Computer to plate (CTP) 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.

Negative lithographic printing plate

Agfa Advantage DL violet laser fotosetter with VPP68 plate processor

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.

[edit] Advantages of CTP

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%.^[1] 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-inch plates per hour @ 1270dpi (dots per inch), whilst for commercial applications a CTP system could output 60 B1 plates @ 2400dpi for higher screen rulings.

Small portrait Shree 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.

[edit] Types of CTP-Plates (Computer-to-plate)

[edit] 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

[edit] 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 %

[edit] photopolymer plates

• photosensitivity between 830 to 1.070 nm
• high laser energy of up to 500 mJ/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

[edit] Disadvantages of CTP vs. traditional production

• 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, you have to create a completely new, imposed plate.^[2]

[edit] References

[edit] See also

• Computer to film
• Color printing
• Digital press

[edit] External links

Wikimedia Commons has media related to: Computer to Plate

• Michael Limburg: Der digitale Gutenberg in der Google Buchsuche