi    75 lpi   150 lpi

Analog vs. Digital
The analog world of commercial printing prints dots in varying sizes. The digital world prints in grids of dots. Increasingly, digital printers use techniques that overlap dots to achieve greater variability in dot sizes.
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References in periodicals archive ?
La figura 18 muestra diferencia entre halftoning de difusion de error convencional, el metodo de Levien y difusion de error con el filtro hexagonal, usando una imagen homogenea con un nivel de gris 1/2 (figura 18(a)) como entrada.
Hasta la fecha han propuesto varios modelos que representan el SVH [9], dentro de los cuales, la funcion de sensibilidad al contraste (FSC) propuesta por Nasanen [9, 10] es considerada en la construccion de varios metodos de halftoning basado en la DBS.
A fin de evaluar la calidad de las imagenes halftone generadas por los seis principales metodos de halftoning descritos en la seccion anterior, se realizo una evaluacion sugestiva llamada MOS (Mean Opinion Score), que consiste en promediar los puntajes asignados a cada imagen halftone generada por los seis metodos.
Otro asunto importante para las aplicaciones de la tecnica de halftoning es la complejidad computacional de cada metodo.
En este articulo se hizo una revision de los principales metodos de halftoning, los cuales son ordered dither, difusion de error incluyendo las versiones de enfatizacion de borde, difusion de punto, ruido verde y busqueda binaria directa (DBS).
Ademas de la impresion en papel y el despliegue de imagenes en pantalla donde la tecnica de halftoning es indispensable, recientemente se ha considerado como una herramienta importante en varios campos de computacion y comunicacion.
Gooran, "A novel hybrid amplitude modulated/ frequency modulated halftoning based on multilevel halftoning", Journal of Imaging Science and Technology, vol.
Vaidyanathan, "Recent Advances in Digital Halftoning and Inverse Halftoning Methods", IEEE Trans.
Evans, "Adaptive Threshold Mo dulation for Error Diffusion Halftoning", IEEE Trans.
Vaidyanathan, "Optimized Halftoning Using Dot Diffusion and Methods for Inverse Halftoning", IEEE Trans.
Neuhoff, "Least-Squares Model Based Halftoning", IEEE Trans.