PDF is suitable for print publishing features

The characteristics of PDF for printing and publishing are mainly divided into two aspects: first, it continues to support prepress and printing workflows, and second, each PDF description page is independent of each other.

1. The importance of page independence

Physically, a Pootscript file describes pages that are connected to each other. They are arranged in the order of the contents of the publication. After being output on a hard copy device, a sequence of consecutive pages is obtained. These pages have a sequential relationship, a logical relationship, or a causal relationship. In the file structure, each Postscript file is actually a collection of Postscript instructions, which are divided into two parts: object definition and description. The description is about the description of the object. Because of this, it is possible to generate correlation between the object and the object. , and the relevance of the object to the object causes the relevance of the page because the related object may be in a different physical page.

The biggest drawback of page correlation is that it is very error-prone when outputting. For example, when RIP interprets an object on page 5, it finds that it is related to the object on page 2, then RIP will jump to the 2nd page. Page, reinterpret the object, and return to page 5. If we only need to re-interpret it once, the problem is not big. It is a waste of time. But the problem is that a related object may be interpreted again after being reinterpreted, so that the result of repeated interpretation is the multiple nesting of the interpretation, which causes the Postscript interpreter to issue a limit error message or an overflow error when it is output.

The fundamental difference between PDF and Postscript is that RDF is a document format, not a page description language. Although it also describes objects, because there is no programming structure, pages and pages are not related. Therefore, after the application Acrobat Distiller, which generates the PDF file, "distills", the relevance of the page to the page is cut off. From this it can be seen that the page-independent nature of PDF enables it to meet the basic functions of cross-media publishing and can be used for print publishing, electronic publishing or web publishing without additional processing.

2. PDF print publishing function

Since PDF is based on Postscript technology, there should be no doubt that it should be published in print. However, in the early days of its introduction, the PDF format provided only a limited degree of print publishing capabilities until the release of Acrobat 3.0. Considering that there have been many articles on the printing and publishing function of PDF, there is no intention to discuss it in more space here. To put it together, PDF's support for print publishing manifests itself in:

(1) PDF, like Postscript, generates objects using a method similar to the printing process (template coloring), which is the most fundamental attribute of PDF:

(2) Beginning with version 1.2, PDF has begun to support the CMYK color space, which is necessary for the realization of print reproduction:

(3) Each Postscript file or EPS file is always related to the page. This is the main reason why a work flow based on PS or EPS file often generates a limit check error or overflow error, but when PS file or EPS file is converted into After the PDF file, the relevance of the page is cut off to ensure that each PDF page can be stably output:

(4) Open prepress interface QPI (Open Prepress interface) is supported to achieve high resolution image substitution because digital images used for printing purposes usually have high spatial resolution and tonal resolution, and thus image files The amount of storage is quite large. In order to reduce the burden of "carriage", it is necessary to adopt a low-resolution representative image at the time of typesetting, and to replace it with a high resolution image at the time of output:

(5) Support for composite font technology, all required fonts in the publication can be displayed on the page;

(6) Support trapping to solve the problem that existing printing equipment may appear "white" at the edge of the subject due to overprinting;

(7) Built-in digital screening algorithm, which allows to specify parameters such as dot shape, screen number and screen angle for different publishing requirements and printing quality;

(8) It supports the clipping path, so that the clipping path output by the image processing software can be used as the boundary of the character winding;

(9) Support for color tone images to achieve monochromatic prints with more layers of secondary copies, suitable for printing high-quality prints;

(10) Support separation color space to facilitate conversion from other image modes to CMYK mode;

(11) Providing bite marks, cutting marks, signal strips, or gray scales on certain pages, which is conducive to printing plate installation before printing, inspection overprint accuracy, and inspection of print quality.

The functions of PDF support printing and publishing can also be mentioned, but the above list is the main content.