;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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;~002933 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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Z00~933 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
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 . ~
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
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 , ' ' ~ ' ~002~3 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
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
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 '' ; G ' ~002933 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
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 :
~:OOZ933 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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200~933 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.