halftone

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halftone

Art a tonal value midway between highlight and dark shading

halftone

[′haf‚tōn]
(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.

halftone

(graphics)
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.

halftone

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.
References in periodicals archive ?
Wu, "Multimedia data hiding and authentication via halftoning and coordinate projection," EURASIP Journal on Advances in Signal Processing, vol.
Comparisons of various methods (advantages (+), moderate (~), shortcomings (-), unknown Quality Robustness Complexity Capacity [1] ~ + ~ - [2] ~ - ~ - [3] - + + - [6] ~ - + ~ [7] + ~ + ~ [10] + - - ~ [11] + - ~ ~ [12] + - + ~ [14] x + ~ x [19] x x ~ ~ [20] x + - x [21] x - + - [22] ~ + - ~ [23] x ~ - ~ ICPT + - ~ + Additional feature (s) [1] Inverse halftoning [2] Reversible Data Hiding [3] Visual cryptography.
En esta seccion, se presenta una descripcion de cada uno de los principales metodos de halftoning, los cuales son metodo de ordered dithering, metodo de difusion de error, incluyendo version de enfatizacion de borde, metodo de difusion de punto, metodo de ruido verde, metodo de busqueda binaria directa.
La figura 5 muestra los resultados de halftoning usando las matrices de umbral de las figuras 3 y 4.
Cabe mencionar que el metodo de difusion de error pertenece a halftoning FM, por la naturaleza de su proceso.
Este metodo de halftoning fue desarrollado por Knuth [8], tiene como objetivo conservar las buenas caracteristicas del metodo de difusion de error mientras que tambien ofrece un paralelismo sustancial.
Puesto que hay 64 clases, el algoritmo completa el halftoning en 64 pasos.
El analisis espectral de las imagenes de halftone generadas por el metodo de difusion de error muestra que su frecuencia principal es mas alta que la de otros metodos de halftoning [11].
In conventional halftoning, Parker explained, at the elemental level a 50% screen in a given square group of pixels would show a dark patch over half the pixels in the center of the square.
Another quality halftoning method, error diffusion (the concept for which dates from the mid-1970s), Parker said "produces a very nice pattern" but exists simply as an algorithm rather than a screen.
Error diffusion does have built-in sharpening that makes images more appealing, Parker conceded, adding that many consider it "just about the best halftoning technique" for laser-printed images.
At RCT, Baker said the halftoning software can indeed be plugged into midrange and high-end imagesetters and that he is talking to vendors of 2,500-dpi output devices.