We would like to focus on preventing the submission of files that are potentially faulty or less than perfect, saving time and – last but not least – costs and annoyance in the ever shortening production processes.
This is why we are aiming to help you with our PDF Creation Guide, and our PDF Verification Guide supporting the checking of the finished PDF documents. Unfortunately, due to the complexities of the PDF files, the most common file errors are not always easy to find and fix, and thus, it is reasonable to know about them and eliminate their root causes in the source file.
Most common file errors and their effects
|Problem||Possible effect||Can be fixed||Additional expenditure||Approval required|
|1. Low resolution||Pixelated print||No||Yes||Submission cannot be corrected and used to create an acceptable product|
|2. Bleed is missing||Trimming problems||No||Yes|
|3. Font is not embedded||Missing characters||No||Yes|
|4. Superfluous registration marks||Trimming problems||No||Yes|
|5. Incorrect die line separation||Problem with die cutting||No||Yes|
|6. Page cannot be identified||Collation problems||No||Yes|
|7. Content near trim line||Trimming problems||No||Yes|
|8. Bad color separation||Problem with printing||Yes||Yes||Yes||Material can be fixed, but it is possible that it will not fully meet the customer’s requirementsl|
|9. Die line not defined||Deviation from the correct size||Yes||Yes||Yes|
|10. Incorrect page size||Deviation from the correct size||Yes||Yes||Yes|
|11. Incorrect color space (RGB)||Color mismatch||Yes||Yes||Yes|
|12. Incorrect color space (ICC)||Color mismatch||Yes||Yes||Yes|
|13. Incorrect overprint (black, die line)||Problem with printing||Yes||Yes||Yes||Material that requires correcting before it can be printed|
|14. Thin lines in 4 colors||Problem with printing||Yes||Yes||Yes|
|15. Total color coverage is excessive||Problem with printing||Yes||Yes||Yes|
|1. Low resolution
An image with a resolution of less than 150 dpi is considered a low resolution image. Such images should be avoided, because even if they look good on a 72 dpi screen, they do not contain enough details for high-resolution prints (up to even 2400 dpi). In such cases, the so called pixelation of the image becomes noticeable, which can greatly reduce the appeal of the finish product. Thus it is important to ensure that a suitable set of images is selected, because if an image does not have enough details from the outset (which is true for images downloaded from the Internet), you will just waste your time setting its resolution to a higher value in the image editor, because the you will not get a better quality image!
|2. Missing bleed
If the bleed is missing, it can lead to problems with trimming in the case of graphical elements that extend to the edge of the page. In such a case, a larger area should be printed and trimmed back to a small size in order to avoid having a white (unprinted) frame around the printed area. Please always check the presence of the bleed in the finished PDF file, and set up the layout of the page properly, using the correct trimbox size settings. The recommended size of the bleed is 5 mm, for coverboard 15 mm! Hint: When editing a publication, start with setting the bleed to the correct size so that you can base your edits on that bleed without having to deal with it later.
|3. Font is not embedded
Since the RIP program should interpret the PDF file accurately in the course of processing and rasterization, it is extremely important to ensure that the PDF includes all the required information. One important piece of such information pertains to the use font sets. Since we treat a PDF document as a closed file, it should contain every information that is necessary to interpret it. There are two alternative methods for embedding fonts that can be selected at the time of creating the PDF file. Partial embedding (subset) which embeds only the characters that are actually used, and full embedding of the entire font set. There is a third option, which can be safely used to avoid issues related to problems with fonts: converting text to splines after editing the publication. Then the text will be encoded as a series of vector objects instead of characters in the file.
|4. Superfluous registration marks
Registration marks that desktop publishing applications optionally insert into the document at the time of creating the PDF file are completely unnecessary as the final product will be printed sheet by sheet instead of page by page, and for this reason our printing house uses its own printing marks for setting registration marks which are different from those offered by the DTP programs. These superfluous marks are rather detrimental as they usually take up much needed millimetres from the bleeds on the pages, which are absolutely necessary in terms of the production technology. Hint: When creating PDF files, you can turn off the use of automatic marks (Marks and Bleeds). Please do not use marks other than crop marks!
|5. Incorrect die line separation
For die cut products it is important to ensure that he die line drawing required for making the die cutting tool is perfectly aligned with the graphics, but it is also easy to separate them in the file as no part of the die line drawing should appear in the printed product after printing. The easiest way to ensure it is to add the elements of the die line drawing to a dedicated spot color channel (that will not be used for printing). It is also important to set the elements of the die line drawing to overprint as this ensures that an inverted version of the die line will not appear in the print after turning off the separation containing the die line drawing. Hint: Check the die line setting in the finished PDF file by turning off the color channel containing the die line drawing in the Output Preview menu item of Adobe Acrobat Pro.
|6. Page cannot be identified
It is difficult to identify pages (which jeopardizes proper collation) if the publication does not contain page numbers and the names of the submitted files do not make it clear where a given page is placed within the publication. For this reason, if you do not submit all the pages of the entire publication in a single PDF file, then you should be particularly careful to name those file unambiguously. For example, pages15-38.pdf, pages39-45.pdf.
|7. Content near trim line
Red lines in the figures show where the cuts will be made. It is easy to see that in one of the cases the content elements are too close to the trim lines. In such a case there is a risk that due to the inaccuracy of the trim inherent in the technology, which can be 1 or 2 mm, a few important parts of the page may be removed. It is reasonable, therefore, to place important content elements that will not extend into the bleed, at least 3 or 4 mm from the trim line that indicates the place where the cuts will be made.
|8. Incorrect color separation
As the correct color separation is commonly determined by the parameters of the product to be made, incorrect color separation will mostly occur when the received file contains color channels other than those specified in the order. This means that a file submitted for a product that should be printed in at least one spot color (Pantone) will not be suitable if every element in the file has been separated as CMYK values. However, it would not be acceptable either if a spot color channel remained accidentally in a publication file that should be printed in CMYK colors. Another common error in single color products (e.g. containing text to be printed only in black) is to leave some element with a CMYK color fill in the file. Hint: It is always a good practice to have the finished PDF file checked with the Output Preview feature of Adobe Acrobat Professional to make sure if it complies with the requirements.
|9. Undefined trim line
It is absolutely necessary to define the exact location of the trim in the files, since the submitted graphical content that includes the bleed is larger than the final trimmed size so the position of the trim within that size makes quite a difference. Essentially there are two days to define the trim. The first is to use a drawn crop mark to indicate the place of the trim, but this is the less preferable solution due to the fact that the registration marks (mentioned in point 4) can reduce the bleed in certain cases. A more practical approach is to add the correct trim box setting, indicating clearly the place of the trim, to the PDF file as metadata. This trim box size can be interpreted by the PDF workflow software used at the printing house, and with it you can always add the crop marks automatically at the correct position. Hint: In the page-setter application, the size of the document (page) should always be identical to its final trimmed size, which makes it easy to use the correct trim box setting.
|10. Incorrect page size
Files in which the specified final trim size differs from what was indicated in the order submitted to us will be considered as files having an incorrect page size. This is also true for cases described in point 9 (undefined trim), if the exact position of the trim cannot be established in the publication.
|11. Incorrect color space (RGB)
Printing presses use the CMYK color system so the images to be printed should also be encoded in the CMYK color system. Cameras and monitors operate in the RGB color system so images in the submitted final version of the publication should be converted from RGB color space into CMYK. Since the colors that can be rendered in the two color systems differ, the conversion typically leads to changes in coloration, which make it particularly important not to perform the conversion in the printing house, but during the initial phase of image editing so that the colors are set to the correct color space. Hint: When you convert colors, always make sure you use the correct color profile settings! A misconfigured ICC color profile may produce incorrect color separations! See point 12 (Incorrect color space (ICC)).
|12. Incorrect color space (ICC)
The color space is incorrect if color separation was not carried out in accordance with the printing technology or the ICC color profile that is suitable for the paper to be used for printing. You will find more details about the correct color profiles in the Color management/ICC color profile menu item on our website. It is a frequent mistake that color separation is performed by leaving the default settings of Photoshop set to the U.S. Web Coated (SWOP) color profile, which is incompatible with the European standards and leads to unexpected differences in color. Hint: If you view the file on a suitably calibrated monitor, with the correct color profile you can simulate, with good approximation, the printed colors, and consequently you can correct the images in the retouching phase to achieve the best possible rendering.
|13. Incorrect overprint (thin lines, die lines)
A graphical element is called ‘overprinted’ if it does not affect the fill of other graphical elements it overlaps. If something is not overprinted, then it will knock out the other object below it. Both cases may be good and bad depending on the situation and the intended visual effect. It is, however, very important to understand that due to the stretching of paper, the alignment of elements that are not overprinted can be imprecise, and for this reason it is recommended that you should always set lower grade black texts, thin rules, bar codes, etc. to ‘overprint’ if they overlap any other objects. However, setting “white colored” object to ‘overprint’ should be avoided as this would make them disappear in the print. For die line drawings, it is particularly important to always set the elements of the die line drawing to ‘overprint’. Hint: In order to avoid unexpected results, always turn on the Overprint Preview display mode in your graphics program, which is capable of simulating the effect of overprint settings.
|14. Thin lines in 4 colors
Offset printing involves transferring single color separations (CMYK) onto the paper in a series of operations performed by the printing press, which requires that you pay particular attention to the perfect alignment of the individual colors. Due to the characteristics of the technology, the print is also exposed to moisture, which means that certain parts of the images can be highly sensitive to color alignment and the possible stretching of the paper. Such elements are thin rules in several colors (CMYK colors printed over each other) or thin inverse lines on multi-color surfaces. Hint: Please avoid using multi-color or inverse colored rules thinner than 0.2 pt, especially if you use thin-lined or low grade multi-color letters.
|15. Total ink coverage is excessive
When using sheet-fed offset printing technology, the total coverage of color separations (CMYK) printed over each other should not exceed 280% ideally. 300% total coverage may even lead to severe printing problems. For this reason, please avoid using image elements of this kind. If you need to print elements in deep black color on a large surface, then we recommend that the coverage of such surfaces should be K:100% + C:40%. Hint: You can use the Tools/Print Production/Output Preview feature of Adobe Acrobat Pro to check the color separation (total coverage) of the individual surfaces in the finished PDF file.