Apparatus for encoding of information

• US 4,396,947 A
• Filed: 03/26/1980
• Issued: 08/02/1983
• Est. Priority Date: 02/20/1979
• Status: Expired due to Term

• Current Assignee: Payview Limited
• Original Assignee: Payview Limited
• Inventors: Cheung, William S. H.
• Primary Examiner(s): BUCZINSKI, STEPHEN C
• Application Number:
  US06/134,185
• Time in Patent Office: 1,224 Days
• Field of Search: 358/120, 358/123, 358/124
• US Class Current: 380/222
• CPC Class Codes: H04N 7/167 Systems rendering the television signal unintelligible and subsequently intelligible

Abstract

A composite video signal containing an information portion and a synchronization pulse is encoded by shifting the level of the synchronization pulse and also by inverting the information portion. The encoding is switched on and off at a randomly chosen frequency, under the control of random number generator enabled at regular intervals. The encoded signal is transmitted with a data signal representing the random number so that a receiver can decode the received signal. The transmitted data can include details of undesired recipients, to disable their decoders. Applied to a pay TV system, the transmitted data can include the rate to be charged for the program and a billing mechanism at the receiver will meter the appropriate charge.

Claims

1. An apparatus for scrambling a video signal, said video signal representing a plurality of sequential lines in a plurality of fields separated by vertical synchronization pulses comprising:

means for generating a binary code identifying a starting line in each field of said video signal, said starting line separating an unscrambled portion from a scrambled portion, subsequent fields of said video signal having a different starting line;

means for changing the luminance level and chrominance of alternate lines of a video signal following said starting line whereby a scrambled signal is produced, and a portion of said field contains alternate scrambled lines separated by unscambled lines; and

subsequent fields have a different number of alternate scrambled lines separated by unscrambled lines.

3. The apparatus of claim 1, further comprising means for shifting the level of a vertical synchronization pulse associated with at least one of said fields.

2. An apparatus for scrambling a video signal of the type representing a plurality of horizontal lines of a picture field for display on a television receiver comprising:

a source of video signals;

a random number generator means for providing a starting signal during each field of said video signal, said starting signal occurring at a substantially random interval for identifying the beginning line of a scrambled portion of said field;

means for changing the luminance level and chrominance of the video signal representing a plurality of alternate lines of the lines occurring subsequent to said starting signal, whereby a video signal is produced having an unscrambled portion and a scrambled portion which randomly varies between fields, said scrambled portion comprising scrambled lines separated by unscrambled lines, and subsequent fields having a different number of alternate scrambled lines separated by unscrambled lines.

4. The apparatus of claim 2, further comprising means for shifting the level of a synchronization pulse associated with a picture field.

5. A receiving apparatus for descrambling a television signal comprising:

means for supplying a video signal representing a plurality of lines of a field, a first portion of said field being scrambled by inverting the brightness level of alternate lines in said portion, said alternate lines being separated by unscrambled lines, and a remaining portion which is unscrambled, subsequent fields of said video signal having a different number of alternate scrambled lines separated by unscrambled lines;

means for supplying a signal identifying the first line of said plurality of lines in said scrambled portion; and

means for inverting the brightness level of every other line subsequent to said first line represented by said video signal for the remaining portion of said scrambled portion in response to said signal identifying said first line.

6. A receiving apparatus for descrambling a television signal comprising:

means for supplying a video signal representing a plurality of lines in a field, said plurality of lines comprising a first unscrambled portion, and a second scrambled portion which have the voltage level representing the luminance level and chrominance of alternate lines shifted, said alternate lines separated by lines which do not have the voltage representing the luminance level and chrominance shifted, subsequent fields of said video signal having a different number of alternate scrambled lines separated by unscrambled lines;

means for shifting said voltage representing said luminance and chrominance of said alternate lines for restoring the luminance level and chrominance of said lines.

7. The apparatus of claim 6, further comprising means for altering the level of a synchronization pulse associated with a field of said video signal.

8. A method for scrambling a video signal, said video signal representing the luminance level and chrominance of a plurality of lines comprising a plurality of fields separated by vertical synchronization pulses comprising:

shifting the level of at least one of said vertical synchronization pulses; and

changing the luminance level and chrominance of portions of said video signal representing alternate lines of a portion of said fields whereby the luminance level and chrominance of said alternate lines is changed, said alternate lines being separated by unshifted lines, the number of said alternate lines separated by unshifted lines changing in successive fields.

9. The method of claim 8, wherein the portion of said field which contains said alternate lines varies between fields.

10. The method of claim 9, wherein the line at which said portion begins varies between fields.

11. The method of claim 9, wherein the portion of said field which contains said alternate lines varies randomly between fields.

12. The method of claim 10, wherein the line at which said portion begins varies between fields.

13. A receiving apparatus for descrambling a video signal comprising:

means for supplying a video signal, said video signal representing the brightness level of a plurality of lines comprising a plurality of fields separated by vertical synchronization pulses, each of said fields having an unscrambled portion and a scrambled portion comprising a number of alternate lines which have a level shifted a predetermined amount thereby distorting the luminance level and chrominance associated therewith, each of said alternate lines separated by an unshifted line having a correct brightness level and chrominance, subsequent fields of said video signal having a different number of alternate scrambled lines separated by unscrambled lines;

means for supplying an identifying signal for identifying the portion of each field which contains said scrambled alternate lines; and

means for shifting the luminance level and chrominance of said video signal representing said alternate lines without shifting the remaining lines in response to said identifying signal, thereby restoring the brightness level of said alternate lines contained in said scrambled portion.

14. A receiving apparatus for descrambling a video signal comprising:

means for supplying a video signal representing the luminance level and chrominance of a plurality of lines comprising a plurality of fields separated by vertical synchronization pulses, at least one of said vertical synchronization pulses having a level different from preceding synchronization pulses, each of said fields having a portion containing alternate lines which have a brightness level shifted in level a predetermined amount thereby distorting the brightness level associated therewith, said alternate lines being separated by lines having a correct brightness level, the number of alternate lines having a shifted brightness level separated by lines having a correct brightness level changing in successive fields;

means for shifting the level of said one vertical synchronization pulse to correspond to the level of the remainder of said vertical synchronization pulses;

means for supplying an identifying signal for identifying the portion of each field which contains said alternate lines; and

means for shifting the luminance level of said video signal representing said alternate lines in response to said identifying signal, thereby restoring the luminance level of said alternate lines.

15. A method for scrambling a video signal comprising:

generating during each vertical interval a random number identifying a horizontal line of a subsequent field of said video signal;

counting subsequent horizontal lines following said identified line; and

inverting alternate of said counted lines following said identified horizontal line, whereby a portion of said subsequent field contains an unscrambled portion and a remaining scrambled portion of alternate inverted lines, and the number of alternate scrambled lines in subsequent fields separated by unscrambled lines changes.

16. The method of claim 15, further comprising:

inserting a signal representing said random number in said vertical interval, whereby decoding information for said subsequent field is provided with said video signal.

17. A method for unscrambling a video signal, each field of said video signal including a scrambled portion and unscrambled portion, the number of alternate scrambled lines separated by unscrambled lines changing in subsequent fields, said video signal including prior to each field a decoding signal, comprising:

removing said decoding signal from said video signal;

counting each line of said field until a line identified by said decoding signal is received; and

inverting alternate lines of said video signal subsequent to said identified line, whereby said scrambled portion is unscrambled.

18. An apparatus for scrambling a video signal comprising:

a random number generator for producing a random number during a vertical interval of each field;

a preselectable line counter for counting horizontal lines of said video signal, said line counter being preset during each vertical interval with said random number, whereby an output signal is produced when a number of lines are counted corresponding to said random number;

a binary counter for counting two horizontal lines, said counter being enabled by said presettable line counter whereby alternate lines provide an output signal; and

means for inverting the luminance portion of said alternate lines in response to said binary counter output signal whereby a scrambled portion of each field is produced having alternate inverted lines and subsequent fields having a different number of alternate scrambled lines separated by unscrambled lines.

19. An apparatus for descrambling a video signal, said video signal containing a binary descrambling code during each vertical interval, said binary code identifying a starting line of an alternate line scrambling sequence, subsequent fields of said video signals having a different number of alternate scrambled lines separated by unscrambled lines, comprising:

signal processing means for removing said descrambling code from said video signal;

a presettable counter for receiving said descrambling code as a divisor, and counter being connected to count individual video lines subsequent to said vertical interval;

a binary counter connected to count said video lines, said binary counter being enabled by said presettable counter after counting to a number corresponding to said divisor; and

a line inversion means connected to receive said video signal, said inversion means being enabled by said binary counter whereby alternate lines of said video signal subsequent to a line identified by said descrambling code are inverted.