COLOUR – THE BASICS

GRAYSCALE

This is the process of printing exclusively in shades of grey, varying from black to white. It lets you reproduce colour images as high-quality black and white images, using many shades of grey to represent subtle variations in colour and light.

MONOTONE

Monotone printing just uses one ink, whether that is black or another colour. The black in the Greyscale image opposite has been replaced with a specified colour, in this case the Redlin Purple.

DUOTONE

A Duotone is made up of two halftones and is most often used to bring out middle tones and highlights of an image. To create a duotone, a different colour is allocated to a specific part of the tonal range. In the image below, we have used the Redlin Purple for the highlights and midtones and black for the shadows. Duotones only work if the second colour uses a second screen angle than that of the black (45°). The most common colours used are blue, yellow, browns and reds. Tritones and Quadtones allow you to use a third or fourth colour
for finer gradations of control. Thanks in part to Photoshop, duotones, tritones and quadtones can be easily created.

CMYK

CMYK is an abbreviation for Cyan, Magenta, Yellow and Key (black) and is often referred to as Process Colour or Four Colour. The CMY colour model is called a subtractive colour model because inks subtract brightness from white – when all three primary colours (cyan, magenta and yellow) overlap, they create black. However, the black created by the combination of cyan, magenta and yellow is not dense enough to produce strong contrasts, so printers use a black ink instead. The letter “K” represents the black used in four-colour printing.

RGB

RGB is an abrieviation for Red, Green and Blue which is the colour model used in electronic devices and computer screens.

THE COLOUR SPECTRUM CHART

Most prepress files are prepared on electronic devices and therefore in RGB and so need to be converted to CMYK before printing. Neither CMYK nor RGB can reproduce the same amount of colours our eyes can see, but more importantly CMYK cannot reproduce all the colours in the RGB model. Retouchers/photographers often prefer files in this mode as it gives more flexibility in colour adjustment.

HALFTONE LINE SCREEN

Once images have been converted to CMYK, the prepress department applies a line screen to each of the four colours. Smaller dots produce lighter colours and larger dots produce darker colours. Each colour screen is rotated to allow the other colours to show through.
When combined they create a dot pattern or clear rosette. This process is used to create the optical effect of a full colour image, with only using the process colours on press.

SCREEN ANGLE

The rotation or offsetting of the colours or screens generates the required clear rosette patterns and removes any chance of moiré or screen clash when same screen angles are used. C 75° M 15° Y 0° K 45° .

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