Patent US4488176A successfully refreshed from Google Patents.
US4488176A
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Method of and apparatus for modifying a video signal to inhibit recording thereof
Assignee: Nortel Networks Ltd
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Filing: 1981-10-08
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Granted: 1984-12-11
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Expires: 2001-10-08
Abstract
Abstract Video signal lines are added to or omitted from the ends of individual fields of a video signal to produce a modified video signal whose field length varies at a slow rate. The modified video signal can be broadcast and received by conventional television equipment, normal television reception and viewing being not noticeably affected by the variable field length. However, recording of the modified video signal is inhibited because the field length is not constant. The modified video signal is produced by directly modifying the scanning of televising equipment, or by storing the lines of the video signal in a store and reading them in a controlled manner therefrom. A decoder, for producing a constant field length video signal from the modified video signal, is also disclosed.
Inventors
- 👤 John A. Bond
- 👤 Yuan-Lu Li
- 👤 Leslie J. Crane
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 04:51
CPC Classifications
H; H04; H04N; H04N7/00; H04N7/16; H04N7/167; H04N7/171; H04N7/1713; H04N5/00; H04N5/76; H04N5/91; H04N5/913; H04N2005/91357; H04N2005/91385
Claims Analysis
Total Claims: 15
Claim 1
Independent Claim
49 words
A method of modifying a video signal to inhibit recording thereof whilst permitting a television receiver to display a video picture in response to the modified video signal, comprising varying the length of fields of the video signal to produce the modified video signal with a varying field length.
Claim 2
Independent Claim
49 words
A method of modifying a video signal to inhibit recording thereof whilst permitting a television receiver to display a video picture in response to the modified video signal, comprising varying the length of fields of the video signal to produce the modified video signal with a varying field length.
Claim 3
Dependent Claim
36 words
A method as claimed in claim 1 wherein the length of fields of the video signal is varied by selectively omitting lines from and adding lines to the ends of individual fields of the video signal.
Claim 4
Dependent Claim
29 words
A method as claimed in claim 2 wherein the step of adding lines to the ends of individual fields of the video signal comprises repeating lines of said fields.
Claim 5
Independent Claim
37 words
A method as claimed in any of claims 1 to 3 wherein the length of fields of the video signal is varied at a rate which on average is not greater than one line per three fields.
Claim 6
Independent Claim
47 words
A method as claimed in any of claims 1 to 3 wherein the length of fields of the video signal is varied so that a long-term average of the field lengths of the modified video signal is equal to the field length of the unmodified video signal.
Claim 7
Dependent Claim
75 words
A method as claimed in claim 1 wherein the step of varying the length of fields of the video signal comprises storing video signal lines of the video signal to be modified sequentially in a memory and reading said lines from the memory, said lines being read generally sequentially but with lines being omitted from and re-read from the ends of individual fields to produce respectively shortened or lengthened fields in the modified video signal.
Claim 8
Dependent Claim
105 words
Apparatus for converting between a video signal, comprising constant-length fields of video signal lines, and a modified video signal, comprising varying length fields of video signal lines, said apparatus comprising: a memory unit; means for storing the video signal lines of one of said video signals in the memory unit; means for reading video signal lines from the memory unit; and means for controlling the reading means to selectively omit lines from and add lines to individual fields of the video signal lines read from the memory unit whereby the video signal lines read from the memory unit constitute the other of said video signals.
Claim 9
Dependent Claim
105 words
Apparatus for converting between a video signal, comprising constant-length fields of video signal lines, and a modified video signal, comprising varying length fields of video signal lines, said apparatus comprising: a memory unit; means for storing the video signal lines of one of said video signals in the memory unit; means for reading video signal lines from the memory unit; and means for controlling the reading means to selectively omit lines from and add lines to individual fields of the video signal lines read from the memory unit whereby the video signal lines read from the memory unit constitute the other of said video signals.
Claim 10
Dependent Claim
113 words
Apparatus for modifying a video signal comprising fields of video signal lines to inhibit recording thereof whilst permitting a television receiver to display a video picture in response to the modified video signal, said apparatus comprising: a memory unit; means for storing the video signal lines of the video signal in the memory unit; means for reading the video signal lines from the memory unit; and means for controlling the reading means to selectively omit lines from and add lines to individual fields of the video signal lines read from the memory unit whereby the video signal lines read from the memory unit constitute a modified video signal having a varying field length.
Claim 11
Dependent Claim
113 words
Apparatus for modifying a video signal comprising fields of video signal lines to inhibit recording thereof whilst permitting a television receiver to display a video picture in response to the modified video signal, said apparatus comprising: a memory unit; means for storing the video signal lines of the video signal in the memory unit; means for reading the video signal lines from the memory unit; and means for controlling the reading means to selectively omit lines from and add lines to individual fields of the video signal lines read from the memory unit whereby the video signal lines read from the memory unit constitute a modified video signal having a varying field length.
Claim 12
Dependent Claim
57 words
Apparatus as claimed in claim 8 wherein the memory unit serves to store digital signals, the storing means comprises means for converting the video signal from an analog signal to digital signals, and the reading means comprises means for converting digital signals read from the memory unit to an analog signal to constitute the modified video signal.
Claim 13
Dependent Claim
82 words
Apparatus as claimed in claim 8 or 9 wherein the control means comprises means for storing a memory address relating to the storage in the memory unit of the vertical interval in each field of the video signal, and means responsive to each such stored memory address for selectively controlling the reading means to omit lines from or re-read lines at the end of the previous field of the video signal stored in the memory unit to produce the modified video signal.
Claim 14
Independent Claim
93 words
A method of converting a modified video signal, comprising varying length fields of analog video signal lines, to an analog video signal of constant field length, comprising converting the analog video signal lines to digital signals, storing the digital signals in a memory unit, reading the digital signals from the memory unit at a constant field rate by selectively omitting digital signal lines from and adding digital signal lines to the digital signals read from the memory unit, and converting the resultant digital signals to said analog video signal of constant field length.
Claim 15
Independent Claim
93 words
A method of converting a modified video signal, comprising varying length fields of analog video signal lines, to an analog video signal of constant field length, comprising converting the analog video signal lines to digital signals, storing the digital signals in a memory unit, reading the digital signals from the memory unit at a constant field rate by selectively omitting digital signal lines from and adding digital signal lines to the digital signals read from the memory unit, and converting the resultant digital signals to said analog video signal of constant field length.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1987-12-11 | 1988-06-11 | 1988-12-11 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1991-12-11 | 1992-06-11 | 1992-12-11 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1995-12-11 | 1996-06-11 | 1996-12-11 | $7700.00 | Window Closed / Lapsed |