Video copy protection

Details Video copy protection Video copy protection

1997-04-14

1999-03-16

Cain, David

Cryptography

Cryptanalysis

380 5, H04N 7167

Patent

active

058839593

ABSTRACT:
Regular burst signals from video line (n+0) to line (n+3) are replaced by modified burst signals which function as copy prohibit signals. The phase of the modified burst signals is controlled by controlling at least one of the orthogonal vectors into which the phase of the regular burst signal is resolved; and the phase vector of the modified burst signals is equal to the average value of the phase vector of the regular burst signals in lines (n+0) through (n+3). The phase vector of the modified burst signal in line (n+2) exhibits a phase difference of 135.degree. from the phase vector of the original regular burst signal in that line and causes image disturbances when the thus-modified video signal is recorded and reproduced by a VCR. The phase vector of the modified burst signal in each of lines (n+0), (n+1) and (n+3) exhibits a difference as small as 45.degree. from the phase vector of the original regular burst signal in those lines.

REFERENCES:
patent: 5608799 (1997-03-01), Ryan et al.
patent: 5651065 (1997-07-01), Stufflet al.
patent: 5661801 (1997-08-01), Sperber
patent: 5784523 (1998-07-01), Quan et al.

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