How does a 4 colour CMYK printer manage to create different colours

02 May 2014

Creation of different tones and colours
Designjet printers rely on a basic optical illusion where the ink dots can be varied by way of size, shape or space to create a variety of gradients and colour shades (see examples below, courtesy of wikipedia.org). The importance of the Designjet printhead is not to be overlooked because due to recent printhead technological advancements a new 4 colour Designjet now outperforms many of the older 6 colour Designjets in terms of colour gamuts.


However, one of the drawbacks of a 4 colour CMYK printer has always been that it's simply more difficult to produce deeper or more intense 'lighter' colours using dots - this is because the dots are spaced a greater distance apart to create the illusion of a lighter colour - and as this distance increases so the individual dots become more visible to the human eye. Hence the introduction of the two further ink colours - light Cyan and light Magenta.

 

Halftone dots  Colour halftoning with CMYK separations

Above left: Array of black dots to create illusion of a tonal graduation    
Above right: CMYK printer, showing how different patterns and dot sizes create the illusion of different colours 

How the dots are actually created
Ink travels from the ink cartridges, and then journeys into what's called the Printheads (or a single Print head) - sometimes moving between the two via a tubes system. In short, the printhead has many nozzles or holes which are so fine that they are smaller in diameter than a human hair (70 microns). Ink is released from these nozzles and dots are created to form an image - you may recognise the use of Red Green and Blue dots on your television screen to create images. All Designjets utilise CMYK colours. Interestingly, this is the exact order that the inks are laid onto the media - first Cyan, then Magenta, next Yellow, followed by the 'Key' colour of Black - hence the term CMYK.


Final point of interest 

Interestingly, the 3 colours CMY will, when used together, produce a murky black colour. The reason the Designjet uses Black is to avoid using too much ink (to keep the cost of print down), avoid the issue of some media being oversaturated with ink and to create a black with more depth of tone. This is why you will often find your printer has used other colours even though you've only been printing in black! 

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