BACKGROUND OF THE INVENTION

The present application discloses an improvemen of the Repeat Merged Frame Method described in U.S. Lette Patent No. 4,266,240, issued to the applicant hereof, by providing better masking of the second video source in th imagery of the first video source as rendered by a standa television receiver. This is achieved by the encoder whi alternates the polarity of the amplitude scaled second video signal at the line rate rather than the frame rate, thereby minimizing the flicker effect associated with fra rate polarity alternation. This improved Repeat Merged Frame Method is designated as the Repeat Merged Frame/ Alternate Line Method. In addition, a Repeat Merged Fiel Method is disclosed. This method, which is similar to the Repeat Merged Frame Method, merges and repeats consecutive fields rather than consecutive frames of the first video source, while alternating the polarity of the amplitude scaled second video signal at the field rate rather than the frame rate, thus providing improved temporal resolutio of the rendered imagery.

This invention relates to an improved television system. More specifically, it relates to a television system which provides several methods of encoding two vide sources of real-time color television images, which may be either independent or stereoscopic pairs, for transmission over a standard television broadcast channel, or transfer over a closed circuit channel. The encoding methods pro¬ vide compatibility with standard receivers which render th imagery corresponding to the first video source. The syst also provides several methods of decoding the second video signal as required by the non-standard television receiver

Stereoscopic television is currently used in industry, education, medicine, and other fields to pro¬ vide a three-dimensional display of a live or recorded scene which is remote from the viewer ^f s field of view. These currently used systems are closed circuit systems usually requiring two transmission channels, each having the bandwidth of a standard television channel.

A method for encoding and decoding a stereo¬ scopic pair of color video signals transmitted over a standard television broadcast channel is described in U.S. Patent No. 3,896,487.

According to the inventioia., the luminance com¬ ponent of the second image of the stereo pair is employed for effecting an additional amplitude modulation of the chrominance subcarrier of the first image, while the chrominance component of the second image of the stereo pair is employed for effecting an -additional quadrature modulation of the chrominance subcarrier of the first image by means of a second subcarrier.

As pointed out in the patent, a disadvantage of this method of coding the chrominance component of the second image, is the sensitivity of the color subcarrier signals to distortions of the differential phase type inherent in the NTSC method, as well as to parasitic suppression of one sideband of the modulated signal. It is further shown in the patent, that the encoding methods provide compatibility only with standard monochrome tele- vision receivers, and not with standard color television receivers.

It is believed that prior to ϊ:he present inven¬ tion, there has not been available a compatible television system having means for encoding two video sources of

color television picture information, comprising an independent or stereoscopic pair of real-time images, for transmission over a standard television broadcast channel and having means for recovering the two video source signals for display. The attributes of such a system are apparent. They include the capability of conveying and rendering two real-time color television pictures by mean of a standard broadcast channel while maintaining compat¬ ibility with standard monochrome and color television re¬ ceivers. Thus, the need for such a system has gone unfulfilled.

It is accordingly a general object of the prese invention to overcome the aforementioned limitations and drawbacks associated with known encoding and decoding methods and to fulfill the needs mentioned by providing a television system having all of the desirable attribute noted above..

It is a particular object of the invention to provide an improved television system,

It is a further object of the invention to pro¬ vide a television system utilizing techniques of encoding two video signals to produce a composite transmission whi is compatible with existing monochrome and color televisi receivers.

Another object of the invention is to provide a television system utilizing decoding techniques which permit individual or simultaneous display of the encoded video signals.

It is still another object of the invention to allow for conversion of the two video signals comprising a stereoscopic pair into a format for time sequential

presentation of stereoscopic imagery on a single display device.

Other objects will be apparent in the following detailed description and the practice of the invention.

SUMMARY OF THE INVENTION

The foregoing and other objects and advantages which will be apparent in the following detailed descrip- tion of the preferred embodiment, or in the practice of the invention, are achieved by the invention disclosed herein, which generally may be characterized as a tele¬ vision system comprising: means for providing a first video signal; means for providing a second video signal in time synchronism with said first video signal; encoding means for forming a composite video signal of said first video signal and said second video signal, said encoding means including means for amplitude scaling said first video signal and said second video signal; means for trans mitting said composite video signal to means for receiving said composite video signal, said receiving means ^* includ¬ ing means for decoding said second video signal from said received composite video signal, said decoding means including means for amplitude scaling said received co po- site video signal.

BRIEF DESCRIPTION OF THE DRAWINGS

Serving to illustrate exemplary embodiments of the invention are the drawings of which;

FIGURE 1 is a block diagram of the video encoder utilized in the Repeat Merged Frame/Alternate Line method;

FIGURE 2 is a block diagram of the video decoder utilized in the Repeat Merged Frame/Alternate Line method;

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FIGURE 3 is a block diagram of the video encode utilized in the Repeat Merged Field Method;

FIGURE 4 is a block diagram of the video decode utilized in the Repeat Merged Field Method;

FIGURE 5 is a timing diagram for the alternate embodiments of the video encoder and video decoder.

DESCRIPTION OF PREFERRED EMBODIMENT

In order to understand the symbolic representa- tion of the encoding and decoding functions that form par of this discription, and their schematic embodiments, it will be helpful to refer to the timing diagrams shown in FIGURE 5.

In FIGURE 5a, N represents the current televisi frame number of the video source, where sequential frames are consecutively numbered.

FIGURE 5b shows the current television line number, n, of the video source.

In FIGURE 5c, F is a derived binary logic signa indicating an odd or an even current frame number, where F=l represents an odd number and F=0 represents an even number. In FIGURE 5d, f is a derived binary logic signal indicating an odd or an even current television field of the video source where f=l represents an odd field com¬ prised of odd numbered television lines, and f=0 repre¬ sents an even field comprised of even numbered television lines.

It is seen that the odd field comprises the set of consecutive odd numbered television lines and the even field comprises the set of intervening consecutive even numbered television lines.

In FIGURE 5e, y is a derived binary logic signal which is preset at the beginning of a frame, and toggles from line to line.

In FIGURE 5f, FΦy is a derived binary logic signal which represents the logical Exclusive OR function of F and y.

In FIGURE 5g, FΦfθy is a derived binary logic signal which represents the logical Exclusive OR function of F and f and y.

Other logical functions such as AND, OR and NEGATION are represented by the symbols • , + and ~ , respectively.

The derived binary logic signals described above are formed by currently used techniques, however, in order to derive the F signal at the receiver, it is necessary to transmit an odd numbered frame synchronizing signal, in addition to the standard synchronizing signals, to uniquel tag odd numbered frames. This synchronizing signal may conveniently be transmitted during the vertical retrace of alternate frames. Methods of inserting this additional synchronizing signal at the transmitter and recovering it at the receiver are not addressed since they are well know by those skilled in the art.

In order to afford a complete understanding of the invention and an appreciation of its advantages, a description of several alternate embodiments is presented below.

ENCODING AND DECODING METHODS

Two alternative and preferred methods of per¬ forming the encoding and corresponding decoding functions are disclosed, These methods are, the Repeat Merged Fram Alternate Line Method, and the Repeat Merged Field Method The first method is a variant of the Repeat Merged Frame Method disclosed in U.S. Letters Patent No. 4,266,240. Its advantage is masking the second video source in the imagery rendered by a standard television receiver is provided by the encoder, which alternates the polarity of the amplitude scaled second video signal at the line rate rather than the frame rate. In the second method, which is similar to the Repeat Merged Frame Method; the encoder merges and repeats consecutive fields of the first video source rather than consecutive frames, and alternates the polarity of the amplitude scaled second video signal at the field rate rather than the frame rate.

Those functions as may be required for trans- mission, reception, synchronization, black level insertio and methods for the display of the rendered video- imagery are not addressed since they are well known by those skil in the art. However, it is noted that in the exemplary embodiment of the invention, the encoded video signal in- formation may be transmitted to the receiver by means of a standard broadcast channel, a closed circuit channel, video recording and subsequent playback or any sequence of the preceding methods.

The encoding process provides a composite video signal such that a standard television receiver will render the imagery corresponding to the first video source A non-standard television receiver, i,e. , one with means for decoding the second video signal, will render the imagery corresponding to the second video source and/or

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the imagery corresponding to the first video source. The means for rendering the imagery corresponding to the - first video source is provided by a standard video channel as in the standard television receiver, and requires no decoder.

I. The Repeat Merged Frame/Alternate Line Method

a) Encoding

The first video signal component is formed, during an odd numbered frame, by summing the first video signal, amplitude scaled by a first factor, h, correspond¬ ing to the current frame, and the similarly scaled first video signal corresponding to the preceding frame, with its chrominance component inverted, to form a merged frame, while during the succeeding even numbered frame, this previously formed merged frame is repeated with inter changed chrominance inverted components.

T e second video signal component is formed, by scaling the amplitude of the second video signal by a second scaling factor, g, which is smaller than the first factor, and then alternating the polarity of the resultant at the line ^" rate,

The encoded video signal comprises the video sum of the first and second video signal components.

The encoding function for the Repeat Merged Frame/Alternate Line Method may be written as:

^r _E (N,n) •= h [V _A (N-l , n) ] 1

+ h [V _A (N ,n) ] ^• [F]

+ h [V _A N-2 ,n) ] • [F] (1

+ g [V _B CN ,n) ] ^• [F*y]

- g [V _B (N ,n) ^• [F-Φy]

where: N Currem t frame number n = Current line number h ≡ First scaling factor (a constant term) g ≡ Second scaling factor (a constant term or a non-linear term; g<h) V.(N,n) ≡ First video signal corresponding to frame N, line n V„(N,n) ≡ Second video signal corresponding to frame N, line n

V _F (N,n) ≡ Encoded video signal corresponding to frame N, line n ^Indicates inverted chrominance component

The resulting encoded signal is shown as a function of time in FIGURE 5h.

The encoder implementation is shown In FIGURE 1 As shown therein, the first video signal, V.CN.n), is applied to Attenuator 40 with transfer function, h, to provide a first component, h[V.(N,n)]. This component is also delayed for one frame time by Frame Delay Unit 41 to provide the signal, h[V. (N-l,n)] , which is applied to Chrominance Inverter 48 (comprising for example Chro - inanee/Luminance splitter 73 and Analog Difference Ampli¬ fier 74) and Frame Delay Unit 42. The output signal of Chrominance Inverter 48 provides a second component, h[V "(N-l,n)] , and the output of Frame Delay Unit 42 pro¬ vides a third component, h[V _A (N-2,n)] .

The first and third components are time multi¬ plexed by their associated Analog Gates 45 and 46, under control of signals F and F, respectively, into Analog Summing Amplifier 47. The second component provides a third input to Analog Summing Amplifier 47. It is the sum of these three components that comprise the first video component of the encoded video signal. The second video signal, Vn(N,n), is applied to Attenuator 3 with transfer function g to provide the signal, g[V _B (N,n)]. The resulti signal, g[Vg(N,n)], is applied to Video Inverter 4, to provide its inverse signal -g[V _β (N, )] . These latter two signals are then gated by Analog Gates 6 and 5 (the analog input is denoted by "a") , to provide the requisite alter¬ nating polarity signal, comprising the second component of the encoded video signal, .to Analog Summing Amplifier 2. T e gating signals F$y and FΦy provide the polarity switching function.

The output of Analog Summing Amplifier 47 Is the encoded video signal corresponding to the encoding functio described by equation (1) ,

A standard television receiver; or the standard video channel of a non-standard receiver, receiving this encoded composite video signal, will render the imagery corresponding essentially to the first video signal.

b) Decoding

The second video signal is extracted from the encoded composite video signal by forming, during even numbered frames , the absolute difference between the currently arriving encoded video signal, scaled by the scaling inverse of the encoder's second scaling factor, g ^~ , and the similarly scaled encoded video signal which arrived one frame earlier with its chrominance component

inverted; and forming during odd numbered frames, the absolute difference between the similarly scaled encoded video signal which arrived two frames earlier, and the similarly scaled encoded video signal which arrived one frame earlier, with its chrominance component inverted.

The decoding function for the Repeat Merged Frame/Alternate Line Method may be written as:

V _D (N,n) - ;-l[V _E (N-2,n)] - g ^" l[V _E *(N-l,n)f] ^• [F-y]

+ [g-l[V _E *(N-l,n)] - g-l[V _E (N-2,n) ^• [F-y]

+ fg ^"1 [V _E *(N-l,n)] - g- ¹ [V _E (N,n)]^] ^• [F-y]

+ [g- ¹ [V _E (N,n)] - ^• [F-y]

The resulting video signal that is displayed on a non-standard television receiver is found by performing the specified decoding function on the encoded video sig¬ nal. The result may be expressed as:

V _D (N,n) = V _B *(N-l,n)

+ V _B (N-2,n) - [F] (3

+ V _B (N,n) ^• [F]

The resulting decoded signal is shown as a func¬ tion of time in FIGURE 5i.

The second video signal component, which is the desired one, is seen to be, for odd numbered frames, the sum of the second video signals corresponding to the pre¬ ceding two frames, while for even numbered frames , it is the sum of the second video signals corresponding to the current and preceding frames, resulting in a repeat merged frame display of the second video source.

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The decoder implementation is shown in FIGURE 2. As shown therein, the composite video signal, V _E (N,n) , is applied to Amplifier 70, with transfer function g ^" l, to provide a first component, g ^~ l[V _E (N,n)] . This component is also delayed for one frame time by Frame Delay Unit 71 to provide the signal, g~l[V _E (N-l,n)] , which is applied to Chrominance Inverter 84 and Frame Delay Uni 72. The output signal of Chrominance Inverter 84 provides a second component, g- ^J -[V _E ' ^' (N-l,n)] , and the output of Frame Delay

Unit 72 provides a third component, g"l[V _E (N-2,n)] , Four algebraic difference signals are formed by the Analog Difference Amplifiers 75, 76, 77 and 78 where the first difference between the third component and the second component, g[V _E CN-2,n)3 - g ^-J -[V _E (N-l,n)], is formed by Analog Diff rence Ampli ier 77; the second dif erence between the second component and the third component, g-l[V _E *(N-l,n)] - g ^-1 [V _E (N-2,n)] , is formed by Analog Difference Amplifier 78; the third difference, between the second component and the first component, g~ ⁱ [V _E ^" (N-l,n)] g~l[V _E (N,n)] , is formed by Analog Difference Amplifier 76; and the fourth difference between the first component and the second component, g~l[V _E (N,n)] - g ^~ l[V _r ^:' ( -l,n)] , is formed by Analog Difference Amplifier 75. These four dif¬ ference signals are time multiplexed by their associated Analog Gates, as shown, into Analog Summing Airplifier 83 to yield the video signal, V _D (N,n) , corresponding to the decoding function described by equation (2) . The gating signals, Fy, Fy, Fy and Fy, provide the appropriate time multiplexing.

II. The Repeat Merged Field Method

a) Encoding

The first video signal component is formed, during an odd numbered field, by summing the first video

signal, amplitude scaled by a first factor, h, corres¬ ponding to the current field, and the similarly scaled first video signal corresponding to the preceding field to form a merged field, while during the succeeding even numbered field, this previously formed merged field is repeated.

The second video signal component is formed, by scaling the amplitude of the second video signal by a second scaling factor, g, which is smaller than the first factor, and then alternating the polarity of the resultan at the field rate.

The encoded video signal comprises the video su of the first and second video signal components.

The encoding function for the Repeat Merged Fie Method may be written as:

V _E (N,n) = h[V _A (N,n)] + [V _A (N-l,ii+l)]^ * f + [ ι[V _A (N,n+l)] + h[V _A (N-l,n+2)f] - f

(4 + g[V _B (N,n)] - f - g[V _B (N,n)] • f

he resulting encoded signal is shown as a func¬ tion of time in FIGURE 5j ,

The encoder implementation Is shown in FIGURE 3. As shown therein, the first video signal, \ ⁷ _A (N,n), is applied to Attenuator 140 with transfer function, h, to provide a first component, h[V _A (N,n)]. This component is also delayed for 262 line times by Delay Unit 141 to pro¬ vide a second component, h[V _A (N-l,n+l)]f + h[V _A (N,n+l)]f which is also applied to 262 line Delay Unit 142.

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The output of 262 line Delay Unit 142 provides a second component, h[V _A (N-l,n+2)] .

The first and second components are time multi¬ plexed by their associated Analog Gates 145 and 146, under control of signals f and f, respectively, into Analog Summing Amplifier 147, It is the sum of these two compo¬ nents that comprise the first video component of the encoded video signal. The second video signal, V„(N,n), is applied to Attenuator 103 with transfer function, g, to provide the signal g[VgQT,n)]. The resulting signal, g[V _β (N,n)], is applied to Video Inverter 104, to provide its inverse signal -g[Vg(N,n)]. These latter two signals are then gated by Analog Gates 106 and 105 (the analog input is denoted by "a") , to provide the requisite alter- nating polarity signal, comprising the second component of the encoded video signal, to Analog Summing Amplifier 102. The gating signals f and f provide the polarity switching function.

The output of Analog Summing Amplifier 147 is th encoded video signal corresponding to the encoding functio described by equation (4) .

A standard television receiver, or the standard video channel of a non-standard receiver, receiving this encoded composite video signal, will render the imagery corresponding essentially to the first video signal.

b) Decoding

The second video signal is extracted from the encoded composite video signal by forming, during an even numbered field, the difference between the currently arriving encoded video signal, scaled by the scaling in- verse of the encoder's second scaling factor, g ^~ , and

the similarly scaled encoded video signal which arrived 262 lines earlier, and during the ensuing odd numbered field, repeating this previously formed difference signal

The decoding function may be written as:

V _D (N,n) = [^g ^"1 [V _E (N-l,n+2] - g-l[V _E (N-l,n+l)] ~ ^■ f

+ [V ^l [V _E (N,n+l)] - g- ^l [V _E ( ,n) - f (

The resulting video signal that is displayed on a non-standard television receiver is found by performing the specified decoding function on the encoded video signal. The result may be expressed as:

V _D (N,n) = [V _B (N-l,n+2) + V _B (N-l,n+l)] - f

+ [V _B CN,n+l) + V _B (N,n)] ^• f

The resulting decoded signal is shown as a function of time in FIGURE 5k.

The decoder implementation is shown in FIGURE 4. As shown therein, the composite video signal, V _E (N,n), is applied to Amplifier 170, with transfer function g ^~ , to provide a first component, g~l[V _F (N,n)] , which is applied to Analog Difference Amplifier 173. This compo¬ nent is also delayed for 262 line times by Delay Unit 171 to provide the signal, g"l[V_(N-l,n+l)] • f + g~i ^J -[V _E (N,n+l)] ^• —f, which is also applied, to Analog

Difference Amplifier 173.

The output signal of Analog Difference Amplifier 173 provides a first component, g~l[V _E (N-1,n-KL)]f + g~ ¹ [V _E (N,n+l)]f - g ^_1 [V _E (N,n)]. This signal is applied to 262 line Delay Unit 172 to provide a second component,

g-! [V _E (N-l ,n+2) ] ^■■ - g-l [V _E CN-l ,n+l) ] f - g-l [V _E (N ,n+l) ] f .

These two components are time multiplexed by their associated Analog Gates 174 and 175 as shown, into Analog Summing Amplifier 176 to yield the video signal V^(N,n) , corresponding to the decoding function described by equation (5) . The gating signals f and f provide the appropriate time multiplexing.

A variant of the Repeat Merged Field Method, replaces the f and f gating signals applied to Analog Gates 105 and 106 shown in FIGURE 3 with FΦfθy and F#f#y, respectively, to alternate the polarity of the amplitude scaled second video signal at the line rather than the field rate. In addition, the Analog Difference Amplifier shown in FIGURE 4 is replaced by an Absolute Difference Amplifier, or functional equivalent.

Although not specifically indicated, the recovered composite video signal, representing the imagery of the first video source, and the decoded video signal, representing the imagery of the second video source, are each processed by conventional luminance and chrominance circuitry to provide the Y, (R-Y) , CG-Y) and (B-Y) signals as required by a three gun Cor equivalent) picture tube. The chrominance circuitry includes a chrominance de¬ modulator.

As indicated in the exemplary encoder, and de¬ coder embodiments, the function of the Chrominance In- verter is to correct the phase of the delayed Cby an odd number of television lines) video signal relative to the chrominance subcarrier reference signal.

The equivalent function may be performed by alternating, at the applicable rate and time, the polarity

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of the chrominance subcarrier reference signal as applied to the chrominance demodulator, thus permitting the deletion of the Chrominance Inverter and associated cir¬ cuitry from the exemplary decoder embodiments.

COMPONENT CONSIDERATIONS

The components used in the encoder decoder and converter embodiments all utilize conventional technologi however, the currently emerging charge coupled device (CC technology may provide a significant cost and size ad¬ vantage when applied to the Delay Units shown in the en¬ coder and decoder embodiments.

Fairchild Camera and Instrument Corp, is curren developing a television field store device based on charg coupled device technology, The design objectives of this device are to provide storage capacity of.640X256 picture elements, corresponding to 163,840 analog "bits" at a maximum bit rate of 12MHz, on a chip area of 170 mil x 760 mil.

Although the invention has been described as

/ applied to the NTSC system of television, it can, with suitable modification, be made to apply to other tele- vision systems such as, for example, modified NTSC

C625 lines/50 fields) , Phase Alternation Line (PAL) or

Sequential with Memory (SECAM) .

Similarly, although the invention has been described as applied to color television systems, it is also applicable to monochromatic television systems.

Accordingly, it is clear that the above descrip¬ tion of the alternative and preferred embodiments in no wa limits the scope of the present invention which is defined by the following claims.