PRINTERS

Printers

To convert the pixels on the screen of your PC's monitor to a physical form you need a printer. Printers come in all sorts of shapes and sizes. Some types are better at certain tasks than others.

The rise of the printer

It used to be so simple. Once, there was very little choice if you wanted a printer. Generally, the same manufacturer made the only printer available for a particular computer model. Now, however, we are spoilt for choice. Printers are ubiquitous. This has partially been driven by improvements in technology. However, the biggest influence on the rise of the printer has been digital photography. Interest in photography is booming like never before. It's only natural that photographers want to be able to make a permanent, physical copy of their favorite images. Printers allow a photographer to control every aspect of image making, from initial exposure through to the final print. Not so very long ago this level of control was only available to those who were willing to spend hours in a darkroom.

This book is an introductory guide to printers and printing. It is biased more toward image-making with inkjet printers, but there is more general information about the concept of printing to be found too. As much as I like seeing images onscreen, there is nothing more satisfying than looking at a well-crafted print. Creating a print is an art in itself, but it is an art that can be learnt and, for the satisfaction it brings, ¡swell worth learning.

Printer types

Dot matrix

This is the simplest and most basic of the printer types currently on sale today. Dot matrix printers are only really suitable for printing text — though simple graphics can also be printed. The print is formed by a print head comprised of a vertical array of rods. These rods can be raised or lowered to create different patterns. The print head scans back and forth across the printer paper. As it does so the rods strike an ink-soaked ribbon to transfer ink to the paper. It's the rapid repositioning of the rods that forms the shape of the text or graphics.

Dot matrix printers, though simple, are generally very rugged devices. They are also usually cheap to run. Although the print quality isn't usually high, they are ideal for situations where a large amount of text or simple graphical data needs to be printed regularly.

Laser

Laser printers use light in the form of a laser to create a printed output. The laser beam projects an image of the page being printed onto a photosensitive rotating drum. The drum is initially given a positive electrostatic charge. As the laser projects the page onto the drum, the areas where there is type or an image switch to being negatively charged. Once the drum is ready it is coated in toner, which is also positively charged. The toner clings to those areas of the drum that have a negative charge, but is repelled by those areas with a positive charge.

Paper is then drawn into the laser printer and given a negative charge in the process. The paper is fed around the drum, and toner is transferred from the drum to the paper. As the paper passes over the drum it is given a positive charge to stop it sticking. Once past the drum, the paper passes through a pair of heated rollers that fuse the toner permanently to the paper (and make the paper warm to the touch as it comes out of the printer). Although the process sounds complicated — which it is! — laser printers are capable of printing documents extremely quickly. They are also generally inexpensive to run, and a typical toner cartridge is often capable of printing thousands of pages before it needs replacing.

Initially, laser printers only used black toner. Now, color laser printers are available at relatively affordable prices. Color laser printers work on the same principle as their monochrome cousins. However, they also include three other toner cartridges: cyan, yellow, and magenta. It's the toner from the four cartridges combined that allows the laser printer to print in full color.

A big drawback with laser printers is that they can only use a limited range of paper types. Since the printing process involves heat, paper with a plastic or resin coating cannot be used without risking damage to the printer. Although the print from modern color laser printers is very high quality it is not considered to be photo-quality. Laser printers are excellent for creating proof documents for checking, but less suitable for making exhibition-ready photographic prints.

Dye-sublimation

Dye-sublimation printers use heating elements in a print head to transfer dye onto the surface of the medium being printed to. The dye is stored as a solid on a long cellophane ribbon comprising three colored panels — cyan, magenta, and yellow — followed by a protective overcoat. This type of ribbon is often referred to as CMYO. The panels are the same size as the material being printed on, so to create a 10 x 12in. (25 x 30cm) print the ribbon would need to be at least 10in. (25cm) wide by 48in. (1.2m) long (four panels, 12in. in length). However, most ribbons are longer to allow a number of prints to be made before a replacement ribbon is required.

When an image is printed, the first of the colored panels and the medium being printed to are aligned and pass through the printer. During this process the heating elements inside the print head rapidly change temperature to vary the amount of dye being transferred. As the dye is heated up it turns to gas, which solidifies on the medium as it cools.

The medium is then drawn back into the printer and aligned with the next colored panel, and the process repeats. The three colors combined produce the full color image. The final panel — the overcoat — bonds to the medium to form a protective layer. This is partially to protect the print from light scratching, but also to stop the dye from running if exposed to warmth later on.

The main advantage of the dye-sublimation process is that the print is made of a continuous tone (unlike inkjet prints — see page 14). This means that prints have the look of a traditional darkroom print.

Another advantage of dye-sublimation printers is that they are very clean. Unlike inkjet printers the dye is never in a liquid form, so there is never any risk of ink spills. A dye-sublimation print is also dry as soon as it is finished — unlike an inkjet print, it can be handled immediately. The final advantage is that it is very easy to calculate the cost of a print, as a ribbon is designed to produce an exact number of prints before it needs to be replaced.

For the creative printer, the big disadvantage is that the media that can be used to print to is limited, particularly in comparison to an inkjet printer. The paper used must have a special coating able to take the dye successfully. This makes dye-sublimation printers unsuitable for printing text documents on standard office paper.

The range of paper sizes that...