In the prepress digital workflow, in order to make the page data seamlessly exchange between devices and software, many companies and organizations have been working on the development of reliable file formats. The main file formats for prepress data exchange are now Application file format, PostScript, EPS, PDF, PDF/X, TIFF/IT, Copydot, etc., the format of the file is different, and its flexibility and reliability are different.
1 application file format
The application file format refers to the file format of the application software such as desktop design, typesetting, and word processing, such as .PSD format, .CDR format, .PM65 format, .DOC format, and the like. The application file format is very flexible. Moreover, the files created by the desktop application only emphasize the graphic content of the design creation, and do not contain all the elements required for the print output, some lack the ICC profile, the color definition space, and the images in some files are used. Links are not embedded directly, some do not determine trapping data, and some files cannot embed the fonts used. Reliability is very low.
2 PostScript format
Because the application file format is so flexible that it can't be applied to prepress workflows, Adobe has developed the page description language PostScript, which encodes all the elements (text, graphics, images) in a file. At the time of output, the code is interpreted by the interpreter (RIP) into a language that the output device can recognize, thereby outputting the complete page.
PostScript files cannot be edited after they are generated. If there is a problem after RIP, you must return to the software used in the original production to modify it. This greatly enhances the reliability of the file, reduces the error rate of the file, but also reduces the flexibility of the file.
The PostScript format is versatile and can be output on any PostScript-capable output device, and is widely used in prepress output applications.
3 EPS format
The EPS format is a packaged PostScript file format and is a professional file version of the page description language PostScript. Use the PostScript language to describe the graphics, images, and text elements in the page, and then wrap all the elements together to form an EPS file. The structure of the EPS file is very similar to that of the PS file. In addition to the PostScript body, you can select a low-resolution preview image.
The EPS format is very widely used in prepress workflows, and almost all prepress applications can generate or call EPS files. EPS files can be nested and used in the PostScript file.
When an EPS file is imported into another page, all the objects form a whole, and the element contents cannot be edited separately, and only the whole can be scaled, rotated, cut, and the like.
4 PDF format
PDF (Portable Document Format) is also a data format for describing files. It is based on PostScript and describes pages in a way similar to PostScript. But PDF is a file structure that has advantages that are not available in the PostScript format.
PostScript files are not page-independent and cannot handle individual pages in a file. PDF files are page-independent and interactive; PDF also has soft and hard platform independence in different environments (different hardware) Equipment, different operating systems) The layout and content of the PDF files are the same; the most important is that the PDF format solves the font problem in the prepress workflow, and the fonts can be embedded in the PDF file. Output on any device guarantees consistent fonts. As can be seen from these advantages, the PDF format is more reliable than the PostScript format in prepress data exchange.
Adobe Acrobat can be used to easily modify the contents of a PDF file. When a large modification is required, it is best to convert the PDF file to a source application file and modify it in the source application.
The reliability of the PDF format has made it widely used in prepress data exchange and has become the main file format in digital workflows. [next]
5 PDF/X format
Although the PDF format has many advantages, in the data exchange, the flexibility of the PDF file format is too high, the parameter setting is many, and it is easy to generate errors. In order to further improve the reliability of prepress data exchange, prepress equipment manufacturers and software development. Businesses and related organizations have developed a unified PDF/X standard that limits the flexibility of PDF formats and standardizes PDF file formats.
PDF/X is a subset of PDFs designed to make prepress data exchange more reliable. The PDF/X standard series released by ISO is divided into three categories: PDF/X-1a, PDF/X-2, and PDF/X-3.
1) PDF/X-1a
The PDF/X-1a standard only allows full exchange of CMYK data and spot color data, and RGB or Lab color modes are not available. It is forbidden to use encryption and OPI objects to embed the fonts used. The standard is the most reliable and the least flexible.
2) PDF/X-3
PDF/X-3 is an extended set of PDF/X-1a standards. However, in addition to CMYK and spot color data, it also allows the use of RGB color data and device-independent color data (such as CIE LAB), and color management of these color data. The target of the output of the file may not be unique. The file is also embedded in the font used. The PDF/X-3 standard is more flexible than the PDF/X-1a standard.
3) PDF/X-2
PDF/X-2 is the most flexible format standard in the PDF/X standard. It can convert multiple color data like PDF/X-3, and it also supports partial exchange, supporting external objects like OPI. It allows both the sending and receiving sides of the PDF file to exchange information according to the file. It is not required to embed the fonts used.
Data exchange has become more reliable in PDF workflows built using the PDF/X standard. On the one hand, the compatibility between hardware and software of different vendors based on standards is improved; on the other hand, the versatility of standards-based PDF files has greatly promoted the development of digital workflow.
6 TIFF/IT format
TIFF/IT files only contain bitmap data. Without vector data, all text, graphics, and images are converted to high-resolution bitmap data, and then compressed and stored in an appropriate manner. Since TIFF is a bitmap file format, there is no problem of font mismatch and text error. The TIFF format has a high image quality and is suitable for the exchange of prepress raster data files. It is a very stable file format.
7 Copydot format
The meaning of Copydot is to "copy" the dots on the existing film into a digital bitmap file, that is, digitize the existing film and restore it to an electronic file.
In the prepress data format, the Copydot format is the closest to the final form and the most reliable data format. The Copydot format data is actually equivalent to the digital film. The copied digital dot is consistent with each dot on the original film. The Copydot format file can be directly used for output to the film, plate, or direct printing, without the need for screening.
Although the PDF, PDF/X, and TIFF/IT formats prevent text garbled and image replacement errors, there is nothing to do with the problem of image screening. When the prepress data of these formats are output at different locations, the RIP parameter settings are different due to different manufacturers' RIP characteristics, and the variability of RIP screening (changes in dot shape and angle) causes differences or errors in the output. . The Copydot format already includes the dot information, and the output will be exactly the same.
The Copydot format is the most reliable, but the flexibility is also the worst. In the Copydot file, the page cannot be resized or rotated, and cannot be color managed, overprinted, and color proofed; it is not controlled by ordinary RIP correction; the file is very large and needs to be compressed; when using Copydot scanner to obtain Copydot data, The accuracy of the scan is very high in order to replicate the film feed point.
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