The effect of PDF page structure on the efficiency of digital imposition
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In the digital imposition version (referred to as the large version), the physical structure of the PDF page, the bleeding method and the page size and other structural attributes are the key factors affecting the layout and positioning of the PDF page on the large version. A PDF page with a complete canonical page structure can adopt a uniform and efficient layout and positioning method when it is used in a large format. A non-standard page structure requires a variety of processing solutions, which is labor intensive, inefficient, and error-prone. This paper analyzes the structure of PDF pages, and combines the Signastation software to summarize the positioning methods of different structure PDF pages in the layout of the layout. Finally, from the specification of PDF page design, specification page preprocessing, etc., the strategy of improving the efficiency of the layout is proposed.
First, the PDF page structure
The composition of the PDF page, the page bleed mode, and the page size are the main factors that affect the structure of the PDF page.
1. PDF page composition
In general, when creating a PDF page with software such as Indesign, Illustrator, or Acrobat, a complete PDF page consists of a Media Box, a Trim Box, a Crop Box, and a Bleed Box. Bleed Box) and the Art Box consist of five physical boxes, as shown in Figure 1.
1.1 Media Box. The media box is the largest box on the page, containing all the objects of a page, including text, images, and tags on the page. The media box defines the range of physical media that needs to be printed on the page. In addition to the graphic content, it also includes cutting marks, color control bars, and the like.
1.2 finished trim box (Trim Box). The finished trim box determines the final effective size of the page after printing and cutting. The finished trim box corresponds to the actual size of the page (finished size). If a PDF document contains a trim box, the size of the trim box is equal to the final product size.
1.3 Crop Box: Defines the part of the page to be cropped after it is displayed or printed. Unlike other boxes, it has no physical page geometry, and the Crop Box is smaller than the Media Box.
1.4 Bleed Box. The bleed box is the size outside the range of the page crop marks. All page sections between the bleed box and the trim box will be cropped at the end.
1.5 content box (Art Box). If a PDF page is to be placed in an application, the Art Box will determine the area of the page that will be placed.
2.PDF page bleeding method
The PDF page bleeding method is also different due to the pre-press design requirements and habits. Generally, there are the following cases (16 cases with a finished product size of 210×285 mm, and a single side bleeding of 3 mm):
2.1 trilateral bleeding. That is, the head, the foot, and the incision each bleed 3mm, and the mouth is not bleeding, the PDF page size is 213×291mm.
2.2 bleeding on all sides. That is, the sky, the foot, the incision and the ordering mouth each bleed 3mm, the PDF page size is 216×291mm.
2.3 no bleeding. This situation is generally the text of the book, left blank, without bleeding, the single page size is 210 × 285mm.
3.PDF page size
3.1 single page file. At this point the size of the PDF page is the finished size plus the bleed size.
3.2 spread file. At this point, the size of the PDF page is twice the size of a single-page file, depending on the size of the finished product and the way it is bleed. For example, if two 16-page pages with a finished product size of 210×285 mm are combined into one spread document, and the three-side bleeding method is adopted, the file size is 426×291 mm.
In prepress production, the actual PDF page structure will vary depending on the knowledge, experience, habits, and standardization of prepress job management. Some PDF pages are very standard, including the media box (Media Box), the finished trimming box (Trim Box), the bleeding frame (Bleed Box) and other structural frames, and the bleeding method and size are uniform (such as the single-side 3mm bleeding single) Page); some are not standardized, no structure box is defined, and the size of the bleeding is inconsistent with the way. Non-standard PDF page structure will increase the workload of prepress processing and the probability of error.
Second, the layout of the PDF page layout in the large version
1. Large format structure
The large layout structure is determined by many factors such as printer size, plate size, paper size, and PDF page structure. Figure 2 shows the large version of the layout defined in the Signastation software, including plate bites, paper bites, home pages (PDF pages), gutters, cut lines, and various markers. The home page is used for the layout of the PDF page on the large version, and is divided into a left home page and a right home page. The home page size is determined by the actual size (finished size) and the size of the bleed.
2. Positioning of PDF pages
According to the PDF page structure, the type of the homepage is defined in the layout software, and the method of page positioning is determined, including the homepage type, the actual size (finished product size), the setting of the bleeding size, and the size of the page displacement. And direction, etc., as shown in Figure 3.
There are two page positioning schemes in Signastation for different PDF page structures: automatic and user-defined.
2.1 Auto: The system automatically places the page into the large version file according to the PDF page structure. The rules are as follows:
If the PDF page contains a Trim Box, the bottom left corner of the trim box is aligned with the bottom left corner of the finished product size of the home page; if there is no Trim Box, there is a crop box (Crop Box) ), the bottom left corner of the Crop Box is aligned with the bottom left corner of the finished product of the home page; if neither the Trim Box nor the Crop Box is available, there is a Media Box. Then align the lower left corner of the media frame with the bottom left corner of the actual size of the home page.
2.2 User Defined: Allows the user to accurately locate the PDF page by setting the page offset. The most important parameter here is the offset (Offset). The offset refers to the offset value of the coordinate origin of the PDF page relative to the origin of the large version of the home page. There are three setting methods.
From the trim box: The trim box here refers to the Trim Box. At this time, the coordinate origin of the PDF page is in the lower left corner of the trimming box, and the homepage origin is in the lower left corner of the finished product size. The layout system can automatically recognize the coordinate origin and align without displacement. This method is equivalent to the "automatic" approach.
Centering: The PDF page is placed in the home page in a centered form, which applies to PDF pages with consistent four-sided bleeding.
Custom: Mainly used for PDF pages without setting the trimming frame, bleeding frame, etc. The positioning of the PDF page needs to be achieved by setting the displacement in the X and Y directions.
Offset X: The distance the origin of the PDF page is offset from the homepage origin in the X direction (horizontal direction). Offset Y: Offset of the origin of the PDF page relative to the homepage origin in the Y direction (horizontal direction). As shown in Figure 4.
3. Page positioning instance
Take a cross-page file as an example. Assume that the finished product size is 210×285mm, the PDF page is a spread document, and the single page is three-sided bleeding, each side is 3mm, the PDF spread file size is 426×582mm, and the PDF page does not have a trimming box (Trim Box). . There are two ways to deal with this type of page in the layout:
3.1 Method 1: Split the spread document into a single page file, set the left and right home pages for the single page file, and shift the X and Y directions. The split page has three-sided hemorrhage with a size of 213×291mm; the left page has a displacement of (X:-3 mm, Y:-3mm), and the right page has a displacement of (X:0 mm, Y:-3mm) .
3.2 Method 2: Do not split the spread file, use the displacement to locate. At this time, the displacement value of the left page is (X: -3 mm, Y: -3 mm), and the displacement of the right page is (X: -213 mm, Y: -3 mm).
For other PDF page structures, different page positioning methods are required, which increases the variability and complexity of the layout operation, reduces the reliability of the layout operation, and affects the normal operation of the post-press processing. Therefore, how to standardize the PDF page structure, simplify the layout work, improve the reliability and efficiency, is a problem worthy of attention in prepress work.
Third, standardize the PDF page structure to improve the efficiency of the layout
1. Specification of the design of PDF pages
Develop standard workbooks for PDF page design, train employees, communicate with customers, and expect employees and customers to design PDF pages in accordance with standardization requirements. There are:
1.1 In the Indesign and Illustrator software, create a page frame such as a Media Box, a Trim Box, or a Bleed Box for a PDF page.
1.2 Set the four-sided bleeding for the PDF page when setting the page properties, and unify the bleeding size.
2. Use Acrobat and Pitstop software to standardize PDF page processing
For non-standard PDF pages, use Acrobat and Pitstop software to process before the big version, mainly:
2.1 For pages with triple bleeds, the page is treated as a four-sided bleed by increasing the page size in Acrobat.
2.2 For a cross-page file, you should first split the page into a single-page file, and then proceed to the layout job.
2.3 Add a page structure box such as Media Box, Trim Box, and Bleed Box to the page in Pitstop, as shown in Figure 5. In this way, the software can automatically recognize the page structure frame and automatically locate it when the layout is large.
3. Standardize the use of the large version of the software
For different PDF pages, a unified PDF page positioning template is created in the layout software to form a job specification, so that different operators have the same operation method.