Visual communication services are mainly classified into paper-based communications and display-based communications. These are also called hard-copy type and soft-coyp type communications, respectively. Here, an outline of display applications in the soft-copy type communication services is presented. Nowadays, many kinds of soft-coyp type communication services have been introduced according to transmitted picture type and communication system type. Transmitted picture type implies text, graphics, photo-graphics, and motion pictures. Communication system type means the communications between terminals, and between computer and terminals. The former is called end/end communication and the latter is called center/end communication. Typical end/end communication services include video conference and telewriting, and typical center/end communication service is videotex. Display devices play an important role in the terminal equipment of the soft-copy communication services. However. the display devices have been developed for major markets such as TV receivers, computer terminals and so on. Therefore, the most appropriate display device for each soft-copy communication system has been applied, as follows. Videotex is the service mainly for information inquiry, and includes many kinds of data types such as text, figures, and/or photographics. According to these data types, display terminals of standard resolution, 250x200 dots, or high resolution, 500x400 dots, are selectively used. The text display capability is about 500 and 2000 alphanumeric characters, or 120 and 500 kanji characters , respectively. Though only CRTs are employed as display devices ; smaller size and lower costs for the terminal equipment are strongly expected in the expansion of videotex. However, adoption of new display devices is not so easy, because videotex service needs high display quality in color and resolution. Video conference means the communication conference between remotely located rooms which are equipped with TV camera and TV display. Usually, there are several participants on one end, therefore, special display equipments with very large screen, now, about 40" CRT or over 60" projection type CRT, are employed. In this system, display equipment size becomes very large in not only screen size but also in depth size. Therefore, the large size flat display is well suited to this field. However, display of color and motion pictures, high brightness and contrast, and wide viewing angle are also necessary. Hence, new devices must meet these requirements for the video conference system. Telewriting is the service for transmitting handwritten characters and drawings. Presently. sketch tablet type and black-board type terminals are available, with the CRTs been also used for display equipment. Future sketch tablet type terminal may utilize the same surface for input and output operations, therefore, the new flat type display device is expected to provide this combined function. As for a blackboard type terminal, a new flat display device with large screen is necessary instead of the CRT. The video telephone implies a personal use telephone with picture, and is at the experimental stage, because of expensive cost in transmission line and terminal equipment. Additionally, services transmitting simple pictures via a low bit-rate communication channel are becoming available. In this case, a lower quality picture may be allowed, permitting the adoption of promising new display. These soft-copy type communications are still at the early stage, and will make remarkable progress in future. This progress may depend greatly on the display devices. Though the CRT has still many problems, it may continue to be dominant until the early 90's also in this field. Nevertheless, new display devices will be gradually introduced into some specific services such as telewriting or video telephone services.
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