Left: Halftone dots. Right: how the human eye would see this, when viewed from a sufficient distance. Halftone is the reprographic technique that simulates continuous tone imagery through the use of equally spaced dots of varying size.[1] 'Halftone' can also be used to refer specifically to the image that is produced by this process.[1] Image File history File links Halftoning_introduction. ...
A continuous tone image is one where each color at any point in the image is reproducted as a single tone, and not as discrete halftones, such as one single color for monochromatic prints, or a combination of halftones for color prints. ...
Where continuous tone imagery (film photography, for example) contains an infinite range of colors or greys, the halftone process reduces visual reproductions to a binary image that is printed with only one color of ink. This binary reproduction relies on a basic optical illusion—that these tiny halftone dots are blended into smooth tones by the human eye. This article or section does not cite its references or sources. ...
Color is an important part of the visual arts. ...
Grey or gray (see spelling differences) is a color between white and black. ...
The binary numeral system, or base-2 number system, is a numeral system that represents numeric values using two symbols, usually 0 and 1. ...
An optical illusion is always characterized by visually perceived images that, at least in common sense terms, are deceptive or misleading. ...
Just as color photography evolved with the addition of filters and film layers, color printing is made possible by repeating the halftone process for each subtractive color—most commonly using what is called the 'CMYK color model.' [2] The semi-opaque property of ink allows halftone dots of different colors to create another optical effect—full-color imagery.[1] An undated color photograph from 1905 to 1915 by Sergei Mikhailovich Prokudin-Gorskii Color photography was explored throughout the 1800s. ...
Coloured and Neutral Density filters An optical filter is a device which selectively transmits light having certain properties (often, a particular range of wavelengths, that is, range of colours of light, or polarizations), while blocking the remainder. ...
Subtractive color mixing An 1877 color photo by Louis Ducos du Hauron, a French pioneer of color photography. ...
It has been suggested that process color be merged into this article or section. ...
An ink is a liquid containing various pigments and/or dyes used for coloring a surface to render an image or text. ...
History
- Invented by Stephen H. Horgan, a crude halftone screen was used by the New York Daily Graphic to print "the first reproduction of a photograph with a full tonal range in a newspaper" on March 4, 1880 (entitled "A Scene in Shantytown").[3]
- In 1881, Frederick E. Ives (1856–1937) worked on the first commercially-produced plates for halftone printing.[3]
Traditional screening | Typical Halftone Resolutions | | Screen Printing | 45-65 lpi | | Laser Printer (300dpi) | 65 lpi | | Laser Printer (600dpi) | 85-105 lpi | | Offset Press (newsprint paper) | 85 lpi | | Offset Press (coated paper) | 85-185 lpi | The most common method of creating screens—amplitude modulation—produces a regular grid of dots that vary in size. Amplitude modulation (AM) is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. ...
The other method of creating screens—frequency modulation—is used in a process named "stochastic screening." Frequency modulation (FM) is a form of modulation which represents information as variations in the instantaneous frequency of a carrier wave. ...
Resolution of halftone screens The resolution of a halftone screen is measured in lines per inch (lpi). This is the number of lines of dots in one inch, measured parallel with the screen's angle. Known as the screen ruling, the resolution of a screen is written either with the suffix lpi or a hash mark. E.g. 150lpi or 150#. Lines per inch (LPI) is a measurement of printing resolution in systems that use a halftone screen. ...
The higher the pixel resolution of a source file, the greater the detail that can be reproduced. However, such increase also requires a corresponding increase in screen ruling or the output will suffer from posterization. Therefore file resolution is matched to the output resolution. An example of a photo in JPEG format (24bit colour or 16. ...
Multiple screens and color halftoning
Three examples of color halftoning with CMYK separations. From left to right: The cyan separation, the magenta separation, the yellow separation, the black separation, the combined halftone pattern and finally how the human eye would observe the combined halftone pattern from a sufficient distance. When different screens meet, a number of distracting visual effects can occur, including the edges being overly emphasized, as well as a moiré pattern. This problem can be reduced by rotating the screens in relation to each other. This screen angle is another common measurement used in printing, measured in degrees clockwise from a line running to the left (9 o'clock is zero degrees). Image File history File links Halftoningcolor. ...
It has been suggested that Line moiré be merged into this article or section. ...
Halftoning is also commonly used for printing color pictures. The general idea is the same, by varying the density of the four primary printing colors, cyan, magenta, yellow and black (abbreviation CMYK), any particular shade can be reproduced. In this case there is an additional problem that can occur. In the simple case, one could create a halftone using the same techniques used for printing shades of grey, but in this case the different printing colors have to remain physically close to each other to fool the eye into thinking they are a single color. To do this the industry has standardized on a set of known angles, which result in the dots forming into small circles or rosettes. Cyan, magenta, yellow, and key (black) CMYK (or sometimes YMCK) is a subtractive color model used in color printing. ...
To the naked eye, you cannot really see the dots. With a microscope or a magnifying glass, you can see the individual dots that make up the image. This is an illusion of many graphic artists use to create their designs.
Digital halftoning Digital halftoning has been replacing photographic halftoning since the 1970s when 'electronic dot generators' were developed for the film recorder units linked to color drum scanners made by companies such as Crosfield Electronics, Hell and Linotype-Paul.
In the 1980s halftoning became available in the new generation of 'imagesetter' film and paper recorders that had been developed from earlier 'laser typesetters'. Unlike pure scanners or pure typesetters, imagesetters could generate all the elements in a page including type, photographs and other graphic objects. Early examples were the widely used Linotype Linotronic 300 and 100 introduced in 1984, which were also the first to offer PostScript Rips in 1985. PostScript (PS) is a page description language and programming language used primarily in the electronic and desktop publishing areas. ...
A raster image processor (RIP) is a component used in a printing system which produces a bitmap. ...
Early laser printers from the late 1970s onward could also generate halftones but their original 300 dpi resolution limited the screen ruling to about 65 lpi. This was improved as higher resolutions of 600 dpi and above, plus dithering techniques were introduced.
All halftoning uses a high frequency/low frequency dichotomy. In photographic halftoning, the low frequency attribute is a local area of the output image designated a halftone cell. Each equal-sized cell relates to a corresponding area (size and location) of the continuous-tone input image. Within each cell, the high frequency attribute is a centered variable-sized halftone dot composed of ink or toner. The ratio of the inked area to the non-inked area of the output cell corresponds to the luminance or graylevel of the input cell. From a suitable distance, the human eye averages both the high frequency apparent gray level approximated by the ratio within the cell and the low frequency apparent changes in gray level between adjacent equally-spaced cells and centered dots.
Digital halftoning uses a raster image or bitmap within which each monochrome picture element or pixel may be on or off, ink or no ink. Consequently, to emulate the photographic halftone cell, the digital halftone cell must contain groups of monochrome pixels within the same-sized cell area. The fixed location and size of these monochrome pixels compromises the high frequency/low frequency dichotomy of the photographic halftone method. Clustered multi-pixel dots cannot "grow" incrementally but in jumps of one whole pixel. In addition, the placement of that pixel is slightly off-center. To minimize this compromise, the digital halftone monochrome pixels must be quite small, numbering from 600 to 2,540, or more, pixels per inch. Suppose the smiley face in the top left corner is an RGB bitmap image. ...
This example shows an image with a portion greatly enlarged, in which the individual pixels are rendered as little squares and can easily be seen. ...
References - ^ a b c Campbell, Alastair. The Designer's Lexicon. ©2000 Chronicle, San Francisco.
- ^ McCue, Claudia. Real World Print Production. ©2007, Peachpit Berkeley.
- ^ a b Meggs, Philip B. A History of Graphic Design. John Wiley & Sons, Inc. 1998. p 141
See also Screentone is a generic name for a technical drawing technique for applying various textures to surfaces from a specially preprinted sheet. ...
A phenomenon in printing and graphic arts whereby printed dots are perceived and actually printed bigger as intended. ...
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