This guide details the differences between RGB and CMYK colour gamuts, explaining why CMYK should be used for commercially printed documents and finally showing how to check the colour settings in most commonly used software packages.
What We'll Be Covering
When ordering from instantprint please note that we do not check documents colour set up and our design online tool automatically converts all colours to CMYK. In certain cases this can cause noticeable colour variation.
Colour Gamut Differences
With RGB colours the graphics are made up from Red, Green and Blue, with CMYK the colours are made up from Cyan, Magenta, Yellow and Black.
CMYK colours are subtractive meaning the starting canvas is white and colours are added to block out parts of the spectrum. RGB colours are additive meaning that the starting point is a black canvas (i.e. a computer screen) and colours are added to create the final image.
Why Do Print Files Need to Be CMYK?
The RGB colour spectrum is much larger than the CMYK spectrum. i.e. there are colours that can be created in RGB that are not available CMYK. This problem is most apparent with very bright colours such as a fluorescent orange or green. Commercial presses print onto white paper using CMYK colours, in order to get the best results files should be prepared with this in mind. Below shows examples of files submitted in RGB colour that have been automatically converted into CMYK before printing.
Converting RGB Files to CMYK and Re-Balancing Colour
Using software such as photoshop is possible to readjust the colour balance after conversion to more closely match the intended colour output. If using RGB elements i.e. images in the design stage it is worth converting the elements into CMYK and re-balancing the colours during the design process.
The above image shows the original image on the left in RGB and then the CMYK converted image on the right.
Creating Files in CMYK
When designing any file for print it is important to set up and design the document in CMYK colour. This will save any problems trying to adjust colours afterwards which can be very difficult if not impossible. Not all software is able to create files in CMYK colour mode. For example Microsoft Word and Powerpoint are only able to create documents in RGB which must be converted before prinitng. If you send us a native Word or Powerpoint files we will convert them into a CMYK pdf and will send a proof for checking. The following software is shown in this guide; Adobe Photoshop, Adobe InDesign, Adobe Illustrator and Microsoft Publisher.
1.) Adobe Photoshop
Colour settings in Photoshop are determined when the document is created, the screen below shows the correct colour settings. You can also check colour settings when a document is open by clicking on Image, then mode as shown by the second image below.
2.) Adobe InDesign
With inDesign the colours are converted when the file is exported to pdf. Selecting pdf/x-1a:2001 preset will ensure that the document is CMYK.
3.) Adobe Illustrator
In adobe illustrator the colour mode is set when the document is created. When saving as a pdf select pdf/x-1a:2001 from the drop down presets list.
4.) Microsoft Publisher
When the document is open click file – info – commercial print settings – choose colour model. This will allow you to set the colour mode that you would like the document to be set up in.
The software shown above represents the most commonly used desktop publishing software for creating print files however documents can be created in many other packages. If using other software key settings are as follows; Colour mode CMYK (Sometimes called process colours). Colour profile: Fogra 39 (ISO 12647-2:2004). Where possible export as a PDF/x-1a:2001.
Do's and Don'ts
Finally, a couple of quick pointers to help you understanding the issue and assist in checking.
- Do use printed CMYK colour swatches to check colours if unsure.
- Do check proofs on screen using a colour calibrated monitor (if possible). Be aware that with uncalibrated screens colours will vary from monitor to monitor.
- Do print samples using a commercial proof printer with output profile set to Fogra39.
- Do use Acrobat pro output preview tool to check colours when output to Fogra39.
- Don't check colours against desktop printer samples as their profiles will generally try to emulate RGB colours as opposed to printing the true CMYK colours.