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The digital television transition, also called the digital switchover or analog switch-off (ASO), is the process in which analog television broadcasting is converted to and replaced by digital television. This primarily involves the conversion of analog terrestrial television to digital terrestrial. However, it also involves analog cable conversion to digital cable, as well as analog to digital satellite. In many countries, a simulcast service is operated where a broadcast is made available to viewers in both analog and digital at the same time. As digital becomes more popular, it is likely that the existing analog services will be removed. In some cases this has already happened, where a broadcaster has offered incentives to viewers to encourage them to switch to digital. In other cases government policies have been introduced to encourage or force the switchover process, especially with regard to terrestrial broadcasts. Government intervention usually involves providing some funding for broadcasters and, in some cases monetary relief to viewers, to enable a switchover to happen by a given deadline. The switchover for individual countries varies; in some countries it is being implemented in stages as in India and the United Kingdom, where each region has a separate date to switch off. In others, the whole country switches on one date, such as the Netherlands, which switched off all analog services on 11 December 2006. Some countries have different switch off dates for each channel, such as China where CCTV channels 1-5 were switched off first. ==Purpose of the transition== Almost all analog formats in current use - PAL, NTSC, and SECAM - were standardised between the 1940s and the 1950s and have had to be adapted to the technological innovations since then. Initially offering only black and white images with monophonic sound, the formats have had to be modified to broadcast in colour and with stereo sound, second audio program (SAP), captioning, and other information all while being backwards compatible with televisions unable to use the features. Additionally, engineers have had to implement these protocols within the limits of a set bandwidth and the tolerances of an inefficient analog format. However, during this time, the application and distribution of digital communications evolved. Digital television transmission more efficiently uses the available bandwidth and can easily integrate other digital services. While analog video and audio broadcasts can not efficiently include ''other'' digital services, they have the advantage of greater area coverage because a degraded signal can still be usable to a fringe user while a digital one will just drop off. * For the end-user, digital television has the potential for resolutions and sound fidelity far higher than those of analog broadcasts. It is also possible to offer far more channels by way of digital multiplexing, and subchannels, distinct simulcast programming, from the same broadcaster. However, most free-to-air broadcasters do not have the finances to operate multiple channels with the same quality of content on all channels; also the more channels provided has the impact of decreasing the bandwidth available to the existing channel(s) meaning overall lower picture quality due to compression artifacts and non-proportional anamorphic widescreen digital scaling. * For government and industry, digital television reallocates the radio spectrum so that it can be auctioned off. In the subsequent auctions, telecommunications industries can introduce new services and products in mobile telephony, wi-fi Internet, and other nationwide telecommunications projects. *Impact on public-access television: decreased allocations available, expensive digital equipment cost replacement and lower broadcast area coverage due to digital drop-off. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Digital television transition」の詳細全文を読む スポンサード リンク
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