Computer to plate
Encyclopedia
Computer to plate is an imaging
technology used in modern printing processes
. In this technology, an image created in a Desktop Publishing
(DTP) application is output directly to a printing plate
.
This compares with the older technology, Computer to film
(CTF), where the computer file is output onto a photographic film
. This film is then used to make a printing plate, in a similar manner to a contact proof in darkroom photography.
Advantages of CTP vs. CTF
CTP has several advantages over conventional platemaking. In CTP, one generation (transfer of film image to the printing plate) is removed from the printing process (eliminating the need for film and related developer chemicals), increasing sharpness and detail. CTP avoids potential losses in quality that may occur during film processing, including scratches in the film, and variations in the exposure. An imagesetter usually has an accuracy rate of +/-2%. Plates are produced in less time, are more consistent, and at a lower cost. CTP can also improve registration
and image-to-edge repeatability over traditional methods.
In CTP, the media is registered (held in precise position) in the platesetter during imaging, and does not rely on a separately-aligned pin grid, as is the case with film. Defects due to dust, scratches or other artifacts are minimized.
CTP systems can significantly increase plate production outputs. Platesetters for newspaper production can output up to 300 12 inches (30.5 cm) plates per hour at 1270 DPI (dots per inch
), whilst for commercial applications a CTP system could output 60 B1
plates at 2400 DPI for higher screen rulings
.
Small portrait presses that typically create 1 or 2 color output can use anything from a standard laser printer, for low quality/low volume, up to a higher-end dedicated platesetter for higher quality and volume.
Disadvantages of CTP vs. CTF
• Restricted to digital format. CTP productions require that the basis for the printed matter as well as the imposition, be digital.
• Remaking of plates. If for some reason a CTP plate is damaged, if an error occurs when it's ripped or if something has to be corrected after the plate is exposed, a completely new, imposed plate must be created.
Imaging
Imaging is the representation or reproduction of an object's outward form; especially a visual representation .- Imaging methodologies and technologies :...
technology used in modern printing processes
Printing
Printing is a process for reproducing text and image, typically with ink on paper using a printing press. It is often carried out as a large-scale industrial process, and is an essential part of publishing and transaction printing....
. In this technology, an image created in a Desktop Publishing
Desktop publishing
Desktop publishing is the creation of documents using page layout software on a personal computer.The term has been used for publishing at all levels, from small-circulation documents such as local newsletters to books, magazines and newspapers...
(DTP) application is output directly to a printing plate
Lithography
Lithography is a method for printing using a stone or a metal plate with a completely smooth surface...
.
Computer to film
Computer to Film is a print workflow involving the printing from a computer, straight to film. This film is then burned onto a lithographic plate, using a plate burner. The plate is then put on an offset printing press to make a product...
(CTF), where the computer file is output onto a photographic film
Photographic film
Photographic film is a sheet of plastic coated with an emulsion containing light-sensitive silver halide salts with variable crystal sizes that determine the sensitivity, contrast and resolution of the film...
. This film is then used to make a printing plate, in a similar manner to a contact proof in darkroom photography.
Technology
CTP methods differ according to the construction type of the imagesetter and the light source used to expose the plate surface. In terms of construction type there are three different kinds: internal drum, external drum and flat-bed imagesetters. The two main light sources used to expose the plate are ultraviolet light lamps and laser diodes. The wavelength and energy of the laser diodes depend on the type of plate that is used. This technology is mainly use in newspaper and magazine printing.Internal drum imagesetters
In an internal drum imagesetter the plate is put into a cylinder, while the imaging head moves along the axis of the cylinder to expose the plate. The rotating mirror at the end of the imaging head rotates around its axis to beam the laser on the desired part of the fixed plate. The construction type makes it more difficult to use several lasers at the same time, but just using one laser also has advantages like uniform beam intensity over the whole plate.External drum imagesetters
The plate is wrapped around a drum that can rotate around its axis, while the imaging head that projects the image on the plate can move along this axis to focus the laser beam on the surface. The simple construction type makes it possible to arrange multiple image heads next to each other and use them simultaneously. This leads to a decrease of the imaging time needed to expose a whole printing plate.Flat-bed imagesetters
The image is reproduced line by line on a fixed flat printing plate by a laser beam that is deflected by a rotating polygon mirror and then onto the printing plate. Because of the setup the laser beam be-comes less accurate at the edges of the printing plate and is therefore mainly smaller formats or production with lower quality expectations.Photopolymer plates
- photosensitivity between 400 to 550 nm
- low laser energy of 100 to 200 µJ/cm2 needed for exposure
- run lengths of up to 200.000 prints
Silverhalogen plates
- silverhalogen aluminium printing plates
- photosensitivity between 400 to 700 nm
- low laser energy of 1 to 2 µJ/cm2 needed for exposure
- run lengths of up to 150.000 prints
- resolution to 250 LPI possible
- dot reproduction 1–99 %
Thermal plates
- photosensitivity between 830 to 1.070 nm
- high laser energy of up to 500 µJ/cm2 needed for exposure
- run lengths of up to 100.000 prints
- resolution to 200 LPI possible
- dot reproduction 1–99%
- high process stability
- many providers
- processing in the daylight possible
Advantages of CTP vs. CTFComputer to filmComputer to Film is a print workflow involving the printing from a computer, straight to film. This film is then burned onto a lithographic plate, using a plate burner. The plate is then put on an offset printing press to make a product...
CTP has several advantages over conventional platemaking. In CTP, one generation (transfer of film image to the printing plate) is removed from the printing process (eliminating the need for film and related developer chemicals), increasing sharpness and detail. CTP avoids potential losses in quality that may occur during film processing, including scratches in the film, and variations in the exposure. An imagesetter usually has an accuracy rate of +/-2%. Plates are produced in less time, are more consistent, and at a lower cost. CTP can also improve registrationPrinting registration
In color printing, registration is the method of correlating overlapping colors on one single image. There are many different styles and types of registration, many of which employ the alignment of specific marks.-Purpose:...
and image-to-edge repeatability over traditional methods.
In CTP, the media is registered (held in precise position) in the platesetter during imaging, and does not rely on a separately-aligned pin grid, as is the case with film. Defects due to dust, scratches or other artifacts are minimized.
CTP systems can significantly increase plate production outputs. Platesetters for newspaper production can output up to 300 12 inches (30.5 cm) plates per hour at 1270 DPI (dots per inch
Dots per inch
Dots per inch is a measure of spatial printing or video dot density, in particular the number of individual dots that can be placed in a line within the span of 1 inch . The DPI value tends to correlate with image resolution, but is related only indirectly.- DPI measurement in monitor...
), whilst for commercial applications a CTP system could output 60 B1
ISO 216
ISO 216 specifies international standard paper sizes used in most countries in the world today. It defines the "A" and "B" series of paper sizes, including A4, the most commonly available size...
plates at 2400 DPI for higher screen rulings
Halftone
Halftone is the reprographic technique that simulates continuous tone imagery through the use of dots, varying either in size, in shape or in spacing...
.
Small portrait presses that typically create 1 or 2 color output can use anything from a standard laser printer, for low quality/low volume, up to a higher-end dedicated platesetter for higher quality and volume.
Disadvantages of CTP vs. CTFComputer to filmComputer to Film is a print workflow involving the printing from a computer, straight to film. This film is then burned onto a lithographic plate, using a plate burner. The plate is then put on an offset printing press to make a product...
• Restricted to digital format. CTP productions require that the basis for the printed matter as well as the imposition, be digital.• Remaking of plates. If for some reason a CTP plate is damaged, if an error occurs when it's ripped or if something has to be corrected after the plate is exposed, a completely new, imposed plate must be created.
External links
- CTP market in India
- Michael Limburg: Der digitale Gutenberg in Google Books Germany