Controversy marks the evolution of advanced TV standards

Electronic News, Sept 18, 1995 by David B. Hack

Washington--A top Apple Computer executive attacked Grand Alliance advanced television (ATV) proposals at the sixth Digital Systems Information Exchange but his remarks about the work of the Federal Communication Commission's (FCC) ATV advisory committee (ACATS) and the Grand Alliance of television manufacturers provoked strong comment and rebuttal, both at the recent conference where they were made and since.

The remarks by Donald A. Norman, Apple's advanced technology group VP, keynoted a meeting of 75 industry and government leaders to discuss existing viewpoints and guide standards development for future digital video systems. The meeting was jointly convened by the U.S. Activities division of the Institute of Electrical and Electronic Engineers (IEEE-USA) and the Society of Motion Picture and Television Engineers (SMPTE).

The IEEE and the SMPTE held the conference to see what remains to be done in working toward standards for interoperability between and among signals intended for over-the-air broadcast of advanced digital television (ADTV) and those of the various networks of the developing National Information Infrastructure (NII).

IEEE-USA reports of the meeting indicate that Dr. Norman outlined four technical considerations central to the presentation of computer graphics on digital television displays and digital television on computer displays: interlace versus progressive scanning; refresh rates; pixel aspect ratios; and allowance for inclusion of data and program code in the video program stream.

Dr. Norman said that, in order to present text and data legibly, screens must have high resolution and square pixels and be progressively scanned and frequently refreshed.

He explicated a familiar case against interlace, saying that it causes great problems in joining digital video data streams with multimedia and Internet functions (such as browsing in hypertext). In addition, Dr. Norman said that very high picture refresh rates, at least 70 per second, are required to eliminate brightness flicker on large screens. He suggested a compromise standard of 24 frames per second, the same as feature films, to allow for simple conversion of other schemes already in use and easy conversion by integer multiples, up to 72 frames per second.

In rebuttal, SMPTE president Stanley Baron (of NBC), who chairs an International Telecommunications Union (ITU) task force on international digital television standards, defended the Grand Alliance ATV proposals and argued that they allow for versatility, affordability and compatibility between wireless services, computer applications, and wired communications media.

Mr. Baron said that he disagreed with about everything Dr. Norman said. "I've been involved in digital television for over 30 years. I've tackled some of these insurmountable problems and I've found that they are not insurmountable," he stated.

"The Grand Alliance system was broadened," Mr. Baron continued, "to accommodate a broad spectrum of applications. Some people who have more narrowly focused goals feel that some of the things it provides should be taken out of the system because they're contrary to their business requirements.

"In the specific issue of interlace, if you've dealt with discrete cosine transforms, and you have a limited data space, you soon run out of data space for the high-motion, high-detail case."

Mr. Baron said that the standard technique is to go with subsampling. One of the best understood methods of subsampling is interlace. One way of looking at the Grand Alliance system is that all of the offerings are progressive scan, except that they've agreed on one method of subsampling in those conditions where the data channel is overwhelmed. "So you have the progressive scan system. I can't understand why you can't allow high-motion, high-detail content to use interlace."

Mr. Baron described the structure of digital information systems in terms of modules that provide audio and image source coding, multiplexing and transport, and the channel coding and modulation schemes related to the transport medium. He reminded the audience that the ATV standard is a transmission and transport standard, not a display standard.

Mr. Baron provided a list of ITU recommendations and proposed standards which define each of the above modules. He covered steps taken by his task force to provide harmonization and interoperability among wireless services, computer applications and wired communications media. He then described how the proposed ATV standards for the U.S. comply with the ITU requirements.

Mr. Baron described how systems based on the multiplex structure of the MPEG-2 transport stream are "designed to interface cleanly with ATM-switched network environments and contain sufficient tools to provide a clean interface with computer-imaging applications."

He continued, "The number of MPEG-2 imaging engines offered at the SIGGRAPH meeting in July demonstrates the acceptance of that standard by the computer industry.

"All of the work that has (been done) in the advisory committee, all of the work in the ATSC, comports completely with the work of the ITU, and vice versa. We're not just choosing a national system for a national information infrastructure or local infrastructure. One can look at it as an information infrastructure that will work for everybody."