The commonest type of photo printer for home use is the inkjet printer, which is available from most major manufacturers. This type of printer has a head which moves rapidly over the surface of the paper. The head is made up of number of tiny nozzles, through which minute droplets of ink are sprayed onto the paper. The head needs to pass over each line several times to build up the colour image, so image printing is slower than text printing and uses more ink.
Older printers generally used one ink cartridge for black and another for the three additive primary colours, Red, Green and Blue. Newer printers use multiple colour cartridges, including lighter shades such as grey, light magenta and light yellow. This makes the printer better at reproducing subtle colour variations, such as skin tones, and is better at reproducing shadows and highlights. If a colour runs out, only a single cartridge needs to be replaced.
The other main type of home printer is the dye-sublimation (dye-sub) type, which is popular for small dedicated photo printers. These usually have a maximum print size of 6 x 4 inches, although there are some A4-sized models. Dye-sub printers use a ribbon made up of coloured panels of dye which is transferred to treated paper by a thermal process. The ribbon needs to be replaced after a specific number of uses, so paper and ribbons are often sold together as a pack, with just enough paper for the lifetime of the ribbon. Ribbons carry cyan, yellow and magenta dye and the image is built up one colour at a time. Dye-sub printers are generally slower and more expensive than an equivalent inkjet printer. However, they produce almost perfect photo-quality prints, since the image is built up in transparent layers rather than a pattern of tiny dots. Some manufacturers claim that dye-sub prints are more resistant to fading.
Microsoft have some useful tips on printing digital images here.
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