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United States Patent (19) 11) 4,222,068 Thompson 45) Sep

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United States Patent (19) 11) 4,222,068 Thompson 45) Sep United States Patent (19) 11) 4,222,068 Thompson 45) Sep. 9, 1980 3,716,654 2/1973 Hendrickson et al. 54 SUBSCRIPTION TELEVISION APPARATUS 3,777,053 12/1973 Wittig et al. AND METHODS 3,789,131 1/1974 Harney . (75) Inventor: John R. Thompson, Los Angeles, 3,801,732 4/1974 Reeves . Calif. 3,813,482 5/1974 Blonder . 3,824,332 7/1974 Horowitz . 73) Assignee: American Television and 3,919,462 11/1975 Hartung et al. Communications Corporation, 4,022,972 5/1977 Pires . Englewood, Colo. 4,068,264 1/1978 Pires . 4,081,832 3/1978 Sherman . (21) Appl. No.: 957,176 FOREIGN PATENT DOCUMENTS 22 Filed: Nov. 2, 1978 1188200 4/1970 United Kingdom . 51 Int. Cl. ......................... H04N 7/16; H04K1/04 52 U.S. C. ..................................... 358/120; 358/124 Primary Examiner-S. C. Buczinski 58 Field of Search ................................ 358/120, 124 Attorney, Agent, or Firm-Finngegan, Henderson, Farabow, Garrett and Dunner 56) References Cited 57 ABSTRACT U.S. PATENT DOCUMENTS Subscription apparatus and methods wherein an en 2,612,552 9/1952 Crotty et al. coder begins inversion of a video signal during the last 2,619,530 1 1/1952 Roschke . 2,705,740 4/1955 Druz . horizontal trace line of a randomly selected vertical 2,755,332 7/1956 Druz . interval and continues to invert trace lines in the follow 2,755,333 7/1956 Druz . ing field of the video signal. The encoder also suppres 2,769,025 10/1956 Hoffmann et al. ses the amplitude of randomly selected horizontal 2,907,816 10/1959 Weiss. blanking pulses only during fields of the video signal 2,929,865 3/1960 Van Jepond . while maintaining unaltered the absolute amplitude 2,961,481 11/1960 Hammond, Jr. et al. differential between the horizontal blanking pulses and 2,972,009 2/1961 Roschke. 3,069,492 12/1962 D'Agostini. associated horizontal synchronization pulses. A de 3,078,337 2/1963 Shanahan et al. coder reinverts trace lines of the field following detec 3,081,376 3/1963 Loughlin et al. tion of an inverted last horizontal trace line of a vertical 3,081,377 3/1963 Watters. interval. The decoder also selectively rebiases the video 3, 147,061 9/1964 Walker, Jr. et al. signal to restore the horizontal blanking pulses upon 3,184,537 5/1965 Court et al. detection of a suppressed amplitude during the front 3,242,258 3/1966 Salit et al. porch of a horizontal blanking pulse. Reinversion of the 3,313,880 4/1967 Bass . trace lines and rebiasing of the blanking pulses is 3,439,113 4/1967 Walker . achieved by selective reference biasing of a video mod 3,460, 161 8/1969 Waller et al. ulator circuit in the decoder. 3,527,877 9/1970 Walker . 3,530,232 9/1970 Reiter et al. 3,684,823 8/1972 McVoy. 18 Claims, 15 Drawing Figures WIDE0 IdER AND AASIF? SIAI (SCILLAIOR 46 At 180 PitSES 42 ca "t, of 24 Hatfit 8 AORONA X DRIFAISES 44 7 Ital Bli Shah 48 St. PJLSES SUPPRESSION EN) OF FiFi) SIGIS 404 case if 420 AEA t (ERSION S/ALS U.S. Patent Sep. 9, 1980 Sheet 1 of 11 4,222,068 S S. S www. W s tSPsNee < S s SS SSuraaaa-SS s "nis S 9. ve | ww S s S2 S SS SS S S S S S Sa -e-70/I/7d// 70/1/7/Wy U.S. Patent sep. 9, 1980 Sheet 2 of 11 4,222,068 s 5S. g SS SS SS Sis Sa S SS Sis S S Sis --00A/id47 ----70/I/7dhy U.S. Patent Sep. 9, 1980 Sheet 3 of 11 4,222,068 ES d - - - - - - - - - - - - - - - - - --------- a - - - - - c - - - - - - - - - - n 99 99 tasS %0 U.S. Patent Sep. 9, 1980 Sheet 6 of 11 4,222,068 U.S. Patent Sep. 9, 1980 Sheet 7 of 11 4,222,068 //797%)/6 U.S. Patent Sep. 9, 1980 Sheet 9 of 11 4,222,068 Z29 219 3787W9/07 070/A //////$ U.S. Patent Sep. 9, 1980 Sheet 10 of 11 4,222,068 - ------------------------------------------- - 070/A 4,222,068 1. 2 code, keying signal, or encoding signal, to allow a de SUBSCRIPTION TELEVISION APPARATUS AND coder to correctly reinvert the randomly inverted por METHODS tions of the scrambled signal. While systems have been described which employ BACKGROUND OF THE INVENTION 5 aspects of both horizontal synchronization modification I. Field of the Invention and video signal polarity modification to generate a The present invention relates to apparatus and meth scrambled signal, such systems also require the further ods pertaining to the encoding and decoding of a televi inefficient process of generating, communicating, and sion signal in a manner which deters unauthorized utili decoding of some form of encoding signal in addition to zation of the signal. 10 the scrambled video signal. II. Description of the Prior Art It is therefore an object of the present invention to Present day subscription television systems are based economically and efficiently render the video portion of on the generally accepted fact that rendering a video the television signal scrambled to the point of being picture unviewable in a normal television receiver is effectively unwatchable when displayed on a standard most easily and effectively accomplished by simply 15 television receiver. upsetting the horizontal synchronization of the re Another object of the present invention is to provide ceiver. It is known that horizontal synchronization can a subscription television system in which the scrambling effectively be upset for standard NTSC receivers by of the video signal is secure in that it becomes difficult simply removing the horizontal synchronization pulses and costly for an unauthorized viewer to reconstruct to or by suppressing the horizontal synchronization pulses 20 an acceptable viewing level. below the average video level of the signal. This causes A further object of the present invention is to provide the television receiver to try to lock horizontally on a scrambling system having encoding and decoding random video peaks transmitted during the active or devices which are economical to manufacture and in video trace line portions of the video signal rather than stall and yet provide a high quality video picture with a on the actual horizontal synchronization pulses. The 25 fact that the horizontal synchronization pulses are no minimum of distortion and a minimum of viewer aware longer consistently processed also destroys a receiver's ness that the picture is reconstructed from a previously ability to use a color reference burst associated with the scrambled transmission. horizontal synchronization signals, thereby causing More specifically, it is an object of the present inven inaccurate color reproduction. 30 tion to provide a subscription television system wherein However, known systems which employ removal or no complex control codes, keys or encoding signals are suppression of horizontal synchronization pulses, re transmitted to control operation of a decoder, but rather quire employment of an encoding signal, such as a con the system employs a decoder which operates without trol code or keying signal, to allow a decoder to recon preestablished or encoder-controlled format to follow struct the missing or suppressed horizontal synchroniza 35 the transmission sequence of suppressed horizontal tion pulses. For example, the control code or keying blanking pulses and inverted video signals as they oc signal may take the form of negative going encoding C. pulses inserted in selected locations of the horizontal Additional objects and advantages of the invention blanking pulses. In the alternative, a totally independent will be set forth in part in the description which follows, signal, which contains the critical encoding information 40 and in part will be obvious from the description, or may needed to reconstruct the horizontal synchronization be learned by practice of the invention. The objects and pulses may be sent by a separate communication me advantages of the invention may be realized and ob dium, such as the audio portion of the television signal tained by means of the instrumentalities and combina or a telephone land line. tions particularly pointed out in the appended claims. In addition to having the disadvantage of requiring 45 transmission of an encoding signal to reconstruct the SUMMARY OF THE INVENTION missing or suppressed horizontal synchronization To achieve the foregoing objects, and in accordance pulses, presently known systems, which employ hori with the purposes of the invention as embodied and Zontal synchronization pulse suppression or removal, broadly described herein, a subscribed television system generate pictures which during a sequence with a sta 50 is provided for selectively communicating a composite tionary vertical (gray or black) line will sometimes video signal having fields with horizontal trace lines allow a normal receiver to horizontally lock and display separated by horizontal blanking pulses having front a recognizable picture, albeit with severe color distor porches followed by horizontal synchronization pulses tion. and the video signal further having vertical intervals Some known subscription television systems employ 55 separating the fields, the vertical intervals containing circuitry to invert all or selected portions of the video vertical synchronization information followed by hori signal to prevent unauthorized demodulation of the zontal trace lines separated by horizontal blanking video signal content. For example, systems have been pulses. The system of the present invention comprises: described which transmit even number fields with a (a) video encoder means for randomly inverting the conventional polarity and transmit odd number fields 60 polarity of the video signal by inverting the polarity of with reverse polarity with the resultant video signal a trace line of randomly selected vertical intervals and generating a blank or washed-out picture in a standard by inverting the trace lines of associated fields follow television receiver.
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