Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
;2002933
A~PARATUS FOR GENERATING SUPERIMPOSED TELEVISION IMAGES
The field of the present invention is apparatus for
forming superimposed television images comprising in particular a
background television image and an overlay image.
For various home television applications it may be
desirable to superimpose one television image over another
whereby the viewer sees a combined image. Such apparatus may be
useful in displaying messages over a background television image
that a viewer can read while observing the principal image. In a
broader sense, however, it may be desirable to develop a
capability for superimposing television images originating from
cable television, broadcast television, computers, video game
machines, VCR tapes, or other sources, over television images
originating from similar or other sources. For example, an
inexpensive hybrid video game which combines television or VCR
images with computer generated images ~ight prove useful. Such a
device could be used for interactive educational programming that
mixes computer images and broadcast television images. A user
might also wish to combine subliminal self help messages with
normal television programming.
Apparatus capable of achieving the fore~oing objectives
should preferably be low in cost, easy to manufacture and simple
to install. No modification of existing television, VCR, or
computer equipment should be required. Such apparatus should
preferably operate without regard to the carrier frequency of the
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background image, or even without regard to whether the
background image possesses a carrier at all. Emission of radio
frequency interference should also be avoided. In light of these
concerns, the wide variety of sophisticated apparatus presently
in use in the television industry for mixing modulated or
unmodulated television signals to form a combined output signal
may prove inappropriate in home use applications.
The present invention is directed to a device for
generating a superimposed television image over another
television image. To that end, means are provided whereby a
secondary television image signal may be used to selectively
attenuate or boost the signal strength of a primary television
image. Means may be further provided for open air mixing of
audio signals, including a subliminal audio signal corresponding
to a subliminal secondary television image --.
Figure 1 is a block diagrammatic illustration of an
apparatus constructed in accordance with an embodiment of the
present invention as arranged in combination with a television
set and a videocassette recorder.
Figure 2 is a schematic representation of an apparatus
constructed in accordance with an embodiment of the present
invention arranged for implementation with a television set and a
videocassette recorder.
Figure 3A is a graphic representation of one horizontal
scan line of a signal representing a secondary television image
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from a videocassette recorder showing the standard
synchronization pulse and the video signal.
Figure 3B is a graphic representation of the output of
the video threshold converter portion of an apparatus constructed
in accordance with an embodiment of the present invention.
Figure 3C is a graphic representation of a composite
television image generated by an apparatus constructed in
accordance with an embodiment of the present invention.
Figure 3D is a graphic representation of a standard RF
television signal.
Referring to Figure 1, a device constructed in
accordance with one embodiment of the present invention comprises
seven components, including a voltage regulator, an audio
amplifier, a video threshold convertor, RF protection, an RF
amplifier/buffer, a switchable RF attenuator, and a
normal/subliminal selector switch. The voltage regulator
receives a 9 volt DC input from a standard plug-in wall
transformer and provides an output which provides an input
voltage to the RF amplifier/buffer, the switchable RF attenuator,
the video threshold converter and the audio amplifier. The RF
protection circuit receives an RF signal from a cable or antenna.
If the apparatus is in the non-operational mode, the RF signal is
passed directly as an RF input to the VCR. If the apparatus is
in the operational mode, the RF signal from the cable or antenna
is passed through the RF protection circuit, the RF amplifier/
buffer, the switchable RF attenuator, the normal/subliminal
selector switch and to the RF input of a television. The video
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threshold convertor receives a video output signal from a VCR and
generates an output signal to the switchable RF attenuator. The
normal/su~liminal selector switch receives an RF signal from a
VCR. As suggested by the designation "normal/subliminal," the
output signal from the VCR may be a subliminal visual andtor
audio signal such as a self help message that does not produce a
conscious sensation or perception in the viewer. If the
apparatus is in the non-operational state, the RF signal to the
television is the output from the switchable RF attenuator. The
audio amplifier receives an audio signal from a VCR and generates
an audio output.
Referring to Figure 2, the voltage regulator of Figure
1 is represented in principal part by the capacitors Cl and C2,
the resistor R7, the LED D3 and the integrated circuit U1. The
input to the voltage regulator is a 9 volt DC 100 milliamp signal
from a standard plug-in wall transformer connected to the power
jack J7. The capacitor Cl is used to filter the rectified DC
voltage presented at J7. The integrated circuit Ul is a standard
linear integrated circuit implemented to regulate the unstable DC
voltage presented by Cl to a definable 6 volts DC. The capacitor
C2 is used to assist Ul by acting as an energy storage device,
thus providing energy when an instantaneous high current event
takes place. The LED D3 is used as a visual annunciator to
signi~y that the device is both powered up and operating in the
composite image generating mode. The resistor R7 is used to
regulate the current through (and thus the brightness of) the ~ED
D3. The voltage regulator output is represented by Vcc and is a
stable six volt DC signal.
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The optional audio amplifier of Figure 1 is represented
in principal part by the resistor R13, the variable resistor R9,
the capacitor C10, the integrated circuit U2 and the speaker SP1.
The input to the audio amplifier is an audio output signal from a
VCR or the like. The resistor R13 is used to limit the AC
voltage presented to the audio amplifier U2. This limits the
maximum volume setting to a level within the specifications of
U2. The variable resistor R9 is used to control the AC voltage
presented to the audio amplifier U2. This is the audio message
volume control. The integrated circuit U2 is implemented as an
audio amplifier. In the present embodiment, U2 is a low voltage
audio power amplifier available from National Semiconductor
Corporation, bearing the designation LM386. The LM386 is an
eight pin power amplifier for use in low voltage applications.
In the present application, pins ~, 3, 4, 5, and 6 are utilized
as shown in Figure 2 such that U2 provides a maximum usable power
output of 250 milliwatts at 8 ohms.
The video threshold convertor is represented in
principal part by the capacitors C8 and Cll, the resistors R8,
R12 and R15, the variable resistor Rll and the integrated circuit
U3. The input to the video threshold convertor is a video signal
from a VCR or the like provided at the jack Jl. The resistor R8
provides DC termination of the composite video signal presented
at J1. The capacitor C11 is used to AC couple the standard video
signal presented at J1 with the signal required by the voltage
comparator U3. That is, the capacitor C11 removes the DC
component from the J1 video signal. The variable resistor R11 is
used to set the DC bias point of the negative input of the
voltage comparator U3. This variable resistor may be replaced by
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two fixed resistors once an optimum setting (ratio) is
determined. The resistors R12 and R15 are used to set the DC
bias point of the positive input of the voltage comparator U3.
The capacitor C8 is used as an energy storage device providing
the voltage comparator U3 with the instantaneous current required
during switching. This capacitor should be located as near to
the voltage comparator U3 as is physically possible. The
integrated circuit U3 is an 8 pin voltage comparator whose
internal output transistor switches on in the event that the DC
level-shifted composite video signal presented to its negative
input becomes greater than the static DC voltage presented to its
positive input. In the present embodiment, U3 is a voltage
comparator available from National Semiconductor Corporation,
bearing the designation LM311. As shown in Figure 2, pins 1, 2,
3, 4, 7, and 8 are employed. The output of U3 is provided at pin
7. As hereinafter discussed, this output is adjusted to
eliminate the standard television synchronization pulses from the
VCR video signal as well as low luminance background noise. The
video threshold converter output at pin 7 of the comparator U3
provides an RF attenuation signal to the switchable RF
attenuator.
The RF protection circuit is represented in principal
part by the capacitors C3 and C4, the resistor R16 and the diodes
D4 and D5. The resistor R16 is used to drain any possible
parasitic DC voltage build-up that may occur on standard RF
signal sources, such as an antenna. The capacitor C3 is used to
AC couple the standard RF signal presented to J3. The diodes D4
and D5 are used to limit the voltage presented by C3 to a 1 volt
swing. This will act as overload protection to the circuits
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involved with the standard RF signal presented to J3. In the
present embodiment, the diodes D4 and Ds are high conductance
ultra fast switching diodes available from Fairchild, a
Schlumberger Company, bearing the designation lN914. The
capacitor C4 is used to AC couple the signal presented by the RF
protection circuit to the signal required by the RF
amplifier/buffer.
The RF amplifier/buffer is represented in principal
part by the capacitors C5, C6 and C9, the resistors R1, R2, R3,
R4 and R5 and the transistor Q1. The resistors Rl, R2, R3, R4
and R5 are used to DC bias the transistor Ql to act as a gain
stabilized DC amplifier. In the present embodiment, Ql is an
overlay, double-diffused, gold-doped, silicon epitaxial NPN
device available from National Semiconductor Company, bearing the
designation 2N3904. The capacitor C5 is used to reduce the
effective AC emitter resistance. The resistor C9 is used as an
energy storage device providing the RF amplifier/buffer with
greater power supply noise immunity. This capacitor should be
placed as near to the transistor Q1 as is physically possible.
The capacitor C6 is used to AC couple the signal presented by the
RF amplifier/buffer to the signal required by the switchable RF
attenuator.
The switchable RF attenuator is represented in
principal part by the capacitor C7, the resistors R6, R10 and
R17, the variable resistor R14 and the diodes D1 and D2. The
resistor R6 is used to cause the RF signal presented by the RF
amplifier/buffer to center around the regulated 6 volt power
signal. The diodes D1 and D2 are used to reduce the effective AC
resistance of this siqnal path by an adjustable amount. Reducing
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the AC resistance causes a determinable RF attenuation. The
variable resistor R14 is used to determine the effective AC
resistance presented by Dl and D2 if the switchable RF attenuator
is actively attenuating. This is the video message intensity
control. The resistor R10 is used to limit the amount of
attenuation attainable with the switchable RF attenuator. This
prevents high current switching activity which could otherwise
result in undesirable RF emissions. The capacitor C7 is used to
AC couple the signal presented by the switchable attenuator to
the signal required by the RF receiver connected to the jack J6.
The resistor R17 is used in conjunction with R3 to balance the
RF signal presented to J3 by providing an effective AC resistance
of 75 ohms as presented by this device.
The normal/subliminal selector switch is represented in
principal part by the switch SWl. When SWl is in the off state,
no power is provided from J7 to the voltage regulator and an RF
signal from a VCR or the like is provided from the jack J5 to the
jack J6 to provide an RF input to a television or the like. When
the switch SWl is in the on position, power is provided from the
jack J7 to the voltage regulator and the jack J6 is disconnected
from the jack J5 and connected to the output of the switchable RF
attenuator.
Referring to Figures 2 and 3, the input ~1 of the video
threshold convertor represents the video input from a secondary
image source, such as a video cassette recorder, which, as
indicated, may be a subliminal message. A graphic representation
of that signal is shown in Figure 3A. The signal received at J1
is a standard composite video signal which provides the necessary
voltage information to the scanning means of a composite video
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monitor or television picture tube as scanning occurs line by
line across the tube. The video input at Jl includes the
standard synchronization pulse that would normally be received by
the monitor or television. As shown in Figure 3A, the video
input signal at J1 also includes signal information corresponding
to one line of the video image to be displayed. In this case,
the message "no good no" in red, white and red letters,
respectively, represents the image to be displayed. Figure 3A
illustrates the signal information corresponding to one line of
this message. It includes both intensity and color information.
Figure 3B illustrates the output signal from pin 7 of
the voltage comparator U3. As shown, the synchronization pulse
from the video input signal at J3 has been eliminated by
adjustment of the video threshold adjustor R11. The threshold
adjustor has further been set so as to pass only a signal
representing the message "good".
Figure 3D shows a standard modulated RF signal from a
cable or antennae presented at J3.
Figure 3C shows a composite video signal representing
the output from the switchable RF attenuator to J6. As shown,
the RF signal is selectively attenuated in response to the video
threshold convertor output at pin 7 of the voltage comparator U3
in a manner corresponding to the message "good". Attenuation of
the RF signal cause6 the corresponding pixel(s) on the video
monitor or television screen for the line being scanned to change
color and intensity (i.e., to form "holes" in the primary image),
whereby the message "good" from the secondary video source will
appear on the primary television image. The variable resistor
R14 enables the intensity of the message to be adjusted.
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The input J2 of the audio amplifier represents the
audio output from a secondary source such a video cassette
recorder. By adjustment of the variable resistor R9, the volume
of the audio output from the speaker SPl may be selected. The
output from the speaker SPl and a primary audio signal from the
television speaker are thus selectively mixed by open air mixing.
Thus, a television image superimposing apparatus has
been disclosed which generates a combined television image by
selectively attenuating a primary television image signal in
response to a secondary television image signal. While
embodiments and applications of this invention have been shown
and described, it would be apparent to those skilled in the art
that many more modifications are possible without departing from
the inventive concepts herein. The invention, therefore, is not
to be restricted except in the spirit of the appended claims.
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