Projectors

Enable images on the computer screen to be magnified and projected onto a bigger screen. Modern projectors use two types of technologies, the LCD system (also used in monitors as discussed above) and the digital light processing (DLP) system. Using the LCD system, images are projected as light shines through a layer of liquid crystal cells. On the other hand, DLP system uses tiny mirrors that reside on a special microchip called the Digital Micromirror Device (DMD). Images created using DLP are smoother and have better contrast than those created using LCD.

Output Devices: Printers

There are a number of types of printers that perform a variety of functions. This section compares and contrasts the four major types of printers.

Ink Printers

A wide variety of ink printers is available today. They use ink-jet, bubble-jet, and other technologies, but in the end, they all perform the same function: spraying and dyeing the page with color. Originally, ink printers came in black only; now they are hard to find. Color dyes have become cheaper and easier to produce, and "photo-quality" has become a major selling point with ink printers. These printers are rated according to their resolution and color depth. Color depth is the range of colors that any given drop may represent. Unlike monitor resolution, which is a measurement of pixels across and down the screen, printer resolution is measured in dpi, the number of dots per inch (horizontally or vertically) that a printer can place on a page. Sometimes the dpi is the same both horizontally and vertically, such as 1200 dpi. Other times, the horizontal and vertical dpi differ—as in1440x720 dpi.

Printers usually use a four-color process, CMYK (cyan, magenta, yellow, and black), to produce various colors. Sometimes a three-color process is used, excluding the color black because it can be produced by mixing the other three colors. In a typical printer, each dot is composed of one or two drops of ink, giving about 15 colors.

Multiple drops of colors can also be placed on a single dot to produce more colors. Hewlett-Packard attempts to achieve better quality by increasing the color depth in its printers by layering multiple color drops within a single dot to create better image quality. Read the article on HP's color layering technology.

Dye-Sublimation Printers

Dye-sublimation printers are used mainly to print high-quality images like those at a photo lab. Solid dyes consisting of the four colors, cyan, magenta, yellow, and black are used. However, in contrast to ink printers, instead of using multiple drops of CMYK colors to create a specific color, continuous-tone imaging is possible. This means that varying mixtures of CMYK color dyes can be used to represent different colors, achieving photo-like quality. The print head heats and vaporizes the dyes to allow them to permeate the glossy surface of the printing paper before they solidify. In dye-sublimation, printing colors are infused with the paper.

Laser Printers

Laser printers use toner cartridges that contain toner, a colored powder. The laser printer uses a laser beam to charge the image of the page onto a photoelectric drum. When the paper runs through the printer in between the drum and the toner cartridge, the electro-magnetic charge of the drum picks up the toner and then transfers it to the paper. A heat and pressure system then fuses the powder to the page.