Apparatus for encoding and decoding information
AssigneePayview Limited
InventorWilliam S. H. Cheung
Life of this patent
Estimating the term…
Abstract
Apparatus for encoding and decoding information. Multiple scrambling techniques are provided to prevent unauthorized reception of a television picture signal. A first mode of scrambling provides for shifting randomly occurring horizontal synchronization pulses within each field of video signal producing horizontal as well as vertical instability. Video line inversion of selected lines within a field comprises a second mode of scrambling of the signal. A third mode of scrambling provides for amplitude shifting the television signal during selected portions of the signal which contains luminance and chrominance information following a line synchronization pulse.
Claims20
An apparatus for scrambling a video signal, said video signal comprising a series of signals each representing lines within a field, each of said series of signals preceded by a line synchronization pulse for positioning a scanning beam in a television receiver comprising:
- means for generating a random number N during each of said fields, said random number changing with subsequent fields;
- means for producing random synchronization data from said random number, said data occurring coincident with certain of said synchronization pulses at an irregular interval;
- means for altering the level of said certain synchronization pulses;
- means for polarity inverting a plurality of alternate lines of a field of said video signals, said alternate lines being separated by a non-inverted line, the first of said inverted lines being identified by said random number which changes for subsequent fields;
- and
- means for combining a signal representing said random number with said video signal during a vertical interval thereof, whereby a scrambled video signal containing decoding data, a plurality of alternate inverted lines with randomly modified synchronization pulses is produced, subsequent fields, having different synchronization pulses with altered levels and having a different number of alternate lines inverted.
An apparatus for scrambling a video signal representing a plurality of lines in a picture, said video signal amplitude modulating a radio frequency carrier signal comprising:
- means for generating a random number for each field of said video signal;
- a first scrambling means for inverting the polarity of a plurality of alternate lines of said video signal identified by said random number before modulating said carrier signal, whereby a scrambled video signal results;
- a second scrambling means for modifying the amplitude of a portion of said modulated carrier signal representing a line identified by said random number, whereby said video signal is first scrambled at a video level and subsequently scrambled at an RF level;
- and
- means for transmitting said carrier signal having an inverted video signal portion and a modified amplitude along with said random number.
An apparatus for scrambling a video signal comprising:
- means for generating a random number identifying a scrambling sequence for each field of said signal;
- means for producing random synchronization data from said random number, said data identifying certain line synchronization pulses within said field;
- means for altering the level of said certain synchronization pulses;
- means for modulating said video signal on a radio frequency carrier signal;
- means for modifying the amplitude of a portion of said modulated radio frequency carrier signal identified by said random number without modifying a line synchronization portion of said radio frequency carrier signal;
- and
- means for combining said random number and radio frequency carrier whereby a scrambled video signal including decoding data is produced.
An apparatus for scrambling a video signal comprising:
- means for generating a signal identifying portions of a video signal to be polarity inverted;
- first scrambling means for inverting said identified portion of said video signal;
- means for modulating said video signal on a radio frequency carrier signal;
- second scrambling means for modifying the amplitude of a portion of said radio frequency carrier signal carrying picture information, whereby said video signal is scrambled before and after modulating said radio frequency carrier;
- and
- means for combining said signal identifying said portions with said video signal, whereby a composite scrambled signal is produced including a decoding signal.
An apparatus for scrambling a video signal, said video signal comprising a plurality of signals representing individual lines of a picture field, said signals each being separated by a line synchronization pulse identifying the beginning point of a line comprising:
- means for randomly identifying the first of a plurality of said lines to be scrambled, whereby said plurality of lines are randomly selected for each field;
- means for inverting the polarity of alternate lines following said identified line, whereby the brightness level of said alternate lines is modified;
- means for identifying certain of said line synchronization pulses, said certain pulses occurring at an irregular interval, the pattern of said identified line synchronization pulses changing every field;
- means for modifying the level of said identified synchronization pulses;
- and
- means for combining a data signal identifying said first line and identifying modified synchronization pulses with said video signal, whereby a composite scrambled video signal is produced including decoding data having a different number of alternate inverted lines and a different set of modified synchronization pulses in subsequent fields.
An apparatus for scrambling a television video signal, said signal comprising a plurality of line synchronization pulses separating a plurality of signals representing the brightness level of lines of a field comprising:
- means for generating a random number N preceding each of said fields;
- means for counting said line synchronization pulses, said counter being preset by said random number whereby an output occurs after N lines have been produced;
- gate means connected to be enabled by said counter after N line synchronization pulses have been counted, said gate means connected to provide line synchronization pulses after being enabled;
- means for dividing pulses produced by said gate means whereby pulses are produced at an irregular interval after N lines have occurred;
- and
- means for modifying line synchronization pulses in said video signal which are coincident with pulses produced by said means for dividing whereby modified line synchronization pulses are produced in an irregular pattern.
In a system for scrambling television signals wherein a plurality of synchronization pulses separating signals representing lines following a predetermined line in a field are modified to form a predetermined pattern with unmodified synchronization pulses, a decoding apparatus comprising:
- a video signal detector for supplying said video signal;
- a line chop pulse generator for supplying chop pulses in response to said video signal;
- counter means for counting each of said lines in said video signal, said counter means providing an output when said predetermined line is counted;
- a flip-flop connected to said counter means, said flip flop providing an output which changes state each time said counter provides an output signal;
- a gate means connected to receive line chop pulses and pulses from said flip-flop whereby regular sets of pulses are produced;
- a divider for receiving said sets of synchronization pulses from said gate means, said divider being preset to a number identifying said predetermined pattern, said divider producing synchronization command data;
- and
- means for modifying said video signal line synchronization pulses which correspond to said synchronization command data whereby said modified pulses are restored to a level corresponding to unmodified synchronization pulses.
In a television scrambling system having a plurality of lines in a video signal field inverted, the first of said inverted lines being identified by data contained within a vertical interval, and where a plurality of synchronization pulses at an irregular interval within a field are level shifted with respect to the remaining synchronization pulses, a decoder comprising:
- means for supplying said video signal;
- means for removing said data from said vertical interval;
- a line chop pulse generator;
- a counter for counting said lines;
- means for presetting said counter with a divisor corresponding to said data whereby said counter provides an output signal when the number of pulses counted is equivalent to said data, said output signal occurring at the time said first inverted line is being received;
- means for inverting a plurality of inverted lines following said first line;
- means for producing synchronization command data identifying said level shifted synchronization pulses comprising:
- a flip-flop connected to be toggled by said counter output signal,
- an AND gate having one input connected for receiving line chop pulses and a remaining input connected to said flip-flop, said AND gate providing a series of chop pulses at a regular interval,
- a divider for receiving said series of chop pulses, said divider providing an irregular pattern of chop pulses coincident with said shifted synchronization pulses;
- and
- means for level shifting synchronization pulses occurring simultaneously with said divider output signal whereby said synchronization pulses are restored to a level for correctly displaying a line following said synchronization pulses.
An apparatus for encoding a television signal comprising:
- means for supplying a video signal comprising a plurality of lines forming multiple fields;
- said lines comprising an information portion preceded by a line synchronization portion;
- means for generating between each of said fields a unique binary code identifying at least one line of a succeeding field;
- means for amplitude modulating a radio frequency signal with said video signal;
- means receiving said radio frequency modulated signal for subsequently changing the amplitude level of said modulated radio frequency signal at a portion corresponding to the information portion of said identified line without modifying said synchronization line portion;
- and
- means for combining said unique binary code with said radio frequency signal, whereby a scrambled video modulated signal including decoding data is produced.
An apparatus for decoding a scrambled television signal, said television signal including a radio frequency carrier signal modulated with a video signal representing a plurality of lines comprising a plurality of fields, said radio frequency carrier signal being subsequently amplitude level shifted over a portion representing at least one line of each field of said video signal, and including a decoding signal identifying said at least one line comprising:
- means for converting said radio frequency signal to an intermediate frequency signal;
- means for shifting the amplitude of said intermediate frequency signal in response to a decoding signal;
- and
- means for removing said decoding signal from said television signal, said means for removing said decoding signal connected to said means for shifting, whereby said intermediate frequency signal is descrambled by restoring the amplitude of portions of said intermediate frequency signal identified by said decoding signal corresponding to said at least one line.
Dependencies are inferred from the claim text.