Is 720p High Definition?

A recent announcement by the International Telecommunications Union (ITU) has affirmed that ABCís selected production and transmission standard of 720p is not considered high definition. The announcement caught many by surprise, especially with progressive scanning getting rave reviews at last fallís SMPTE conference.Giuliano Rossi, Senior Counselor and head of the study group department of the ITU Radiocommunications Bureau, said 720p is presently not considered a HD format because of ""claimed lesser performance"" when compared to other formats included in Recommendation ITU-R BT.709.3.""The reasons for not including a present the 720p format among the recommended HDTV production formats were based on the lack of sufficient evidence about its performance vis-avis any other system,"" Rossi said. ""In particular, a comparison based on subjective test was actually considered necessary. The above reasons have lead to the establishment of an expert group which will evaluate the system with the task to come to conclusions in the next (few) months.""David Wood, head of new technology at the EBU technical department, said, ""In terms of a definition for high-definition television, an existing ITU report (809) cities a requirement when the HD system is interlaced scanned of twice the number of lines as in conventional systems. Thus a 1080i system could be considered HDTV. When the system is progressively scanned however, the definition does not technically apply."" The controversy clearly leaves ABC and anyone else considering 720p production equipment in a quandary.When asked about the controversy, ATSC Executive Director Craig Tanner claimed it was a ""production format issueÖ on which ATSC does not have a formal opinion. We have both 720p and 1080i and 1080p (at 24 and 30 frames per second) in the ATSC DTV standard, but we have no effort underway to make judgements about these production formats. Our emission standard accommodates both. It is an appropriate issue for ITU-R, however.""Antoon G. Uyttendaele, ABC-TV science and technology senior adviser and member of the U.S. ITU delegation was more direct saying. ""It has been suggested by the ITU Radiocommunications Assembly that only one technical standard should be recommended for each radiocommunication application unless good reasons can be offered to do otherwise. This is a very laudable objective but hardly applicable in an environment where standard setting activities cannot keep up with the fast pace of technology change.""Since we a ABC had no HDTV equipment at the time we had to make our decisions, we had the choice of using the 1080i format or a superior non-ITU format,"" he said. ""Should we have chosen 1080i just because it was an ITU Recommendation? We believe that 720p will deliver superior pictures to our viewers as it is well known that interlace is a considerable source of difficulties for all forms of picture processing, including compression.""While ITU-RBT.709.3 states that 1080i meets ""quality goals"" set for HDTV, Uytenndaele said, ""Unfortunately, we have not been able to find an ITU document that states what these ""quality goals"" are and how it has been shown that `080i meets these goals.""One explanation is that the existing ITU report (809) requires that any interlaced HD system be scanned at twice the number of lines as in conventional systems. Thus, a 1080i system could be considered HD by this definition. However, the definition does not apply to a progressively scanned system.To possibly head off a final confrontation, the U.S. has requested the ITU form a 720p technical group to investigate the possibility of the 720p becoming a second HDTV production format. One interesting twist is that while the ITU does not recognize 720p as a HD production format, it does recognize it as a delivery format for HD broadcasting.Although no one at ITU would comment on European countries venturing into HDTV, Wood did say, ""donning an EBU hat, of course, we all know that eventually television will migrate to HDTV and the difference of view are largely only about timing."" Unfortunately for ABC and others planning on using the 720p format, timing is everything.Source: Larry Bloomfield, ìBroadcast Engineeringî