System for encoding and decoding video signals

What is claimed is:

1. A system for multiplexing a first video signal and a second video signal into a compound video signal having a bandwidth substantially less than the sum of the bandwidths of the first and second video signals comprising,

means for providing said first video signal, said first video signal including a plurality of successive lines of signal, each line having a duration of a first predetermined time, said plurality of lines consisting of a first set of alternate lines and a second set of alternate lines,

each line of said first video signal including a first luminance component having frequencies extending over a band of frequencies from zero frequency to a first predetermined frequency, a first color component consisting of sidebands of a subcarrier of one phase modulated in amplitude by a first color signal, and a second color component consisting of side bands of said subcarrier of another phase modulated in amplitude by a second color signal, said other phase being in quadrature to said one phase, said subcarrier having a frequency which is situated near the upper end of said band of frequencies of said first luminance component and which is an odd multiple of one-half of the reciprocal of said first predetermined time,

means for forming a plurality of lines of a first combined luminance signal, said plurality of lines of said first combined luminance signal consisting of a first set of alternate lines and a second set of alternate lines, each line having a duration of said first predetermined time, the amplitude of each line of said first set of alternate lines of said first combined luminance signal being a first linear combination of the amplitudes of lines of said first set of alternate lines of said first luminance signal and the amplitudes of lines of said second set of alternate lines of said first luminance signal, the amplitude of each line of said second set of alternate lines of said first combined luminance signal being zero,

means for forming a plurality of lines of a second combined luminance signal, said plurality of lines of said second combined luminance signal consisting of lines of a first set of alternate lines and a second set of alternate lines, each line having a duration of said first predetermined time, the amplitude of each line of said first set of alternate lines of said second combined luminance signal being a second linear combination of the amplitudes of lines of said first set of alternate lines of said first luminance signal and the amplitudes of lines of said second set of alternate lines of said first luminance signal, said second linear combination of said first luminance signal being independent of said first linear combination of said first luminance signal, the amplitude of each line of said second set of alternate lines of said second combined luminance signal being zero,

means for limiting the bandwidth of said first combined luminance signal to a first predetermined bandwidth,

means for limiting the bandwidth of said second combined luminance signal to a second predetermined bandwidth, said second predetermined bandwidth being substantially less than said first predetermined bandwidth,

means for compressing the duration of each of the lines of said first combined luminance signal to a duration of a second predetermined time less than said first predetermined time to increase the bandwidth thereof to a third predetermined bandwidth, said third predetermined bandwidth being greater than said first predetermined bandwidth,

means for compressing the duration of each of the lines of said second combined luminance signal to a duration of a third predetermined time to increase the bandwidth thereof to said third predetermined bandwidth,

means for providing a second video signal, said second video signal including a plurality of successive lines of signal each line having a duration of said first predetermined time, said plurality of lines consisting of a first set of alternate lines and a second set of alternate lines,

each line of said second video signal including a second luminance component having frequencies extending over a band of frequencies from zero frequency to said first predetermined frequency, a third color component consisting of sidebands of a subcarrier of one phase modulated in amplitude by a third color signal, and a fourth color component consisting of sidebands of said subcarrier of another phase modulated in amplitude by a fourth color signal, said other phase being in quadrature to said one phase, said subcarrier having a frequency which is situated near the upper end of said band of frequencies of said second luminance component and which is an odd multiple of one-half of the reciprocal of said first predetermined time,

means for forming a plurality of lines of a third combined luminance signal, said plurality of lines of said third combined luminance signal consisting of a first set of alternate lines and a second set of alternate lines, each line having a duration of said first predetermined time, the amplitude of each line of said first set of alternate lines of said third combined luminance signal being a third linear combination of the amplitudes of lines of said first set of alternate lines of said second luminance signal and the amplitudes of lines of said second set of alternate lines of said second luminance signal, the amplitude of each line of said second set of alternate lines of said third combined luminance signal being zero,

means for forming a plurality of lines of a fourth combined luminance signal, said plurality of lines of said fourth combined luminance signal consisting of a first set of alternate lines and a second set of alternate lines, each line having a duration of said first predetermined time, the amplitude of each line of said first set of alternate lines of said fourth combined luminance signal being a fourth linear combination of the amplitudes of lines of said first set of alternate lines of said second luminance signal and the ampliutdes of lines of said second set of alternate lines of said second luminance signal, said fourth linear combination of said second luminance signal being independent of said third linear combination of said second luminance signal, the amplitude of each line of said second set of alternate lines of said fourth combined luminance signal being zero,

means for limiting the bandwidth of said third combined luminance signal to said first predetermined bandwidth,

means for limiting the bandwidth of said fourth combined luminance signal to said second predetermined bandwidth,

means for compressing the duration of each of the lines of said third combined luminance signal to a duration of said second predetermined time to increase the bandwidth thereof to said third predetermined bandwidth,

means for compressing the duration of each of the lines of said fourth combined luminance signal to a duration of said third predetermined time to increase the bandwidth thereof to said third predetermined bandwidth,

means for forming a plurality of lines of a first compound video signal, said plurality of lines of said first compound video signal consisting of a first set of alternate lines and a second set of alternate lines, each line of said first set of alternate lines of said first compound video signal being formed by time multiplexing a respective compressed line of said first combined luminance signal and a respective compressed line of said second combined luminance signal, the amplitude of each line of said second set of alternate lines of said first compound video signal being zero,

means for forming a plurality of lines of a seocnd compound video signal, said plurality of lines of said second compound video signal consisting of lines of a first set of alternate lines and a second set of alternate lines, each line of said first set of alternate lines of said second compound video signal being formed by time multiplexing a respective compressed line of said third combined luminance signal and a respective compressed line of said fourth combined luminance signal, the amplitude of each line of said second set of alternate lines of said second compound video signal being zero,

means for interleaving the lines of said first set of alternate lines of said first compound video signal and said first set of lines of said second compound video signal to provide a third compound video signal.

2. The combination of claim 1 including means for transmitting each of the lines of said third compound video signal to a transmission channel.

3. The combination of claim 2 in which said first linear combination is an algebraic sum and in which said second linear combination is an algebraic difference of a line of said first set of alternate lines of said first luminance signal delayed by said first predetermined time and a successive line of said second set of alternate lines of said first luminance signal, and in which said third linear combination is an algebraic sum and in which said fourth linear combination is an algebraic difference of a line of said first set of alternate lines of said second luminance signal delayed by said first predetermined time and a successive line of said second set of alternate lines of said second luminance signal.

4. The combination of claim 3 in which the coefficient of one of the terms of said first linear combination is zero and in which the coefficient of one of the terms of said third linear combination is zero.

5. The combination of claim 3 in which is provided

means for recovering said third compound video signal from said transmission channel,

means for recovering said first compound video signal from said third compound video signal,

means for recovering said compressed first combined luminance signal from said first compound video signal and expanding the duration thereof to the duration of said first predetermined time,

means for recovering said compressed second combined luminance signal from said first compound video signal and expanding the duration thereof to the duration of said first predetermined time,

means for forming the sum of each of said first set of alternate lines of said first combined luminance signal and a respective line of said first set of alternate lines of said second combined luminance signal to reconstitute a respective line of said first set of alternate lines of said first luminance signal,

means for forming the difference of each line of said first set of alternate lines of said first combined luminance signal and a respective line of said first set of alternate lines of said second combined luminance signal to reconstitute a respective line of said second set of alternate lines of said first luminance signal,

means for interleaving said first and second sets of alternate lines of said first luminance signal to reconstitute said first luminance signal.

6. The combination of claim 5 in which said transmission channel is a storage medium and in which is provided means for storing said third compound video signal in said storage medium.

7. The combination of claim 6 in which said storage medium is magnetic tape.

8. The combination of claim 5 in which said means for transmitting each of the lines of said third compound video signal to said transmission channel includes modulating in amplitude a carrier wave with said third compound video signal.

9. The combination of claim 1 in which the bandwidth of said first combined signal is about 3 MHz and the bandwidth of said second combined signal is about 1.35 MHz, and in which the bandwidth of said third combined signal is about 3 MHz and the bandwidth of said fourth combined signal is about 1.35 MHz.

10. In combination:

means for providing a first video signal including a first luminance signal, a first color signal and a second color signal, said first luminance signal, said first color signal and said second color signal each consisting of a plurality of successive lines, each line having a duration of a first predetermined time,

means for linearly combining in accordance with a first linear relationship the amplitudes of lines of said first luminance signal to obtain a first combined luminance signal,

means for linearly combining in accordance with a second linear relationship the amplitudes of lines of said first luminance signal to obtain a second combined luminance signal, said second linear relationship being independent of said first linear relationship,

means for combining in accordance with a third linear relationship the amplitudes of lines of said first color signal to obtain a first combined color signal,

means for combining in accordance with a fourth linear relationship the amplitudes of lines of said second color signal to obtain a second combined color signal,

means for limiting the bandwidth of said second combined luminance signal, said first combined color signal and said second combined color signal in relation to the bandwidth of said first combined luminance signal,

means for compressing the duration of the lines of said first combined luminance signal, said second combined luminance signal, said first combined color signal and said second combined color signal to increase the bandwidth of each of said signals to a first value of bandwidth,

means for forming a plurality of lines of a first compound video signal, said plurality of lines of said first compound video signal consisting of a first set of alternate lines and a second set of alternate lines, each line of said first set of alternate lines of said first compound video signal being formed by time multiplexing respective compressed lines of said first combined luminance signal, said second combined luminance signal, said first combined color signal and said second combined color signal, the amplitude of each line of said second set of alternate lines of said first compound signal being zero,

means for providing a second video signal including a second luminance signal, a third color signal and a fourth color signal, said second luminance signal, said third color signal and said fourth color signal each consisting of a plurality of successive lines, each line having a duration of said first predetermined time,

means for linearly combining in accordance with a fifth linear relationships the amplitudes of lines of said second luminance signal to obtain a third combined luminance signal,

means for linearly combining in accordance with a sixth linear relationship the amplitudes of lines of said second luminance to obtain a fourth combined luminance signal,

means for combining in accordance with a seventh linear relationship the amplitudes of lines of said third color signal to obtain a third combined color signal,

means for combining in accordance with an eighth linear relationship the amplitudes of lines of said fourth color signal to obtain a fourth combined color signal,

means for limiting the bandwidth of said fourth combined luminance signal, said third combined color signal and said fourth combined color signal in relation to the bandwidth of said third combined luminance signal,

means for compressing the duration of the lines of said third combined luminance signal, said fourth combined luminance signal, said third combined color signal and said fourth combined color signal to increase the bandwidth of each of said signals to said first value of bandwidth,

means for forming a plurality of lines of a second compound video signal, said plurality of lines of said second compound video signal consisting of lines of a first set of alternate lines and a second set of alternate lines, each line of said first set of alternate lines of said second compound video signal being formed by time multiplexing respective compressed lines of said third combined luminance signal, said fourth combined luminance signal, said third combined color signal and said fourth combined color signal, the amplitude of each line of said second set of alternate lines of said second compound video signal being zero,

means for interleaving the lines of said first set of alternate lines of said first compound video signal and said first set of lines of said second compound video signal to provide a third compound video signal.

11. The combination of claim 10 including means for transmitting each of the lines of said third compound video signal to a transmission channel.

12. The combination of claim 11 in which said first linear relationship is an algebraic sum and in which said second linear relationship is an algebraic difference of a line of a first set of alternate lines of said first luminance signal delayed by said first predetermined time and a successive line of a second set of alternate lines of said first luminance signal, and in which said fifth linear relationship is an algebraic sum and in which said sixth linear relationship is an algebraic difference of a line of a first set of alternate lines of said second luminance signal delayed by said first predetermined time and a successive line of a second set of alternate lines of said second luminance signal.

13. The combination of claim 12 in which the coefficient of one of the terms of said first linear combination is zero and in which the coefficient of one of the terms of said fifth linear combination is zero.

14. The combination of claim 12 in which is provided

means for recovering said third compound video signal from said transmission channel,

means for recovering said first compound video signal from said third compound video signal,

means for recovering said compressed first combined luminance signal from said first compound video signal and expanding the duration thereof to the duration of said first predetermined time,

means for recovering said compressed second combined luminance signal from said first compound video signal and expanding the duration thereof to the duration of said first predetermined time,,

means for forming the sum of each of a first set of alternate lines of said first combined signal and a respective line of a first set of alternate lines of said second combined signal to reconstitute a respective line of a first set of alternate lines of said first luminance signal,

means for forming the difference of each line of said first set of alternate lines of said first combined signal and a respective line of said first set of alternate lines of said second combined signal to reconstitute a respective line of a second set of alternate lines of said first luminance signal,

means for interleaving said first and second sets of alternate lines of said first luminance signal,

means for recovering said compressed first combined color signal from said first compound video signal and expanding the duration thereof to the duration of said first predetermined time and repeating each successive line of said expanded first combined color signal to reconstitute said first color signal,

means for recovering said compressed second combined color signal from said first compound video signal and expanding the duration thereof to the duration of said first predetermined time and repeating each successive line of said expanded second combined color signal to reconstitute said second color signal.

15. The combination of claim 14 in which said transmission channel is a storage medium and in which is provided means for storing said third compound video signal in said storage medium.

16. The combination of claim 15 in which said storage medium is magnetic tape.

17. The combination of claim 14 in which said means for transmitting each of the lines of said third compound video signal to said transmission channel includes modulating in amplitude a carrier wave with said third compound video signal.

18. The combination of claim 10 in which the bandwidth of said first combined luminance signal is about 3 MHz, the bandwidth of said second combined luminance signal is about 1.35 MHz, in which the bandwidth of said first combined color signal is about 0.45 MHz, in which the bandwidth of said second combined color signal is about 0.45 MHz, in which the bandwidth of said third combined luminance signal is about 3 MHz, in which the bandwidth of said second combined signal is about 1.35 MHz, in which the bandwidth of said third combined color signal is about 0.45 MHz, and in which the bandwidth of said fourth combined color signal is about 0.45 MHz.

Description Submit all comments and votes

The present invention relates to a system for encoding and decoding video signals to reduce the bandwidth required for the transmission thereof over a transmission channel such as a cable television channel, a broadcast channel or a storage medium.

This patent application is related to patent application Ser. No. 383,067, filed May 28, 1982, now U.S. Pat. No. 4,473,837 and patent application Ser. No. 435,792, filed Oct. 2, 1982, both of which are assigned to the assignee of the present invention.

In a raster scanned television system, the correlation in the horizontal or raster scanned direction automatically results in a low bandwidth signal. Also, a high degree of correlation exists between lines in the vertical direction. Prior art systems of bandwidth reduction converted each pixel to a digital value of a predetermined number of bits with each pixel being assigned the same number of bits. Bandwidth was reduced by reducing the number of bits per pixel by relatively complex digital processes such as transform coding, adaptive differential pulse code modulation, etc. The resulting digital signal was transmitted in digital form. Such systems required large bandwidths, or with reduced bandwidth picture quality was impaired, unless relatively costly processing was utilized.

The present invention takes advantage of the natural correlation in a television picture in the horizontal and vertical directions for bandwidth reduction without significant impairment of the reproduced picture. This is accomplished by processing the television signal for bandwidth reduction in particular ways and transmitting it entirely in the analog domain.

An object of the present invention is to provide a bandwidth reduction system in which two video signals are passed simultaneously over a frequency channel having sufficient bandwidth to pass one video signal.

Another object of the present invention is to provide a substantially two-to-one bandwidth reduction system in which the cost of delivering two video signals is only slightly greater than the cost of delivering a single video signal.

A further object of the present invention is to reformat a television signal so that it cannot be monitored by a conventional television receiver.

In carrying out the invention in one embodiment thereof there is provided a first video signal including a first luminance signal, a first color signal and a second color signal, said first luminance signal, said first color signal and said second color signal each consisting of a plurality of successive lines, each line having a duration of a first predetermined time.

Means are provided for linearly combining in accordance with a first linear relationship the amplitudes of lines of said first luminance signal to obtain a first combined luminance signal.

Means are provided for linearly combining in accordance with a second linear relationship the amplitudes of lines of said first luminance signal to obtain a second combined luminance signal, said second linear relationship being independent of said first linear relationship.

Means are provided for combining in accordance with a third linear relationship the amplitudes of lines of said first color signal to obtain a first combined color signal.

Means are provided for combining in accordance with a fourth linear relationship the amplitudes of lines of said second color signal to obtain a second combined color signal.

Means are provided for limiting the bandwidth of said second combined luminance signal, said first combined color signal and said second combined color signal in relation to the bandwidth of said first combined luminance signal.

Means are provided for compressing the duration of the lines of said first combined luminance signal, said second combined luminance signal, said first combined color signal and said second combined color signal to increase the bandwidth of each of said signals to a first value of bandwidth.

Means are provided for forming a plurality of lines of a first compound video signal, said plurality of lines of said first compound video signal consisting of a first set of alternate lines and a second set of alternate lines, each line of said first set of alternate lines of said first compound video signal being formed by time multiplexing respective compressed lines of said first combined luminance signal, said second combined luminance signal, said first combined color signal and said second combined color signal, the amplitude of each line of said second set of alternate lines of said first compound signal being zero.

A second video signal is provided including a second luminance signal, a third color signal and a fourth color signal, said second luminance signal, said third color signal and said fourth color signal each consisting of a plurality of successive lines, each line having a duration of said first predetermined time.

Means are provided for linearly combining in accordance with a fifth linear relationships the amplitudes of lines of said second luminance signal to obtain a third combined luminance signal.

Means are provided for linearly combining in accordance with a sixth linear relationship the amplitudes of lines of said second luminance to obtain a fourth combined luminance signal.

Means are provided for combining in accordance with a seventh linear relationship the amplitudes of lines of said third color signal to obtain a third combined color signal.

Means are provided for combining in accordance with an eighth linear relationship the amplitudes of lines of said fourth color signal to obtain a fourth combined color signal.

Means are provided for limiting the bandwidth of said fourth combined luminance signal, said third combined color signal and said fourth combined color signal in relation to the bandwidth of said third combined luminance signal.

Means are provided for compressing the duration of the lines of said third combined luminance signal, said fourth combined luminance signal, said third combined color signal and said fourth combined color signal to increase the bandwidth of each of said signals to said first value of bandwidth.

Means are provided for forming a plurality of lines of a second compound video signal, said plurality of lines of said second compound video signal consisting of lines of a first set of alternate lines and a second set of alternate lines, each line of said first set of alternate lines of said second compound video signal being formed by time multiplexing respective compressed lines of said third combined luminance signal, said fourth combined luminance signal, said third combined color signal and said fourth combined color signal, the amplitude of each line of said second set of alternate lines of said second compound video signal being zero.

Means are provided for interleaving the lines of said first set of alternate lines of said first compound video signal and said first set of lines of said second compound video signal to provide a third compound video signal.

The third compound video signal is transmitted over a transmission channel to a receiving station where it is recovered. The first compound video signal is recovered from the third compound video signal and inverse operations are utilized for reconstituting the first luminance signal, the first color signal and the second color signal.

The features which are believed to be characteristic of the present invention are set forth with particularity in the appended claims.

The invention itself, both as to its organization and method of operation, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawings in which:

FIGS. 1A, 1B and 1C show in the aggregate a block diagram of apparatus for the processing of a first video signal and a second video, each including luminance and chrominance components into a resultant signal of a bandwidth comparable to the bandwidth of one of the video signals and for the transmission of the resultant signal over a transmission channel of bandwidth normally used for a single video signal.

FIGS. 2A, 2B and 2C show in the aggregate a block diagram of apparatus for receiving the resultant signal from the transmission channel of the apparatus of FIG. 1 and for the processing thereof to reconstitute either one of the first and second video signals.

FIG. 3A is a diagram of the U.S. standard television signal showing the vertical blanking interval of the first field of a frame and the horizontal blanking and scanning lines prior to and subsequent to the vertical blanking interval. The diagram also shows horizontal synchronization pulses, vertical synchronization pulses, equalizing pulses, and color burst signals.

FIG. 3B is a diagram of the U.S. standard television signal showing the blanking interval of the second field of a frame and horizontal blanking and scanning lines prior to and subsequent to the vertical blanking interval. The diagram also shows horizontal synchronization pulses, vertical synchronization pulses, equalizing pulses, and color burst signals.

FIG. 4 shows a diagram of the bands of frequencies occupied by the luminance and chrominance components of a television signal.

FIGS. 5A-5J are diagrams of the video signals, drawn to a common time scale, occurring at various points in the apparatus of FIGS. 1A-1C. The point of occurrence of a signal of FIGS. 5A-5J in the block diagrams of FIGS. 1A-1C is identified by a literal designation corresponding to the literal designation of the figure. The amplitude of each horizontal line of a first video signal to be processed is symbolically indicated by the designation l with a subscript to indicate the position of the line in the sequence of lines of a frame. The amplitude of each line of a second video signal to be processed is symbolically indicated by the designation l' with a subscript to indicate the position of the line in the sequence of luminance lines of a frame.

FIG. 5A shows several consecutive lines, l.sub.1 -l.sub.10, of the luminance component of a first video signal.

FIG. 5B shows the video signal of FIG. 5A delayed by a period of one line.

FIG. 5C shows the amplitude summation of successive non-overlapping pairs of lines utilizing the video signal of FIG. 5A and the video signal of FIG. 5B to provide a first combined signal. Successive lines are separated by a blank period equal to the period of a line.

FIG. 5D shows the amplitude difference of successive non-overlapping pairs of lines utilizing the video signal of FIG. 5A and the video signal of FIG. 5B to provide a second combined signal. Successive lines are separated by a blank period equal to the period of one line.

FIG. 5E shows several consecutive lines, l'.sub.1 -l'.sub.10, of the luminance component of a second video signal. The second video signal is delayed in relation to the first video signal by the time of one line.

FIG. 5F shows the video signal of FIG. 5E delayed by a period of one line.

FIG. 5G shows the amplitude summation of successive nonoverlapping pairs of lines utilizing the video signal of FIG. 5E and FIG. 5F to provide a third combined signal. Successive lines are separated by a blank period equal to the period of a line.

FIG. 5H shows the amplitude difference of successive nonoverlapping pairs of lines utilizing the video signal of FIG. 5E and the video signal of FIG. 5F to provide a fourth combined signal. Successive lines are separated by a blank period equal to the period of one line.

FIG. 5I shows a compound video signal obtained by combining the first combined signal of FIG. 5C and the third combined signal of FIG. 5G.

FIG. 5J shows a compound video signal obtained by combining the second combined signal of FIG. 5D and the fourth combined signal of FIG. 5H.

FIG. 6A shows a diagram of the bandwidth limitation of the luminance sum signal of FIG. 5I by filter 151 of FIG. 1B.

FIG. 6B shows a diagram of the bandwidth limitation of the luminance difference signal of FIG. 5J by filter 121 of FIG. 1B.

FIG. 6C shows a diagram of the bandwidth of the first color sum signal on bus 62 by filter 131.

FIG. 6D shows a diagram of the bandwidth of the second color sum signal on bus 62 by filter 141 of FIG. 1B.

FIG. 6E is a diagram of the response of the vestigial sideband filter 137 of the transmission station of FIG. 1.

FIG. 7 shows two successive lines of a compound video signal.

FIG. 8 is a block diagram of the line decoder and waveform generator 53 of the transmission station of FIGS. 1A, 1B and 1C.

FIG. 9 is a block diagram of the frame sync generator 130 of FIG. 1C.

FIG. 10 is a circuit diagram of the sync line detector 201 of FIG. 2A.

FIGS. 11A-11G are diagrams of waveforms drawn to a common time scale useful in explaining the operation of the frame sync generator 130 of FIG. 1C and the sync line detector of FIG. 2A.

Referring now to FIGS. 1A, 1B and 1C, there is provided a transmitting station 10 including a first video subsystem 11 for processing a first video signal, a second video subsystem 12 for processing a second video signal, a bank of four single pole-double throw switches 13, 14, 15 and 16, a third video subsystem 17 for processing the video signals of video subsystems 11 and 12 combined by the switches 13-16, and a carrier subsystem 18 for encoding the video signals processed by the third video subsystem 17 on a carrier.

The first video system 11 includes a first video signal source 20 which provides at its output a standard color television or video signal of the form shown in FIGS. 3A and 3B. The standard television signal includes horizontal synchronizing pulses, vertical synchronizing pulses, horizontal blanking pulses, vertical blanking pulses, color burst signals, and luminance and chrominance signals. Each frame of the television signal includes a pair of interlaced fields as shown in FIGS. 3A and 3B. FIG. 3A is a diagram of the standard television signal showing the vertical blanking interval of the first or odd field of a frame and also showing the horizontal blanking interval and the horizontal scanning lines prior to and subsequent to the vertical blanking interval. FIG. 3B shows a diagram of the second or even field of the standard television signal showing the blanking interval of the second field of a frame and also showing the horizontal blanking interval and the scanning lines prior to and subsequent to the vertical blanking interval. FIG. 4 shows a diagram of the bands of frequencies occupied by the luminance and chrominance components of a complete color picture or video signal. The luminance component is contained in a band of frequencies extending from zero to 4.5 MHz with cutoff at about 4.2 MHz. The frequencies of the luminance signal are centered about even multiples of one-half of horizontal line scanning frequency. In order to represent both hue and saturation, the chrominance signal includes first and second independent components. Conventionally, these two components are called I and Q. The I component consists of sidebands of an in-phase or first color subcarrier modulated in amplitude by a first color signal which are contained in a band of frequencies from about 2 MHz to about 4.2 MHz. The first color signal is a first linear combination of red, green and blue color signals in accordance with U.S. color television standards. The Q component, consists of side bands of a second subcarrier in quadrature phase relationship to the first subcarrier modulated in amplitude by a second color signal which is contained in a band of frequencies from 3.0 MHz to 4.2 MHz approximately centered about the frequency of the subcarrier. The second color signal is a second linear combination of the red, green and blue color signals in accordance with U.S. color television standards. The frequency of the color subcarrier is an odd multiple of one-half of the line scanning frequency of about 14.750 KHz.

The first video system 11 also includes a color burst and sync clipper circuit 21, a one-line delay circuit 22, a summation amplifier 23, and a differential amplifier 24. The color burst and sync clipper circuit 21 has an input terminal 21a, and an output terminal 21b. In response to the television signal applied to its input terminal 21a, the color burst and sync clipper 21 clips or removes the color burst signals and sync pulses from the television signal to provide a video signal at the output terminal 21b in which burst signals and the horizontal and the vertical synchronizing pulses are deleted to facilitate the processing of first video signal. The one-line delay circuit 22 is a delay line, such as a charge coupled delay line, having an input terminal 22a, an output terminal 22b and a clock terminal 22c. The summation amplifier 23 has a pair of input terminals 23a and 23b, and an output terminal 23c. The differential amplifier 24 has a noninverting terminal 24a, an inverting terminal 24b and an output terminal 24c.

The first video subsystem also includes a synchronous demodulator circuit 40 for synchronously demodulating the first and second color components from the color television signal. The synchronous demodulator includes a band pass filter 41, a first demodulator 42, a second demodulator 43 and a phased shifter 44. The synchronous demodulator circuit 40 also includes an input terminal 40a, an input terminal 40b an output terminal 40c and an output terminal 40d. A television signal including color components in the form of modulation on a subcarrier are applied at input terminal 40a. A subcarrier signal of reference phase is applied at input terminal 40b. A first color signal is obtained at output terminal 40c and a second color signal is obtained at terminal 40d. The first color signal is designated R-Y, where R is the signal corresponding to the red component and Y is the sum of the red, blue and green components of the picture represented by the video signal. The second color signal is designated B-Y, where B is the signal corresponding to the blue component of the picture represented by the video signal. The band pass filter 41 with its input terminal connected to input terminal 40a filters the color subcarrier components in the band of 3.0-4.2 MHz of the television signal. The filtered signal is applied to one input of demodulator 42 and to one input of demodulator 43. The phase shifter 42 with its input connected to input terminal 50d of frame synchronizer 50 provides at one output thereof a subcarrier of zero phase which is applied to another input of the first demodulator 42 and also provides at another output thereof a subcarrier of 90.degree. reference phase which is applied to another input of the second demodulator 43. At the output of the first synchronous demodulator 42 which is connected to output terminal 40c is obtained the first color signal of the video signal from source 20. At the output of the second synchronous demodulator 43 which is connected to terminal 40d is obtained the second color signal of the video signal from source 20.

The second video subsystem 12 includes a second video signal source 30 providing a standard color television signal at its output terminal 30a, a color burst and sync clipper circuit 31, a first one-line delay circuit 32, a second one-line delay circuit 33, a summation amplifier 34 and a differential amplifier 35. The color burst and sync clipper circuit 31 has an input terminal 31a and an output terminal 31b. In response to the television signal appearing at its input terminal 31a, the color burst and sync clipper clips or removes the color burst signals and the sync pulses from the television signal to provide a video signal at the outut terminal 31b in which the color burst signals and the horizontal and vertical synchronizing pulses are deleted to facilitate the processing of the second video signal. The one-line delay circuit 32 is a charge delay line, such as a charge coupled delay line, having an input terminal 32a, an output terminal 32b and a clocking terminal 32c. The one-line delay circuit 33 is also a delay line, such as a charge coupled delay line, having an input terminal 33a and an output terminal 33b and a clocking terminal 33c. The summation amplifier 34 has input terminals 34a and 34b and an output terminal 34c. The differential amplifier 35 has a noninverting input terminal 35a, an inverting input terminal 35b and an output terminal 35c.

The first video subsystem also includes a synchronous demodulator circuit 45 for synchronously demodulating the first and second color components from the color television signal. The synchronous demodulator includes a band pass filter 46, a first demodulator 47, a second demodulator 48 and a phased shifter 49. The synchronous demodulator circuit 45 also includes an input terminal 45a, an input terminal 45b, an output terminal 45c and an output terminal 45d. A television signal including color components in the form of modulation on a subcarrier are applied at input terminal 45a. A subcarrier signal of reference phase is applied at input terminal 45b. The first color signal is obtained at output terminal 45c and the second color signal is obtained at terminal 45d. The band pass filter 46 with its input terminal connected to input terminal 45a filters the color subcarrier components of the television signal. The filtered signal is applied to one input of demodulator 47 and to one input of demodulator 48. The phase shifter 49 with its input connected to input terminal 50d of frame synchronizer provides at one output thereof a subcarrier of zero phase which is applied to another input of the first demodulator 47 and also provides at another output thereof a subcarrier of 90.degree. reference phase which is applied to another input of the second demodulator 48. At the output of the first synchronous demodulator 47 which is connected to output terminal 45c is obtained the first color signal of the video signal from source 30. At the output of the second synchronous demodulator 48 which is connected to terminal 45d is obtained the second color signal of the video signal from source 30.

Switches 13-16 are high speed switches such as those fabricated by means of MOSFET circuits. The switch 13 has a pole terminal 13a, a first contact terminal 13b and a second contact terminal 13c. The switch 14 has a pole terminal 14a, a first contact terminal 14b and a second contact terminal 14d. The switch 15 has a pole terminal 15a, a first contact terminal 15b and a second contact terminal 15c. The switch 16 has a pole terminal 16a, a first contact terminal 16b and a second contact terminal 16c.

The transmitting station 10 also includes frame synchronizer 50 having a first input terminal 50a, a second input terminal 50b and output terminals 50c, 50d and 50e. Frame synchronizer 50 functions in response to a first video signal applied to first input terminal 50a from source 20 and to a second video signal applied to second input terminal 50b to provide at the output terminal 40c the second video signal from source 30 with the horizontal lines thereof in synchronism with the horizontal lines of the first video signal. In addition, the frame synchronizer 50 provides at output terminal 50e the composite synchronizing signal of the first video signal from source 20 including the vertical synchronization and horizontal synchronization pulses. Also, the frame synchronizer provides at output terminal 50d a subcarrier signal of 3.58 MHz synchronized with the color burst signals of the first video signal and also in synchronism with the color burst signals of the second video signal at output terminal 50c. The frame synchronizer 50 is a standard component commercially available as Model 2525 from Microtime Company of Bloomfield, Conn.

The transmitting station also includes a master sync generator 51 which has input terminals 51a and 51b, and output terminals 51c, 51d, and 51e and a frequency multiplier 52. The multiplier 52 provides an output of 14.3 MHz in response to the 3.58 MHz signal applied to the input thereof from terminal 50d of frame synchronizer 50. In response to composite sync from terminal 50e of frame synchronizer 50 applied to input terminal 51a and a 14.3 MHz signal obtained from the output multiplier 42 and applied at terminal 51b, the master sync generator 51 provides at output terminals 51c through 51e, respectively, an even line of a frame signal, a vertical drive signal synchronized with the vertical sync pulses of the video signal of source 20, and a horizontal drive signal synchronized with the horizontal synchronizing pulses of the video signal. The master sync generator 51 is a standard component commercially available as Integrated Circuit Type-3252B TV Sync Generator from Fairchild, A Schlumberger Company, of Mountain View, Calif.

The transmitting station 10 also includes a line decoder and waveform generator 53 having input terminals 53a and 53b and having output terminals 53c and 53d and a frame detector 54 for developing a pulse at the output thereof