RGB and CMYK are simply recipes for creating millions of colours using only three or four base colours, because it’s simply not practical to have each colour separately presented on screen or printed from individual inks.
RGB: This is the model (recipe) that screens use (TVs and Monitors). By using different mixes of Red, Green and Blue a vast array of different colours can be created in a similar way to natural light. As with light, this is an ‘additive’ colour system, if there is no light of any of the three colours then the screen will be black. Adding the three RGB colours in different quantities will give you millions of shades and hues and if you have a ‘full’ intensity of each colour, the light — and therefore the screen — will be white. The RGB gamut (i.e range of shades or hues) is vast, but not as large as the visible spectrum.
CMYK: This is the model used for print and is composed of Cyan, Magenta, Yellow and Black (K stands for ‘key’) in various combinations. It is a ‘subtractive’ system — the more of each base colour you add the darker the finished colour. The CMYK range (or gamut) is smaller than the RGB one and has some specific limitations – it can’t represent some ranges of greens, blues and purples, generally ones that are intense and very vivid. However it still produces a remarkable number of colours, as you may now appreciate next time you pick up a magazine, catalogue or colourful book cover. Generally all these will have been printed in CMYK, and definitely so in the case of any photos on the page. Look carefully and you may see the fine dots of each colour that when laid down in a particular pattern produce the effect of a solid image. In theory, black can be created from C,M and Y, but in practice it produces a muddy brown or similar so the key (K), which is generally black, is used to create darker shades and to print true black text.
What should I look out for?
- Any image you have that is RGB may not convert to CMYK without losing some hues that fall outside the CMYK range (or gamut) so your image in rare cases may change when printed from the original you see on screen.
- Logos or similar graphics created as an image (jpeg, png, tiff etc) will be in RGB or CMYK. Any part of these files that look black will actually be produced out of a mix of all the constituent colours. Not only is this unnecessary, it may cause a muddy result and be more expensive to print than is absolutely necessary. Professional logos should be created as vector EPS files to avoid this problem, JPEG and PNG files can then be created from this original when applicable.
When Pixooma designs a logo we provide you with a range of file formats including JPEG and TIFF (in both RGB and CMYK formats), but they will have been converted from the original vector file (also supplied to you) which will have been designed using only spot colours.