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41-419: The most noticeable result of using light cyan and light magenta inks is the removal of a distinct and harsh halftone or dither dot appearance that appears in prints that use light shades of cyan or magenta on the pure CMYK ink configuration. Usually when printing a dark color the printer will saturate the area with colored ink dots, but will use fewer ink dots to create the effect of a light color. The result

82-442: 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). These angles are optimized to avoid patterns and reduce overlap, which can cause colors to look dimmer. Halftoning is also commonly used for printing color pictures. The general idea

123-520: 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,

164-419: A category based descreening. Additionally, they can do edge detection to enhance the details around edge areas. The results can be further improved by generative adversarial networks . This type of network can artificially generate content and recover lost details. However, these methods are limited by the quality and completeness of the used training data. Unseen halftoning patterns which were not represented in

205-412: A corresponding increase in screen ruling or the output will suffer from posterization . Therefore, file resolution is matched to the output resolution. The dots cannot easily be seen by the naked eye, but can be discerned through a microscope or a magnifying glass. When different screens are combined, a number of distracting visual effects can occur, including the edges being overly emphasized, as well as

246-414: A practical way to realistically reproduce photographs onto the printed page, but most common mechanical printing processes can only print areas of ink or leave blank areas on the paper and not a photographic range of tones; only black (or coloured) ink, or nothing. The half-tone process overcame these limitations and became the staple of the book, newspaper and other periodical industry. William Fox Talbot

287-422: A proper descreening strategy since they generate different patterns and most of the inverse halftoning algorithms are designed for a particular type of pattern. Time is another selection criteria because many algorithms are iterative and therefore rather slow. The most straightforward way to remove the halftone patterns is the application of a low-pass filter either in spatial or frequency domain. A simple example

328-408: A regular grid of dots that vary in size. The other method of creating screens, frequency modulation , is used in a process also known as stochastic screening . Both modulation methods are named by analogy with the use of the terms in telecommunications. Inverse halftoning or descreening is the process of reconstructing high-quality continuous-tone images from the halftone version. Inverse halftoning

369-539: A way of breaking up the image into dots of varying sizes, he did not make use of a screen. In 1882, the German Georg Meisenbach  [ de ] patented a halftone process in Germany which he named autotype  [ de ] . His invention was based on the previous ideas of Berchtold and Swan. He used single lined screens which were turned during exposure to produce cross-lined effects. He

410-442: Is a Gaussian filter . It discards the high-frequency information which blurs the image and simultaneously reduces the halftone pattern. This is similar to the blurring effect of our eyes when viewing a halftone image. In any case, it is important to pick a proper bandwidth . A too-limited bandwidth blurs edges out, while a high bandwidth produces a noisy image because it does not remove the pattern completely. Due to this trade-off, it

451-446: Is a stub . You can help Misplaced Pages by expanding it . Halftone Halftone is the reprographic technique that simulates continuous-tone imagery through the use of dots, varying either in size or in spacing, thus generating a gradient-like effect. "Halftone" can also be used to refer specifically to the image that is produced by this process. Where continuous-tone imagery contains an infinite range of colors or greys ,

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492-445: Is an ill-posed problem because different source images can produce the same halftone image. Consequently, one halftone image has multiple plausible reconstructions. Additionally, information like tones and details are discarded during halftoning and thus irrecoverably lost. Due to the variety of different halftone patterns, it is not always obvious which algorithm to use for the best quality. There are many situations where reconstruction

533-489: Is credited with the idea of halftone printing. In an 1852 patent he suggested using "photographic screens or veils" in connection with a photographic intaglio process. Several different kinds of screens were proposed during the following decades. One of the first attempts was by William Leggo with his leggotype while working for the Canadian Illustrated News . The first printed halftone photograph

574-496: Is desired. For artists, it is a challenging task to edit halftone images. Even simple modifications like altering the brightness usually work by changing the color tones. In halftone images, this additionally requires preservation of the regular pattern. The same applies to more complex tools like retouching. Many other image processing techniques are designed to operate on continuous-tone images. For example, image compression algorithms are more efficient for those images. Another reason

615-447: Is hard to notice with yellow because yellow is perceived as a very light color. However, the individual cyan and magenta ink dots will stand out in a sparse pattern due to their darker color against a white background; the result is undesirable when it is noticed. By using light cyan or magenta, the printer can saturate areas that would typically use halftoning with these inks to remove the look of sparse magenta and cyan dots. The downside

656-415: Is important to provide a reasonable quality. The main steps of the procedure are the removal of halftone patterns and reconstruction of tone changes. In the end, it may be necessary to recover details to improve image quality. There are many halftoning algorithms which can be mostly classified into the categories ordered dithering , error diffusion , and optimization-based methods. It is important to choose

697-409: 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; for example, "150 lpi" or "150#". The higher the pixel resolution of a source file, the greater the detail that can be reproduced. However, such increase also requires

738-510: Is not able to reconstruct reasonable edge information. Further improvements can be achieved with edge enhancement. Decomposing the halftone image into its wavelet representation allows to pick information from different frequency bands. Edges are usually consisting of highpass energy. By using the extracted highpass information, it is possible to treat areas around edges differently to emphasize them while keeping lowpass information among smooth regions. Another possibility for inverse halftoning

779-606: Is noted for co-inventing the half-tone engraver with George-Édouard Desbarats . He had several patents to his name, including leggotyping and granulated photography. Leggo was born in Quebec City on January 25, 1830, to William Augustus Leggo, a bookbinder and engraver, and Margaret Grant. After graduating from Quebec High School , he apprenticed as an engraver, first to his father and then to Cyrus A. Swett in Boston. Leggo worked with his brothers Thomas, Edward, and Henry in

820-448: Is the printer needs approximately twice as much light cyan and magenta ink in areas to achieve the same saturation as pure cyan/magenta which can lead to excess ink usage. The result, however, is significantly better for some photos. CcMmYK colorants reduce graininess in the middle tone region. This reduced graininess typically improves the photographic appearance of blue skies and some flesh tones . This color-related article

861-442: Is the same, by varying the density of the four secondary 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

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902-459: Is the usage of machine learning algorithms based on artificial neural networks . These learning-based approaches can find the descreening technique that gets as close as possible to the perfect one. The idea is to use different strategies depending on the actual halftone image. Even for different content within the same image, the strategy should be varied. Convolutional neural networks are well-suited for tasks like object detection which allows

943-481: Is the visual aspect since halftoning degrades the quality of an image. Sudden tone changes of the original image are removed due to the limited tone variations in halftoned images. It can also introduce distortions and visual effects like moiré patterns . Especially when printed on newspaper, the halftone pattern becomes more visible due to the paper properties. By scanning and reprinting these images moiré patterns are emphasized. Thus, reconstructing them before reprinting

984-404: 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 ". The semi-opaque property of ink allows halftone dots of different colors to create another optical effect: full-color imagery. Since the location of the individual dots cannot be determined exactly,

1025-669: The dots partially overlap leading to a combination of additive and subtractive color mixing called autotypical color mixing . While there were earlier mechanical printing processes that could imitate the tone and subtle details of a photograph, most notably the Woodburytype , expense and practicality prohibited their being used in mass commercial printing that used relief printing. Previously most newspaper pictures were woodcuts or wood-engravings made from hand-carved blocks of wood that, while they were often copied from photographs, resembled hand drawn sketches. Commercial printers wanted

1066-553: The early 1890s. The development of halftone printing methods for lithography appears to have followed a largely independent path. In the 1860s, A. Hoen & Co. focused on methods allowing artists to manipulate the tones of hand-worked printing stones. By the 1880s, Hoen was working on halftone methods that could be used in conjunction with either hand-worked or photolithographic stones. Prior to digitised images, special photographic techniques were developed to break grayscale images down into discrete points. The earliest of these

1107-403: 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. 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

1148-408: 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. Though round dots are the most commonly used, many dot types are available, each having its own characteristics. They can be used simultaneously to avoid the moiré effect. Generally, the preferred dot shape is also dependent on

1189-853: The family engraving business before partnering with George-Paschal Desbarats and Stewart Derbishire as Wm. A Leggo and Company on January 21, 1863. George-Paschal's son, George-Édouard Desbarats, joined the partnership when Derbishire died in March 1863, and became sole partner when his father died in November 1964. The two patented "Leggotyping", a type of photomechanical reproduction for letterpress printing , on February 27, 1865. Leggo and Desbarats founded Leggo and Company in Montreal on January 21, 1868. Desbarats' newspapers, Canadian Illustrated News (est. October 1869) and L'Opinion publique (est. January 1870), both made use of Leggotyping. In 1873,

1230-430: The halftone image. The lookup table provides a continuous-tone value for a given pixel and its distribution. The corresponding lookup table is obtained before using histograms of halftone images and their corresponding originals. The histograms provide the distribution before and after halftoning and make it possible to approximate the continuous-tone value for a specific distribution in the halftone image. For this approach,

1271-591: The halftone process reduces visual reproductions to an image that is printed with only one color of ink, in dots of differing size ( pulse-width modulation ) or spacing ( frequency modulation ) or both. This reproduction relies on a basic optical illusion : when the halftone dots are small, the human eye interprets the patterned areas as if they were smooth tones. At a microscopic level, developed black-and-white photographic film also consists of only two colors, and not an infinite range of continuous tones. For details, see film grain . Just as color photography evolved with

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1312-431: The halftoning strategy has to be known in advance for choosing a proper lookup table. Additionally, the table needs to be recomputed for every new halftoning pattern. Generating the descreened image is fast compared to iterative methods because it requires a lookup per pixel. William Leggo William Augustus Leggo (25 January 1830 – 21 July 1915) was a Canadian inventor , engraver and businessperson . He

1353-497: 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

1394-623: 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. However, digital image processing has also enabled more sophisticated dithering algorithms to decide which pixels to turn black or white, some of which yield better results than digital halftoning. Digital halftoning based on some modern image processing tools such as nonlinear diffusion and stochastic flipping has also been proposed recently. The most common method of creating screens, amplitude modulation , produces

1435-546: The printing method or the printing plate. 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

1476-411: The training data are rather hard to remove. Additionally, the learning process can take some time. By contrast, computing the inverse halftoning image is fast compared to other iterative methods because it requires only a single computational step. Unlike other approaches, the lookup table method does not involve any filtering. It works by computing a distribution of the neighborhood for every pixel in

1517-411: Was "screening" where a coarse-woven fabric screen was suspended before the camera plate to be exposed, breaking the incoming light into a pattern of dots via a combination of interruption and diffraction effects. The photographic plate could then be developed using photo-etching techniques to create a printing plate. Other techniques used a "screen" consisting of parallel bars (a Ronchi ruling ), which

1558-460: Was an image of Prince Arthur published on October 30, 1869. The New York Daily Graphic would later publish "the first reproduction of a photograph with a full tonal range in a newspaper" on March 4, 1880 (entitled "A Scene in Shantytown") with a crude halftone screen. The first truly successful commercial method was patented by Frederic Ives of Philadelphia in 1881. Although he found

1599-413: Was improved as higher resolutions of 600 dpi and above, and 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,

1640-404: Was the first to achieve any commercial success with relief halftones. Shortly afterwards, Ives, this time in collaboration with Louis and Max Levy, improved the process further with the invention and commercial production of quality cross-lined screens. The relief halftone process proved almost immediately to be a success. The use of halftone blocks in popular journals became regular during

1681-414: Was then combined with a second exposure with the same screen oriented at another angle. Another method was to expose through a screen-plate with crossing lines etched into the surface. Later, either photographic contact screens were used, or sometimes no screen at all, exposing directly on a lithographic (extremely high contrast ) film with a pre-exposed halftone pattern. The resolution of a halftone screen

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