Prepress Guide

2014-10-11 07:47:00


1. Page material preparation

The following guide lines will assist you when you are preparing page material. The more carefully you prepare the material before it is sent to press, the more time will be saved in the production stage. Unnecessary costs are not encountered and the end result is a project that is on time and on budget.



General guidelines


1.1.1  Page size and trimming margins


1.1.2  Avoid text cutting


1.1.3  Naming files


1.1.4  File extensions


1.1.5  File compression


1.1.6  Line thickness


1.1.7  Reverse text (white text)


Colour specifications


1.2.1   4-colour production


1.2.2   Spot colour


1.2.3   Transparent elements


1.2.4   Rich black


1.2.5   Trapping


1.2.6   Overprint settings at BPG




Use of images


1.4.1  Image resolution


1.4.2  Total Ink Coverage in CMYK images


1.4.3  Dot gain


1.4.4  Enlargement of images in publications


1.4.5  Image format


1.4.6  Image linking


Raw text




1.6.1  Content proof


1.6.2  Contract proofs


1.6.3  Observing environments of proofs


1.1 General guidelines

1.1.1 Page size and trimming margins


The size of the publication has to be exactly the same as the final trimmed size of the product. Bleed should extend 1/8" over the final trim.


1.1.2 Avoid text cutting

You will avoid text cutting if you do not position text or other essential elements (e.g. logos) closer than 3/16" from the trimming line. With perfectbound products the effect of the spine has to be taken into account for text that crosses the double-page spread. In normal cases a 1/8" margin is sufficient.
With perfectbound products the effect of side gluing has to be taken into account with the inside covers and on the first and last pages of the contents. Side gluing reduces the usable page area by around 1/8" starting from the spine.


1.1.3 Naming files

When the pages are in digital format, they are distinguished from each other on the basis of their file names. For the automated imposition process it is important, that the pages are put in to order according to the page numbers. The clearest way to name the pages is to start the name with 3-digit page number (001_, 002_, etc).

Naming instructions:

  • Use as short file name as possible. Maximum total length is 31 chars.

  • In file names use only numbers 0-9 and letters a-z.

  • Do not use spaces; replace them with underscore character (_).

  • Do not use other special characters (i.e.!,@,#,$,%,&,* etc.).

  • Use a file extension at the end of the name.

  • Use a period (.) only in front of a file extension.

  • For sinfle ppage files, use the page number in the name.

  • If a same file contains several pages, they must be consecutive in page number order and without empty pages (Unless thier are Blanks in the job).

  • If the product contains language or other versions, always add the version to the name.

  • Examples of a good file name: 001_catalog8_ENG.pdf or 007_012_catalog8_ENG.pdf

1.1.4 File extensions

Always use a file extension after a file name. Some of the most common file extensions are given below:

  • .pdf   common with images and graphics, an EPS image may also be compressed

  • .ps  common with images

  • .eps   common compression format for images, especially on the Internet

  • .tif   the 'portable document format' developed by Adobe is in very widespread use

  • .jpg   PostScript file

  • .qxp   QuarkXPress document

  • .indd   InDesign document

  • .sit   Stuffit compression program

  • .zip   ZipIt or WinZip compression program

1.1.5 File compression

When sending files across the internet (via FTP or email) ALWAYS compress Your files. This will help by reducint transmission time, but more importantly it will help reduce the chances of file curruption durning transmission. . In a Mac environment we recommend using Stuffit. In a Windows environment we recommend using WinZip or simaler products.


1.1.6 Line thickness

Don't use 'hairlines' when specifying the thickness of lines. The true thickness of hairlines varies depending on the software used and the printing resolution. Specify line thickness either in points or in millimetres. The smallest recommended line thickness is 0.25 points. We do not recommend the use of thin lines with half tones or many colours. The minimum thickness of reverse lines is 1 point.


1.1.7 Negative text (white text)

Depending on the paper weight, paper quality, etc. the printing process might have dimensional changes in a paper.The dimensional changes of the paper can cause regidtration problems on press.This problem appears especially clearly, when a small size, white text is used on a 4-colour image or an multicolour element. These problems are compensated at BPG's prepress and press stages, but the best result will be reached, if you pay attention to the following recommendations when using white text on multicolour surface:

  • Use at least 8 pt type size

  • Use font type with even thickness (grotesk, sans serif)

  • Use bold or heavy typefaces.


1.2 Colour specifications

Specify all colours as process colours (CMYK).


1.2.1 4-colour production

In 4-colour production define all colours as process colours (CMYK). It is very important, that the final file contains only elements with process colours.
If you have used spot colour definitions in a 4-colour job, check that also them have been changed to process colours. So you can be sure, that elements and colours are reproduced correctly in the print. See more next paragraph.


1.2.2 Spot colour

Define the colour as a spot colour in layout software and prepare a files in same way as in normal CMYK production. BPG's prepress system separates the spot colour as attitional separations.

Do not place a spot colour and a transparent element so, that they overlap each other. This is because the spot colour may change to process colour in the area the elemets are overlapping, when so called transparency flattening task is done.
Transparent elements are e.g. the shadow made in InDesign, or a .psd file with removed background and without clipping path.The transparency flattening is a task, which needs to be done before plate output.The flattening is made as following:

- when you prepare a PDF via PostScript file, the flattening is done when preparing the PS file.
- If you are exporting a PDF file from InDesign, the flattening is done only when the PDF format is 1.3.
- If you export with format 1.4 or higher, the flattening is done not until in a print house.
If you have used spot colors and transparent elements on a same page, check the file carefully before sending it to the print house.


1.2.3 Transparent elements

In 4-colour jobs both transparent elements and with them overlapping elements, must be in the same colour space (CMYK), in order that the elements and colours reproduce right. Otherwise there will be an error on page, when transparencies are flattened. An error could appear e.g. as white background in the area, where the elements overlap each other. InDesign's 'drop shadow' is an example of transparency.
Transparency flattening is a task, which must be performed before the plate output. InDesign's transparencies are flattened, when you prepare a PostScript or when you export file to PDF format 1.3. Transparencies are preserved, when you export the file to PDF format 1.4 or higher, in which case the flattening is done in prepress process at BPG . 
The best way is to make the flattening when preparing PDF files. For that reason we require you to prepare PDF:

- either via PostScript 
- or export it to PDF format 1.3.


Check the result with Acrobat's Output Preview -function. 
You can preview the elements that will be flattened already with InDesign's 'Flattener Preview' function. .

1.2.4 Rich black

In order to achieve a strong deep black in bigger colour surfaces we recommend the use of
100 % black (K),
30 % cyan (C)

Avoid the use of small size white text with rich black, because of misregistration in a print. See more about negative text from paragraph 1.1.8.


1.2.5 Trapping

Trapping is used to eliminate misregistration, which could be caused e.g. by the streching of paper.When trapping the adjacent coloured objects slightly overlap each others. Due to overlapping a small misregistration does not show in print.
Use of trapping makes multicolour printing easier especially, when printing paper with poor dimension stability. Normally uncoated, low grammage paper causes easier misregistration. Already in planning stage you can minimize easily showing misregistration problems by avoiding the use of small point size white text (negative text) on multicolour elements. If this kind of text is used through the product, the misregistration is obvious although trapping has been used. Check our recommendation for negative text in paragraph 1.1.8.
In case the trapping is desirable, it should be a part of page making process.As a default BPG traps all files using our default settings.


1.2.6 Overprint settings at BPG 

Overprinting means that the printing colours are on top of each other. A layout application defines whether a colour is the result of overprinting or non-overprinting.As a default setting, coloured elements should not be overprinting elements. BPG uses the following settings in its prepress workflow:

  1. 100% black is overprinting.

  2. CMYK white is knocked out.

  3. The overprint settings for coloured elements are preserved.

In other words, the prepress system ignores a document's 100% black and CMYK white settings. 100% black is always an overprint colour and colours under a CMYK white element are always knocked out.

When producing pages, please pay attention to the overprinting settings for coloured elements that will be preserved in BPG's process.This will help you to avoid unexpected surprises in the final product.



Metallic spot colours (like silver) must be knocked-out from other colours, because of their high opacity and quite weak trapping features.


Checking the overprint


In advance, check from the document that the print result will be as desired. You can do this, for example, using InDesign CS versions or with Adobe Acrobat 6 Pro or newer versions.

In Acrobat 7 do as follows:


  1. Open a PDF file in Acrobat 7.

  2. Choose from Advanced menu Overprint Preview or Output Preview.

  3. Check on the monitor that the page looks the way you want. With Overprint Preview you can see overprinting even more clearly, when you choose Color Warnings and tick the Show Overprinting.


If you don't have either of these two settings on,Acrobat discards the document's overprint settings on screen.

Likewise, if you have printed a proof, its validity depends on the printer's or RIP's settings, which might differ from BPG's settings.

Setting 1: Set 100 % Black to Overprint

Setting at BPG : ON

In other words, the document settings are discarded. The setting is on, because a black body text is often placed on a coloured surface. If the colour surface is opened under the text, a slight misregistration will disturb the reading of the text. With this setting 100% black is always the overprinting colour, regardless of the settings in a document.

Example: 100% black element on a picture.

Print result: The tones in the picture can be seen under the 100% black element, because it cannot fully hide the picture. The darkness of the black element varies according to the tones in the picture. Correction: Change the tone of the element to something other than 100% black, e.g. add 5% cyan or make a rich black. The image will then be opened under the element.


NOTE! Do not use the correction to black body text. It must be always pure 100% black.

Desired result   Printed result


Setting 2: Set Overprint CMYK White to Knock Out

Setting at BPG : ON

In other words, the document settings are discarded.

Example: White text defined incorrectly as overprint colour.

NOTE! If you are viewing this situation in Acrobat with Overprint Preview on, you can see only the blue element, because white text is transparent in 4-colour printing.

Print result: White text is seen in the blue element, because its overprint definition is removed in BPG's prepress process.

Correction: Is corrected in BPG's prepress process. Still the best solution is to correct the problem already in your native document, provided that you notice the problem, e.g. with Acrobat's Overprint Preview

Original PDF file viewed in Acrobat with Overprint Preview.   Print result


Setting 3: Set Colors to Knock Out

Setting at BPG : OFF

In other words, the document's settings are preserved.

Example: Text defined incorrectly as overprint colour. In the printed product the text should have a blue colour.

Print result: Text has dark green or dark grey colour, because yellow surface is not opened under the text.

Correction: The overprinting definition must be removed in the original document.

Desired result   Print result


1.3 Fonts

BPG recommends the use of Adobe Type 1 or Open Type fonts. Other font types can cause faulty appearance in prepress process.

Avoid font problems
If you make a PostScript file, include all the fonts that you use. Convert fonts in EPS files into paths.

Please note!

  • If you use ATM Deluxe to manage fonts, check in the program settings that font substitution is not on. When substitution is on, ATM replaces any font your system lacks with an MM font.

  • Don't use so-called system fonts. They vary slightly in different operating systems and might cause erroneous word division in texts, even in PDF files.

  • Don't ever use "fast buttons" in software when changing a font to italics, bold, underlined, shaded or transparent. Changes made with fast buttons behave differently depending on fonts or RIP. To avoid these problems, always use genuine fonts.

  • Exception!

    If you work with PC software and you use ATM for font management, please note: where fonts appear in a font list so that the style is separated by a comma from the ordinary name of the font (e.g. AGaramond, Italic), always choose the standard font (e.g. AGaramond) and make the desired style using the "fast button" (italics, bold). Only then will the abovementioned fonts print correctly.


1.4 Use of images


Image resolution


The screen line ruling is determined. Ensure that the resolution of the high-res according to the paper and printing images you are using is sufficient. Ideally the machine used. image resolution is twice the screen line.

Guideline values for image resolution:


Product Image resolution Screen line ruling
Sheetfed printing (Brochures, etc.) 300 ppi 150 lpi (60 l/cm)


Total Ink Coverage in CMYK Images

The total sum, in percentage, of partial colours in the darker areas of an image are determined according to the paper and printing machine used. In addition, this value is also affected by any UCR or GCR function that is used. Today, the ICC profiles used include this information and print houses often deliver their own output profiles to their customers.
When converting in Photoshop, for example, an RGB image to CMYK, the total ink coverage of the CMYK image is determined according to the program settings. See section 2, Colour Management, for further information.
The total ink values used for BPG's ICC output profiles are described in the table below. The total ink values in the table - and the functionality of the profiles - are based on the inks being run on the printing machine at standard density.


Guideline values for total ink coverage (TIC)


Sheetfed printing   340 %


Dot Gain

Dot gain is determined in images according to the print method, paper and the colours used. At BPG , the differences between presses are compensated for in plate production.

Target dot gain in sheet-fed offset with coated paper (Type 1)


File   Dot gain on paper
10%   4%
50%   14%, +/- 4%
80%   11%


The main rule with other paper types is that papers with lower quality, e.g. uncoated, have a higher dot gain. To the contrary, papers with even higher quality might have a lower dot gain.
In practice, different dot gains mean, for example, that an image made for a newspaper printed on a sheet-fed machine and on coated paper looks rather pale. For this reason, it is important to know at the image production stage from which process and on what kind of paper the work will be printed. Also, dot gain values are included in an ICC profile.

Enlargement of images in publications
If the image resolution is in accordance with the guideline values, you can scale the image in publications by 50% to 130%. The greater the change in image size, the poorer the quality of the printed image. If you intend to reduce the size of the image by more than 50%, make the change in the image processing program. If the image enlargement is over 130%, we recommend that the original is scanned again.

Image format
The colour format of images must be CMYK, when making print ready PDF. Further information is given in item 3.1.2 Supported image formats. 

Image linking

The images ought to be in the publication as links (supplied as documents). Don't position an image in the publication so that a perfect copy of the image is inside the publication.


1.6 Proofs

Always supply a proof of the very latest version. If possible, a 1:1 scale version of the proof should be given. If the proof is not 1:1 scale, this should be clearly marked.


Digital proofs

In a digital prepress process, proofs are also printed from digital material. Digital proofs can be divided into two groups, content proofs and contract proofs. With a digital contract proof is meant a proof with accurate colours, which means that the colours of proof and printed matter are inside a small tolerance.


1.6.1 Content proof

The proof is produced using a printer or copier. The proof can be used to make a rough check on the accuracy of the text and colouring ('red is red'), but the colours do not correspond to the printed end product.


1.6.2 Contract proofs

By contract proofs is meant proofs which can be used to check colour tones. The proof is made on a proofing machine calibrated for print quality (e.g. Digital Cromal, Iris). Along with the proofs come quality control elements, which can be used to measure the colour tones, dot gain and overprint values of the print. We require the use of quality control elements.

PLEASE NOTE! With contract proofs the following limitations may be encountered:

  • It is not always possible to predict the influence on print quality of the paper used in the printing.

  • It is not always possible keep the final printed product identical to the proof as far as all colour tones are concerned.

  • If the digital proof technique does not produce halftone dots, moir effects caused e.g. by difficult textile patterns might not be reproduced on the proofs.

1.6.3 Observing environments of proofs

The colours of contract proofs, as well print, must be examinated in standard lights D50 (5000 K). A change in lights changes also the viewing of colours in a observer's eye. Note, that between print and proof, the change can be different due to different materials.


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