Colour systems for the print process

Key aspects of digital Colour theory

Print v Screen (subtractive v additive)
Colour systems
Assigning colour to a digital document

Subtractive colours (print)

The more colours you layer on top of each other the less light is
reflected - colours are subtracted so it becomes darker until you end up with black.
Subtractive colour is what happens when you mix paint, print a picture, or highlight a word on a page.

Aditive Colurs (scrren)

The exact reverse of Subtractive colour, the more colours you mix the lighter it becomes.
Additive colour occurs with televisions, computer monitors and all screen based images.

Colour systems

CMYK (print) vs RGB (screen)

RGB has a wider more viberant rande of colours that it can produce on screen where as CMYK cannot produce such a range that is why a photograph or picture may not print on a four coulur printer as viberant asthe original picture. The image above shows the different coour systems an the coulours that can be produced within them, the image below shows an RGB colour gradient and the CMYK equivlant, you can see clearly the difference in vibrancy. 

CMYK is the colour system used when printing, there are four plates, or four coulr seperations Cyan, Magenta, Yellow and Black, these four colours mixed make the veriety of colours you see when printing as shown in this picture of the angle of the north.

When printing in CMYK the printer uses a series of dots layerd over one an other to create the final image, on low quality print jobs this is quite visable on more high quality printing it is very difficult to see even with a loupe. 

Colour Systems 

Terminology 

CMYK (cyan/magenta/yellow/key black – 4 colour process) Subtractive.
This is used in the most common printed process called litho or offset litho RGB (red/green/blue – screen based) Additive.

Greyscale (Black and white continuous tone and any shade of grey, such as a black and white photograph)

Duotone (when a continuous tone image is printed in 2 or more spot colours – this term is also generally used when describing tri and quadtones.

Spot colour (one or more specially mixed colours as opposed as a result of a CMYK or RGB mix)

Mono (like greyscale but with a coloured ink, ie: one colour and percentage tints of that colour, plus the colour of the material it’s printed on)

Definitions 

• CMYK DEFINITION: Stands for "Cyan Magenta Yellow Key Black." These are the four basic colors used for printing color images. Unlike RGB (red, green, blue), which is used for creating images on your computer screen,

• CMYK colors are "subtractive." This means the colors get darker as you blend them together. Since RGB colors are used for light, not pigments, the colors grow brighter as you blend them or increase their intensity.

• SPOT COLOUR Print technicians around the world use the term spot colour to mean any colour generated by a non-standard offset ink; such as metallic, fluorescent, spot varnish, or custom hand-mixed inks. (as opposed to obtaining a colour by via mix of cmyk)

• GREYSCALE One colour black and all the shades of grey through to white (black and white photography is grey scale)

• MONOCHROME (mono)Monochromatic colours are all the colours of a single hue derived from one colour and extended using the shades,tones and tints of that colour.

• HALFTONE This is a mechanical process (as opposed to chemical) for converting tonal values into a series of dots that although solid dots, when printed give the impression of continuous tone