Motion video signal processing for recording or reproducing – Local trick play processing – With randomly accessible medium
Reexamination Certificate
2000-03-29
2004-11-30
Nguyen, Huy (Department: 2616)
Motion video signal processing for recording or reproducing
Local trick play processing
With randomly accessible medium
C380S203000
Reexamination Certificate
active
06826352
ABSTRACT:
BACKGROUND OF THE INVENTION
Conventional videotape recorders have an automatic gain control circuit which measures the level of a pulse (called “sync pulse”) in a video signal. The circuit uses the measured level to develop a gain correction signal that is used to keep the video level applied to an FM modulator in the videotape recording system (VCR) at a fixed, predetermined value. It is conventional to prevent unauthorized copying of a videotape, by use of the fact that such a circuit of a videotape recorder is sensitive to pulses added to a normal video signal to prevent copying as described in, for example U.S. Pat. No. 4,631,603 granted to Ryan (i.e., Ryan '603, that is incorporated by reference herein in its entirety).
U.S. Pat. No. 5,583,936 granted to Wonfor et al. (i.e., Wonfor '946, also incorporated by reference herein in its entirety) describes a number of enhancements (hereinafter “retrace enhancers”) to a video anti-copying process of the type described above or to anti-copy processes that cause attenuation (as described in e.g. U.S. Pat. Nos. 5,130,810 and 4,918,098 granted to Ryan (Ryan '810 and '098) and 4,163,253 granted to Morio et al. (Morio '253). Specifically, Wonfor '936 describes e.g. introduction into the overscan portion of the television picture, just prior to the horizontal or vertical sync signals but in active video, a negative going waveform that appears to the television receiver (TV set) or videotape recorder (VCR) to be a sync signal, thereby causing an early horizontal or vertical retrace.
One version provides a waveform (called horizontal retrace enhancer) in the right overscan portion of the picture, that results in a checker pattern of alternating gray and black areas (illustrated in
FIG. 1A
as ES
0
-ES
6
). This causes the TV set on which the illegal copy is played to horizontally retrace earlier than normal in selected lines, with a consequential horizontal shift of the picture information on those lines. This substantially degrades picture playability. In another version, another waveform (called vertical retrace enhancer) introduces a gray pattern (illustrated in
FIGS. 1B and 1C
as GP
0
-GP
2
and GP
3
-GP
5
respectively) at the bottom overscan portion of the picture, which causes vertical picture instability (also called “jitter”). It is noted that the features in the waveforms of
FIGS. 1A-1C
designated as ES
0
-ES
6
, GP
0
-GP
2
and GP
3
-GP
5
, are illustrated in dashed lines to indicate that the video levels thereof are variable.
Circuitry
10
for inserting the above-described horizontal and vertical retrace enhancers is shown in block form in FIG.
1
D. The main video signal path includes an input clamp amplifier A
1
(or DC restored amplifier), a sync pulse narrowing circuit
13
, a mixing point
15
at which the waveform components of the checker pattern and the vertical modification (jitter inducing) waveforms are added, and an output line driver amplifier A
2
. Amplifier A
1
ensures that the video signal at blanking is at a known pre-determined DC level before adding any additional waveform components to that video signal. The resulting clamped video signal is applied to mixing point
15
with a source impedance Ro, typically greater than 1000 ohms. In this case also the video input signal into circuit
10
of
FIG. 1D
may have the last 9 lines of each field blanked to a reference level. U.S. Pat. No. 4,695,901(i.e., Ryan '901, incorporated by reference herein in its entirety) shows a switching circuit for blanking.
A process control and signal generation path includes a sync separator
11
, a control circuit
12
, circuits VR
1
-VR
4
to generate the required signal voltages which will be added to the main video signal, and a switch selection system
14
-
1
through
14
-
4
which applies the required signal voltages to the mixing point
15
under the control of the control circuit
12
. That is, the retrace enhancers to be injected are applied to the mixing point
15
with a source impedance typically less than 50 ohms. The input video is DC restored by the input video clamp amplifier A
1
.
When it is required to modify the input video signal, for example with a checker component, the appropriate signal is selected and applied to the mixing point
15
at the low source impedance, which overrides the input video signal from amplifier A
1
and effectively replaces the input video signal with the required signal. When the input signal is to remain unchanged, the switch elements
14
-
1
to
14
-
4
are all in the open state, with the result that the video signal passes unchanged to the output line driver amplifier A
2
. The resulting video signal at the mixing point
15
is applied to line driver amplifier A
2
to provide standard output signal level and output impedance. Sync separator
11
provides composite sync pulses and a frame identification signal required by the process control circuit
12
. The process control circuit
12
generates control signals to turn on the signal selection switches
14
-
1
to
14
-
4
at the precise time and for the required duration that the various signals, that is, the horizontal or vertical retrace enhancers, are to replace the input video signal.
Various signals which replace the input video signal consist preferably of a high or low steady state DC signal level. For example the checker signal “high level” is a mid-gray level, typically of about 30% of peak white, whereas the checker signal “low level” is black level or blanking level. These various level signals are generated from potentiometers VR
1
, VR
2
, VR
3
, VR
4
(or alternatively from voltage divider resistors for fixed preset signal levels) connected across appropriate supply voltage lines. These signals are applied to the corresponding selection switch elements
14
-
1
,
14
-
2
,
14
-
3
,
14
-
4
via unity gain operational amplifiers to ensure the required low output impedance into the mixing point
15
.
Control circuit
12
generates the appropriate switch selection control pulses for addition of the horizontal and vertical retrace enhancers (see FIGS.
3
A-
3
C). Checker pulses (horizontal retrace enhancers) are applied only to selected lines. One example starts the checker pattern at the tenth line containing picture information, that is, after the end of vertical blanking and ends it ten lines before the last line containing picture information, that is, 10 lines before the start of the succeeding vertical blanking interval. Similarly, the vertical jitter signals (vertical retrace enhancers) are applied only to selected lines, for example the last nine lines prior to the vertical blanking interval. Hence, both the checker pattern and vertical jitter signals require control signals with both horizontal and vertical rate components.
The video input signal also is buffered by the amplifier A
3
and is coupled to the sync separator
11
which provides the composite sync pulses and frame identification (e.g., square wave) signals of previous mention. The composite sync pulses are applied to a phase-locked loop (PLL) located in the control circuit
12
. The phase control of the PLL using a potentiometer is adjusted so that the horizontal rate output pulse starts at the required start point of the checker, typically two microseconds before the start of horizontal blanking. The output signal of the PLL is used to derive the horizontal rate component of both the checker and vertical modification signals.
A burst gate output signal from the sync separator
11
is inverted by an inverter U
5
which provides a clamping pulse for clamp amplifier A
1
. It is to be understood that the circuit
10
(
FIG. 1D
) can be coupled to receive an input signal from a circuit that implements an attenuation-based anti-copy process.
Wonfor '936 describes a sync pulse narrowing circuit and method that is used by itself or in cascade (as shown in Wonfor's
FIG. 6
a
block
96
; see also
FIGS. 13A
,
13
B,
14
A and
14
B) with any other signal modification techniques. The method narrows the
Almeida George
Macrovision Corporation
Nguyen Huy
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