Digital data encoding in video signals using data modulated carrier signals at non-peaks in video spectra
First Claim
1. A system for communicating digital information in a video signal, said video signal having a spectrum associated therewith, comprising:
- an encoder arranged to add a carrier signal modulated by digital information to said video signal, said modulated carrier signal at other than a frequency corresponding to a peak in the video spectrum, anda receiver arranged to optically sense said video signal and to recover said encoded digital information in said video signal.
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Accused Products
Abstract
Digital information is encoded in the video portion of a television signal such that "n" (n is an integer) bits of the digital information are carried by each successive frame in a group of frames. The digital information is encoded by modulating a carrier signal, using, for example, either amplitude shift keying (ASK) or frequency shift keying (FSK), and the modulated carrier is then added to the video signal selectively, only in portions of the television program that (a) are not likely to be perceptible by a viewer, and (b) are of sufficient intensity to transmit the data. The video signal including the encoded digital data, may be transmitted, in real time, to a television receiver, or recorded for later playback. In either event, at a receiver, when the video signal containing the encoded information is displayed on a screen, the image is sensed or "viewed" by a photo detector, the output of which is applied to a band pass filter having a center frequency that corresponds to the oscillator frequency(s) in the encoder. The filter output is thresholded or FM detected, so that the receiver can recover the encoded data. By appropriately including checks bits and synchronization patterns, the bit stream output from the decoder can be synchronized, and the original encoded data recovered. Advantageously, the frequency of the oscillator in the ASK or FSK encoder is chosen so that the energy added to the video signal is in a portion of the frequency spectrum that otherwise contains little energy. This makes the added digital data imperceptible to a viewer. If desired, the same data may be repetitively encoded in several groups of frames, so as to increase the redundancy and thus the reliability of the overall system.
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Citations
11 Claims
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1. A system for communicating digital information in a video signal, said video signal having a spectrum associated therewith, comprising:
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an encoder arranged to add a carrier signal modulated by digital information to said video signal, said modulated carrier signal at other than a frequency corresponding to a peak in the video spectrum, and a receiver arranged to optically sense said video signal and to recover said encoded digital information in said video signal. - View Dependent Claims (2, 3)
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4. An encoder arranged to encode n bits of digital information in each successive frame of a video signal, said video signal having a spectrum associated therewith, comprising
a buffer for storing said digital information, means for obtaining a synchronization signal synchronized with the frame rate of said video signal, means responsive to said synchronization signal for generating a modulated carrier signal during each frame interval, said modulated carrier signal at other than a frequency corresponding to a peak in the video spectrum, said modulated carrier signal being formed by controlling the output of an oscillator in accordance with the value of the next n bits from said buffer, and means for combining said modulated carrier signal with said video signal.
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6. A receiver arranged to recover n bits of encoded digital information included in each successive frame of a video signal, said video signal having a spectrum associated therewith, comprising
a photo detector responsive to the picture generated by said video signal, means for amplifying the output of said photo detector, means for filtering the output of said amplifying means to isolate a component at a particular frequency, said frequency being other than a frequency corresponding to a peak in the video spectrum, and means for applying the output of said filtering means to a decoder to recover said encoded digital information.
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7. A receiver, including
a photo detector for viewing a television signal display containing encoded information mixed with a video signal, said video signal having a spectrum associated therewith, said encoded information being represented by at least one frequency component at a frequency which is not likely to be perceptible to a viewer of said video signal, said frequency being other than a frequency corresponding to a peak in the video spectrum, means including a band pass filter having a center frequency that is the same as said frequency of said frequency component, for isolating said frequency component from the output of said photo detector, and thresholding means for recovering said encoded information from said isolated frequency component.
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8. A method for encoding digital information in the video portion of a television signal such that "n" (n is an integer) bits of the digital information are carried by each successive frame in a group of frames, said television signal having a spectrum associated therewith, comprising the steps of
encoding said digital information using either amplitude shift keying (ASK) or frequency shift keying (FSK), and selectively adding said encoded digital information to said video signal, only in one or more portions of the spectrum other than those which correspond to a peak in said spectrum, wherein said encoding steps includes the steps of storing digital information to be encoded in a buffer, reading out "n" bits of stored data from the buffer during each frame interval, in synchronization with the video signal frame rate, and using the output from said buffer to control the state of an ASK or FSK encoder.
Specification