5.3 Output equipment

5.3.1 Methods and means of an image output

There are more or less successful attempts to classify methods and means of obtaining intermediate and final images in the reproduction [5.6; 5.7]. However, the dynamics of development in this area in recent decades has been so high that now and then there are appeared new technologies and it often turns out that they do not fit into one or another pre-developed scheme of specification.

The approach based on the assignment of a detailed name to a particular tool, which, characterizing its features, allows to determine its place among others, is also ineffective for systematization. Used in wide practice the names of the various graphic methods and devices are for the most part uninformative, highly contingent and riddled with professional jargon and advertising persuasion.

For example, the term "digital color proof" is relatively capacious, because it indicates both the purpose of the image and the source of its production as an coded numeric array. However, behind the scenes there are important aspects related to the type of used physical process and material, the structure of the image, etc. In the concept of "analog color proof", the generally accepted meaning of the first word indicates the way of representation of the electric signal. In fact, there is no such signal in this technology at all for the source data is comprised by color separated halftone transparencies.

Little informative and does not reflecting the essence of the device construction is today often the adjective "digital". For example, the design of a “digital scanner” is only completed by an analog-to-digital converter or processor that forms a digital file. The digital printer, on the contrary, begins with the digital-to-analog converter and the final impact on the printed material is controlled by analog currents and voltages of rather great power.

It is often more productive than the classification itself to combine the features underlying it into homogeneous groups, for example, on such signs as:

- image production purpose;

- nature of its structure;

- physical process used;

- material applied;

- type of source information, etc.

By its purpose, intermediate images obtained in the illustrative printing may be:

- printing plate;

- halftone transparency;

- “hard” or “soft” proof;

- reproducible layout, etc.

Traditional processes of transfer of full-format intermediate copies on a transparent and opaque substrate (transparencies, pigment paper, etc.) to the printing plates are described in detail and systematized in the literature [5.6; 5.8; 5.9]. So, there are considered below only those where the source image data is presented by an electric signal in its analog or digital form.

Such signal controls the laser or LED radiation to create or update a latent electrographic image for each print within a run in some methods of digital printing (Computer-to-Print). Similar signal is used in the Computer-to-Plate concept, which had, in some other form, place long before the computer prepress technologies. Recording of transparencies undermines, in turn, the traditional plate making as a mandatory follow-up phase. The “hard”- and “softproof” can be obtained as with the mechanicals, and using electric image signal.

The image obtained as a result of the prepress operations can have a linework (LW), continuous tone (CT) and halftone structure.

The category of LW images includes films, plates and proofs containing text, drawings and other binary images, such as engravings.

CT transparencies were used in plate making for collotype and gravure printing. In fact, the CT structure is inherent in some kind of color proofs produced, for example, by recording on a photo sensitive paper.

In the vast majority of images on films and plates of monochrome and multicolor printing, as well as on the high-level hardproofs (true proofs) are halftones using the autotype principle of a continuous tone simulation.

A significant distinguishing feature of image output technology is the nature of the physical impact on the material of the copy. It can use the "contact" and be "non— impact " (NIP-Non-Impact Printing). In this sense, there are also:

-electro-mechanical and laser engraving;

- photographic, electrophotographic, electrographic, magnetographic, inkjet, etc. recording;

- transfer of the dye from the donor tape, its thermal sublimation, electrolytic deposition on the substrate, etc.

An important feature is the type of material on which a particular kind of a copy is formed prior to the print run. In these purposes the metals and their alloys, photographic film and paper, photopolymers, plastics, etc. are used. Sensitive layers of transparencies and plates can use silver or, without it, be five or six orders of magnitude less sensitive.

The above features are combined in a variety of ways in a great number of obsolete, existing and emerging prepress technologies. Consider below only some characteristic examples.