The initial version of the system was calledIDTV[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 ofmultipath propagation) and NTSCluminance and chroma crosstalk reduction (by way of filtering),[6] without requiring any extra information being broadcast. These early studies were done byNTV,[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 asITU-R recommendation BT.797 - "CLEARVISION".[9] Public broadcasting began on NTV in August 1989, under the name ofEDTV-I or "Clear-Vision",[8][1][5] ending on July 24, 2011.
Tests for an updated system known asEDTV-II[10][11] or "Wide-aspect Clear-vision"[1][3] started in 1994.[12] EDTV-II supported480p[13] progressive scan,[14] wide-screen[15] anddigital audio. Public broadcasting began in July 1995 byNTV.[8][16][17][5][2] The standard was published asARIB 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 inletterbox format (with black bands on the top and bottom of the screen)[14] on regular4:3 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 asFriday Road Show.[21][circular reference] At the time ofTOKYO MX[22] start in 1995, more than half of its broadcasts were in widescreen using EDTV-II, such asTokyo NEWS.[21] Interest was predicted to be high, with manufacturers such asSony andMitsubishi 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-definitionMUSE system.[21] Widescreen EDTV-II broadcasts gradually disappeared, withWorld Heritage, broadcast bySony, 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 byISDBdigital broadcasts after 2012.
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 andlow-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 thecolor subcarrier, with visibility minimized on regular 4:3 televisions. The vertical helper (VH) carries the missing verticalluminance 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 divisionmultiplexing into the active area of the letterbox signal.
^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.Bibcode:1995ITCE...41..634N.doi:10.1109/30.468089.
