Data Flow Transmission and Control in Digital Process

In the field of modern printing production, digital workflow has become an inevitable trend of development. While the digital technology revolution brought many advantages to the printing industry, it also brought some new problems that needed to be solved.

The job information in the digital workflow exists in the form of data, any small mistake or small error will result in the failure of data transmission or abnormal output results. It also exceeds the operator's control ability and it is difficult or impossible to check the problem. These variables become uncontrollable factors in prepress operations. In order to ensure the correct and smooth flow of data, we must find a practical method of data flow control.

I. Transfer of data flow in digital workflow

In the printing industry, there are two kinds of information flow in the printing job, namely, "graphic information flow" and "production control information flow." Graphic information flow solves the problem of "doing"; and controlling information flow solves the problems of "how to do" and "what to do." In the digital process, both types of information are digital and can be stored, processed, and delivered by computer storage.

1. Transmission of Graphical Information Streams Graphical information is information that needs to be transmitted to the public. In a completely digital production process, people use texts such as a keyboard to input text, use a mouse or a digitized graphic board to perform graphic input, apply a scanner to digitize images, and then perform text typesetting, graphic processing, image correction, and editing in a computer. Graphic and composition processing, etc. Finally, a PS file or a PDF file of a printed page is formed, a “RIP” is used to form a layout information that can be recorded in a digital flow, and a component color film or a printing plate is output by a laser image-setter or a plate-setter. The printed matter is printed, and the final printed product is obtained after the printing process. Figure 1 shows the transfer process of graphic and textual information in a digital workflow.

2. Delivery of production control information flow In the entire printing process, from the beginning of printing tasks and prepress processing, the computer acquires and acquires various digital production control information, and these control information enter the digital workflow. The graphic and text copying process is continuously updated and eventually passed on to the equipment involved in the printing and postpress processing processes. The printing and postpress processes are controlled so that the entire production process and production equipment status are under the control of the production control information flow. Under the operation. Figure 2 shows the flow of production control information flow in the digital flow.


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Second, data flow control node and method in digital process

File preflight

Once the printing unit receives the document, the first step is to pre-check the document. Since the customer source files are relatively focused on the design effect, the output factors are generally not considered too much. Therefore, it is necessary to establish a document pre-screening check before the prepress output. Will cause the output error to be excavated and corrected as much as possible in the front end, which can provide guarantee for the worry-free output of the subsequent process; at the same time, due to taking into account the output and printing factors, it can help achieve the preview of the file. The final result of printing is consistent.

The preflight of the document mainly includes factors such as page size, bleeding size, text content, font usage, image format, image link, color mode, special effects, overprinting, and trapping.

For example, Adobe InDesign is a typesetting software that includes a file preflighting function. Using this "preflight" command, you can check all fonts, link images, colors, print settings, etc., in the file you want to print, and display where errors may occur. . As shown in Figure 3, it is the summary information of each aspect displayed in preflight in Adobe InDesign.

The files are pre-checked and then solved for the problems. As shown in Figure 3, the warning message shows that 7 of the linked images use the RGB color space, so find 7 images using the RGB color space in the "Links and Images" column, and convert them in image processing software such as Photoshop. After entering the CMYK mode, import it to the appropriate location in Adobe InDesign.

2. Printout

After the file preflighting step is completed, it is usually necessary to print out the file, and generally, PS printing or PDF output is directly performed. The print-generated PS or PDF file is an overall description of the page content, and is also the first integration of the text, graphics, images, and their relationships within the page. Only when the content information is converted into a digital file in PS or PDF format through the page description language can it be received by the following links for the digital printing production process.

When printing files, you must pay attention to the options such as print page size, output color settings, and font download. Adobe InDesign is used as an example.

(1) Printed page size Printed page size determines the size of a single-page smaller version of the file. This size should be at least the same as the size of the document. If various marks are added or bleeding is set during printing, the printed page size should be within the size of the original document. Based on the mark and the size of the bleeding. Figure 4 prints page size settings.
(2) Output color setting Since the file is ultimately used for print output, "composite CMYK" or "color separation" can be selected during printout. However, in the actual prepress operation, color separation is generally performed in the back-end RIP, so it is appropriate to select "composite CMYK" at this point. As shown in Figure 5 for the output color settings.
(3) font download options Fonts are a more troubling problem in prepress processing, and many times we encounter such font problems. The settings for font download are mainly directed to the processing of no Postscript word in the print font. Usually we select "subset", which means that only the font information needed to be downloaded in the layout is downloaded to the output device. If you select “None”, it means that font downloading is not used. Therefore, the generated PS file does not contain font and text information, causing the subsequent links to be interrupted by mistakes. Figure 6 shows the font download option.

3. PDF normalization

PDF normalization is the first process that a digital workflow needs to perform after receiving a file. Only through the standardized documents can the normal circulation and output in the later production process. The main function of PDF normalization is to convert the input source files of different formats into a standardized PDF file format in the process. At the same time, the file is further checked for pre-flight. Usually, the font information, image resolution and color mode need to be checked again. The result of correct and smooth passage should be that the generated normalized PDF file contains all the font information on the page, and the resolution of all graphics and images is 300dpi or more. The color modes are all in accordance with the printed CMYK mode.

(1) Page size

PDF normalization can reset the size of the input file. If there is a “default page size” option in the Refine template of the Kodak Prinergy workflow, the user can select the page size of the input file itself. Through normalization, you can also ignore the page size of the file itself, and redefine the page size in the Refine process. This size can be customized by the user according to your needs. In order to match the large version and meet the output requirements, the small page size should be the same as the small size set in the larger version.

(2) Font detection

The font problem has always been one of the more difficult solutions in the prepress process. The PDF normalized file must contain all the font information, so as to ensure that the font content in the file is intact in the back-end output. Normally, the normalization process provides further checks on the fonts while also providing solutions for missing fonts, whether to interrupt the normalization process or to use alternative fonts, depending on the user's requirements for file fonts. Generally, fonts are embedded into files or converted into curves at the front end, and the font process will no longer occur in the normalization process.

(3) Image resolution and color mode detection

In order to obtain high-quality prints, the print image generally has a resolution of not less than 300 dpi, but sometimes different image resolutions may be set depending on the specific use of the print. The color mode of the print file is CMYK mode. The normalization process can check the resolution of the image in the file and its color mode to ensure that the print output requirements are met.

4. Digital layout

The emergence of digital imposition software has completely eliminated the traditional process flow of manual imposition, which is a necessary part of modern digital production processes. The major version is to solve the problem of folding, that is, how to arrange smaller pages in a layout.

In the transmission process of the prepress data stream, the digital layout link determines the production control information such as the large print size, printing method, cutting line, register line, style and position of the folding line, and controls these operations. The information is transmitted to the post-press processing equipment accurately, and the printed product that meets the requirements can be obtained.

Current digital workflows typically receive large-scale scenarios generated by Preps or Signastation imposition software (Founder Streamflow combines text and composer software together). The imposition plan is imported into the process in the file format of PJTF or JDF and smoothly circulated therein. Take Preps imposition software as an example.

(1) binding style and printing method

The binding style of the printed product determines the order in which the pages are discharged into the larger version of the template, ie the binding style determines the way of folding. Preps offers 5 kinds of binding styles, including free-binding, glue-binding, saddle-stitching, twin-joint and single-joint. Users can choose different binding styles according to the requirements of printed products. As shown in Figure 7, Preps provides the binding options.

The choice of printing method depends on how the job will run on the press. When print jobs appear to be non-sticking, in order to save the cost of printing plates, it is often necessary to create a large version of the template in a variety of printing methods so that each page meets the requirements of the whole paste. Preps offers a variety of printing methods, including stencil printing, self-turning, flip, single-sided printing, and double-sided printing. Figure 8 shows the printing options offered by Preps.

(2) Several layout sizes

The most important thing in digital layouts is to know the dimensions of the layouts and their relationship. Small size refers to the finished product size. The large print size refers to the print sheet size, which is the size of the printed paper. The device page size refers to the page size supported by the output device, ie the film size or the plate size, which is determined by the output device. The relationship between the three layout sizes is shown in Figure 9. To set the bleeding size for smaller pages, the paper size increases accordingly.

(3) Various control marks

Preps uses two template marks, one is SmartMark, which can be placed and resized dynamically; the other is a static mark whose position is determined by coordinates. Adding various control marks on the large version is to monitor the printing process and the post-printing process, such as cutting marks, folding marks, labeling, and color measuring bars. These control information will guide the back-end printing and post-press processing equipment how to work, and provide data basis for its accurate operation.

5. After RIP output

The current popular digital workflow includes integrated or separate RIP processors. After importing the imposition plan, put the normalized stand-alone PDF small version page into the large version plan. The integrated large-scale page needs to be processed by RIP first, and the layout content information is converted into record data that can be recognized by the output device before the large-format version can be output. The RIP in the process supports different back-end outputs, such as output film, computer-to-plate, digital proofing, and digital printing. The key settings for RIP output are the following two.

(1) Screening parameters

The network parameter settings mainly include the dot shape, screen number, screen angle, and output device resolution. The operator must select the appropriate screening parameters based on the quality requirements of the printing job and its use. Some process software can call the dot gain compensation curve to output a printing plate that is more in line with printing requirements, such as Prinergy, Founder, etc.

(2) Large version output size

The final large format output size depends on the type of output device. This size must be consistent with the large format size set in the large format solution, so that the correct output can be achieved under the premise of quality assurance. The same can be output