Input Devices

The most common input devices are the mouse and the keyboard. With increased available bandwidth and speed, and decreased cost, other types of input devices are becoming more widely used. Some of them are briefly discussed below:

Cameras

Digital Camera

Enables photos taken to be stored in digital form, which can uploaded onto a computer.

Web Camera (webcam)

Captures live video and sends the compressed image stream to the computer or to other computers via the Internet. Compressing an image reduces the size of the image data, as well as the quality of the image. The more compression used, the poorer the image quality. It is often used to send images in real time as in a video teleconference. As a consequence of sending real-time video over low bandwidth connection, the image will not be as clear.

Digital Camcorders

Record video in digital form with slight compression (with a small loss in image quality), which can be uploaded onto a computer without further loss in image quality. Recorded video can also be edited using movie-editing software. Images recorded by a digital camcorder are more clearer than those captured by a webcam. However, recording using a camcorder requires more bandwidth than recording via a webcam. Today, many camcorders have a FireWire jack/interface to enable the host computer to provide enough bandwidth for the camcorder to send moderately compressed video in real-time to the computer.

Scanners

Convert a 2-D physical image (for example, a photograph or a paper copy of an image) into a digital image that can be viewed and edited on your computer. For example, you can use a scanner to convert a physical photo into a digital photo, and send the digital photo to a friend over the Internet.

Output Devices: Monitors and Projectors

Monitors and projectors are typical devices to view outputs on a screen.

CRT Monitors

Cathode ray tube (CRT) monitors used to be the most common type of computer monitors until LCD monitors (discussed below) began to gain popularity. CRT monitors use three electron beams to create colors, red, green, and blue. To generate the color white, all three beams are fired simultaneously. To create the color black, all three beams are turned off. Other colors are created using different mixtures of these three color beams. They are inexpensive and dependable for displaying images on screen. Cathode ray tubes are also found in conventional TV sets.

LCD Monitors

Liquid crystal display (LCD) monitors produce images by manipulating light within a layer of liquid crystal cells. They are also known as flat-panel screens. Compared to CRT monitors, they are compact, lightweight, and easy-to-read. They also emit less radiation than the CRT monitors. LCD monitors are used in notebook computers and desktop computers. Although mostly considered an output device, LCD monitors can also serve as input devices, called touch-screen monitors.

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.

Дата добавления: 2015-11-14