1、Rec. ITU-R BT.797-1 1RECOMMENDATION ITU-R BT.797-1PARAMETERS FOR 4:3 ENHANCED TELEVISION SYSTEMSTHAT ARE NTSC-COMPATIBLE(Question ITU-R 42/11)(1992-1994)Rec. ITU-R BT.797-1The ITU Radiocommunication Assembly,consideringa) that new digital technology offers storage, filtering and processing capabilit
2、ies that will permit separatescanning standards for the picture source, emission and in the display;b) that in Japan a 4:3 NTSC-compatible enhanced television system, CLEARVISION, has been operational sincethe end of August 1989 (see Annex 2, 3);c) that in Canada and the United States of America stu
3、dies are underway on advanced television systems (seeAnnex 2),recommends1. that the parameters for an enhanced 4:3 NTSC system in Japan should be those defined in Annex 1.ANNEX 1In principle, the parameters of an enhanced 4:3 NTSC system should be fully compatible with the existingtelevision system.
4、 For enhancement of picture quality, the following methods could be used.At the studio side: an enhancement of the resolution: higher resolution signal sources; an enhancement of the chrominance signal: pre-compensation of detail in highly saturated colour pictureswhich are specified in Appendix 1 t
5、o Annex 1; an enhancement of the luminance signal: adaptive emphasis of high-frequency components which arespecified in Appendix 1 to Annex 1;At the emission side: a reduction of the ghost interference: insertion of ghost-cancelling reference signals.At the receiver side, it could be applicable to e
6、nhance the picture quality: progressive scanning display and/or three dimensional Y/C separation filter and the ghost-cancellationcircuit.2 Rec. ITU-R BT.797-1APPENDIX 1TO ANNEX 1Pre-compensation of chrominance(Quasi-constant luminance processing)The chrominance signal is enhanced as follows: the re
7、d signal before pre-gamma compensation with an amplitude of 50% plus 20% sub-carrier level isused as a reference; a pre-compensation of 2 dB for 50% saturated red signal and of 10 dB for 100% saturated red signal isused.The saturation level for red signal is specified as follows:(C K/C) 100%where:C
8、: red signal voltage amplitudeK : green and blue signal amplitude.Adaptive emphasisThe following emphasis curve is applied to enhance the luminance signal. “0” frequency meansunder 0.5 MHz.0 1 2 3 401234FIGURE 1Frequency (MHz)Compensation(dB)Time constant: 100 nsD01FIGURE 1D01 = 6.5 cmANNEX 2Factors
9、 affecting the choice of parameter values for enhanced 4:3 NTSC-compatibletelevision for terrestrial broadcasting1. IntroductionSince the development of electronic television, the art has experienced a continuous evolutionary developmentwhich has produced a stream of improvements in the quality of p
10、ictures displayed to the viewer. A quantum step inquality occurred with the introduction of colour. New digital technology now offers storage, filtering and processingcapabilities that will permit separate scanning standards for the picture source, emission and in the display, therebyproviding incre
11、ased quality through conventional television systems. New distribution media having wider bandwidth,such as broadcasting satellites, will permit new services with increased definition and wider aspect ratios.Rec. ITU-R BT.797-1 32. Definition of termsThe term “enhanced NTSC television” designates a
12、number of different improvements applicable to 525/60television systems, providing an aspect ratio of 4:3 or wider, either with unchanged or with new emission standards.The term “enhanced television” is used here to include all television systems (from source to display) notcovered by Recommendation
13、 ITU-R BT.470 (Conventional television systems). It is noted that the signal format maychange at different parts of the signal chain.Enhanced NTSC television systems may be classified according to the following parameters: aspect ratio 4:3; signal format: composite based on NTSC.It should be noted t
14、hat there exists no clear definition of some of the terms widely used in the description ofenhanced television systems. For example: Compatibility: various degrees of compatibility are possible. These range from full compatibility withexisting systems, through systems that share the same scanning fo
15、rmats, to systems that have no directcompatibility with existing systems. The compatibility can also apply only to parts of the system, forexample, receiver compatibility. Resolution: enhanced television systems do not necessarily imply the provision of increased resolution; insome circumstances the
16、 resolution may be reduced as a result of other enhancements, such as provision ofa wider aspect ratio.3. Enhancements for 4:3 NTSCEnhancements to conventional television systems are expected to be introduced in the areas listed below, all ofwhich will contribute, in a varying degree, to improving t
17、he overall quality of the received television picture: alias effects generated by the scanning process, luminance/colour difference cross-effects, signal processing capability, generation of moir and non-linear signal distortion in video tape recorders, immunity to transmission impairments, receiver
18、 decoding and display techniques.The composite signal format NTSC suffers from noticeable signal impairment due to cross colour and crossluminance. Significant quality improvements can be achieved by the use of multi-dimension separation filters based online stores or frame stores. Complementary pre
19、-filtering of the video before colour encoding can further improve picturequality.When appropriate filtering is applied ahead of the display, further improvements in the effective verticalresolution can be achieved by filtering at the source. The so-called Kell effect, that results from the excess N
20、yquistmargin in the vertical sampling (scanning) of the image that must be allowed at the camera to avoid aliasing, reduces theeffective vertical resolution of a television system.Work has been reported in numerous publications in the United States of America, Japan and in othercountries on investig
21、ations to devise enhancements to the composite NTSC system.4 Rec. ITU-R BT.797-1In Japan an NTSC-compatible enhanced television system, known as CLEARVISION has been operationalsince the end of August 1989. The new system includes hardware for five key techniques: higher resolution signalsources, pr
22、e-compensation of detail in highly saturated colour pictures, adaptive emphasis of high frequency componentsin the luminance signal, insertion of a ghost-cancelling reference (GCR) signal for ghost reduction in television receiversand receivers with 525-line progressive display and three dimensional
23、 Y/C separation filters. Subjective tests using 18still pictures showed an improvement of about 1.5 grades on the ITU-R 7-point comparison scale. Ghost interference,evaluated as grade 2.5 on a 5-point impairment scale, was improved to better than grade 4 at most of the locations tested.4. Display en
24、hancementThe availability of low-cost field stores in domestic receivers permits separation of the display scanningparameters from those of the emission standard. Cross-colour and cross-luminance in composite systems can besignificantly reduced by luminance/chrominance separation filters using frame
25、 stores. An increase in the field frequencycan eliminate large area flicker. An increase in the number of lines and the use of sequential scanning can significantlyreduce the inter-line flicker and the line crawl that occur in conventional television systems.In Japan, a scan-conversion system using
26、a motion-adaptive spatio-temporal interpolation filter with receiverframe memory has been developed to reduce interlaced line-scanning impairments. It improves picture quality for bothstill and moving pictures.In Japan, a multi-scan high definition 16:9 projection display has been developed to displ
27、ay HDTV,conventional television and other signals, such as the output of personal computers. A range of vertical scanningfrequencies from 40 to 120 Hz is provided. Horizontal scanning frequencies from 15 to 70 kHz are possible. NTSCsignals are displayed using a high-resolution scan converter, which
28、doubles the number of NTSC scanning lines throughmotion-adaptive frame combing. A personal computer output can be superimposed onto the double-scanned NTSCsignal, thus widening the applications of the display.Production of television receivers with functions adapted to the CLEARVISION system such as
29、 “motion-adaptive three-dimensional Y/C separation” and “progressive scan display” has taken place since 1988, and severalmodels of display sizes of 29 in (74 cm) to 37 in (94 cm) for CRT and 43 in (109 cm) to 120 in (305 cm) for projectiontype are being produced. Decoders for professional use adapt
30、ed to CLEARVISION for large displays are also beingplaced on the market by manufacturers.Regarding the ghost rejecting equipment for GCR signals, each of the receiver manufacturers is presentlyproducing and selling their own tuner adapter containing the ghost cancelling function.5. Ghost cancellatio
31、nIt has long been recognized that multipath interference is a serious problem and that ghost cancellation couldoffer significant quality improvements to the existing television services.A reference signal as given in Recommendation ITU-R BT.1124 is inserted in the field-blanking interval.6. Future d
32、evelopmentsIn Japan, the Broadcasting Technology Association established the methods required to provide theimprovements for enhanced wide aspect NTSC at the beginning of 1992. Approximately one year later at the beginningof 1993, provisional specifications were to be decided on, and indoor and outdoor experiments conducted. At thebeginning of 1994, final specifications were to be submitted to the EDTV Committee of the TelecommunicationsTechnology Council. Actual application of a second generation system is expected to start in 1995._
