Converting RGB colours to CMYK colours

RGB and CMYK are known as ‘colour spaces’, and these 'colour spaces' create the colours you see on all printed matter and on your computer screen right now.

• RGB stands for Red, Green and Blue; and RGB is the ‘colour space’ used by computer monitors and digital cameras.
• CMYK stands for Cyan, Magenta, Yellow and Black. All conventional and digital printing presses use CMYK.

The problem is that RGB and CMYK have different colour ‘gamuts’. A colour gamut is the range of colours that a colour space can reproduce. RGB has a wider colour gamut than CMYK. That is, RGB is capable of reproducing more colours than CMYK. RGB tends to be able to reproduce colours at the extremes of red, green and blue that CMYK is incapable of reproducing. In other words, bright reds, greens and blues will not be quite so bright when converted to CMYK. You will, for instance, see this in particular when converting a deep cobalt blue sky to CMYK.

It is highly likely that the images and background tints you work with whilst preparing your job will use the RGB colour space. At some stage they will need to be converted to CMYK.

The raster image processors (RIPs) that all presses use to prepare files for printing have built-in RGB to CMYK conversion ‘algorithms’. These automated results can be less than satisfactory, and we don’t have a great deal of control over the automated process. Therefore, if we receive files contain elements in the RGB colour space, we convert them prior to sending files to our presses' RIPs using a standard we have found to be predictable and satisfactory.

However, it is far better if you do the conversion. You will see the result for yourself. In many cases, you won’t see any difference. Simply put: very few colours have troble converting from RGB to CMYK. If you do it yourself, however, you can see for yourself if you are not happy with the result, and you can do something about it. You can, for instance, open the image in Adobe PhotoShop and make adjustments that may enable you to recover some of the brightness lost in the conversion process. You might also experiment with different conversion profiles to see which provides the best result.

Even though computer monitors display colours in the RGB colour space, your job will look more like the printed job if you convert it to CMYK and then view it on your monitor. We recommend you carry out the conversion process early in the process of preparing your job.

So please, for the best results, make sure your job has been converted from RGB to CMYK before sending it to us.

If you can’t work out how to work in the CMYK colour space in your software, please feel free to contact us for advice.

If colours are absolutely critical, then please consider asking for a hard copy proof. We will print two copies, send one copy to you, and retain the second copy so we can match it when we print your job. It will usually be printed on the press your job will be printed on, and on the paper you have requested.