Prepress proofing
A proof (or test) referred to the pressure being anticipated simulation of print results for revision. Historical ( in letters sentence ) came through the proofs.
Basics
In practice is meant by a proof usually display on at least a paper-like substrate. In the broader sense of the word but can also mean intangible simulation methods (eg, soft proofing, ie the representation on the computer screen ).
With a proof one would like to simulate an early stage in the production chain, such as the printed label will look like. The background is that errors are more costly in conventional printing processes such as offset printing, gravure printing or flexographic printing, the later they are discovered. If a printmaker recognizes a set of error already on the screen, it will cost him a few seconds and a few keystrokes to correct him. If the error persists, not discovered until the finished engraved gravure cylinder depends on the machine, the job of the machine must be taken to be corrected and later taken back into the machine. This results in significant costs and problems in production planning.
While for recognizing simple sentence error certainly no proof is still required - after all, they are to be assessed clearly already on the screen, or after output on standard office printers - there is a box where it matters most to the specific qualities of proofing systems: the color.
Basically, it is when creating a print template - what is happening today usually set on the computer - not readily possible to predict the later appearance of the printed result exactly. Even the colors of the screen have - due to the fact that this is a self-luminous objects using additive color mixing - a different look than the later Drucks. This basic difference can not be fully compensated by calibration techniques and color management.
The usual color printing systems for office applications are not suitable for generating color-accurate simulations. Although in principle they often work with the same color mixing technology such as the classical printing methods ( subtractive color mixing using the CMYK color model with the primary colors cyan, magenta, yellow and black), for example, the color coordinates of the primary colors, the grid methods differ for Halftone, the tone value between dataset and print results and much more. Of course it is possible to achieve this type of printer output that " something like" looks like the later printing.
For professional applications, however, this is totally inadequate. Here it is important to be able to make a precise statement about the future of color before printing. On the basis of a color proof then changes to the template can be discussed, and if the proof fails to satisfaction, it can be used as a contract proof, that constitute the legally binding template for a print job. On this basis, for example, complaints can be made later if the result of the contact pressure deviates too much from proof ( Delta E color difference ).
Just This again indicates that a proof the flow of color information of file or movie must anticipate very accurate up to the pressure and the. Possibly on multiple machines and multiple pressure method For this requirement, the independent discipline of color management developed.
Proofing methods can be distinguished according to whether they are analog or digital.
Analog proofing methods
Analog (or " conventional" ) Proof methods presuppose the existence of printing films and work in most cases with photographic means. The basic principle is usually the application of a UV - radiation- sensitive coloring layer on a substrate ( lamination of a film or dusted with a color toner ). In this color layer of ink film is placed and exposed. Through a photochemical process, the non-printing and non- color-bearing points are modified so that they can be washed out during subsequent development process. The color-bearing points, however, remain on the proof and thus form the respective color separation. The whole has to be repeated for each color separation.
This analog proofing method, such as Match Print or Kodak cromalin by DuPont, are associated with a certain amount of manual work. It must be laminated, powdered, mounted, exposed and developed, so that the time required by an experienced user, for the preparation of a four color proof A2, is in both processes approximately an hour. In addition, the analog proofing method with their standard color foils are and powder usually only a single printing process on conventional substrates, such as the Euro scale offset printing designed. They can be adjusted by varying the exposure times to close tolerances to in-house standards, at best, still. Textile and screen printing and other special printing processes usually can not be reproduced. One advantage of the analog method, however, is that they inherently mimic the grid of the original printing process, thus making scanning related problems such as moire, etc. visible. They are also characterized by high stability and reproducibility of the results.
Digital proofing methods
Since the mid- nineties, digital methods have gained more and more importance in prepress. Today, an estimated 90 % of all print templates are completely or partially produced digitally. Logically today are digital proofing systems the method of choice. Finally, it would be nonsensical and expensive to make a print film alone for the proof, if such - is not required to print - for example, when working with a CtP system. In addition, digital proofing systems work - once installed correctly - usually faster, less complicated and less expensive than their analog counterparts. The hardware consists of an electronic printer, which operates in one of the non-impact process, so, for example, an inkjet or Thermosublimationsgerät. The associated software (usually a combination of raster image processor, Color Management Module and Workflow solution) is responsible to process the incoming data and convert it into the printer-specific format. Moreover, here the color management is done.
With digital proofing systems, color matching is usually controlled color profiles ( a distinction here between ICC-based and proprietary color profiles ). This makes them much more flexible than analog systems, because by the simple replacement of the profiles a variety of printing processes, domestic and industry standards can be reproduced. Also, it is possible to achieve matching results on inkjet printers of different manufacturers and designs.
However, digital printing methods are still partially rumored deficits in the quality of reproduction. Deep drawing, gradients, difficult gray balances and similar demanding image parts of the analog proofing method usually somewhat better, ie, the contact pressure similar, are listed.
Classification of proofs based on liability
Digital -made prints can be roughly that interests or their liability divided. The nature of the creation of these prints is not considered.
Layout proof
If the correctness of the content and placement of the elements used to show. In this case, no to little value is placed on the color matching. Often, a smaller version is made. To use this arise most often electrophotographic printing systems.
Position proof
Displays the placement (stand) of the pages on the sheet. It should be generated from the information by a Raster Image Processor (RIP) prepared for the exposure of the printing form data. Colour accuracy is not necessarily given. Today common term: Formproof.
Color- and legally binding proof ( contract proof )
A color proof is to predict the printed result with regard to color almost. When such proof is as binding, regulate the Print Media Standard and ISO 12647-7. In addition to a halftone proof, arrive at the screening method used, as they are provided by the manufacturer of the printer driver, and raster proofs can be generated that simulate the grid later used in printing ( offset rosette ). Today, almost all inkjet printers are used for creating proofs, which are driven by RIPs with built-in color management system. In order for a contract proof is as binding and legally binding as a basis for the continued pressure, the imprint of a UGRA / Fogra media wedge is required. The normalized values of the media wedge can be measured on the proof. If the deviations are within the specified limits of the ISO standard are, a test report is printed or glued on, which documents the accuracy of the proofs within the tolerances. This test report is a contract proof is colorless and legally binding.