In prepress and printing, a system in which electronic page infiormation is used to guide lasers in the direct imaging of a printing plate, eliminating the need for a negative to be produced. CTP (also known as direct-to-plate) systes are increasingly being incorporated into all-digital prepress and printing workflows.
In a CTP system, dighital information from a page file is sent in PostScript form to an off-press device known as a platesetter, which reads the file information and exposes the data onto polyester plates that are ready for press. Although imagesetters have long been able to image onto polyester plate material, the material itself was not capable of holding very high resolution images or very high line screens. New developments, however, now enable polyester plates to hold up to 133 lpi screens, and new imagesetters and platesetters can image them with increasing degrees of quality. Even newer systems can image plates while they are mounted on the plate cylinder of a printing press. In addition, new systems can also output color-separated files and image each of the four process color plates in sequence, often while on press, which ensures that successive colors remain in register.
CTP systems have taken off in recent years, despite the high costs of the systems. As all-digital workflows become more prevalent, CTP (and perhaps even direct digital printing) will play a large role in the future of printing.