Cryptography – Video cryptography
Reexamination Certificate
1998-11-06
2002-02-19
Peeso, Thomas R. (Department: 2132)
Cryptography
Video cryptography
C380S210000, C380S213000
Reexamination Certificate
active
06349139
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to video signal scrambling systems and, more particularly, to a coring system for providing a substantially stable color subcarrier signal while retaining full luminance resolution, in line time shifting or position modulating video scrambling apparatus.
The U.S. Pat. Nos. Re. 35,078 ('078), 5,438,620 ('620) and 5,504,815 ('815) of previous mention, incorporated herein by reference, disclose typical line positional shifting video scrambler processes and apparatus. Such line positional or time shifting video scramblers include a video comb filter or equivalent luminance/chrominance separator to separate the composite input signal into luminance and chrominance components (see
FIG. 1A
) or luminance and demodulated chrominance R-Y and B-Y components (see FIG.
1
B). The separated signals then are shifted in time or position via suitable memories, such as first-in-first-out (FIFO) memories, or variable delay lines. In
FIG. 1A
, the chrominance signal first is time shifted (that is, scrambled) and then is color subcarrier stabilized in both phase and frequency (for example, via a heterodyning process), before being added to the scrambled luminance signal, to provide a composite color stabilized time or position modulated scrambled video output signal. In
FIG. 1B
, where the R-Y and B-Y demodulated chrominance components are provided, the time shifted or position modulated R-Y and B-Y components are re-encoded with a stable color subcarrier frequency and phase before being added to the time shifted or position modulated luminance signal to provide a composite color stabilized time shifted or position modulated scrambled video output signal.
However, the video comb filter or luminance/chrominance separator of the above scrambling systems does not provide perfect separation of the chrominance (chroma) and luminance (luma) components. Therefore residual chroma remains in the luma channel in the scrambling systems described above. Normally, imperfect luminance-chrominance separation is not a problem in equipment such as television sets. That is, in such equipment, the residual chrominance in the luminance channel still is stable chrominance and thus does not contribute to chrominance instabilities in, for example, the television set. However, once the luma channel is time shifted by the scrambling process, the residual chroma becomes unstable in phase and frequency. When the time shifted or (low frequency) position modulated luminance channel signal with the unstable residual chroma is added to the stabilized time shifted chroma channel signal, a composite video signal is produced with small, but visible, unstable chroma phase and amplitude errors when scrambled and later descrambled. These unstable chroma phase and amplitude errors cause low frequency color streaking or hue and saturation noise throughout the television field.
FIG. 1A
illustrates a basic video path for a scrambling system
10
which employs a signal wobbling technique, such as described in the '620 and '815 patents of previous mention. A program video signal, such as a composite video signal, is supplied via an input lead
12
to a comb filter
14
. The elements
76
,
78
and
80
shown in
FIG. 4
of the '620 and '815 patents exemplify elements which can be used to form the comb filter
14
in FIG.
1
A. The comb filter
14
provides outputs of a luma signal with residual chroma, and a chroma signal. The luma signal along with its residual chroma are supplied to a time shift element
16
to effect the scrambling process, whereby the element
16
, provides a shifted luma signal with shifted unstable phase residual chroma. The chroma signal is supplied to a second time shift element
18
which provides the previously mentioned scrambling of the chroma signal. It is to be understood that the time shift elements
16
,
18
could be position modulation elements as well. Both of the time shift (or position modulation) elements shift the video signal by an equal amount as part of the particular scrambling process used. The output of the time shift element
18
, comprising the time shifted chroma signal, is supplied to a chroma subcarrier stabilizer
20
. The chroma subcarrier stabilizer
20
is comparable to the hetrodyne element
100
in
FIG. 4
of the '620 and '815 patents, and provides a shifted chroma signal with stable phase. The outputs of the chroma subcarrier stabilizer
20
and of the time shift element
16
are supplied to the inputs of an adder circuit
22
, which produces a scrambled video signal having chroma subcarrier instabilities on an output lead
24
.
FIG. 1B
illustrates a basic video path for a scrambling system
30
which employs a signal wobbling technique such as described in the '078 patent of previous mention. A program video signal, such as a composite video signal, is supplied via an input lead
32
to a comb filter/chroma demodulator circuit
34
. The element
16
shown in
FIG. 4A
of the '078 patent exemplifies an element which can be used as the comb filter/chroma demodulator circuit
34
in FIG.
1
B. The comb filter/chroma demodulator circuit
34
provides outputs of a luma signal with some residual chroma, a R-Y component and a B-Y component. The luma signal along with its residual chroma are supplied to a time shift or position modulation element
36
, which provides a scrambled luma signal formed of a shifted luma signal with shifted unstable phase residual chroma. The R-Y and B-Y signals are supplied to a two channel time shift element
38
which provides scrambled R-Y and B-Y component signals. The time shift elements
36
,
38
shift the respective video signal by an equal amount as part of the scrambling process. The outputs of the time shift element
38
, comprising the time shifted or position modulation R-Y and B-Y signals, are supplied to a chroma encoder
40
. The chroma encoder
40
is comparable to the encoder element
25
in
FIG. 4A
of the '078 patent of previous mention, and provides a scrambled chroma signal with stable phase. The outputs of the chroma encoder
40
and of the time shift element
36
are supplied to the inputs of an adder circuit
42
, which produces a scrambled video signal having chroma subcarrier instabilities on an output lead
44
.
One solution for removing the unstable residual chroma from the positionally shifted luma channel includes the application of a notch filter in the luminance channel, wherein the filter has a frequency band around the color subcarrier frequency and its color sidebands. However, this solution severely degrades the luminance resolution and thus degrades the frequency response of the video scrambler's and thus the descrambler's output. The degraded resolution eliminates much of the advantage that video comb filters provide, since comb filters normally aid in gaining full luminance resolution. Accordingly, there is a need for a solution that eliminates the unstable chroma phase and amplitude errors without degrading the luminance frequency response and the resultant resolution of the signal scrambling system.
SUMMARY OF THE INVENTION
An object of the present invention is to retain full luminance resolution of video scrambling systems while providing a substantially stable color subcarrier. The stable subcarrier phase and amplitude appear in the resulting composite video output signal, corresponding to the time shifted or position modulated scrambled video signal. The increased stability substantially reduces or eliminates chroma noise due to imperfect luminance/chrominance signal separation. That is, it is the intent of the present invention to substantially remove the unstable residual chroma color subcarrier caused by the small amount of chroma signal which leaks into the luma channel, so when the signal in the positionally modulated or time shifted (wobbled) luminance channel is summed with the signal in the positionally modulated or time shifted stable chroma color subcarrier channel, color
Alameida George
Macrovision Corporation
Nguyen Frank
Peeso Thomas R.
LandOfFree
Method and apparatus for minimizing chroma subcarrier... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for minimizing chroma subcarrier..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for minimizing chroma subcarrier... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2980529