Convert RGB to CMYK the right way
It’s not always easy to convert RGB to CMYK. If you’ve got an ordinary photograph then usually a simple profile switch in Photoshop will do the job – however, vibrant colours don’t hold so well with this quick conversion. The reason behind this is explained in our CMYK & RGB Explanation, but in brief, screens and print use different amounts of colours and our eyes receive these differently. This means a vibrant block of RGB colour may be dulled down if it is not converted properly. Here’s a quick run down as to the best way to convert RGB to CMYK whilst preserving as much vibrancy and colour detail as possible in Photoshop.
Check which profile to target
CMYK profiles can vary, it’s best to check with your printer which profile they would prefer your files to be supplied in. If this is difficult a standard CMYK profile will suffice – ideally with a FOGRA management profile.
Open your image in Photoshop
Open up your RGB image in Photoshop. It’s a good idea to check the resolution at this point to make sure it’s print-ready (300dpi or above) and then go to your Edit menu and select Convert to Profile…
Selecting target profile and conversion options
Ideally you want to select a Working CMYK profile and Relative Colorimetric is the preferred Intent. Check the preview box to see how your image will look once converted, if there is a vast difference in colour at this point – and one you’re not happy with – select the drop-down of Intent and select Perceptual.
Relative Colorimetric vs Perceptual
These two rendering intents are a way of interpreting colours that are outside of the target profile’s gamut range. Relative Colorimetric works by pulling in the individual colours that are currently outside of the gamut range, leaving colours within that range as close to their original RGB colours as possible. Perceptual, however, shifts all the colours in the image so their relationship remains the same. This means by pulling in one colour that is out of the gamut range, all the colours will shift in the same way – this usually ends up with the image looking slightly weaker and with a yellowish tint.
Save the image
Now all you need to do is save your image in a high-resolution format and include it in your print design. Simple!