Why Are Some HD Channels 1080i, While Others Are 720p?

Written by Clearly Resolved
Sunday, 20 May 2007

[ Q ] I understand that ABC is broadcasting in 720p, while NBC and CBS are going with 1080i. Why the lack of uniformity?

[ A ] First off, your understanding is correct. In fact, the majority of HD programmers in the US use the 1080-line interlaced (1080i) format, but there are notable exceptions -- the ABC and FOX national broadcast networks, ESPN's national HD channels, and FOX's regional HD sports network channels all broadcast in the 720-line progressive format (720p).

The existence of multiple HD formats is sometimes a source of confusion for consumers who are just starting to learn about HDTV. Considering that most of us have grown up with a single, narrowly defined national TV standard, that confusion is understandable -- but it's most definitely not a bad thing.

The first and most important thing to know is that the existence of these multiple HDTV formats should not be cause for concern about system incompatibilities or premature obsolescence. The way the multi-standard HDTV approach has been implemented, video sources and HDTV displays are designed to recognize and deal with the reality of multiple formats and to ensure that consumers are able to view all available high-definition and standard-definition content, regardless of whether it's delivered as 720p, 1080i or 480i.

Still, you might be thinking it would have been better to have just a single, universal HDTV format. Hold that thought.

A big part of the rationale for a multi-format standard was to address the conflicting needs and desires of the companies and industries who collaborated in the mid-1990s to create the new HD specification. In particular, there were irreconcilable differences between the old-school TV networks and the relatively upstart, but opportunity-minded personal computer industry.

Several of the TV industry representatives involved in the process insisted that the new standard should be built on a foundation of interlaced video, so that picture resolution could be maximized within the finite bandwidth allocated to TV stations for over-the-air broadcasting; on the other side, the computer guys were absolutely wedded to progressive video, due to how video standards had evolved in the PC industry.

These industry-versus-industry differences ultimately led to the decision to have two primary HD delivery formats -- 1080i for the traditionalists and 720p for the newcomers.

Although the 1080-line progressive (1080p) format was also given the seal of approval as part of the original standards-setting process, it wasn't really viewed as a consumer format, at least not to begin with. This was due to the fact that 1080p was then considered to be too bandwidth-intensive to be viable for over-the-air broadcasters or cable/satellite networks. And after all, broadcast, cable and satellite were the main vehicles then envisioned for the delivery of HD programming.

As a result, 1080p was viewed as a format that would be used primarily for production purposes -- for example, for content mastering and archiving. It's only in recent years, with the development of much more efficient digital video compression, that 1080p has become viable for the consumer market.

The fact that 1080p turned out to be a convenient afterthought demonstrates the ultimate wisdom in taking a flexible approach to deciding HDTV standards: technology is simply changing too quickly to adopt inflexible, one-size-fits-all rules.

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