Multiple Sub-Nyquist Sampling Encoding


MUSE, commercially known as Hi-Vision was a Japanese analog high-definition television system, with design efforts going back to 1979. Traditional interlaced video shows either odd or even lines of video at any one time, but MUSE required four fields of video to complete a single video frame. Hi-Vision also refers to a closely related Japanese television system capable of transmitting video with 1035i resolution, in other words 1035 interlaced lines. MUSE was used as a compression scheme for Hi-Vision signals.

Overview

It used [|dot-interlacing] and digital video compression to deliver 1125 line, 60 field-per-second signals to the home. The system was standardized as ITU-R recommendation BO.786 and specified by SMPTE 260M, using a colorimetry matrix specified by SMPTE 240M. As with other analog systems, not all lines carry visible information. On MUSE there are 1035 active interlaced lines, therefore this system is sometimes also mentioned as 1035i. MUSE employed 2-dimensional filtering, dot-interlacing, motion-vector compensation and line-sequential color encoding with time compression to "fold" or compress an original 30 MHz bandwidth Hi-Vision source signal into just 8.1 MHz.
Because MUSE was different as it used a four-field dot-interlacing cycle, taking four fields to complete a single MUSE frame. The interlacing was done on a pixel-by-pixel basis, reducing both horizontal and vertical resolution by half for each field of video, unlike traditional interlacing which only reduced vertical resolution and so only stationary images were transmitted at full resolution. This meant that moving images were blurred since MUSE lowered the resolution of material that changed greatly from frame to frame. MUSE used motion-compensation, so camera pans maintained full resolution, but individual moving elements could be reduced to only a quarter of the full frame resolution. As a result, the mix of motion and non-motion was encoded pixel-by-pixel, making it less noticeable.
Japan began broadcasting wideband analogue HDTV signals in December 1988, initially with an aspect ratio of 2:1. The Sony HDVS high-definition video system was used to create content for the MUSE system, but didn't record MUSE signals. It recorded Hi-Vision signals which are uncompressed.
By the time of its commercial launch in 1991, digital HDTV was already under development in the United States. Hi-Vision MUSE was mainly broadcast by NHK through their BShi satellite TV channel, although other channels such as WOWOW, TV Asahi, Fuji Television, TBS Television, Nippon Television, and TV Tokyo also broadcast in MUSE.
Later improvements, known as the MUSE-III system, increased resolution in moving areas of the image and improved chroma resolution during motion. MUSE-III was used for broadcasts starting in 1995 and a few Hi-Vision MUSE LaserDiscs. There were many early complaints about the large size of the MUSE decoder led to the development of a miniaturized decoder.
On May 20, 1994, Panasonic released the first MUSE LaserDisc player. There were also a number of players available from other brands like Pioneer and Sony.
Despite shadows and multipath issues in this analog transmission mode, Japan switched to a digital HDTV system based on ISDB. Hi-Vision continued broadcasting in analog by NHK until 2007. Other channels had stopped soon after December 1, 2000 as they transitioned to digital HD signals in ISDB, Japan's digital broadcast standard.

History

MUSE was developed by NHK Science & Technology Research Laboratories in the 1980s as a compression system for Hi-Vision HDTV signals.
  • 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. MUSE was transmitted at a frequency of 21 GHz or 12 GHz.
;Modulation research
  • Japanese broadcast engineers had been studying the various HDTV broadcast types for some time. It was initially thought that SHF, EHF or optic fiber would have to be used to transmit HDTV due to the high bandwidth of the signal, and HLO-PAL would be used for terrestrial broadcast. HLO-PAL is a conventionally constructed composite signal and uses 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.PAF, or phase alternating by field was also experimented with, and it gave much better decoding results, but NHK abandoned all composite encoding systems. Because of the use of satellite transmission, Frequency modulation should be used with power-limitation problem. FM incurs triangular noise, so if a sub-carrierred composite signal is used with FM, demodulated chroma signal has more noise than luminance. Because of this, they looked at other options, and decided to use component emission for satellite. At one point, it seemed that FCFE, I/P conversion compression system, would be chosen, but MUSE was ultimately picked.
  • Separate transmission of and components was explored. The MUSE format which 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 emphasised prior to modulation at the transmitter and de-emphasized at the receiver.

    Technical specifications

MUSE's "1125 lines" are an analog measurement, which includes non-video scan lines taking place while 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 that have actual detail, so NTSC's 525 lines become 486i, 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, multiply 29.9 lines per MHz of bandwidth. - 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. 1125 lines was selected as a compromise between the resolution in lines of NTSC and PAL and then doubling this number.
MUSE employs time-compression integration which is another term for time-division multiplexing, which is used to carry luminance, chrominance, PCM audio and sync signals on one carrier signal/in one carrier frequency. However, TCI achieves multiplexing by compression of the contents in the time dimension, in other words transmitting frames of video that are divided into regions with chrominance compressed into the left of the frame and luminance compressed into the right of the frame, which must then be expanded and layered to create a visible image. This makes it different from NTSC which carries luminance, audio and chrominance simultaneously in several carrier frequencies. Hi-Vision signals are analog component video signals with 3 channels which were RGB initially, and later YPbPr. The Hi-Vision standard aims to work with both RGB and YPbPr signals.
Key features of the MUSE system:
  • Scanlines : 1,125/1,035
  • Pixels per line : 1122 /748
  • Reference clock periods: 1920 per active line
  • Interlaced ratio: 2:1
  • Aspect ratio 16:9
  • Refresh rate: 59.94 or 60 frames per second
  • Sampling frequency for broadcast: 16.2 MHz
  • Vector motion compensation: horizontal ± 16 samples / frame, a vertical line ± 3 / Field
  • Audio: "DANCE" discrete 2- or 4-channel digital audio system: 48 kHz/16 bit /32 kHz/12 bit
  • DPCM Audio compression format: DPCM quasi-instantaneous companding
  • Required bandwidth: 27 MHz Usable bandwidth is 1/3 of this, 9 Mhz due to the use of FM modulation for transmission.

    Colorimetry

The MUSE luminance signal encodes, specified as the following mix of the original RGB color channels:
The chrominance signal encodes and difference signals. By using these three signals, a MUSE receiver can retrieve the original RGB color components using the following matrix:
The system used a colorimetry matrix specified by SMPTE 240M. The chromaticity of the primary colors and white point are:
The luma function is specified as:
The blue color difference is amplitude-scaled, according to:
The red color difference is amplitude-scaled, according to:

Signal and Transmission

MUSE is a 1125 line system, 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 aspect ratio and an optimal viewing distance of roughly 3.3H. In 1989 this was changed to a 16:9 aspect ratio.
For terrestrial MUSE transmission a bandwidth limited FM system was devised. A satellite transmission system uses uncompressed FM.
Before MUSE compression, the Hi- Vision signal bandwidth is reduced from 30 MHz for luminance and chrominance to a pre-compression bandwidth of 20 MHz for luminance, and a 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 composite video NTSC signal - with the at the lower frequencies and the 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 luminance| and Chrominance|. This reduces the effective frequency range and lowers the required power. Approximately 570 W would be needed in order to get a 40 dB of signal to noise ratio for a separate 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 and 1.6 MHz for. With this in place, the power requirements drop to 260 W of power.