Multiple sub-Nyquist sampling encoding

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MUSE (Multiple sub-Nyquist sampling encoding), was an analog high-definition television system, using dot-interlacing and digital video compression to deliver 1125-line (1920x1035 [1] ) high definition video signals to the home. Japan had the earliest working HDTV system, MUSE, which was named Hi-Vision [2] (a contraction of HIgh-definition teleVISION) with design efforts going back to 1979. The country began broadcasting wideband analog HDTV signals in 1989 using 1035 active lines interlaced in the standard 2:1 ratio (1035i) with 1125 lines total. By the time of its commercial launch in 1991, digital HDTV was already under development in the United States. Hi-Vision continued broadcasting in analog until 2007.

Contents

The system was standardized as ITU-R recommendation BO.786. [3]

MUSE video was often produced using Sony HDVS equipment. MUSE video was interlaced, 60 field-per-second (1125i60) video. [2]

History

MUSE, a compression system for Hi-Vision signals, was developed by NHK Science & Technology Research Laboratories in the 1980s, employed 2-dimensional filtering, dot-interlacing, motion-vector compensation and line-sequential color encoding with time compression to 'fold' an original 20 MHz source Hi-Vision signal into a bandwidth of 8.1 MHz.

Modulation research

Hi-Vision was mainly broadcast by the NHK through their BShi satellite TV channel.

Technical specifications

DPCM Audio compression format: DPCM quasi-instantaneous companding

MUSE is a 1125 line system (1035 visible), and is not pulse and sync compatible with the digital 1080 line system used by modern HDTV. Originally, it was a 1125 line, interlaced, 60 Hz, system with a 5/3 (1.66:1) aspect ratio and an optimal viewing distance of roughly 3.3H.

For terrestrial MUSE transmission a bandwidth limited FM system was devised. A satellite transmission system uses uncompressed FM.

The pre-compression bandwidth for Y is 20 MHz, and the pre-compression bandwidth for chrominance is a 7.425 MHz carrier.

The Japanese initially explored the idea of frequency modulation of a conventionally constructed composite signal. This would create a signal similar in structure to the Y/C NTSC signal - with the Y at the lower frequencies and the C above. Approximately 3 kW of power would be required, in order to get 40 dB of signal to noise ratio for a composite FM signal in the 22 GHz band. This was incompatible with satellite broadcast techniques and bandwidth.

To overcome this limitation, it was decided to use a separate transmission of Y and C. This reduces the effective frequency range and lowers the required power. Approximately 570 W (360 for Y and 210 for C) would be needed in order to get a 40 dB of signal to noise ratio for a separate Y/C FM signal in the 22 GHz satellite band. This was feasible.

There is one more power saving that appears from the character of the human eye. The lack of visual response to low frequency noise allows significant reduction in transponder power if the higher video frequencies are emphasized prior to modulation at the transmitter and then de-emphasized at the receiver. This method was adopted, with crossover frequencies for the emphasis/de-emphasis at 5.2 MHz for Y and 1.6 MHz for C. With this in place, the power requirements drop to 260 W of power (190 for Y and 69 for C).

Sampling systems and ratios

The subsampling in a video system is usually expressed as a three part ratio. The three terms of the ratio are: the number of brightness ("luminance" "luma" or Y) samples, followed by the number of samples of the two color ("chroma") components: U/Cb then V/Cr, for each complete sample area. For quality comparison, only the ratio between those values is important, so 4:4:4 could easily be called 1:1:1; however, traditionally the value for brightness is always 4, with the rest of the values scaled accordingly.

Chroma subsampling ratios.png

Sometimes, four part relations are written, like 4:2:2:4. In these cases, the fourth number means the sampling frequency ratio of a key channel. In virtually all cases, that number will be 4, since high quality is very desirable in keying applications.

The sampling principles above apply to both digital and analog television.

MUSE implements a variable sampling system of ~4:2:1 ... ~4:0.5:0.25 depending on the amount of motion on the screen. Thus the red-green component (V, or Cr) has between one-half and one-eighth the sampling resolution of the brightness component (Y), and the blue-yellow (U, or Cb) has half the resolution of red-green, a relationship that is too complex to easily depict using the diagram above.

Audio subsystem

MUSE had a discrete 2- or 4-channel digital audio system called "DANCE", which stood for Digital Audio Near-instantaneous Compression and Expansion.

It used differential audio transmission (differential pulse-code modulation) that was not psychoacoustics-based like MPEG-1 Layer II. It used a fixed transmission rate of 1350 kbp/s. Like the PAL NICAM stereo system, it used near-instantaneous companding (as opposed to Syllabic-companding like the dbx system uses) and non-linear 13-bit digital encoding at a 32 kHz sample rate.

It could also operate in a 48 kHz 16-bit mode. The DANCE system was well documented in numerous NHK technical papers and in a NHK-published book issued in the USA called Hi-Vision Technology.

The DANCE audio codec was superseded by Dolby AC-3 (a.k.a. Dolby Digital), DTS Coherent Acoustics (a.k.a. DTS Zeta 6x20 or ARTEC), MPEG-1 Layer III (a.k.a. MP3), MPEG-2 Layer I, MPEG-4 AAC and many other audio coders. The methods of this codec are described in the IEEE paper: [11]

Real world performance issues

MUSE had a four-field dot-interlacing cycle, meaning it took four fields to complete a single MUSE frame. Thus, stationary images were transmitted at full resolution. However, as MUSE lowers the horizontal and vertical resolution of material that varies greatly from frame to frame, moving images were blurred. Because MUSE used motion-compensation, whole camera pans maintained full resolution, but individual moving elements could be reduced to only a quarter of the full frame resolution. Because the mix between motion and non-motion was encoded on a pixel-by-pixel basis, it wasn't as visible as most would think. Later, NHK came up with backwards compatible methods of MUSE encoding/decoding that greatly increased resolution in moving areas of the image as well as increasing the chroma resolution during motion. This so-called MUSE-III system was used for broadcasts starting in 1995 and a very few of the last Hi-Vision MUSE LaserDiscs used it ("The River" is one Hi-Vision LD that used it). During early demonstrations of the MUSE system, complaints were common about the decoder's large size, which led to the creation of a miniaturized decoder. [10]

MUSE's "1125 lines" are an analog measurement, which includes non-video "scan lines" during which a CRT's electron beam returns to the top of the screen to begin scanning the next field. Only 1035 lines have picture information. Digital signals count only the lines (rows of pixels) that have actual detail, so NTSC's 525 lines become 486i (rounded to 480 to be MPEG compatible), PAL's 625 lines become 576i, and MUSE would be 1035i. To convert the bandwidth of Hi-Vision MUSE into 'conventional' lines-of-horizontal resolution (as is used in the NTSC world), multiply 29.9 lines per MHz of bandwidth. (NTSC and PAL/SECAM are 79.9 lines per MHz) - this calculation of 29.9 lines works for all current HD systems including Blu-ray and HD-DVD. So, for MUSE, during a still picture, the lines of resolution would be: 598-lines of luminance resolution per-picture-height. The chroma resolution is: 209-lines. The horizontal luminance measurement approximately matches the vertical resolution of a 1080 interlaced image when the Kell factor and interlace factor are taken into account.

Shadows and multipath still plague this analog frequency modulated transmission mode.

Japan has since switched to a digital HDTV system based on ISDB, but the original MUSE-based BS Satellite channel 9 (NHK BS Hi-vision) was broadcast until September 30, 2007.

Cultural and geopolitical impacts

Internal reasons inside Japan that led to the creation of Hi-Vision

MUSE, as the US public came to know it was initially covered the magazine Popular Science in the mid-1980s. The US television networks did not provide much coverage of MUSE until the late 1980s, as there were very few public demonstrations of the system outside Japan.

Because Japan had its own domestic frequency allocation tables (that were more open to the deployment of MUSE) it became possible for this television system to be transmitted by Ku Band satellite technology by the end of the 1980s.

The US FCC in the late 1980s began to issue directives that would allow MUSE to be tested in the US, providing it could be fit into a 6 MHz System-M channel.

The Europeans (in the form of the European Broadcasting Union (EBU)) were impressed with MUSE, but could never adopt it because it is a 60 Hz TV system, not a 50 Hz system that is standard in Europe and the rest of the world (outside the Americas and Japan).

The EBU development and deployment of B-MAC, D-MAC and much later on HD-MAC were made possible by Hi-Vision's technical success. In many ways MAC transmission systems are better than MUSE because of the total separation of colour from brightness in the time domain within the MAC signal structure.

Like Hi-Vision, HD-MAC could not be transmitted in 8 MHz channels without substantial modification and a severe loss of quality and frame rate. A 6 MHz version Hi-Vision was experimented with in the US, but it too had severe quality problems so the FCC never fully sanctioned its use as a domestic terrestrial television transmission standard.

The US ATSC working group that had led to the creation of NTSC in the 1950s was reactivated in the early 1990s because of Hi-Vision's success. Many aspects of the DVB standard are based on work done by the ATSC working group, however most of the impact is in support for 60 Hz (as well as 24 Hz for film transmission) and uniform sampling rates and interoperable screen sizes.

Device support for Hi-Vision

Hi-Vision LaserDiscs

On May 20, 1994, Panasonic released the first MUSE LaserDisc player. [12] There were a few MUSE LaserDisc players available in Japan: Pioneer HLD-XØ, HLD-X9, HLD-1000, HLD-V500, HLD-V700; Sony HIL-1000, HIL-C1 and HIL-C2EX; the last two ones have OEM versions made by Panasonic, LX-HD10 and LX-HD20. These could play Hi-Vision as well as standard NTSC LaserDiscs. Hi-Vision LaserDiscs are extremely rare and expensive.

The HDL-5800 Video Disc Recorder recorded both high definition still images and continuous video onto an optical disc and was part of the early analog wideband Sony HDVS high-definition video system which supported the MUSE system. Capable of recording HD still images and video onto either the WHD-3AL0 or the WHD-33A0 optical disc; WHD-3Al0 for CLV mode (up to 10 minute video or 18,000 still frames per side); WHD-33A0 for CAV mode (up to 3 minute video or 5400 still frames per side).

The HDL-2000 was a full band high definition video disc player.

Video cassettes

W-VHS allowed home recording of Hi-Vision programmes.

See also

The analog TV systems these systems were meant to replace:

Related standards:

Related Research Articles

Analog television Television that uses analog signals

Analog television is the original television technology that uses analog signals to transmit video and audio. In an analog television broadcast, the brightness, colors and sound are represented by amplitude, phase and frequency of an analog signal.

Digital television transmission of television audiovisual signals using digital encoding

Digital television (DTV) is the transmission of television audiovisual signals using digital encoding, in contrast to the earlier analog television technology which used analog signals. At the time of its development it was considered an innovative advancement and represented the first significant evolution in television technology since color television in the 1950s. Modern digital television is transmitted in high definition (HDTV) with greater resolution than analog TV. It typically uses a widescreen aspect ratio in contrast to the narrower format of analog TV. It makes more economical use of scarce radio spectrum space; it can transmit up to seven channels in the same bandwidth as a single analog channel, and provides many new features that analog television cannot. A transition from analog to digital broadcasting began around 2000. Different digital television broadcasting standards have been adopted in different parts of the world; below are the more widely used standards:

NTSC Analog color television system developed in the United States

The abbreviation NTSC can refer to the National Television System Committee, which developed the analog television color system that was introduced in North America in 1954 and stayed in use until digital conversion. NTSC is also an abbreviation for the National Television Standards Committee, a subset of the National Television System Committee that was responsible for producing the detailed technical specifications for the transmission standard. It is one of three major analog color television standards, the others being PAL and SECAM.

PAL Colour encoding system for analogue television

Phase Alternating Line (PAL) is a colour encoding system for analogue television used in broadcast television systems in most countries broadcasting at 625-line / 50 field per second (576i). It was one of three major analogue colour television standards, the others being NTSC and SECAM.

SECAM French analog color television system

SECAM, also written SÉCAM, is an analog color television system first used in France. It was one of three major color television standards, the others being PAL and NTSC.

Interlaced video

Interlaced video is a technique for doubling the perceived frame rate of a video display without consuming extra bandwidth. The interlaced signal contains two fields of a video frame captured consecutively. This enhances motion perception to the viewer, and reduces flicker by taking advantage of the phi phenomenon.

Chroma subsampling is the practice of encoding images by implementing less resolution for chroma information than for luma information, taking advantage of the human visual system's lower acuity for color differences than for luminance.

ITU-R Recommendation BT.601, more commonly known by the abbreviations Rec. 601 or BT.601 is a standard originally issued in 1982 by the CCIR for encoding interlaced analog video signals in digital video form. It includes methods of encoding 525-line 60 Hz and 625-line 50 Hz signals, both with an active region covering 720 luminance samples and 360 chrominance samples per line. The color encoding system is known as YCbCr 4:2:2.

The Integrated Services Digital Broadcasting is a Japanese standard for digital television (DTV) and digital radio used by the country's radio and television networks. ISDB supersedes both the NTSC-J analog television system and the previously used MUSE Hi-vision analog HDTV system in Japan as well as the NTSC, PAL-M, and PAL-N broadcast standards in South America and the Philippines. Digital Terrestrial Television Broadcasting (DTTB) services using ISDB-T started in Japan in December 2003 and Brazil in December 2007 as a trial. Since then, many countries have adopted ISDB over other digital broadcasting standards.

Advanced Television Systems Committee (ATSC) standards are an American set of standards for digital television transmission over terrestrial, cable and satellite networks. It is largely a replacement for the analog NTSC standard and, like that standard, is used mostly in the United States, Mexico, Canada, and South Korea. Several former NTSC users, in particular Japan, have not used ATSC during their digital television transition, because they adopted their own system called ISDB.

Serial digital interface

Serial digital interface (SDI) is a family of digital video interfaces first standardized by SMPTE in 1989. For example, ITU-R BT.656 and SMPTE 259M define digital video interfaces used for broadcast-grade video. A related standard, known as high-definition serial digital interface (HD-SDI), is standardized in SMPTE 292M; this provides a nominal data rate of 1.485 Gbit/s.

Broadcast television systems are the encoding or formatting standards for the transmission and reception of terrestrial television signals. There were three main analog television systems in use around the world until the late 2010s: NTSC, PAL, and SECAM. Now in digital terrestrial television (DTT), there are four main systems in use around the world: ATSC, DVB, ISDB and DTMB.

HD-MAC was a proposed broadcast television systems standard by the European Commission in 1986, a part of Eureka 95 project. It is an early attempt by the EEC to provide High-definition television (HDTV) in Europe. It is a complex mix of analogue signal, multiplexed with digital sound, and assistance data for decoding (DATV). The video signal was encoded with a modified D2-MAC encoder.

576i Standard-definition video mode

576i is a standard-definition video mode originally used for terrestrial television in most countries of the world where the utility frequency for electric power distribution is 50 Hz. Because of its close association with the colour encoding system, it is often referred to as simply PAL, PAL/SECAM or SECAM when compared to its 60 Hz NTSC-colour-encoded counterpart, 480i. In digital applications it is usually referred to as "576i"; in analogue contexts it is often called "625 lines", and the aspect ratio is usually 4:3 in analogue transmission and 16:9 in digital transmission.

High-definition video is video of higher resolution and quality than standard-definition. While there is no standardized meaning for high-definition, generally any video image with considerably more than 480 vertical scan lines or 576 vertical lines (Europe) is considered high-definition. 480 scan lines is generally the minimum even though the majority of systems greatly exceed that. Images of standard resolution captured at rates faster than normal, by a high-speed camera may be considered high-definition in some contexts. Some television series shot on high-definition video are made to look as if they have been shot on film, a technique which is often known as filmizing.

PCM adaptor encodes digital audio as video

A PCM adaptor is a device that encodes digital audio as video for recording on a videocassette recorder. The adapter also has the ability to decode a video signal back to digital audio for playback. This digital audio system was used for mastering early compact discs.

Multiplexed Analogue Components

Multiplexed analogue components (MAC) was a satellite television transmission standard, originally proposed for use on a Europe-wide terrestrial HDTV system, although it was never used terrestrially.

Analog high-definition television has referred to a variety of analog video broadcast television systems with various display resolutions throughout history.

Television standards conversion is the process of changing a television transmission or recording from one television system to another. The most common is from NTSC to PAL or the other way around. This is done so television programs in one nation may be viewed in a nation with a different standard. The video is fed through a video standards converter, which makes a copy in a different video system.

High-definition television (HD) describes a television system providing an image resolution of substantially higher resolution than the previous generation of technologies. The term has been used since 1936, but in modern times refers to the generation following standard-definition television (SDTV), often abbreviated to HDTV or HD-TV. It is the current de facto standard video format used in most broadcasts: terrestrial broadcast television, cable television, satellite television, and Blu-ray Discs.

References

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