Introduction to HD

Fujio, Takashi, J. Ishida, T. Komoto, and Taiji Nishizawa (1980), High definition television system – signal standards and transmission, SMPTE Journal, 89 (8): 579–584 (Aug.).

Fujio, Takashi (1981), “High definition television systems: desirable standards, signal forms, and transmission systems,” in IEEE Tr. Comm. 29 (12): 1882–1891 (Dec.).

Fujio, Takashi, et al. (1982), High Definition television, NHK Science and Technical Research Laboratories Technical Monograph 32 (June).

Developmental HD systems had 1125/60.00/2:1 scanning, an aspect ratio of 5:3, and 1035 active lines. The alternate 59.94 Hz field rate was added later. Aspect ratio was changed to 16:9 to achieve international agreement upon standards. A count of 1080 image rows was eventually agreed upon to provide square sampling. The developmental 1035i (1125/60) system, standardized in SMPTE 240M, was discussed in the first edition of this book.

This chapter outlines the 1280× 720 and 1920× 1080 image formats for high-definition (HD) television, and introduces the scanning parameters of the associated video systems such as 720p60 and 1080i30.

Today’s HD systems stem from research directed by Dr. Fujio at NHK (Nippon Hoso Kyokai, the Japan Broadcasting Corporation). HD has about twice the vertical and twice the horizontal resolution of conventional television, a picture aspect ratio of 16:9, at least two channels of CD-quality audio, and a frame rate of 23.976 Hz or higher. By my definition, HD has 3⁄4-million pixels or more. NHK conceived HD to have interlaced scanning; however, progressive HD systems have since emerged.

Studio HD has a sampling rate of 74.25 MHz, 5.5 times that of the BT.601 standard for SD. HD has

a pixel rate of about 60 megapixels per second. Apart from a few annoying exceptions, parameters of R’G’B’ coding are similar those of SD standards – in fact, several parameters adopted for HD in BT.709 have essentially been retrofitted into SD. Details concerning scanning, sample rates, and interface levels of HD will be presented in 1280× 720 HD on page 467 and 1920× 1080 HD on page 473. Unfortunately, the parameters for Y’CBCR colour coding for HD differ from the parameters for SD! Details will be provided in

Component video colour coding for HD, on page 369.

HD scanning

A great debate took place in the 1980s and 1990s concerning whether HD should have interlaced or

720p60

1280 × 720

1080p30,

1080i30

1920 × 1080

1650

In Numerology of HD scanning, on page 395, I explain the origin of the numbers in Figure 15.1.

progressive scanning. At given flicker and data rates, interlace offers some increase in static spatial resolution, as suggested by Figure 8.8 on page 91. Broadcasters have historically accepted the motion artifacts and spatial aliasing that accompany interlace, in order to gain some static spatial resolution. In the HD debate, the computer industry and the creative film community were resolutely set against interlace. Eventually, both camps compromised to some degree and HD standards were established to accommodate both interlaced and progressive image formats. To be commercially viable a receiver must decode both formats, though there is no “legal” requirement to do so.

Figure 15.1 above sketches the rasters of the 1 Mpx progressive system (1280× 720, 720p60) and the 2 Mpx interlaced system (1920× 1080, 1080i30) that were agreed upon. 1280× 720 is very simply related to 1920× 1080: 1280 is two thirds of 1920, and 720 is two thirds of 1080.

ATSC A/53, Digital Television

Standard.

In addition to the 1 Mpx (progressive) and 2 Mpx (interlaced) systems, several SD scanning systems and several additional frame rates were included in the ultimate ATSC standards for U.S. digital television (DTV). Table 15.1 summarizes the “18 formats” that are found in Table 3 of the ATSC’s A/53 standard.

The 1920× 1080 system was conceived as interlacedonly (1080i30), but was adapted to 24 and 30 Hz progressive scan (1080p24, 1080p30) using the standard 74.25 MHz sample rate. The adaptation to 24 Hz was seminal to digital cinema. Figure 15.2 overleaf sketches raster structures for 24 Hz and 25 Hz systems; Table 15.2 summarizes the scanning parameters.

In Sony’s legacy hdcam system, the 1920× 1080 image was downsampled to 1440× 1080, and colour difference signals were subsampled 3:1:1, prior to compression. This was an internal representation only; there was no corresponding uncompressed external interface standard. The current Sony hdcam sr format represents 1920× 1080 image data directly at 4:2:2 (or in some variations 4:4:4), and alleviates the need for such downsampling.

SMPTE ST 274 provides for carriage of a 1920× 1080 image at a frame rate of 25 Hz: 1125 total lines are