Today, we’ve teamed up with the UK’s leading business printing company, Circle Services, to outline to you the correct way to approach business print design, specifically as to whether you should be using RGB or CMYK colour models. There are two different ways to print documents; RGB and CMYK. RGB is a three colour process using, as its name suggests, Red Green and Blue colours which combine to make up a full range of colours. CMYK consists of four colours, Cyan (Blue), Magenta (Red), Yellow and Black. The letter K is used for black for two reasons, one is that black is regarded as the Key colour or the colour to which the other colours are registered to and the other reason being that RGB was created before CMYK and so it was thought that using K would avoid confusion with Blue.
It is possible to create documents in either form and convert later but it has to be remembered that there will be changes which occur in the conversion. These changes are usually to the colours which you have chosen and files converted from RGB to CMYK can often look dull when printed.
To know which form to choose when designing a document you need to consider how your document is to be printed and there are various rules for different processes.
Offset Litho prints in the four colours of CMYK. An offset machine does this by using four different printing plates, one for each colour, which when printed on top of each other combine to make up the full spectrum of colours. This applies to both sheet fed offset and web offset (web offset is where the paper is fed off a continuous long reel of paper rather than single sheets).
When using a Digital printer it is possible to send wither RGB or CMYK as the files will first go through something called a RIP which converts your file to the format used by your particular digital printer. However it is important that you use one or the other and not use a mix of RGB and CMYK. i.e. don't create a CMYK document and then place RGB images inside it as it will confuse the RIP and will probably not look how you expected it to.
If you are going to print from an inkjet printer then it is best to use RGB as inkjet printers have their own built in software which converts from RGB to utilise the ink which the printer has in it. It is now common for desktop inkjet printers to use 6 or more colours especially if printing photographs.
If designing display materials, such as posters, which are going to be printed on a large format printer it is important to know that the large format printer is really just a very large inkjet printer. Large format printers however utilise a wider range of inks, possibly seven or even up to twelve, for smoother colour matching. Once again the machine will have its own way of processing your file to what it wants so it is best to provide an RGB file.
If designing for use on the web you should design in RGB as that is how it will be viewed as all colour monitors display in RGB form.
When converting from RGB to CMYK I would recommend saving the document in both formats. Save the converted file as a separate file because if you find that you later do need an RGB copy you will have to convert back and that could complicate things even more. Also, if you have copies in both formats you have the option of sending either to your printer if they ask for it. You could even send both files and let them work from whichever they prefer to work from. Of course if you send an RGB and they prefer CMYK they can always do the conversion for you but there will be an additional charge and I would always ask to see a printed proof after they have done the conversion. If you do your own conversion you can print your own proof and send it to the printer so that they know what you are expecting.
It is a topic of much discussion and everyone has their own preferred way of doing things. Once you have built up a relationship with a printer you will begin to understand each others needs. This is one reason why you should find a printer you get on with and stick with them. It benefits both of you in the long term.