Digital prepress processing flow and analysis of production points
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The digital workflow is a system and technology based on the digitalization of information to integrate management and control of graphic information and production control information in prepress, printing, postpress and related processes. Prepress processing is an important workflow for printing and reproduction. With the digitization and networking of printing technology, the digital workflow of prepress processing is gradually formed and improved.
With the development and innovation of prepress technology, key technologies such as high-precision graphic digital acquisition, graphic digital processing, computer direct plate making (CTP), and large-scale printing have been continuously broken, and digital prepress graphic processing has begun to be higher and deeper. The level of the field is moving forward, and the digital prepress technology based on this has also been developed accordingly. The following is an analysis of the technical aspects of the digital prepress processing process.
First, the collection of pre-press digital graphic information
The digital collection of prepress images generally includes the collection of originals, the production of graphic images, the entry of texts, and the design of artistic creativity. This process will provide the most original digital information for subsequent computer graphics information processing work, and the input quality will directly affect the copy quality of the printed matter.
1. Digital collection of originals
With the development of digital technology, the digital input and digital manuscript of manuscripts have become a trend. According to the type and principle characteristics of graphic information, different input devices are used to input the original graphic information into the computer. Commonly used input devices are keyboards, mice, light pens and digitizers, scanners, voice input devices, digital cameras and video cameras.
2. Input of the original
Different types of originals have different input methods. Text originals are generally performed in text editing software. Graphic originals are entered using the method drawn on the computer. The input of image originals can be input by scanner and digital camera, or you can purchase photo library or design material.
Regardless of the original, the quality of the printed matter will be directly affected. In summary, the formation of digital originals is as follows.
Second, the processing points of pre-press graphic information
The pre-press image processing system mainly performs the appropriate processing on the graphic information of various originals, and then outputs the printed negative film or printing plate whose image quality and layout are in accordance with the copying requirements. Therefore, the main objects processed by the prepress graphic processing system are text, graphics, and images, and the three are called graphic information, which are basic information elements constituting a printing layout, a publication page, and the like.
1. Processing and control of text.
The word processing should edit the text according to the requirements, determine the appropriate font, font size, line spacing, kerning, design layout requirements, etc., and then layout and layout the text according to the printing requirements.
① Text font selection.
The font refers to the various shapes of the word, and some people say that it is a stroke gesture. Common basic Chinese fonts include Song, Immortal, Scorpion and Black. In addition to these four basic fonts, the word processing software also provides a variety of printed fonts for people to choose, such as the book Song body, newspaper Song body, line body, Li book body, line grass and so on. The font of the text is a standardized text writing style. Different fonts represent different writing styles. Therefore, in printing typesetting, choosing different fonts plays an important role in the quality of printing.
Fonts are best used in common fonts (such as Founder, Wending), try not to use rare fonts. If it has been used, in the software of C o r e l D r a w and I l l u s t r a t o r, the text can be converted into a curve mode, which avoids the problem that the output center cannot be output without the font library. Usually the title should be a sans serif font (such as bold). However, the headline can also be used with a serif font (marked song), which will produce a strong decorative. The text uses a serif word, which is best for Song. There should be no more than 4 fonts used throughout, and usually 3 are enough. If the layout uses a complement file, you must copy the complement file along with the layout file to the output center.
② The font size of the text.
The font size is a measure of the size of the text. There are large and small changes in printed characters. The measurement of the size of Chinese characters in word processing software is mainly based on the number system, the point system and the series system. The international system is a point system, while in the country it is based on the number system, supplemented by the point system. The number system is based on several types of movable words that are not multiples of each other. According to the conversion relationship of double or halving, the system can be divided into four characters, five characters, and six-word system. The smaller the nominal number of the font size, the larger the font size, such as the first word is larger than the second word, and the second word is larger than the third word.
The point system, also known as the pound system (P), is a measure of the "point" value of the shape of the word. According to the printing industry standards, the size of each point value of the font size is approximately equal to 0.35 mm, and the error must not exceed 0. 0 0 5 mm. If the fourth word is changed to a point system, it is equal to 1 4 points, that is, 4 . 9 3 9 mm. The series system is actually a glyph measurement system implemented by a manual photo-setting machine, which is called “level (J or K)” in terms of m m. Each level is equal to 0. 2 5 m m and 1 m m is equal to level 4. The size of the text can be discharged from 7 to 6 2, and also from 7 to 100.
In the computerized photo system, there is a system of numbers. When printing typography, if you encounter a character marked with a number, you must convert the value of the number into a series to master the correct size of the character.
③ Things to be aware of when formatting text.
The layout of the text should be designed and produced according to the requirements of the printing layout. For example, to design a magazine, design and production need to pay attention to the size of the magazine, the type of layout (horizontal or vertical), the font and font size of the text, the number of lines per page and the number of words per line, kerning and line spacing. , the number of columns on the page and the number of words in each column, the spacing of the columns, the placement of the page number and page number, the position of the header and footer, and so on.
In the text layout, there are some prohibitions. For example, at the beginning of each paragraph, the first line should be indented by two words; at the beginning of the line, some punctuation marks, such as a comma, a semicolon, a period, a comma, an exclamation point, and a quotation mark, a lower bracket, a lower book name, etc., cannot be arranged; At the end of the line, you can't put quotes, upper brackets, the name of the book, and the serial number in Chinese. The scores in the numbers, the chemical formula, the year, the sign before the number, the temperature identifier, and the foreign words of the monosyllabic words should not be used. Separately in the upper and lower rows.
2. Production of graphics
The prepress graphic is created by an artificial hand-drawn or computer-aided system, and the vector graphic composed of the outer contour lines is a two-dimensional or three-dimensional visual information body having a certain physical feature.
The commonly used prepress graphics processing software mainly includes: Corel D raw, I llustrator, F reehand, etc. These software can draw vector graphics, mathematically define the processing information of page elements, and can independently move vector graphics and primitives. Transformations such as scaling, rotation, and warping, without affecting the output, and allowing for graphic output at different resolutions. However, if special effects are used in the graphics rendering process, they must be converted to bitmaps to ensure normal output of special effects.
3. Image processing and control
When processing an image, it mainly includes correction of image color, adjustment of tone level, adjustment of sharpness, control of picture format, and the like.
① Process color images in R G B mode.
The R G B color mode is the color representation of the device based on the optical principle. The advantage of using the R G B color space is that the color gamut display space is large and can display more color effects, especially bright and bright colors. However, since the image effect must be converted to CMYK color space when it is used for printing output, some colors will exceed the printing color gamut, and “overflow” will appear. Some RGB gamut space colors cannot be in the CMYK color gamut. display. In addition, since the C M Y K color space is a color space that conforms to people's visual habits, it is easier to grasp the color change when expressing a certain color and its changes. Therefore, image correction is generally performed in the R G B color space, and then the image is finely adjusted in the C M Y K color space.
② Image level adjustment.
The purpose of the level adjustment is first to meet the printing requirements, to handle the high-key, mid-tone and dark-key of the image, and to reproduce the effects of each tone level as much as possible. Secondly, according to the original content and the hierarchical distribution, the accuracy of the important parts is guaranteed. For example, the face, clothes and main image of the character must be clearly leveled, and the facial level difference should not be less than 15%. In addition, adjust the value of extremely high light or extremely dark tone, not large area net, the image dot tone is generally controlled between 2% and 95%.
③ Image sharpness adjustment.
The sharpness of color prints is an important quality indicator for image reproduction. First, the sharpness of the image hierarchy should be adjusted. When performing image scanning, electronic color separation, etc., during the copying process, the transition width of the image layer boundary is gradually widened. The image layer boundary realism cannot be restored, and can be performed during color separation. Level boundary contrast emphasis, virtual mask and electronic effects, etc., thus enhancing the visual clarity of the contrast between the two adjacent levels of the image.
④ Image color adjustment.
Color reproduction is the main content to measure the quality of color printed images. The first thing that needs to be done is to be faithful to the manuscript. In order to ensure the original color effect, prepress design and production personnel must have a certain understanding of the principles of scanning, plate making, printing, etc., and make pre-adjustment of the color error caused by factors such as color conversion, transmission, composition and other factors in the whole process. In addition, color is also affected by people's psychological factors, and it is also processed according to people's psychological color when color correction. For example, to show a warm, happy atmosphere, you can properly make the picture warmer.
Third, the storage format of graphic information
In digital prepress systems, each image processing software has almost different formats for storing images. In order to use existing image files, or to use images in different software, it is necessary to pay attention to the difference in image format, and if necessary, transfer the image format. Therefore, it is necessary to understand the main image formats.
1. J P E G Format: It is mainly used for network transmission. It can store color and brightness changes. It is an image compression format, which can greatly compress images, maximize network resources and increase transmission speed.
2. TIFF format: The image that is mainly used for printing and printing output is recommended to be stored in this format. It can be used for image editing, drawing and page layout. It is a commonly used bitmap image format. TIFF bitmaps can have any size and resolution. rate.
3. EPS format: Mainly used for typesetting application software and drawing application software, it is a mixed image format, and is the only file format that can support transparent white mode in binary image mode. It can record images, graphics and images in one file at the same time. Text, carrying relevant text information. The E P S format is one of the most important file formats in prepress systems, not only because it is rooted in P o s t S c r i p t technology, but more importantly it supports multiple image modes (such as multi-tone images).
4. P D F Format: Developed for multiple output destinations of electronic documents, also known as portable (or portable) file format, with cross-platform operation features, can be used as a common file format in the prepress field.
Fourth, pre-press output precautions
The pre-pressed layout file is sent to the output center for film or plate production. In the pre-press output, there are often problems such as “missing font in file”, “image mode is wrong”, “image resolution error”, etc. It wastes time and wastes money. If the prepress producer knows both the design and the basic workflow of the printing process, he can grasp what should be paid attention to in the prepress design and production, and find out how to avoid mistakes, regardless of the image format, precision, font, There are a lot of things to be aware of in terms of color and design file format.
1 . Textual aspect
In the font used in the layout file, first confirm whether the output center is available. If not, you need to carry it along with the layout file or convert it to curve or raster according to the software you applied, so you can avoid it. The problem is that the output center cannot be output because there is no such font.
The text on the layout file should be more than 3 m m from the edge of the cut to avoid being cut when it is cut after printing.
Do not use overprinting to fill in the black text selected on the layout. Color printing is a four-color overlay, and finally a black version. In order to avoid the problem of overprinting, black text should not be overprinted.
2. Graphic aspect
If the graphic is in T I F F format, delete unnecessary channels and paths before storage. Do not store it as L Z W compression format to ensure that the error message “Image does not exist” will not appear in prepress output.
For all input or self-drawn graphics, the wireframe thickness should be no less than 0.1 m m, otherwise the finished product will be broken or unpresented. In addition, the wire frame cannot be set to “scale with image”, otherwise the irregular line will appear when the output is printed.
3. Image aspect
Determine the color mode and accuracy of the layout image and do the color separation processing. The printed picture is different from the picture displayed by the ordinary computer. The color picture is divided into four colors: blue (C), product (M), yellow (Y), black (B) four-color overprint, the picture mode must be CMYK mode. Therefore, before sending the file to the output, the image of the RGB color mode involved in the file should be converted to CMYK color mode. Black and white pictures are converted to grayscale and monochrome bitmaps. In addition, it is necessary to determine whether there is a color separation error in each spot color version, to avoid output errors caused by overprinting, trapping, etc., to carefully check whether each color version has a color separation error, and ensure that a spot color is not specified as Separate color, or specify a color separation as a spot color. In addition, the image accuracy is at least 300 pixels / inch.
In addition to paying attention to the above points, pre-press output should also carefully check whether the output sub-labels such as bleeding position, imposition, registration line, cutting line, color code, etc. are accurately added, and whether they meet the actual requirements of the customer's equipment, technology, materials, etc. Claim.
Prepress processing is the preliminary work of the printing process. Prepress producers have a good influence on the results of graphic information processing, which directly affects the final printing effect. In the printing industry, practitioners are required to be proficient in computer prepress processing software, familiar with the basic workflow of the printing process, and have the processing ability of good graphic and text information, which can closely integrate the computer desktop operating system and printing professional technology.