Colour specifications

4-colour production

In 4-colour production define all colours as process colours (CMYK). It is very important, that the final PDF 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.

Spot colour

In sheetfed offset production it is possible to print a spot colour. Define the colour as a spot colour in layout software and prepare a PDF in same way as in normal CMYK production. Grafostil’s prepress system separates the spot colour as the fifth separation.

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. You can preview the elements that will be flattened with InDesign’s ”Flattener Preview” function. In Acrobat check the result with Output Preview function.

Rich black

In order to achieve a strong deep black in bigger colour surfaces we recommend the use of

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 an uncoated, low grammage paper causes more 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 white text in paragraph White text.

Grafostil uses trapping in its prepress process. Our workflow software traps according to given definiations and limit values. Notify, that all adjacent colours are not trapped, if their darkness or tone are near each other. In case more trapping is desirable, it should be a part of page making process.

Overprint settings at Grafostil

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.

Grafostil uses the following settings in its prepress workflow:

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 Grafostil’s process. This will help you to avoid unexpected appearance in the final product.

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 and CC versions or with Adobe Acrobat 6 Pro or newer versions. In Acrobat 9 Pro and newer versions the overprint preview is set on in program’s preferences, General –> Page Display. If you do not have overprint setting on, Acrobat discards the document’s overprint settings on screen.

Overprinting can be checked also with Acrobat’s Output Preview option In Acrobat Pro XI do as follows:

1. Open a PDF file and choose from Tools menu Print Production and Output Preview.

2. Check Simulate Overprinting.

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.