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The ink jet printer: technology that takes digital data representing an image or character and produces it on paper with ink drops.

You used to need to shell out serious bucks for a laser printer if you wanted high-quality output--especially if you wanted it to be in color. That's no longer true: Ink jet printers, once relegated to homes for occasional use, have come of age. They can produce great color images at high resolutions. Because prices are dropping even as resolutions improve, laser-printer makers would be wise to look over their shoulders.

• The most common type of ink jet uses thermal technology to produce ink drops.
  
  
• In general, the more ink dots per inch, or dpi, the better the image quality.
  
  
• Printer quality continues to improve as prices steadily drop--although less-expensive models are often slower.
  
  

Ink jet printers create images by squirting colored inks onto paper. Before a document or image can be reproduced onto paper, your computer must translate the data your CPU generates into a language the printer understands. Essentially, the computer tells the printer how to "draw" on the page what you see on the screen.

To produce the words or image contained in that data, the printer squirts drops of ink through extremely tiny nozzles. Bundled together, the hundreds of nozzles form a print head, which travels across the paper printing a horizontal stripe of the picture. The nozzles fire many times per second. After completing a row, the paper is moved and the next strip of the image is printed until the page is complete.

Most ink jet printers use four hues of ink in the well-established color set used on color printing presses--cyan, magenta, yellow, and black, often abbreviated as CMYK. To achieve "photographic quality," or a continuous color tone similar to a photograph, two additional inks are sometimes added: a light cyan and a light magenta, for a total of six colors.

Thermal and Piezo Ink Jets

There are two basic types of ink jet printers: thermal and piezo. Most ink jet printers use thermal ink jet technology, which heats the ink to create a bubble. As the nozzle cools, it creates a vacuum that draws ink from the cartridge to replace the ink that was ejected. The inks must be heat resistant. The time required to heat and then cool the nozzle theoretically slows printing speeds.

Epson uses a proprietary ink jet technology known as piezo. Certain crystals bend when an electric current is applied, in a process known as the piezo-electric effect. In Epson's ink jets, a slice of piezo crystal on each ink nozzle squirts ink onto the page. It works something like an old-fashioned oil can. You push on the bottom and liquid squirts out the other end.

We measure the quality of an ink jet printer in units of dots per inch, or how many ink drops are squeezed onto a square inch of paper. A 720-by-720-dpi ink jet can produce 720 ink drops vertically and 720 ink drops horizontally on every square inch of a printed page.