Clear-Vision

Clear-Vision is a Japanese EDTV (Extended Definition TV)^[1][2] television system introduced in the 1990s, that improves audio and video quality while remaining compatible with the existing broadcast standard.^[1][3] Developed to improve analog NTSC,^[4] it adds features like progressive scan, ghost cancellation and widescreen image format. A similar system named PALPlus was developed in Europe with the goal of improving analog PAL broadcasts.^[5]

The initial version of the system was called IDTV^[5] (Improved Definition Television,^[6] or SuperNTSC^[7]) and was based on advanced signal processing on TV receivers. This allowed improvements such as progressive scan, ghost cancellation (reducing the effects of multipath propagation) and NTSC luminance and chroma crosstalk reduction (by way of filtering),^[6] without requiring any extra information being broadcast. These early studies were done by NTV,^[8] under the direction of the MPT (Ministry of Post and Telecommunications) and the BTA (Broadcasting Technology Association).^[1][5]

This early standard was published as ITU-R recommendation BT.797 - "CLEARVISION".^[9] Public broadcasting began on NTV in August 1989, under the name of EDTV-I or "Clear-Vision",^[8][1][5] ending on July 24, 2011.

Tests for an updated system known as EDTV-II^[10][11] or "Wide-aspect Clear-vision"^[1][3] started in 1994.^[12] EDTV-II supported 480p^[13] progressive scan,^[14] wide-screen^[15] and digital audio. Public broadcasting began in July 1995 by NTV.^{[8][16][17][5][2]} The standard was published as ARIB STD-B9 - "Direct Coding for EDTV-II Television Signal" in 1997^[18] and as ITU BT.1298 - "Enhanced wide-screen NTSC TV transmission system".^[9]

EDTV-II broadcasts are displayed in letterbox format (with black bands on the top and bottom of the screen)^[14] on regular 4:3 NTSC receivers with no decoding ability. Information to reconstruct the original image signal is transmitted as helper signals - HH (horizontal high), VH (vertical high) and VT (vertical-temporal) - placed on the black bars.^[19][9] This solution is similar to the one used on PALplus,^[20] a comparable system to improve analog PAL broadcasts. On compatible TV sets, broadcasts are seen in 16:9 wide-screen retaining the full original 480 line resolution.^[9]

When introduced, EDTV-II was used on many shows by NTV such as Friday Road Show.^{[21][circular reference]} At the time of TOKYO MX^[22] start in 1995, more than half of its broadcasts were in widescreen using EDTV-II, such as Tokyo NEWS.^[21] Interest was predicted to be high, with manufacturers such as Sony and Mitsubishi having 16 to 32'' widescreen EDTV-II compatible TVs available that same year.^[23][24] Yet, due to lack consumer interest, broadcasts returned to regular 4:3 over the years. NHK used the system occasionally, as it was more interested in promoting its own analog high-definition MUSE system.^[21] Widescreen EDTV-II broadcasts gradually disappeared, with World Heritage, broadcast by Sony, being the last show shown using the format.^[25]

Other than widescreen broadcasts, the system gave a limited improvement in image quality, mostly noticeable on larger TV sets. Yet these TVs benefited more from true HDTV broadcasts using the MUSE system, also available at the time.^[5][26] The system was replaced by ISDB digital broadcasts after 2012.

Technical details

The EDTV-II "Clear-Vision" transmission system is based on the following elements:^[9][27]

• Vertical conversion of the original full resolution 480 lines widescreen image to a 360-line 16:9 letterbox picture. High and low-pass filters are used.
• Recovery of original vertical image resolution using helper signals (VH, VT). Taking advantage of the letterbox black bands, these are modulated on the color subcarrier, with visibility minimized on regular 4:3 televisions. The vertical helper (VH) carries the missing vertical luminance details in motionless portions of the picture. The vertical temporal helper (VT) carries information allowing the receiver to reconstruct the original progressive scanning.
• Recovery of original horizontal image resolution using a helper signal (HH), taking advantage of the “Fukinuki hole”. Horizontal luminance between 4.2 - 6 MHz is transmitted by frequency division multiplexing into the active area of the letterbox signal.
• A wide-screen signaling system, according to recommendations EIAJ CPX1204 / ITU BT.1119;^[28]
• The chrominance signal is transmitted in the active area of the letterbox (360 lines).

Some elements are optional, but the standard requires that at least one helper and the wide-screen signaling are used.^[9]

EDTV-II "Clear-Vision" technical details^[20]^[19]^[29]

Aspect Ratio	16:9 letterbox
Active area	360 lines
Black area	120 lines
Horizonal Resolution	0 - 4.2 MHz
Vertical Resolution	0 - 360 lines/height
Vertical High Resolution Helper (VH)	360 - 480 lines/height
Vertical-Temporal Helper (VT)	180 - 360 lines/height
Horizontal Helper (HH)	4.2 - 6.0 MHz
Scanning	576 lines progressive / interlaced

See also

• PALplus (a similar system for PAL broadcasts)
• Enhanced-definition television
• MUSE
• NTSC
• Broadcast television systems
• Widescreen television
• Widescreen signaling

References

1. FUKINUKI, Takahiko (March 1991). "EDTV".
2. "HI-Vision TV is given a low survival rating". Australian Financial Review. February 5, 1992.
3. Pollack, Andrew (September 15, 1994). "Japanese Taking to Wide-Screen TV". The New York Times – via NYTimes.com.
4. Recommendation ITU-R BT.1118-1 - Enhanced compatible widescreen television based on conventional television systems (PDF). ITU. 1997.
5. "Digital Television in Europe and Japan" (PDF).
6. JTEC Panel Report on High Definition Systems In Japan (PDF). U.S. Department of Commerce. 1991.
7. Gerbarg, Darcy (January 31, 1999). The Economics, Technology and Content of Digital TV. Springer Science & Business Media. ISBN 9780792383253 – via Google Books.
8. "Corporate History". NIPPON TV.
9. Recommendation ITU-R BT.1298 - Enhanced wide-screen NTSC TV transmission system (PDF). ITU. 1997.
10. Nakayama, K.; Kojima, T.; Miyaguchi, H.; Sawaragi, T.; Yaguchi, Y. (August 5, 1995). "EDTV-II decoder by SVP2 (the 2nd generation of scan-line video processor)". IEEE Transactions on Consumer Electronics. 41 (3): 634–642. doi:10.1109/30.468089 – via IEEE Xplore.
11. "The Journal of the Institute of Television Engineers of Japan". www.jstage.jst.go.jp.
12. "EDTV2 試験放送 画質評価用スライド放送" – via www.youtube.com.
13. Hori, A. (January 1, 1997). "525-line progressive scan signal digital interface standard and equipment". International Broadcasting Conference (IBC). Vol. 1997. pp. 141–146. doi:10.1049/cp:19971258. ISBN 0-85296-694-6 – via digital-library.theiet.org.
14. Noble, Gregory W. (September 5, 2018). Collective Action in East Asia: How Ruling Parties Shape Industrial Policy. Cornell University Press. ISBN 9781501732034 – via Google Books.
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16. "Telecompaper". www.telecompaper.com.
17. Masataka, Takahashi (July 5, 1996). "The Broadcasting Operation Of EDTV-II (Vide Clear Vision) Programs Especially Master Control Room". ITE Technical Report. 20 (3): 41–45. doi:10.11485/tvtr.20.3_41 – via cir.nii.ac.jp.
18. "About obtaining ARIB Standards (STD-B9)｜Association of Radio Industries and Businesses". www.arib.or.jp.
19. Suzuki, N.; Fukinuki, T.; Kageyama, M.; Ishikura, K.; Yoshigi, H. (January 1, 1994). "Multiplexing scheme of helper signals on bars in EDTV-II". International Broadcasting Convention - IBC '94. Vol. 1994. pp. 32–36. doi:10.1049/cp:19940723 – via digital-library.theiet.org.
20. Mertzios, B. G.; Liatsis, P. (November 8, 1996). Proceedings IWISP '96, 4–7 November 1996; Manchester, UK: Third International Workshop on Image and Signal Processing on the Theme of Advances in Computational Intelligence. Elsevier. ISBN 9780080539768 – via Google Books.
21. "ワイドクリアビジョン - Wikipedia". ja.wikipedia.org.
22. "TOKYO MX 開局の瞬間（199511）". September 20, 2015 – via www.nicovideo.jp.
23. Annual Report 1995 (PDF). SONY. p. 16.
24. "1995年懐かCM【三菱電機】" – via www.youtube.com.
25. "ソニー、TBS「世界遺産」スポンサー撤退 番組は継続". 朝日新聞. April 9, 2015.
26. Hart, Jeffrey A. (February 5, 2004). Technology, Television, and Competition: The Politics of Digital TV. Cambridge University Press. ISBN 9781139442244 – via Google Books.
27. Kageyama, Masahiro (2010). Thesis Research on high image quality and high functionality of television (PDF).
28. CS4954/55 NTSC/PAL Digital Video Encoder (PDF). Cirrus Logic, Inc. 2006.
29. Multiplexing Scheme for Helper Signals in Top and Bottom Bars in EDTV-II. Journal of the Institute of Television Engineers of Japan. 1994.