Encyclopedia of Computer Science and Technology

green PC 215perceived by the human eye. At higher ratios (approaching100:1) the image becomes seriously degraded. JPEG’s abilityto store thousands of colors (unlike GIF’s limit of 256)makes the format particularly suitable for the subtleties ofphotography.PCXPCX is a compressed bitmap format originally used by thepopular PC Paintbrush program. In recent years it has beenlargely supplanted by BMP and TIFF.TIFFTIFF, or Tagged Image File Format, is also a compressedbitmap format. There are several variations by differentvendors, which can lead to compatibility problems. Implementationscan use various compression methods, generallyleading to ratios of 1.5 to 1 to about 2 to 1.Further ReadingBrown, C. Wayne, and Barry J. Shepherd. Graphics File FormatsReference and Guide. Greenwich, Conn.: Manning Publications,1995.Miano, John. Compressed Image File Formats. Upper Saddle River,N.J.: Addison-Wesley Professional, 1999.“Web Style Guide: Graphics.” Available online. URL: http://webstyleguide.com/graphics/. Accessed August 5, 2007.Murray, James D., and William vanRyper. Encyclopedia of GraphicsFile Formats. 2nd ed. (on CD-ROM). Sebastopol, Calif.:O’Reilly, 1996.“Wotsit’s Format: The Programmer’s Resource.” Available online.URL: http://www.wotsit.org/. Accessed August 14, 2007.graphics tabletWhile conventional pointing devices (see mouse) are quitesatisfactory for making selections and even manipulatingobjects, many artists prefer the control available onlythrough a pen or pencil, which allows the angle and pressureof the stylus tip to be varied, creating precise lines andshading. A graphics tablet (also called a digitizing tablet) isa device that uses a specially wired pen or pencil with a flatsurface (tablet). Besides tracking the location of the pen andtranslating it into X/Y screen coordinates, the tablet alsohas pressure sensors (depending on sensitivity, the tabletMany graphics tablets use a stylus or pen. The system can track thepen’s position and, often, the amount of pressure being exerted, anddraw the line accordingly.can recognize 256, 512, or 1024 levels of pressure). In combinationwith buttons on the pen, the pressure level can beused to control the line thickness, transparency, or color.In addition, the driver software for some graphics tabletsincludes additional functions such as the ability to programthe pen to control features of such applications as AdobePhotoshop.The tablet is connected to the PC (usually through a USBport). The pen may be connected to the tablet by a tether, orit may be wireless. If the pen has an onboard battery, it canprovide additional features at the expense of weight and theneed to replace batteries occasionally.A variant implementation uses a small “puck” insteadof a pen. The puck, which can be moved smoothly over thetablet surface, often has a window with crosshairs in thecenter. This makes it particularly useful for tracing detaileddrawings such as in engineering applications.Many artists find that wielding a pen with a graphicstablet offers not only finer control, but also more naturaland less fatiguing method of input than with the mouse.Further ReadingChastain, Sue. “Before You Buy a Graphics Tablet.” Availableonline. URL: http://graphicssoft.about.com/od/aboutgraphics/a/graphicstablets.htm. Accessed August 5, 2007.Kolle, Iril C. Graphics Tablet Solutions. Cincinnati, Ohio: Muska &Lipman, 2001.Threinen-Pendarvis, Cher. The Photoshop and Painter Artist TabletBook: Creative Techniques in Digital Painting. Berkeley, Calif.:Peachpit Press, 2004.green PCThis is a general term for features that reduce the growingenvironmental impact of the manufacture or use of computers.This impact has several aspects: energy consumption,resource consumption, e-waste, and pollution and greenhouseemissions.Energy ConsumptionThe greatest part of a typical computer system’s power consumptionis from the monitor, followed by the hard driveand CPU. It follows that considerable energy can be saved ifthese components are powered down when not in use. Onthe other hand, most users do not want to go through thewhole computer startup process several times a day. Onesolution is to design a computer system so that it turns offmany components when not in use but is still able to restorefull function in a few seconds.When applied to a personal computer, the federallyadopted Energy Star designation indicates a computer systemthat includes an energy saving mode that can powerdown the monitor, hard drive, or CPU after a specifiedperiod elapses without user activity, such that the inactivesystem consumes no more than 30 watts. In the ultimateenergy-saving feature a suspend mode saves the currentstate of the computer’s memory (and thus of program operation)to a disk file. When the user presses a key (or movesthe mouse), the computer “wakes up” and reloads its memorycontents from the disk, resuming operation where it left