Colour Profiles – CMYK & RGB
The main difference in screen and print design is the way colour is used, these differing colour spaces are referred to as CMYK & RGB. When designing for screen the RGB colour space is used – this is because screens and monitors work by shining light into your eyes – a combination of red, blue and green light. The intensity levels at which these lights shine in relation to each other will create different colours. If no light is shining from either channel, it will be black, if each channel is at it’s full intensity, it will appear white.
Print works differently, when looking at a printed document light reflects from the printed surface and reflects into your eyes. If only red, green and blue ink was used there would be a large part of the spectrum unavailable for viewing. Black ink absorbs more light than white paper, therefore, printing black text on white paper means that there is very little reflection from the text, but a lot from the paper – this is why after staring at a page for so long and closing your eyes you can occasionally still see the words in front of you whilst your retinas adjust back to absorbing less light. The inks are layered to create the correct colours in a dotted pattern – for print resolution this is usually 300 dots of colour per square inch (300dpi):
Each layer of colour (CMYK) is imposed onto a printing plate which is installed into separate units of a lithographic press, or different toners are fused to the paper in a digital press.
If you only have RGB images and you want to use them in a print document it’s best to convert them to CMYK first, rather than letting the software or prepress RIP interpret them – that way you know you have the right colour in your output document rather than leaving it to chance. Converting from RGB to CMYK can be a bit tricky – as RGB only has a 3 colour values and no black it can create 4 colour greys for objects that should appear solely in black for print. To find out more about the best way to convert RGB to CMYK check out our tutorial.