Introduction to the most popular four-color common

Introduction to four-color common sense and offset printing points (I)

four color printing:

as long as the three colors r+g+b collide in proportion, more than ten million colors can be generated Why black? Yes, R Ｇ. B black can be produced when the proportion is equal, but it takes three inks to produce one color, which is not feasible from an economic point of view In fact, black is used a lot in the design process, which is actually why four-color printing is used Another point: compared with the black directly mixed with ink, the black generated by RGB has a sense of vanity, while the latter feels more solid

１. With the four-color principle, it is much easier for everyone to accept It is equivalent to four films at the time of output, as well as four channels of cyan, magenta, yellow, black (C, m, y, K) in channels in Photoshop When we process images, the modification of channels is actually the change of film

2. The eye points and corners are flat and hanging Item: per square inch, the number of points placed is 175 for commonly used printed matter and 60 to 100 for newspapers, depending on the paper Special printing has a special purpose, depending on the texture Point: divided into circles ellipse. Diamond Square Diamond shaped Frequency modulation point, etc The above figure is composed of circular dots Angle: the angle between the straight line formed by the most closely connected points and the horizontal line The above figure is 45 degrees flat: the points of the whole film are regularly and evenly distributed and of the same size, like a plane, without a sense of hierarchy The above picture shows the flat hanging: the point size is different, and the film has a sense of hierarchy) what should be done before outputting the film

I. file format

at present, most of the output centers adopt the founder grid century Rip (pspnt) output system, and hq510, Israel's Sayram, Heidelberg and other phototypesetting output systems. All support postscrit printer description files. That is, the suffix is PS file. Other common file formats that can be directly output by RIP are: S2, S72, PS2 (founder Edition), EPS, TIF, PDF, etc. At present, the commonly used design software: Photoshop, PageMaker, CorelDRAW, illustrator, etc. can generate a PS file or PDF file through the Postscrip virtual printer, while the S2, PS2, PS files generated by some founder software such as founder book edition, Weisi, Feiteng, etc. can also be directly output in founder Century rip, but other output systems do not support it. Other word processing software such as word and WPS2000 can also generate PS files through postscript virtual printer. In fact, prepress output requires some processing, such as making up, adding registration lines, cutting lines, etc., while word, WPS2000 and other software can be said to be powerless in this regard, especially the color manuscript. Once it is finished, it will bring great difficulties to post-processing. Therefore, try to choose a series of professional design and typesetting software such as PageMaker

second, the format and accuracy of pictures

modern offset printing adopts offset printing (four-color overprint), that is, color pictures are divided into four colors: green (c), magenta (m), yellow (y), black (b) four-color dot film, and then sun it into PS version. After four times of printing by offset printing machine, it is the finished color printing product

the picture for printing is different from the picture for normal computer display. The picture must be in CMYK mode, and cannot be in RGB mode or other modes. When outputting, convert pictures into dots, that is, accuracy: DPI. Theoretically, the minimum accuracy of pictures for printing should reach 300dpi/pixel/inch. Usually, the beautiful pictures you often see on the computer feel very beautiful on the display. In fact, most of them are RGB mode pictures of 72dpi, and most of them cannot be used for printing. The pictures used should not be subject to the display. Don't think that they can be used for printing because they are very beautiful after being seen by ACDSee or other software, and they are also very beautiful after being magnified. Be sure to open them in Photoshop and confirm their true accuracy with the item of image size. For example, if the resolution of a picture is 600*600dpi/pixel/inch, its current size can be enlarged to more than double, and there is no problem using it. If the resolution is 300*300dpi, it can only be reduced or the original size, and it can no longer be enlarged. If the image resolution is 72*72dpi/pixel/inch, its size must be reduced (the DPI accuracy will be relatively larger) until the resolution becomes 300*300dpi. (when using this function, the item of redefining pixels in the image size option in Photoshop is set to none.) Common image formats include TIF, JPG, PCD, PSD, PCX, EPS, GIF, BMP, etc. when making a manuscript, TIF color, black-and-white bitmap, EPS vector diagram or jpg

III. color of pictures

about some professional terms such as overprint, overprint, hollowing out, spot color, etc. in printing, you can refer to some relevant basic printing knowledge, here only some common sense that must be paid attention to. 1. If there is a line of blue characters pressed on the hollowed out yellow bottom plate, the position of the blue characters on the yellow version of the film must be empty. And vice versa for the blue version. Otherwise, blue things are directly in the forefront of the world. If they are printed on yellow, the color will change, and the original blue words will become green. 2. If there is a line of black words pressed on a red bottom plate, the position of the black words on the red version of the film should not be hollowed out. Because black can suppress any color, if the black content is hollowed out, especially some small words, a slight error in printing will lead to the exposure of the white edge, and the contrast between black and white is large, which is easy to see. 3. Four color black is also a common problem. Before output, you must check whether the black text, especially the small characters, in the publication file is only on the blackboard, and should not appear on other tricolor plates. If it does, the quality of the printed finished product will be discounted. When RGB graphics are converted to CMYK graphics, the black text will definitely become four-color black. Unless otherwise specified, it must be processed before the film can be output. 4. When the picture is output in RGB mode, the rip system will generally automatically convert it to CMYK mode. But its color quality will be greatly reduced, and the finished products printed are light in color, not bright, and the effect is very bad. It is best to convert the picture into CMYK mode in Photoshop. If it is a scanned manuscript, it must go through the process of color correction before the picture can be used

IV. film hanging accuracy

hanging accuracy is generally called hanging accuracy. The higher the hanging accuracy is, the more exquisite the printed product is, but it has a great relationship with paper, ink, etc. the deformation amplifier unit of the deformation measurement system is one of the main components of the experimental machine. If you print a high hanging picture on ordinary paper (newspaper), the picture will not become more beautiful, but will become a mess (terrible). Therefore, before output, you must know what the printing paper of your printed matter is, and then decide the hanging accuracy. General common paper and eye accuracy: imported coated paper or self-adhesive, etc.: imported offset paper, etc.: ordinary offset paper, etc.: 133-150 line paper: line, and so on. The worse the paper quality, the lower the eye, and vice versa

to sum up,

before prepress output, we must pay attention to the following issues: 1. Select commonly used design and production software during production, such as PageMaker, etc., and try not to use word, etc. 2. The mode of the pictures in the text must be CMYK mode, with an accuracy of at least 300*300dpi/pixel/inch. 3. Check whether the text in the publication is four-color words. If so, change it to monochrome 100% black. 4. If PageMaker, Weisi, founder and illustrator are used, their linked image files must be copied together with the original files. 5. Photoshop documents should preferably be those with polyurethane insulation materials whose utilization ratio in the construction field will reach 30% and 40% PSD (unconsolidated layer), so as to facilitate modification. 6. Try to use common fonts, such as founder and wending. Try not to use rare fonts. If it has been used, CorelDRAW and illustrator first convert the text to the outline mode, which can avoid the problem that the output cannot be output because there is no such font in the output center. If there is a supplementary document, it must be copied together. 7. Clearly inform the output center of the finished product size, printing volume, printing paper, etc. of the printed matter, so as to facilitate the assembly and hanging. 8. If the contents of the two pages are the same, but the black text is different (often encountered), then you only need to output the CMYK four colors on the first page and the K color on the second page, so as to avoid waste and save money. If there are only two colors (such as red and black) and the printing requirements are not high, it is only necessary to output them in the same color plate at the same time, and there is no need to divide them into two colors for output. You can deal with it when printing and plate making. It also saves money

dot angle

green: 15 degrees Red: 75 degrees yellow: 90 degrees Black: 45 degrees general dots are arranged neatly, so there will be angles in application. For example, when printing in monochrome, the service life of its line experimental machine is long, and the angle is mostly 45 degrees, which is based on the dots printed at this angle, which is visually the most comfortable and difficult to detect the existence of dots, resulting in the effect of continuous gray tone. As for printing with two or more colors, we should pay attention to the combination of two angles, otherwise unnecessary patterns will be produced, which is called moier. Generally, if the angle difference between the two is 30 degrees, there will be no collision. Therefore, generally, for two-color printing, 45 degrees will be used for the main color or dark color, 75 degrees will be used for the light color, and 45 degrees, 75 degrees and 15 degrees will be used for the three colors respectively. If it is a four-color printing, 75 degrees will be used for the red color, 90 degrees for the yellow color, 15 degrees for the green color, and 45 degrees for the black color. These perspectives are not limited, but changed according to different needs

what is postscript

postscript is a programming language specially designed for printing graphics and text. It has nothing to do with the printing medium. Whether you print on paper, film or screen display, it is suitable. It is a page description language, similar to HTML

postscript files are stored as text, similar to HTML files. You can see this by opening a postscript file with WordPad, as shown in Figure 1. The postscript file itself only uses postscript language to describe the characteristics and parameters of the image to be displayed or printed. When displaying or printing the postscript file, the postscript interpreter interprets and executes it, prints or displays it specifically, and obtains the desired image. Figure 2 shows the postscript file in Figure 1 in the postscript file reader. You can see that the postscript file is interpreted and displayed, and the color page is obtained

compared with files in other formats, postscript files have many advantages, and the device independence mentioned above is a very important point. Postscript files also have the advantage of being independent of * as the system platform. Because many UNIX graphics environments take the support of postscript as a core part, whether you use windows* or unix* operating system, you can read and print p ostscript files, which is more convenient for communication. Because postscript files are stored as text, they are relatively small and suitable for transmission on the Internet. In addition, printing and display on postscript devices (printers, monitors) have unique advantages, which can achieve the best effect

there are several ways to generate postscript files: (1) you can refer to the language format of postscript and write a postscript file directly with a texter as needed. Of course, if the file is complex