Multiple sub-nyquist sampling Encoding system
Encyclopedia
MUSE was a dot-interlaced digital video compression system that used analog modulation for transmission to deliver 1125-line high definition video signals to the home. Japan had the earliest working HDTV system, which was named Hi-Vision (a contraction of HIgh-definition teleVISION) with design efforts going back to 1979. The country began broadcasting wideband analog HDTV signals in the late 1980s using 1035 active lines interlaced in the standard 2:1 ratio (1035i) with 1125-lines total.

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.
  • Japanese broadcast engineers immediately rejected conventional vestigial sideband broadcasting.
  • It was decided early on that MUSE would be a satellite broadcast format as Japan economically supports satellite broadcasting.


Modulation research
  • The idea of frequency modulation of a conventionally constructed composite (Y+C, like NTSC
    NTSC
    NTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...

     and PAL
    PAL
    PAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...

    ) signal was first tested. This was called the HLO-PAL system which used a Phase Alternating by Line with Half-Line Offset carrier encoding of the wideband/narrowband chroma components. Only the very lowest part of the wideband chroma component overlapped the high-frequency chroma. The narrowband chroma was completely separated from luminance. HLO-PAF, with Phase Alternating by Field (like the first NTSC color system trial) was also experimented with, and gave much better decoding results, but NHK abandoned all composite encoding systems when work on dot-interlaced (a.k.a sub-Nyquist) encoding was started. As an interesting side-note, RCA's original 1949 (and FCC rejected) compatible color TV system proposal used horizontal dot-interlacing as a method of encoding the R-G-B color components, as did a variation of the CBS Field-Sequential color system - CBS proposed horizontal dot-interlacing in a desperate attempt to increase horizontal resolution. In television, frequency-interlacing, such as is done with the chroma/luma components in NTSC and PAL color, automatically leads to dot-interlacing - but in those cases, the interlacing is in the vertical direction. Without digital field storage of some sort for playback, horizontal dot-interlacing leads to too much shimmer, dot-crawl, field-flicker and spurious dot-patterns to make the process useful. And it only leads to about a .50% increase in actual resolution.
  • Separate transmission of Y and C components was explored. The MUSE format that is transmitted today uses separated component signalling. The improvement in picture quality was so great that the original test systems were recalled.
  • One more power saving tweak was made: 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 de-emphasized at the receiver.

Technical specifications

  • Aspect Ratio:16:9
  • Scanlines (active/total): 1,035/1,125
  • Pixels per line (approximately): 1060 (still image)/530 (moving)
  • Horizontal lines per picture height: 598 (black-and-white)/209 (chroma)
  • Interlaced ratio: 2:1
  • Refresh rate :59.94 (as with NTSC).
  • Sampling frequency for broadcast: 16.2 MHz
  • Vector motion compensation: horizontal ± 16 samples (32.4 MHz clock) / frame, a vertical line ± 3 / Field
  • Audio:48 kHz 16bit(2ch)/32 kHz 12bit(4ch:3.1)


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 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
Signal to Noise
Signal to Noise is a graphic novel written by Neil Gaiman and illustrated by Dave McKean. It was originally serialised in the UK style magazine The Face, beginning in 1989, and collected as a graphic novel in 1992, published by Victor Gollancz Ltd in the UK and by Dark Horse Comics in the US.The...

 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
Luminance
Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square...

  and C
Chroma
Chroma, the Greek word for color, may refer to:* Colorfulness or chroma, the perceived intensity of a specific color* Chrominance or chroma, one of the two components of a television signal* Chroma, a measure of color purity in the Munsell color system...

. 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
YUV
YUV is a color space typically used as part of a color image pipeline. It encodes a color image or video taking human perception into account, allowing reduced bandwidth for chrominance components, thereby typically enabling transmission errors or compression artifacts to be more efficiently...

) samples, followed by the number of samples of the two color ("chroma") components: U/Cb
YUV
YUV is a color space typically used as part of a color image pipeline. It encodes a color image or video taking human perception into account, allowing reduced bandwidth for chrominance components, thereby typically enabling transmission errors or compression artifacts to be more efficiently...

 then V/Cr
YUV
YUV is a color space typically used as part of a color image pipeline. It encodes a color image or video taking human perception into account, allowing reduced bandwidth for chrominance components, thereby typically enabling transmission errors or compression artifacts to be more efficiently...

, 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.



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.

Audio subsystem: digital audio near-instantaneous compression and expansion

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 (DPCM) 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 and many other audio coders.
The methods of this codec are described in the IEEE paper:

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).

MUSE's "1125 lines" are an analog measurement, which includes non-video "scan lines" during which a CRT
Cathode ray tube
The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...

'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
Kell factor
The Kell factor, named after RCA engineer Raymond D. Kell, is a parameter used to limit the bandwidth of a sampled image signal to avoid the appearance of beat frequency patterns when displaying the image in a discrete display devices, usually taken to be 0.7. The number was first measured in 1934...

 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

One could say that without Hi-Vision, there would be no modern digital HDTV. There is some latent truth in this, but you must look back in time 20 years when Japan was the world's "consumer electronics research heaven".

Internal reasons inside Japan that led to the creation of Hi-Vision
  • (1940s): The NTSC standard (as a 525 line monochrome system) was imposed by the US occupation forces.
  • (1950s-1960s): Unlike Canada (that could have switched to PAL), Japan was stuck with the US TV transmission standard regardless of circumstances.
  • (1960s-1970s): By the late 1960s many parts of the modern Japanese electronics industry had gotten their start by fixing the transmission and storage problems inherent with NTSC's design.
  • (1970s-1980s): By the 1980s there was spare engineering talent available in Japan that could design a better television system.


MUSE, as the US public came to know it was initially covered the magazine Popular Science
Popular Science
Popular Science is an American monthly magazine founded in 1872 carrying articles for the general reader on science and technology subjects. Popular Science has won over 58 awards, including the ASME awards for its journalistic excellence in both 2003 and 2004...

 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
Ku band
The Kμ band is a portion of the electromagnetic spectrum in the microwave range of frequencies. This symbol refers to —in other words, the band directly below the K-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
European Broadcasting Union
The European Broadcasting Union is a confederation of 74 broadcasting organisations from 56 countries, and 49 associate broadcasters from a further 25...

 (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 commonplace throughout the rest of the Old World.

The EBU development and deployment of B-MAC
B-MAC
B-MAC is a form of analog video encoding, specifically a type of B-MAC is a form of analog video encoding, specifically a type of B-MAC is a form of analog video encoding, specifically a type of (Multiplexed Analogue Components (MAC) encoding. MAC encoding was designed in the mid 80s for use with...

, D-MAC
D-MAC
Among the family of MAC or Multiplexed Analog Components systems for television broadcasting, D-MAC is a reduced bandwidth variant designed for transmission down cable....

 and much later on HD-MAC
HD-MAC
HD-MAC was a proposed broadcast television systems standard by the European Commission in 1986 . It was an early attempt by the EEC to provide High-definition television in Europe. It was a complex mix of analogue signal , multiplexed with digital sound...

 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
ATSC
ATSC standards are a set of standards developed by the Advanced Television Systems Committee for digital television transmission over terrestrial, cable, and satellite networks....

 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.

Hi-Vision's long term successes

How Hi-Vision ultimately succeeded technically
  • Japan has its own digital HDTV system (ISDB
    ISDB
    Integrated Services Digital Broadcasting is a Japanese standard for digital television and digital radio used by the country's radio and television stations. ISDB replaced the previously used MUSE "Hi-vision" analogue HDTV system...

    ) that is not tied to any US television standard, except for its backward compatibility with digital NTSC programming.
  • Japan, like Brazil (that has its own TV system derived from NTSC) has a television set manufacturing capability within its economy.
  • The US lost its TV set manufacturing capabilities as the Centerville
    Centerville, Gallia County, Ohio
    Centerville is a village in Gallia County, Ohio, United States. The population was 134 at the 2000 census. It is part of the Point Pleasant, WV–OH Micropolitan Statistical Area. It is located near U.S...

    , Ohio
    Ohio
    Ohio is a Midwestern state in the United States. The 34th largest state by area in the U.S.,it is the 7th‑most populous with over 11.5 million residents, containing several major American cities and seven metropolitan areas with populations of 500,000 or more.The state's capital is Columbus...

     Thomson SA
    Thomson SA
    Technicolor SA , formerly Thomson SA and Thomson Multimedia, is a French international provider of solutions for the creation, management, post-production, delivery and access of video, for the Communication, Media and Entertainment industries. Technicolor’s headquarters are located in Issy les...

     TV set manufacturing facility (once an RCA facility) was closed after 2005. There was a PBS Frontline documentary done on this facility.
  • The US is no longer considered to be the nation with the most advanced research in image compression, specifically digital video. The number of digital image compression patents per year (relating to digital video), and NSF image processing research funding have not substantially changed since the early 2000s.
  • The global analogue and digital HDTV exchange format is 1125/60 – essentially the MUSE format. In DVB modern terminology this would be 1080p/60.
  • The Europeans have had to totally abandon their 1250/50 HD-MAC system, with all archival material being converted into the 1080p/50 format.
  • The separation of color and brightness (in time and or space) in analogue TV transmission systems was proven. MUSE performed in a substandard way even when FM modulated in the VHF and UHF bands.
  • MUSE subsampling may be the preferred technical solution to many cheap DTV set top box decoders for the North American or European markets. The 1080p and 720p transmission formats can be downsampled to 625 line or 525 line resolutions with very few visual artifacts. As MUSE subsampling is adaptive, still images are seen at maximum resolution.

Hi-Vision Laserdiscs

There were a few MUSE laserdisc
Laserdisc
LaserDisc was a home video format and the first commercial optical disc storage medium. Initially licensed, sold, and marketed as MCA DiscoVision in North America in 1978, the technology was previously referred to interally as Optical Videodisc System, Reflective Optical Videodisc, Laser Optical...

 players available in Japan (Panasonic LX-HD10/20 and Sony HIL-C2EX). 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
Sony HDVS
Sony HDVS was a range of high-definition video equipment developed in the 1980s to support an early analog high-definition television system thought to be the broadcast television systems that would be in use today...

 high-definition video
High-definition video
High-definition video or HD video refers to any video system of higher resolution than standard-definition video, and most commonly involves display resolutions of 1,280×720 pixels or 1,920×1,080 pixels...

 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.

See also

The analog TV systems these systems were meant to replace
  • SECAM
    SECAM
    SECAM, also written SÉCAM , is an analog color television system first used in France....

  • NTSC
    NTSC
    NTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...

  • PAL
    PAL
    PAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...



Related standards
  • NICAM
    NICAM
    Near Instantaneous Companded Audio Multiplex is an early form of lossy compression for digital audio. It was originally developed in the early 1970s for point-to-point links within broadcasting networks...

    -like audio coding is used in the HD-MAC system.
  • Chroma subsampling
    Chroma subsampling
    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....

    in TV indicated as 4:2:2, 4:1:1 etc...

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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