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

Creation of different tones and colours

HP Designjet printers rely on a basic optical illusion where the ink from your printer is placed onto your paper or media in a series of small or large dots.

Light Colour - the inks dots are spaced wider apart and are smaller

Vibrant Colour - the ink dots are spaced closer together and are larger

Gradient Colour - the ink dots are spaced closer together and are gradually spaced wider apart to create the illusion of a graduation of colour

Shades of Colours - a different mix or pattern of dots creates different colour shades

If you look at the above image you can see how 3 shades of blue, green and red were created using a mix of Cyan, Magenta, Yellow and Black ink.

How the dots are actually created?

Ink travels from the ink cartridges, and then journeys into what's called the Printheads (or a single Printhead) - 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.

Does a 6 ink printer mean more colour shades then?

Yes and No. Due to recent technological advancements with printheads, a new 4 colour DesignJet now outperforms many of the older 6 colour Graphics printers in terms of the ability to produce a wider range of shades. This is because the latest printheads are more precise with laying down the ink onto the paper and can fire ink at various sizes and angles. However if you compare a new 4 ink printer with a new 6 ink printer, then yes, it will enable you to have far more colour gamuts. The more ink colours you have in your printer, the wider the range of colours you can produce.

Are there any drawbacks using a 4 ink printer?

A 4 colour CMYK printer has always had the issue 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.

Final point of interest - why do printers need all 4 colours to print in black?

Interestingly, the 3 colours CMY will, when used together, produce a murky black colour. The reason the DesignJet uses these colours is to avoid using too much black ink (to keep the cost of print down) and avoid the issue of media being oversaturated with ink. Most importantly, it also creates a black with more depth of tone - you'll probably recall that solid areas of black on your prints many years ago didn't give you anything near the depth of colour you see today. This is why your printer 'insists' on using the other 3 colours, and why you still need to buy all the 4 ink colours even if you only wish to print in black.

Written by Nicola Bray - Resolution GB Limited - www.hpplotter.co.uk