analog phone line— Also referred to as POTS (Plain Old Telephone Service), an analog phone line is a communication line that transmits information. Most homes use analog phone lines, making them popular for videoconferencing. A common problem with analog phone lines concerning videoconferencing is their limited bandwidth (which refers to how fast and how much information transmits over a line in a certain amount of time).
CCD (charge-coupled device)—An instrument with semiconductors arranged so that the output (electrical charge) from one semiconductor is the input of the next semiconductor. This type of array serves as the light-detecting component in many digital cameras, video cameras, and optical scanners. CCDs and CMOS (complementary metal-oxide semiconductor) components are the light-sensitive sensors used to capture digital images. Some manufacturers prefer CCDs while others use CMOS chips instead. CMOS chips are easier and less expensive to make and require less power than CCDs, but CMOS chips are vulnerable to damage from static electricity, and they often do not deliver the same image quality as CCDs.
CMOS (complementary metal-oxide semiconductor)—An electronic component used for RAM (random-access memory) and fast data switching. These semiconductors are made of two metal-oxide field effects transistors for high speed and low power use. However, static electricity can easily damage them. As mentioned in the definition for CCDs (charge-coupled devices), CMOS chips are easier and cheaper to make and require less power than CCDs, but they often do not deliver the same image quality as CCDs.
compression—Compression involves squeezing data down in size. This is an important factor for digital images because if images aren't compressed, a digital camera can only store a few of them in its memory. Some compression types negatively alter an image's quality. Most digital cameras combat this by offering multiple quality settings, making it possible for users to save many low-quality images or just a few high-quality ones. Some cameras also have raw modes that save shots without any compression at all. JPEG (Joint Photographic Experts Group) and FlashPix are two common compression formats used by digital cameras.
digital camera—In short, digital cameras use light-sensitive chips instead of film to capture still or moving images and store them as bits of information in internal or removable memory. Users can quickly transfer images to a computer for use in different applications. For example, users often attach digital images to e-mail messages, use them to enhance World Wide Web pages, or make them into colorful prints with a photo printer.
fps (frames per second)—A measurement of the speed at which a video switches from one frame to the next sequential frame to create the appearance of a moving image. Cameras with higher frame rates typically display video motion that is much smoother. Television-quality motion requires 30fps.
frame rate—A Web camera's frame rate refers to the number of frames (individual pictures) of video it captures per second. Frame rates are usually measured in fps (frames per second). Motion in videos with high frame rates appears more fluid than in videos with low frame rates. About 30fps is required to trick the human eye into seeing full motion. However, due to bandwidth limitations, many transmissions cannot reach that rate, resulting in the jerky, choppy motion that's sometimes associated with videoconferencing.
interpolation—Interpolation refers to the use of software to enhance the true resolution of a digital image and is often used with digital cameras and scanners. Through interpolation, the software copies pixels and pastes them among existing pixels to enhance the image's resolution.
JPEG (Joint Photographic Experts Group)—A color-image graphics compression format named for the committee that designed the standard image compression algorithm. Using compression, computer files can be altered to take up less storage space. In the JPEG image compression system, some data is sacrificed to achieve high rates of compression. Ratios of 100:1 or higher are possible, which means that a 100MB graphics file could potentially be reduced to 1MB in length. However, ratios over 10:1 or 20:1, depending on the particular image, begin to show noticeable image degradation. The more loss tolerated, the more the image can be compressed. Compression is achieved by dividing the picture into tiny pixel blocks, which are halved over and over until the ratio is achieved. JPEG files are supported by Web browsing applications, such as Netscape Navigator and Internet Explorer, and end with either the .JPG or .JPEG extensions.
lag time—Digital cameras typically require a few seconds from when users press the shutter button to when a camera stores the image into its memory; this is the camera's lag time. Also, most cameras need two to 10 seconds to convert an image into digital data, compress it, and store it as a file; this is known as recovery time.
LCD (liquid-crystal display)—The liquid-crystal display is a small monitor on the back of a digital camera that's used to preview and review images. The LCD also acts as a display to help adjust camera settings and scroll through menu options.
megapixel—This term refers to a digital camera feature that allows it to capture an image with a resolution of at least 1 million pixels, such as a resolution of 1,280 x 1,024 pixels. Two megapixel refers to a camera with a resolution of at least 2 million pixels. Three megapixel refers to a model with a resolution of at least 3 million pixels, such as 2,048 x 1,536 pixels.
RAM (random-access memory)—The standard type of memory that you can write data to or read data from. Information in RAM can be stored and accessed randomly, and therefore, more rapidly. RAM, which is also known as main memory, is the vital workspace of computing. The more RAM a system contains, the more information it can handle, and the more programs it can run at one time.
recovery time—Most digital cameras need two to 10 seconds to convert an image into digital data, compress it, and store it as a file; this is known as recovery time. Also, cameras typically require a few seconds from when users press the shutter button to when a camera stores the image into its memory; this is the camera's lag time.
resolution—The resolution of an image refers to its sharpness and clarity and reflects the number of pixels (a pixel is a picture element or a dot in an image) an image contains. The amount of bits used to make up each pixel determines how many colors display in an image. Put simply, a one-bit image appears monochrome, an eight-bit image produces a 256-color display, and a 24-bit image has more than 16 million colors. In general, the higher the resolution an image has, the better the image should be.
storing and transferring images—Most digital cameras use removable memory cards to store images, although a few still use internal memory. When a camera's internal memory is full, you must delete or transfer some images to a computer before you can take more photos. Removable cards are much more convenient because they insert directly into the camera and allow users to interchange them, much like rolls of film, whenever the camera's memory is full. Types of removable cards include 3.5-inch diskettes, PC Cards, and minicards, such as CompactFlash and SmartMedia. The use of removable cards and adapters has made transferring images easier and faster than connecting a camera to the computer's serial port and uploading the images. In addition, many cameras use a USB (Universal Serial Bus) connection for even faster transfer speeds.
TIFF (Tagged Image File Format)—A common way to store bit-mapped graphics images on both PCs and Macintosh computers. TIFF is a platform-independent format, which means a TIFF image created on a PC can be viewed on a Macintosh and vice versa. (Bit-map files, on the other hand, are a graphic format for the Windows environment.) The TIFF format was specifically designed for scanned images and is commonly used for that purpose. It also can be used in some applications to save images created on a computer. TIFF graphics can be color, grayscale, or black and white. The file extension for TIFF images is .TIF.
USB (Universal Serial Bus)—Until recently, most digital cameras transferred images to the computer using a serial cable. Now, more cameras are using the faster USB connection, a new type of external bus expected to replace parallel and serial ports. A USB connection has a maximum transfer speed of 12Mbps (megabits per second). A main advantage of USB over traditional ports is that it offers easy expandability; up to 127 devices can be daisy chained, far more than the number of devices supported by traditional ports. All USB devices support plug and play and hot swapping, as well. The computer automatically recognizes any USB device as soon as it's plugged in or added to the chain. Desktop computers that support USB typically have two four-pin USB ports: one for a keyboard and mouse daisy chain, the other to daisy chain all other USB devices. USB was introduced in computers shipped in 1997 and has received a boost from Windows 98, which offers better support for the standard than Windows 95.
video capture card—Some Web cameras use a video capture card to grab video and convert it into digital information. Other Web cams use a parallel port connection, eliminating the need for a video capture card; however, more Web cams are beginning to use a USB connection instead.
videoconferencing—The face-to-face communication via computers using Web cameras, microphones, speakers, and communication lines to transmit compressed audio and video data. Participants sit in front of a Web camera and speak into a microphone. As this occurs, the data compresses and transmits to another participant who receives the data by viewing the video on a computer screen and hearing audio via the speakers.
Web cameras—These devices, also known as Web cams or desktop digital video cameras, are small, they focus on one object (such as a person sitting at a computer), and they usually sit on top of a PC monitor. Web cams capture still images and video motion and then transmit this data for such purposes as videoconferencing, video e-mail, and enhancing World Wide Web pages.
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