Printers

Printers - they, well, print. There are five main types of printer: laser, inkjet, dot matrix, thermal.

There's also dye sublimation and you might also find solid ink printers around.

laser: expensive to buy, cheap to run, fast, high resolution, quiet(ish), page-based. A page of text/graphics is sent to the printer. The printer stores the whole page (which means it needs at least 2 megabytes of memory nowadays).

The printer uses a laser to draw the image on the page on a sensitive drum. The drum passes near a pool of toner - fine black powder. The areas drawn by the laser are electrostatically charged and attract the toner, so the toner sticks to the areas of the drum that have been drawn on. The drum rotates, depositing the loose toner on a sheet of paper and the paper is drawn through a "baking area" that melts the toner onto the paper.

Laser printers are rated by how big a page they can hold (if the page exceeds the printer's memory, the printer may choke and print part of the page and print the rest of the page on another sheet of paper), how fast they can print (8 pages a minute is typical) and whether they can print in colour (was once very expensive, but getting cheaper.) 

Typical 2003 running cost: a Lexmark 4039 toner cartridge costs $584 and yields about 14,000 pages (approx 4 cents per page).

How laser printers work

inkjet: cheap to buy, expensive to run, slow, medium to high resolution, quiet, pixel based. Inkjet printers take a one-pixel line of the page at a time and squirt ink from little nozzles directly onto the paper. Most are colour-capable, but colour printing is expensive and sometimes requires special (expensive) paper for best results.

Colour can vary from pale to rich and crisp - pages with lots of graphics can be quite soggy when they're printed. The ink is water-soluble (unlike laser printed pages) so don't carry them in the rain.

Beware of cheap inkjet printer prices: the manufacturers get their money back quickly with the cost of replacement ink cartridges. Print speed depends on the density and colours of the material being printed, but is usually slower than laser..

How ink jet printers work

dot matrix: medium expense to buy, medium expense to run, LOUD, low resolution, line-based. Once the only printers available, they now are mainly used when duplicates are required (e.g. the "customer's copy" or a "carbon copy".)

Because dot matrix printers are impact printers - part of the printer actually strikes the paper - they are the only printers that can produce carbon copies. They are commonly found in shops and customer-service departments. The computer sends a line of text to the printer. The printer move its print head across the page on a rail and for each character, the print head shoots out pins (like needles) that hit an inked ribbon against the paper. This shows the "matrix" of pins in a print head.

Dot matrix printer output looks dotty when inspected closely: each dot is a needle hitting the ribbon against the paper.

Quality can be low (unless there are more pins so the dots are close together), and when printing they scream like a cat against a cheese grater. A (close-up, exaggerated) sample of dot matrix output is demonstrated below:

This imaginary printer has a matrix of 6 x 3 pins (6 pins down, 3 pins across): the more pins it has, the better the characters will look. (Stand back from the screen and the output does not look so bad).

In text mode, dot matrix cannot handle proportional fonts (i.e. the printed character "i" will be the same width as the character "m") so printouts look rather awkward. Dot matrix printers can print graphics (rather badly) so the only way to print proportional fonts is in graphic mode (which is slow and noisy enough to bring the RSPCA running to free your cat from the cheese grater.)

Listen to a dot matrix printer screaming (MP3, 70K)

thermal

Hand-held device with inbuilt thermal printer

A label printer

Dye-sublimation - these printers can print photo-lab-quality pictures at home. In dye-sublimation printing, colors are not laid down as individual dots, as is done in inkjet printers. Dye-sublimation printing methods are favored by some graphic designers for high-end proofing and by some businesses who want to produce the best possible color materials in-house.

If you looked inside a dye-sublimation printer, you would see a long roll of transparent film that resembles sheets of red, blue, yellow, and gray colored cellophane stuck together end to end. Embedded in this film are solid dyes corresponding to the four basic colors used in printing: cyan, magenta, yellow and black. The print head heats up as it passes over the film, causing the dyes to vaporize and permeate the glossy surface of the paper before they return to solid form. The hotter the heating element, the more dye is vaporized and diffused onto the paper's surface.

Picture courtesy of http://www.kodak.com/US/images/en/digital/dlc/book2/chapter2/dyeSub.gif

The vaporised colors permeate the surface of the paper, creating a gentle gradation at the edges of each pixel, instead of the conspicuous border between dye and paper produced by inkjets. And because the color infuses the paper, it is also less vulnerable to fading and distortion over time.

Because the color is absorbed into the paper rather than sitting on the surface, the output is more photo-realistic.

Also Known As: dye-sub or dye sub

Advantages
Best image quality. Excellent reproduction of subtle tone and continuous tone images.

Disadvantages
Letter size prints are expensive at $3 to $4 dollars a page. These prints require special coated paper.

Users and Uses
Service bureaux, desktop publishers and graphic artists who require the best quality continuous tone output. Professional photographers using digital cameras and scientists processing data from satellites or digital capture devices will appreciate the subtle detail that dye-sub printers can produce.

(Thanks to Howstuffworks.com for this explanation)