OUGD404 - CMYK/RGB

CMYK and RGB are the two main colour models used in printing. A colour model is a system for creating a range of colours derived from primary colours.

RGB stands for Red Green and Blue - ie. the primary colours. RGB is used for digital displays and is an addictive colour model. This means the model uses light to display colour. By adding the colours together, lighter colours are produced. White is the product of all 3 primary colours in this model - reflecting the way light and the way the colours in the colour spectrum work to create white light.

Notice that in the RGB diagram the overlay of Red and Blue creates Magenta, Blue and Green makes Cyan and Green and Red creates Yellow.

RGB is used in screens - the white of the screen is made so by all pixels lighting up to full intensity. On the other hand, a black screen will be created by all pixels being off, and any colours on a screen made by the pixels illuminated in different values. 
RGB is the standard colour mode used in applications because it offers the most colours. Mixing the primary colours can create many combinations.

CMYK is the colour model used in most printers. In contrast to the RGB model, the creation of lighter colours depends on the removal of ink. This is referred to as a subtractive colour model.
CMYK is made up of Cyan (blue), Magenta (pink), Yellow and Key (black). 

Similarly to the RGB diagram, the overlaps create colours, however these are the primary colours. The combination of colours absorb light to create the colour.

In printing, each colour is put on the page separately, and layered. The result is the colour, printed in tiny dots in varying saturation and in half-tone. This half toning creates the appearance of a solid, by blocking out the light. 

While RGB is used for creating designs for screen purposes, CMYK is used for printing so if you were to print the same picture in both methods the picture would appear different.