Printer Classification

A printer is an output device that prints text or graphics on to paper, card and film. Not all printers can produce high-quality images.

Ink-jet printers
These non-contact printers produce low-cost, high-quality text and graphics in colour by combining cyan, magenta, yellow and black (CMYK). This is a distinct advantage over more expensive laser colour printing methods. They all use some sort of thermal technology to produce heated bubbles of ink that burst spraying ink at a sheet of paper to form an image. As the ink nozzle cools a vacuum is created and this draws in a fresh supply of ink for heating and spraying. The print head prints in strips across the page, moving down the page to build up the complete image with a resolution that can range from 300 to 1200 dpi. They are sometimes referred to as ‘bubble jet’ printers, which is actually the trade name of Canon's own ink-jet technology.

One disadvantage of the ink-jet printer is that the ink cartridges need to be changed more frequently and expensive specially coated paper is necessary to produce really high-quality images, which significantly raise the cost per page. Choosing the right paper for ink-jet printing is important. Some images, especially those with large areas of colour, can ‘bleed’ if the paper is too absorbent or too much ink has been applied. Bleeding causes images to blur as the colours merge and run together.

Another disadvantage of this system of printing is that images are easily smudged as some types of ink take a little time to dry. A further drawback might be that the diameters of the nozzles used in ink-jet printers are very small and can easily become clogged.

Laser printers
These printers use the same technology as photocopier machines. The printer receives data from the computer, which is processed and used to control the operation of a laser beam directing light at a large roller or drum. Altering the electrical charge wherever laser light hits the drum creates the required image. The drum then rotates through a powder called toner. The electrically charged areas attract the powder and the print is made when it is transferred on to the paper by a combination of heat and pressure. Laser printers produce very high-quality text and graphics.

Dye sublimation printers
These low-speed devices produce relatively expensive but high-quality graphic and photographic images. The four coloured inks or dyes (CMYK) are stored on rolls of film. A heating element turns the ink on the film into a gas. The amount of ink that is put on paper correlates to the temperature of the heating element. The temperature varies in relation to the image density of the original drawing or artwork. The reason that it produces images of such high quality is that the ink is applied as a continuous tone rather than as a series of dots and special paper is used that allows the dyes to diffuse into the paper to mix and create precise colour shades.

Thermo autochrome (TA) printing
This method is used to print high-quality images generated by a digital camera. The process is more complex than either ink-jet or laser printing. TA paper contains three layers of coloured pigment, cyan, magenta and yellow, each of which is sensitive to a particular temperature. Three passes are needed to get the three colours to show. The printer is equipped with both thermal and ultraviolet heads; the heat from the thermal head 'activates' the colour in the paper, which is then ‘fixed’ by the ultraviolet light.

Digital printers
These are used to produce photographic quality images from a digital camera without having to transfer data to a computer. The printers can be connected to a monitor for viewing and editing images and layouts. The widespread introduction of digital printers is limited at the time of writing because there are no agreed standards for them. Manufacturers of digital cameras will supply digital printers that match their range of cameras.

Printer classification
Printers are classified by the following:
• The quality of type they produce – either letter quality (as good as a typewriter), near letter quality, or draft quality Ink-jet and laser printers produce letter-quality type.
• The speed at which they print. Printing speeds are measured in characters per second (cps) or pages per minute (ppm). The speed of printers within a particular class can also vary widely. Laser printers print at speeds ranging from four to 20 text pages per minute.
• The effectiveness of the methods used to create colour and more realistic images by employing techniques such as dithering, colour matching between the screen and what appears on paper, half toning and continuous tones.