ng. graphics coprocessor A programmable chip that speeds video performance by carrying out graphics processing independently of the computer's CPU. Among the coprocessor's common abilities are drawing graphics primitives and converting vectors to bitmaps. gray scale A range of luminance levels with incremental brightness steps from black to gray to white. The steps generally conform to a logarithmic relationship. groupware A term for software that runs on a LAN and allows coworkers to work collaboratively and concurrently. Groupware is now being enhanced with video capabilities and many of the new desktop conferencing products offer capabilities commonly associated with groupware. See Global System for Mobile Communications guardband Unused radio frequency spectrum between television channels. Video Communication: the Whole Picture See Graphical user interface. H.221 The framing portion of the ITU-T's H. .320 Recommendation that is formally known as "Frame Structure for a 64 to 1920 Kbps Channel in Audiovisual Teleservices." The Recommendation specifies synchronous operation in which the coder and decoder handshake and agree upon timing. Synchronization is arranged for individual B channels or bonded H0 connections. ITU-T Recommendation, ratified in July of 1995, that H.222 specifies "Generic coding of moving pictures and associated audio information. H.222.0 is entitled, "MPEG-2 Program and Transport Stream" and H.222.1 is entitled, "MPEG-2 streams over ATM." H.223 Part of the ITU-T's H.324 standard that specifies a control/multiplexing protocol, it is formally called "Multiplexing protocol for low bitrate multimedia communication." Annexes, passed in February 1998, deals with video packetization with H.263, and with multimedia mobile communications over error-prone channels. H.225 Part of the ITU-T's H.323 Recommendation. H.225 establishes specific messages for call control such as signaling, registration and admissions as well as the packetizing and synchronizing of media streams. Annex I addresses call signal