Creating colour accurately on paper has been one of the major areas of research in colour printing. Like monitors, printers closely position different amounts of key primary colours which, from a distance, merge to form any colour; this process is known as dithering.

Monitors and printers do this slightly differently however because monitors are light sources, whereas the output from printers reflects light. So, monitors mix the light from phosphors made of the primary additive colours: red, green and blue (RGB), while printers use inks made of the primary subtractive colours: cyan, magenta and yellow (CMY). White light is absorbed by the coloured inks, reflecting the desired colour. In each case, the basic primary colours are dithered to form the entire spectrum. Dithering breaks a colour pixel into an array of dots so that each dot is made up of one of the basic colours or left blank.

The reproduction of colour from the monitor to the printer output is also a major area of research known as colour-matching. Colours vary from monitor to monitor and the colours on the printed page do not always match up with what is displayed on-screen. The colour generated on the printed page is dependent on the colour system used and the particular printer model; not by the colours shown on the monitor. Printer manufacturers have put lots of money into the research of accurate monitor/printer colour-matching.

Modern inkjets are able to print in colour and black and white, but the way they switch between the two modes varies between different models. The basic design is determined by the number of inks in the machine. Printers containing four colours – cyan, yellow, magenta, and black (CMYK) – can switch between black and white text and colour images all on the same page with no problem. Printers equipped with only three colours, can’t.

Many of the cheaper inkjet models have room for only one cartridge. You can set them up with a black ink cartridge for monochrome printing, or a three-colour cartridge (CMY) for colour printing, but you can’t set them up for both at the same time. This makes a big difference to the operation of the printer. Each time you want to change from black and white to colour, you must physically swap over the cartridges. When you use black on a colour page, it will be made up from the three colours, which tends to result in an unsatisfactory dark green or grey colour usually referred to as composite black. However, the composite black produced by current inkjet printers is much better than it was a few years ago due to the continual advancements in ink chemistry.

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