Pre press inspection, what to check? These 8 essential elements must be checked
Pre press is the source of the overall quality of printed products. If there are any quality issues with pre press documents that cannot be detected and injected into the printing production process, the resulting losses are basically irreversible. If there are errors in the electronic files before printing, it will have a significant impact on the printing and processing processes. In severe cases, it may require a complete reprint, which will undoubtedly bring economic losses and even brand reputation damage to the enterprise. What is the pre press quality inspection for? Pre press electronic document inspection should consider multiple factors, including key dimensions such as size, bleeding, print identification, images, text, color, and binding method. Strict quality inspection must be conducted before printing, and any omission in any dimension may pose irreversible quality risks.
We need to check the size and bleeding
When checking the size of graphics and text, comprehensive consideration should be given to various aspects such as paper handover, printing methods, and post printing processing. During the printing process, at least bleeding areas should be left around the graphic and text pages for cutting, and there should be space for aligning the marking lines on both sides of the paper. The biting edge of the paper should also have space for paper handover. According to the cutting and operation conditions of the printing machine and the limitations of paper specifications, the size of graphics and text must comply with the approved paper format limits. So the margin of the incision should be kept at an appropriate distance from the text, otherwise it will reduce the aesthetic appeal of the product and affect its quality. And it is necessary to ensure that the bleeding location is sufficient to prevent white edges from appearing during the process of cutting or folding text. If both sides of the graphic or image along the line are exposed, there is no need for bleeding; If one side is hidden and the other side is exposed, a bleeding area should be left. In addition, the sum of the required printing size and graphic format is the maximum size of the paper accepted for printing.
Secondly, it is necessary to inspect the cutting line and the registration mark
The main functions of the registration mark are twofold: one is to display the accuracy of multi-color printing registration during the production process, and the other is to display the position of the plate alignment mark on the film. Therefore, it is necessary to display the color on each printing plate or each color separation film, which is beneficial for smooth subsequent operations. The black color in the four-color combination can be used as the color of the registration line. If the multi-color or four-color printing plate produced does not have a registration line, it is equivalent to waste and has no value. So it is necessary to inspect some cutting and printing lines, color codes, and overlay lines.
Three things to check: pictures
Firstly, it is necessary to verify the links of the images. If typesetting software (IIIustator, InDesign, CorelDRAW) is used during the design process, the layout file must be copied and packaged together with the linked image file. When importing images, EPS or TIFF format should be used as much as possible. At the same time, it is necessary to verify whether the layout file and image are located in the same folder. If you have deleted or modified page illustrations, don't forget to create new links.
Secondly, it is to verify whether the image resolution in the document meets the printing requirements. Generally, 1000-1200 dpi is the resolution for black and white images, and 300-350 dpi is the resolution for grayscale or four-color images. The resolution will change when you adjust the graphics in the drawing software. If the resolution does not meet the requirements, you must rescan or adjust the zoom ratio.
Thirdly, check the cross page images and ensure that there are no portraits or text on the center line, as the milling depth during the gluing process may obstruct the content. The text on both sides should also leave a 4-5mm space. The paper type, book thickness, and binding machinery of the printing factory are all related to the thickness of the milling back and roughening. When the book thickness or paper thickness changes, the thickness of the milling back and roughening also changes accordingly. The thickness of a book is a factor that must be considered in the process of cross page production.
Figure 3: Checking Layer Information and Deleting Excess Layers
Four must verify the text
Checking text is an indispensable step, and proper use of text in layout design can ensure the correctness of message transmission.
Firstly, verify the background color of the text. Preventing the addition of color blocks on text can easily reduce its clarity, especially when printing small fonts. Therefore, for small fonts, the use of dark backgrounds such as blue purple and blue-green should be reduced, and it is best to choose a light and soft background for readers to read.
Secondly, verify small areas of text. Small text using overprinting technology is particularly prone to blurry handwriting after printing. Colored text is not suitable for use on paper. Colors with low visibility, such as red and gray, should be used more frequently. Colors with high visibility, such as cyan and purple, should be used instead. When printing, other colors of text should be expanded and contracted on the base color to avoid exposing white edges. If the text is black, it can be directly imprinted on the base color.
Finally, verify the font of the text. Special fonts may be used during the production process, so be sure to pay attention before printing, and the text to be printed must be saved in vector format. The contour lines of vector format text are composed of curves with length and direction information. During the printing process, the strokes of the text are delicately curved, and the magnification is particularly high. The clarity of the layout is not affected, and the strokes of the text are still natural. The text in dot matrix format can be clearly seen with jagged edges when enlarged, and as the magnification increases, it becomes clearer. After printing, the layout appears particularly messy, with rough and unnatural stroke transitions.
Figure 4 Check if the file is missing fonts
Check the color five times
When printing, for color modes such as Lab and RGB, monochrome files cannot be applied, only grayscale mode can be applied, while CMYK color mode is applied to color files.
The commonly used binding methods for books include hardcover, glue binding, circle binding, folded binding, and saddle binding. Different binding methods require different emphasis on inspection content. For example, for glue binding, attention should be paid to leaving adhesive space and no key content within 5mm of the text, for circle binding, no key content should be left within the punching position, and for folded binding, the folded part should avoid the content of text seals as much as possible.
Horse riding nail binding is the simplest form of book flat binding. When using this method to package books and periodicals, the maximum number of pages to be pasted on paper exceeding 100g/㎡ is 48, and the maximum number of pages to be pasted on paper less than 100g/㎡ is 96.
Usually, if you want to use lock thread to bind more than 48 page numbers to meet the requirements, paper with a lock thread binding of less than 80g/㎡ needs to be labeled with a cover, and each label must meet 16 page numbers or even more.
Other aspects of inspection
Inspect non printed layers. Deleting non essential items when inspecting non printed layers can reduce memory usage, decrease non essential search work, and thus improve work efficiency. Moreover, if non essential pages are deleted, the page numbers and order can remain unchanged, which is beneficial for reducing film usage fees.
Inspect the smallest object. Before printing production, special attention must be paid to the smallest object during inspection. The smallest object is not only difficult to print, but also easily exposed to sunlight. Moreover, due to the deformation and stretching of paper, printing machinery, and internal factors, there are many aspects to pay attention to when overprinting multi-color lines.
In summary, pre press quality inspection is the forefront of ensuring the quality of printed materials. By conducting necessary checks on core aspects such as file size, bleeding, images, text, and color, errors in the file can be avoided and quality risks can be reduced. Of course, in addition to the skill level mentioned above, printing companies also need to regulate the performance of their staff through a reward and punishment system, strengthen their attention to this work, and accurately output pre press electronic files to help steadily improve the efficiency of product delivery for the enterprise.