Hello! Jess here. I’m one of the Personal Artworkers at instantprint and I wanted to explain the key differences between the RGB and CMYK colour gamuts and why you should use CMYK for commercially printed documents. I’ll also show you how to check the colour settings in some commonly used software programs, like Photoshop and InDesign.
How We Use Colour
It’s important to note that, here at instantprint, we don’t check documents’ colour set up, and when you upload your artwork to our website or send it across to us via email, our proofing tool automatically converts all colours to CMYK, which can cause noticeable colour variation in the finished product.
We’ll always send your altered document back to you as a ‘proof’ which you can then choose to approve for print or reject and resubmit a different piece of artwork. So, make sure to check your proofs before you approve them (we’ll cover how to do this in this guide).
With RGB colours, the graphics are made up from Red, Green and Blue, whereas with CMYK the colours are made up from Cyan, Magenta, Yellow and Black.
CMYK colours are subtractive – this means that the starting canvas is white and as colours are added, it gets darker and darker until it’s black. RGB colours are the opposite; they’re additive, which means you start with a black canvas and colours are added to create the final image.
Learn more about CMYK and how to create true black in printing here.
Why Do Print Files Need to be CMYK?
The RGB colour spectrum is huge – much larger than the CMYK spectrum. This means that some colours, like fluorescent orange and green, aren’t available within the CMYK spectrum. Commercial printing presses, like ours, print onto white paper and we add colours until the canvas is darker, so to get the best end product it’s a really good idea to convert your designs to CMYK before you send it to us.
Even if you send an artwork file in that’s not set up in CMYK, we’ll automatically change it for your when we send your proof. However, this could cause slight colour changes. Here's an example of files that have been automatically converted from RGB to CMYK before going to print.
Converting RGB Files to CMYK and Re-Balancing Colour
If you’re using software like Photoshop, you can choose to convert colours to CMYK and then readjust the colour balance afterwards. If you’re using RGB elements, it’s worth converting these into CMYK and re-balancing the colours during the design process.
Printing in Black and CMYK
Technically if you added cyan, magenta and yellow together in equal and large amounts, it would create black. However, due to impurities of the ink, true black is hard to recreate – that’s why printers include a black ink (K) along with the other colours.
If you want to use black in your design, we recommend using the CMYK values of (30, 30, 30, 100) as we've found this to be the most effective when printing.
Creating Files in CMYK
The easiest way to design artwork for print is to set up and design the whole document in CMYK colour. This will save any problems trying to adjust colours afterwards, which can be quite difficult. Not all software has the ability to create files in CMYK colour (like Microsoft Word and PowerPoint).
If you send us a Word or PowerPoint document, for example, we’ll convert it from RGB to CMYK colour and then send a proof back to you of how this will look. Below you’ll find my guides for: Adobe Photoshop, Adobe InDesign, Adobe Illustrator and Microsoft Publisher.
Adobe PhotoshopYou’ll set your colour settings in Photoshop when the document is first created. Look at the first image below to see the right settings for CMYK.
You can check the settings when the document is open too by clicking on ‘Image’ at the top of your screen and then ‘Mode’.
Adobe InDesignWhen you’re working with InDesign, the colours will be automatically converted to CMYK when the file is exported to PDF by selecting the option: PDF/X-1a:2001.
Adobe IllustratorLike Photoshop, you can set the colour settings when you first create a document in Adobe Illustrator. If you want to convert the colours in an existing file:
• Open it up in Illustrator
• Click File > Document Colour Mode > CMYK Color
• Click the selection tool and drag it over the entire image.
• Click Edit > Edit Colors > Convert to CMYK
Microsoft PublisherTo convert your colour settings in Microsoft Publisher (2003 or later. For the 2016 version there is no way to change the colour setting) first of all open up your document.
• Click File > Info > Commercial Print Settings
• Here you’ll find an option called ‘Choose Colour Model’ – select CMYK
If you’re using any other kind of software, your key settings to make sure you’ve got set up are:
• Colour Mode: CYMK (sometimes called Process Colours)
• Colour profile: Fogra39 (ISO 12647-2:2004)
• Where possible export as: PDF/X-1a:2001
Dos and Don'ts
Here are some quick tips to help with checking that your colours are all set up right:
- Print off some CMYK colour swatches to use to check your colours if you’re not sure how they’ll look when printed.
- If you can, check your proofs on a screen using a colour calibrated monitor – uncalibrated screen colours can vary between monitors. Here’s a great guide for Windows 10 and MacOS for calibrating your monitor.
- Print some samples using a commercial proof printer with the output set to Fogra39.
- Use the Acrobat Pro output preview tool to check colours when you save it with the Fogra39 colour output.
- Don’t check colours against samples you’ve printed off of your desktop printer – they normally try to emulate RGB colours rather than printing the true CMYK colours so might not be accurate.
If you have any questions about colour settings for online printing, feel free to email me and my team at firstname.lastname@example.org and we’ll be happy to help.