Within the government the Department of Defense (DoD), the Defense Advanced Research Projects Agency (DARPA), the National Aeronautics and Space Agency (NASA) and the National Institute of Standards and Technology (NIST) have been researching HDTV for several years, drawing upon the expertise of American industry and academia, to develop standards and prototype technology that balance the special needs of military imaging with the need for affordable, commercial technology. The experts believe today's 720p standard delivers the best image quality at the lowest practical bandwidth, with the fewest image artifacts. HDTV 720p technology is now commercially available at prices comparable to the older interlace technology. This note addresses the adoption of the progressive scanning format (720p) over older interlaced formats for use in future systems and integration into the DoD.

The Department's standards also support a migration to a 1080 progressive scanning format (1080p) as it becomes commercially viable. These standards allow reception of signals from all progressive scanning and interlace HDTV formats, thereby promoting interoperability. Similarly, American HDTV manufacturers are building dual-compatible equipment that supports both the 720p progressive and the1080i interlace formats. However, the DoD does not allow for the production and dissemination of source material in the 1080i HDTV interlace format because the experts determined that it has significant motion image impairment and an inefficient use of scarce bandwidth, both issues of concern for military missions and applications.

The International Telecommunications Union adopted the 1920x1080 progressive scan format as its voluntary standard. The older 1080 interlace portion of the ITU standard dates from 1986 and has not kept pace with the exciting American advances in imaging technology. These advances allow for "technological leap-frog" by bypassing the older interlace format for newer, all-digital, progressive scanning technology. For many of these same reasons, Disney, ABC Television, Fox Television, and the computer industry have adopted the 720p format.

The Department of Defense published DoD/IC/USIGS standards explicitly support 1080 progressive scanning formats, which are endorsed in the ITU voluntary recommendation (ITU-R BT.709-3). The DoD/IC/USIGS standards also allow 720 progressive formats (720p) since 1080 progressive technology is not commercially mature or viable at this time. 1080 progressive technology should be commercially available in approximately five years. The 720p standard was specifically adopted for DoD implementations because it delivers superior quality, artifact-free high resolution images as compared to 1080 interlace images. 720p production equipment can be purchased today, using commercial-off-the-shelf (COTS) technology, at fair market prices comparable to 1080 interlace systems. Since 720p display technology is directly compatible with computer displays, it can be purchased at significantly lower prices than 1080 interlace display systems, with resultant cost savings for the DoD.

Backwards compatibility and interoperability with first generation (18 year old technology) commercial HDTV signals, such as 1080 interlace, is rightfully a DoD concern. The DoD/IC/USIGS VWG standards allow for, if mission needs so dictate, the reception of first generation 1080 interlace signals. This means that the DoD will be able to receive any HDTV signal, from any source (first generation interlace or second generation progressive scan). As already mentioned, the DoD standard does not support the production or generation of 1080 interlace scan for military operations because of its significant motion image impairment artifacts. Such interlace artifacts may lead to the loss of critical intelligence information. Another negative attribute of 1080 interlace is its inefficient use of scarce communications bandwidth. Military missions and applications need the best and most affordable combination of high image quality and efficient bandwidth utilization.

The material that follows delves deeper into DoD detailed technical considerations as regards frequently asked questions (FAQs); it is accompanied with illustrative diagrams and supportive data.

The 1080i format does not provide better picture resolution, nor does it double the resolution of the 720p format. Of the two recognized commercial technology formats for high definition television (HDTV), 720p is the HDTV format that yields the best quality images with the fewest image artifacts. Progressive scan formats compress more efficiently thereby providing a higher quality image to the end user.

The confusion over the differences between different HDTV formats is in large part due to the technically incorrect and exaggerated performance embodied in the very name given to the first generation of interlace HDTV which is called 1080 interlace. The 1080 interlace name was chosen more for its historical similarity with legacy analog standard definition technologies and is essentially an analog marketing description rather than a technical description. One technically correct and temporally normalized description of this signal is 1920x540x60 (1920 horizontal pixels by 540 vertical pixels scanned 60 times every second). The 1080 interlace description is misleading in the ITU-R BT.709-3 standards document because the 1920x1080 interlace raster is identified as 2:1 scanning … here 2:1 means that the 1080 vertical lines are divided by 2: 1080/2= 540. When 1080 interlace is properly characterized as 1920x540x60, it is recognized that 1280x720x60p (1280 horizontal pixels by 720 vertical pixels 60 times every second) delivers greater vertical resolution than 1920x540x60 (720 is better than 540). Interlace proponents claim falsely that 1080 interlace delivers full spatial resolution (1080 lines) while at the same time delivering full temporal resolution (60th of a second). For this reason, these FAQ's will use the term 540/60i to describe the 1080 interlace signal.

A comparison of 1080i (really 540/60i lines) versus 720/60p, which actually delivers 720 lines, is depicted in the following diagram:

To address image pixel counts from a theoretical perspective, 1920x540x60 creates approximately 62 million interlace distorted pixels each second, where 1280x720x60 progressive delivers approximately 55 million crystal-clear pixels each second. Theoretically, the interlace system could produce 13 percent more raw horizontal pixels prior to compression. Theory aside, there are few if any 1920 horizontal pixel systems currently in use today. Manufacturers claim they will deliver 1920 horizontal resolution systems sometime after the year 2000. Until then, the majority of current interlace HDTV systems produce only 1440 horizontal pixels. Furthermore, these same systems actually only generate 1035 2:1 interlace scan lines (1440 x 1035 interlace was a principle technology of the now obsolete and soon-to-be-discontinued national Japanese analog HTDV system). Therefore, images that are today touted as 1080 interlace are actually 1440 x 1035/2 x 60, which equals only 45 million pixels per second. The DoD standard of 1280x720x60 delivers a true count of 55 million pixels each second which is 22% more pixels than what is touted and being marketed as 1080 interlace.

Furthermore, it is fundamentally the quality of the pixels that matter, not the simple raw pixel count. The process of interlace scan image interleaving introduces significant artifacts (clearly visible damage to the image). In the interlace picture illustration above you can see the damage that is done to any part of the image that has any motion. For critical DoD imagery functions, such artifacts are clearly discernable and undesirable. 720 progressive scan has virtually no distortion artifacts, whereas 540/60i has distortion artifacts throughout the image caused by the interlacing scan lines. These interlace distortion artifacts show up in object motion, but also cause still image distortion artifacts on imagery details like herringbone or striped patterns. These interlace distortion artifacts obscure important data and can give the appearance of false data. Lastly, what is called 1080 interlace does not appear to the human eye as 1080 lines, but rather as something more like 700 lines. This known phenomenon is the so-called "Kell Factor," which acknowledges degradation caused by receiver interline flicker and motion during the scanning process. Therefore, 720p is the optimum choice from both a temporal quality and distortion free spatial quality point of view.

Progressive scanning motion imagery also yields significantly superior still image frames as compared to interlace still image frames. Superior quality still images extracted from motion imagery sensors is an important DoD Intelligence-Surveillance-Reconnaissance (ISR) requirement. Progressively scanned images are more "computer friendly" since computer displays are natively progressive built from square pixels, and whereas the majority of DoD/IC/USIGS motion imagery (video) exploitation activities are associated with computer processing systems, native-format progressive imagery will yield better image results for less cost. In December of 1996 the DoD promulgated policy to use progressive scanning imagery formats. This policy was expressed by the Honorable Dr. Paul Kaminski, then DoD Under Secretary for Acquisition and Technology and was submitted to the FCC as an input for the "FCC Fourth Report and Order" (24 December 1996), which launched the national standards for U.S. digital television. It is instructive to note that all professional still cameras and all DoD still imagery sensors generate progressive scan images. Theatrical motion picture film is also based on technology that is very closely represented by progressive scanning.

There is compelling technical evidence that interlace images are harder to digitally compress than are progressive images. Interlace images waste communications bandwidth. This bandwidth wastage can be intuitively understood by looking at the visible artifacts caused by interlace. To a digital compression system as used for HDTV these interlace artifacts produce the same effect as image noise. The more bits you use to code noise, the less bits you have remaining for image quality. Interlace distortion artifacts siphon off bandwidth that should be used to improve image quality.

Not all television stations and equipment manufacturers have opted for the 1080i format. The strongest proponents for the use of 1080 interlace HDTV technologies are NHK - the Japanese government sponsored television network - and SONY. There is significant American commercial interest and activity, most notably in the computer and entertainment industries, in progressive scan technology. Where many of the Japanese manufacturers have chosen to build only 540/60i, other Japanese manufacturers including Matsushita (Panasonic) are building 720p equipment. Many manufacturers are building dual compatible equipment, the same equipment supports both 720p and 540/60i. In the U.S., manufacturers like Tektronix, Leitch, and others are building systems that process both 720p and 540/60i. This is possible in large part because the Society of Motion Picture and Television Engineers (SMPTE) interface standard for HDTV as defined by the SMPTE 292M standard supports both 720p and 540/60i.

From an American perspective, the entertainment community has expressed strong opposition to the use of the 1080 interlace format because of its fundamental degradation of image quality. American computer manufacturers have publicly expressed opposition to use of the 1080i format because of its incompatibility with computer display systems which use progressive-only scanning formats. In the initial public debates over HDTV, American computer manufacturing interests pushed for the use of 480 progressive formats (which they call HD0) as a low cost and initial implementation of digital television. While actually building and shipping 480p systems today, 720p has been adopted and promoted in the Intel / Microsoft / Compaq / Lucent DTV technology roadmap called HD0+ (and HD1). This technology roadmap has been incorporated into the internationally adopted PC-99 open computer manufacturing specification: "PC 99 System Design Guide, A Technical Reference for Designing PCs and Peripherals for the Microsoft Windows Family of Operating Systems" authored by Intel Corporation and Microsoft Corporation. This means that all new specification compliant computers built anywhere in the world will have the ability to process and display 720 progressive images. Starting in 1999 the American computer industry will start shipping thousands if not millions of computers with native 720p capabilities. The PC-99 specification does not mandate the display of 1080 (really 540/60i) interlace.

Of equal importance is the fact that 720p image processing functionality is planned as a core technology of the next generation of the Microsoft Windows NT operating system. Windows NT already functions as a certified workstation implementation of the DoD DII/COE information technology architecture. This combination of new PC-99 hardware (or low cost add in boards) and DoD approved and certified DII/COE software means that 720p HDTV quality battlespace imagery can be processed by every future DII/COE workstation for little or no additional cost. The adoption of the 720p HDTV standard can therefore be seen as an extremely important, long term plan to save millions of American tax dollars.

There is considerable breadth of 720p equipment that is commercially available today. Included is a list of 720p manufacturers and their equipment types that were available at the April 1998 National Association of Broadcasters (NAB) Convention in Las Vegas, Nevada. There will be even more 720p equipment available at the 1999 NAB Convention. It is also important to note that 1080 interlace proponents are planning to move away from 1080i and move towards 1080 progressive scan. SONY as the predominant manufacturer of 1080 interlace equipment has announced that they will begin producing 1080 progressive scan systems using a 24 frames per second refresh rate. This watershed announcement may very well sound the death knell for 1080i, even though 1080/24p equipment will not be available for three to five years.

As this FAQ points out, there is mis-information generated by interlace proponents concerning the relative merits of 540/60i versus 720p formats. The language of the DoD/IC/USIGS VWG HDTV standard includes 1080/24p, 1080/30p, and 720/60p formats. The VWG standards also note that when 1080/50p and 60p technology becomes more mature (and thus more affordable), the DoD standards will migrate to 1080/50p and 1080/60p.

It is instructive to note that the commercial marketplace this past 1998 holiday season rolled out expensive first generation consumer grade HDTV receivers that use conventional analog CRT scanning to display either 1080i or 480p. The simple reason for both is that 480p and 1080i (540/60i) use similar technology to produce images that are very similar in image quality. For next generation, all progressive display technologies, such as high resolution flat panels and solid-state projectors, which are seen by many as the true future display technology for HDTV, 720p delivers significantly improved images.

The simplest way to consider the relative maturity and thus future application of HDTV technology is as follows. Consider that 1080i (1035i) was introduced over 18 years ago and can be considered to be the first generation of HDTV, based in large part on analog techniques. 720p technology can be correctly characterized as the second generation of HDTV, delivering superior images, using less bandwidth, at a price point comparable to or less expensive than interlace technology. Therefore, from a long term financial investment point of view 720p is better than 1080i because 720p will be the future HD imaging standard for some time to come, whereas 1080 interlace is at best an interim technology, built upon legacy equipment and standards, and serves only as a temporary measure arrived at before 720p was a viable alternative. When computer "friendliness" is considered, 720p technology is significantly less expensive than interlace technology. As technology advances permit even higher bandwidth and processing power, the advent of all progressive, higher resolution formats such as 1080 progressive will usher in the third generation of HDTV.

The DoD has made a conscious effort to leap-frog over the older and less capable interlace HDTV first generation and move directly into the affordable and now commercially available progressive HDTV second generation. The DoD is therefore leveraging almost two decades of industrial research and development that lead first to 1080i and now has lead to 720p. The DoD is also actively pursuing R&D activities that will advance the state of DoD technology into the third generation of HDTV, based on 1080 progressive technology.

As final proof that 720p is and will remain a commercially viable imaging format, please note that both Disney's ABC Television Network and the FOX Television Network have announced that they will be using 720p as their HDTV broadcast formats. The NBC Television Network and the CBS Television Network, one of the strongest proponents of 1080 interlace, have indicated that all-progressive scan imagery is the future end point that they are targeting.

The ITU recommendation calls for 1080 progressive scan video, while it also supports the legacy analog technology representations of 1035 interlace and its derivative 1080 interlace. When interlace proponents claim that there is universal acceptance of ITU-R BT.709-3 (1920x1080), yes, there is universal acceptance for the future of 1080 progressive scan. There is not universal acceptance of interlace scan. Please also note that the ITU is actively considering newer, more modern standards which include 720p formats. The ITU-R BT.709.3 voluntary recommendation concerning 1080 interlace is based on technology that is now 18 years old. The interlace portions of the ITU-R BT.709-3 recommendation have not kept pace with the state-of-the-art of advanced all-progressive imaging technology.

After almost two years of research and discussions with industry, academic, and government organizations, the clear government community consensus was that progressive scanning was the most correct choice for DoD/IC/USIGS applications. In the course of its research, the DoD/IC/USIGS Video Working Group proactively sought comments from commercial industry about the most affordable, highest quality standards for high definition video. The DoD feels that its chosen HDTV standards successfully balance the special needs of military imaging with technology that is commercially available and affordable.

All of the DoD/IC/USIGS VWG motion imagery standards are based on commercial technology, using due-process approved American National Standards (primarily SMPTE standards), or internationally recognized ISO standards. The 720 progressive format is explicitly allowed, endorsed, and recognized by the Advanced Television Systems Committee (ATSC) documents as true high definition television. Today's 720 progressive format has been selected by WDI and its ABC Television Network as its HDTV format. The Fox television network has selected 480 and 720 progressive scan as its formats. Other world-wide broadcasters are also considering progressive scan formats. Of critical interest to American competitive interests, the 720 progressive format has been explicitly endorsed and specified by the Microsoft / Intel / Compaq / Lucent "HD0+/HD1" technology roadmap and has been incorporated into the world-wide PC-99 specification for all new computers.

It is envisioned that 720/60p high definition video sensors will form the basis for a technological leap-frog, allowing the initial DoD implementation of HDTV battlespace applications to bypass the first interlace generation and move into the second, all-digital, progressive imagery generation. This is completely in the spirit of Joint Vision 2010 directives to migrate to "dominant battlespace awareness" as a key tenant of future intelligence support to the military. Such applications will include manned and unmanned aerial, ground, sea and sub surface ISR activities.

Today 720p delivers the best image quality at the lowest practical bandwidth, with the fewest image artifacts, and thus delivers the best "bang for the buck" to the American taxpayer. When 1080p technology is commercially available and stable, DoD plans to actively pursue this imaging format. The DoD has several 1080/60p camera/sensor technologies under research and development, with expected initial tests in mid-1999. The adoption of progressive scan technology is an important policy decision that truly positions the DoD to accomplish one of its most critical Joint Vision 2010 objectives: achieve Information Superiority and Dominant Battlespace Awareness.