Television signal processor

Abstract: A device which processes a television signal for transmission in which the television signal is divided into horizontal scanning line units, video signals in two consecutive horizontal scanning periods are compared, and when either part or all of these two signals differ, transmits by means of a television signal transmitter (3, 4, 7A, 7B) only the video signal Vx for that part of the signals which is different, and which uses said transmitted television signal in the television signal receiver (25, 26, 27, 28) to reproduce a complete video signal with all horizontal scanning periods by calculating, mixing, overlaying, or replacing video signal Vx for either part or all of the video signal Vn-1 for the one preceding horizontal scanning period.

Description: Technical Field The present invention relates to a television signal processing device which can be used for discrete transmission of images in video communications, satellite communications, CATV, and other media. Background Art In conventional television signal transmission systems, the television signal is transmitted as an uncompressed signal in which no periods are compressed, or as a signal compressed by horizontal scanning line or field units. However, this latter case requires very large equipment because all complete signals are compressed before transmission. Thus, in conventional time axis compression signal transmission methods, the equipment required for transmission and reception is very large, making use of this method difficult by any broadcasters other than large-scale broadcasting stations. In US-A-3,755,624 representing the closest prior art from which the invention proceeds it is disclosed that in a communication system for transmitting and receiving television information by means of digital codes, the horizontal sync pulses are transformed into a code word, thus leaving time slots in the transmitted waveform which are unoccupied by the digital picture information or the code word representing horizontal synchronization. These time slots are used to transmit additional information such as multiple sound or data channels, or bandwidth compression information. In the case of multiple sound or data channels, the channels are multiplexed and coded and transmitted during the available time slots at a bit rate which is the same as the digital picture information bit rate. In the case of bandwidth compression, an address code word is annexed to the single horizontal synchronization code word to provide an address for each line of picture information in a television frame. With all lines identified by addresses, the system compares each line of picture information with a prior line of picture information having the same address and transmits to the receiver only those lines which represent changes of a certain degree from a prior frame. As a result, redundant picture information is not transmitted thereby reducing the total amount of information transmitted, allowing the transmitter to operate at a reduced bit rate. The receiver stores all lines of information and the store is up-dated by the received non-redundant lines of picture information. During each frame period, the receiver extracts from storage the redundant lines necessary to complete a picture frame. Further, in US-A-4,150,397 a record and playback system for reducing repetition redundancy is described in which during recording, a partially repetitive signal, such as a television signal, is converted into digital data words each representing the signal occurring during a particular TV line subinterval. A comparator unit receives the data words and compares each received word with a word from a recirculating storage that corresponds to the same line subinterval in its frame as that of the compared received data word. When the compared words differ by a predetermined value, the received word replaces the stored word in the storage and is also stored in a changed data memory as an updated data word along with the address words. A recording control circuit intermittently causes the read out of data from the changed data memory for recording at selected positions of a data record. The storage includes alternately operating first and second recirculating storages which each store a set of data words equal in number to the number of data words of one-half a TV frame. Audio data words are stored for recording during vertical blanking intervals of the signal. On playback, a record pickup intermittently reads data words from the record to a record pickup memory whenever this memory is nearly empty. A composite signal generator reconstructs the recorded television signal from data words it receives from the display storage and display control. Disclosure of Invention An object of the present invention is to provide a television signal processor which can transmit a television signal in a short real time, and which has a simplyfied construction. In order to achieve the above and other objects, in accordance with the present invention, there is provided a television signal processor having a receiver for receiving a video signal which includes, in one horizontal scanning period, a section of a second horizontal line video signal which differs from a first horizontal line video signal in one previous horizontal scanning period, and a code indicating the position of the section in said one horizontal scanning period, said receiver comprising a first storage means for storing a video signal for at least a horizontal scanning period, second storage means for storing a video signal for at least a horizontal scanning period, third storage means for storing a video signal for at least a horizontal scanning period, and gate means for gating outputs of said first, second and third storage means; characterized by control means, which receives said code, for controlling the writing and reading a video signal of one horizontal scanning period and for controlling said gate means such that the first horizontal line video signal of said one previous horizontal scanning period is stored in said second storage means, the first horizontal line video signal of said one previous horizontal scanning period stored in said second storage means is read and transmitted through said gate means to said first storage means, the section of the second horizontal line video signal of said one horizontal scanning period is stored in said third storage means, and the first horizontal line video signal of said one previous horizontal scanning period stored in said first storage means is read, and simultaneously the section of the second horizontal line video signal of said one horizontal scanning period in said third storage means is read, and by the use of said code, a portion of the first horizontal line video signal from said first storage means is gated and stored in said first storage means in one horizontal scanning period while the section is not present within said one horizontal scanning period, and the section of the second horizontal line video signal from said third storage means is gated and stored in said first storage means while the section is present in said one horizontal scanning period. Further advantageous embodiments are defined in the dependent claims. An advantage of the present invention is to enable the receipt of one horizontal line video signal without receiving full line data. Namely, only a section of the second horizontal line video signal is sufficient for the receiver to generate a complete second horizontal line video signal. In this way, a portion remaining in the second horizontal line video signal, i.e. a portion other than the section, can be used for receiving some additional information. Brief Description of drawings Fig. 1 is a block diagram of the transmitter side of a television signal processor; Figs. 2, 3, 4, and 5 are waveform diagrams for explaining the operation of the television signal transmitter; Fig. 6 is a block diagram of the receiver side of the television signal processor according to a first embodiment of the present invention; Figs. 7, 8, and 9 are waveform diagrams for explaining the operation of the television signal receiver; Fig. 10 is a block diagram of the receiver in a television signal processor according to a second embodiment of the present invention; Figs. 11 and 12 are waveform diagrams to describe the operation thereof; Fig. 13 is a waveform diagram showing a sample code signal used in the embodiment shown in Fig. 10; Fig. 14 is a block diagram of the television signal receiving processor in a third embodiment according to the present invention; Figs. 15 and 16 are waveform diagrams to describe the operation thereof; Fig. 17 is a block diagram of the television signal receiving processor in a fourth embodiment according to the present invention; Figs. 18 and 19 are waveform diagrams to describe the operation thereof; and Fig. 20 is a waveform diagram showing a sample code signal as used in the fourth embodiment according to the present invention. Modes for Carrying Out the Invention The preferred embodiment of the present invention is described hereinbelow with reference to the accompanying figures. The circuit construction of the preferred embodiment of the signal processing method according to the present invention is shown in Fig. 1. Fig. 1 is a block diagram of the signal processing circuit on the television signal transmission side. In this figure, reference number 1 is the signal source for the television signal, which herein is a signal source for an NTSC television signal 1. Reference number 2 is a sync signal regeneration circuit which regenerates the vertical drive signal VD, horizontal drive signal HD, and the chroma subcarrier fsc from the output 1 from the signal source 1, and generates a clock signal four times the fsc. This 4fsc clock signal is synchronized with the HD, VD, and fsc. Reference number 3 is a one line memory 3, which herein A/D converts the television signal 1 and stores in memory one line of the digitized signal. The clock signals for the one line memory 3 include the 4fsc and the clock signal synchronized thereto. By storing one line of the signal source 1 output signal 1, the output signal 1 is delayed one horizontal scanning period (1H) so that the output signal 3 of the one line memory 3 and the television signal 1 are shifted by one horizontal scanning period as shown in Fig. 2. In Fig. 2, o, p, q, r, and s represent one horizontal scanning period in a single field; in the description hereinbelow, o shall represent the final, i.e., 21st horizontal scanning period (21H), in the vertical fly-back period, p represents the 22H, q the 23H, r the 24H, s the 25H, and so on. The video signal content during each of these periods is represented by A0, A1, A2I. Reference number 4 is a comparator which compares the output television signal 1 from the signal source 1 with the A/D converted, 1H-delayed output television signal 3 from the one line memory 3, and during the period in which the two signals are coincident outputs a coincidence signal, e.g., a high level coincidence signal. The output of the comparator 4 varies with the length of one clock unit in the 4fsc clock signal, but timing control circuit 5 ignores short period coincidence signals, and uses only coincidence signals longer than a predefined period to control the AND gate 8. More specifically in the circuit required to achieve the present invention, because timing control circuit 5 ignores short period coincidence signals and forms a coincidence signal longer than a predefined period, using, for example, a retriggerable multivibrator, the input gate pulse controlling the AND gate 8 can be formed if triggered at the rise of the coincidence pulse in the output of the comparator 4. The output pulse width of the retriggerable multivibrator may be set, for example, at 1/2 to 1/4H. The result, as shown in Fig. 3, is that a coincidence signal is normally output at periods other than tq4 - tq5 during horizontal scanning periods p and q; when a short pulse width coincidence signal is output during periods tq4 - tq5, a high level signal is supplied to the AND gate 8 from the timing control circuit 5 during periods tq4 - tq5, the output signal from the signal source 1 becomes the output signal from the AND gate 8, and is input to the memory 7A (or 7B, the selected memory is switched at each one horizontal scanning period by the signal from the timing control circuit 5). In other words, this is signal 8 shown in Fig. 2; in Fig. 3, during period tq4 - tq5 in which there is a difference between the television signals in the one previous horizontal scanning period (p H) and the current horizontal scanning period (q H), the television signal 8 in q H is taken as the output signal from the AND gate 8. This signal corresponds to C2 of 8 in Fig. 2. In the same way, if the television signals during the q and r horizontal scanning periods are compared and only that part which differs is extracted, the output signal will be that shown by C3 of 8 in Fig. 2. This process is repeated for each horizontal scanning period, and only the difference part is passed through the AND gate 8. This is controlled by the timing control circuit 5 using the output from the comparator 4 and the output from the sync signal regeneration circuit 2. The output from the AND gate 8 is input to the AND gates 9A and 9B. The television signal for the part in which there is a difference between horizontal scanning periods p and r (periods 22H and 24H, i.e., even-numbered scanning periods) is stored in memory 7A through the AND gate 9A. Similarly, the television signal for the part in which there is a difference between horizontal scanning periods o, q, and s (periods 21H, 23H, and 25H, i.e., odd-numbered scanning periods) is stored in memory 7B through the AND gate 9B. In other words, the switch output from the timing control circuit 5 applied to the AND gate 9A and the inverter 9R is a high (low) level on even-number (odd-numbered) horizontal scanning periods, and opens the AND gate 9A (9B), the output of the inverter 9R becomes a low level (high level), and the AND gate 9B (9A) is closed. Therefore, the memory 7A is controlled by the timing control circuit 5 so that it is in a write mode on even-numbered horizontal scanning periods and a read mode on odd-numbered horizontal scanning periods, and the memory 7B is controlled to function in the opposite mode. Writing to the memory 7B is described next. In Fig. 3, 101 and 102 are the signals at the p and q horizontal scanning periods; if it is determined by the comparator 4 when television signals 101 and 102 are compared (corresponding to A2 of 1 and A1 of 3 in Fig. 2) at the time of q H that there is a difference in the signals at tq4 - tq5, the television signal for tq4 - tq5, i.e., signal C2 in 8 in Fig. 2, is written to the memory 7B at the timing indicated by 102. If the memory 7B is a one-line capacity memory and is addressed by row only, the signal is written to the latter half of the one-line memory (the address corresponding to the position of tq4 - tq5 in 102 in Fig. 3). This write position is stored by the timing control circuit 5, and at r H is read as the signal for q' H as shown by 11 in Fig. 2. In other words, as shown by 1 in Fig. 2, when all of the signal A1 at p H is different from A0 at o H, the output of the AND gate 8 is C1 = A1, i.e., the output signal of the signal source 1 is stored in entirety in the buffer memory 7A, delayed 1 H, and read at q H as the signal of the p' H (11 in Fig. 2). In other words, if in one complete horizontal scanning period the signal differs from that of the previous horizontal scanning period, it is delayed one period and the signal for the one complete horizontal scanning period is output from the OR gate 11 as shown by 1 and 11. p', q', and r' of 11 in Fig. 2 indicate that they are delayed one horizontal scanning period from 1. The signal stored to the memory 7B at q H is read out at the tq4 - tq5 timing of 202 or '202. The read timing from memory 7B may be any desired timing. A code signal indicating the position of signal C2 during tq4 - tq5 in signal A2 of the original horizontal scanning period q, e.g. a code signal indicating the positions of the beginning tq4 and the end tq5, is generated by code signal generator 6; if this code signal is inserted with the horizontal sync pulse and the color burst during tq1 - tq3 in Fig. 3, this can be detected at the receiver side, read at the correct timing, and signal A2 can be easily generated from A1 and C2. If this same process is alternately repeated and transmitted for the odd and even lines, signal 11 in Fig. 2 is obtained. C1 (=A1), C3... and C2, C4... are alternately stored to buffer memory 7A and buffer memory 7B, respectively. The formation of 11 in Fig. 2 is described hereinbelow. At horizontal scanning period r, the output signal of the one line memory 3, i.e., A2 in 3, and the output signal of the signal source 1, i.e., A3 in 1, are compared, and that part which is different is passed through the AND gate 8 to store the corresponding part of A3 in the memory 7A, during which time the signal for q' is output from the OR gate 11, i.e., the signal C2 of that part of A2 which differs from A1 is read from the buffer memory 7B. Note that in Fig. 2 the period tq0 - tq3 in Fig. 3, i.e., the horizontal fly-back period, is omitted. At horizontal scanning period S, the output signal from the one line memory 3, i.e., A3 in 3, and the output signal from the signal source 1, i.e., A4 in 1, are compared; that part of the signals which differs is passed through the AND gate 8, the corresponding part of A4 is stored in the memory 7B, and the signal for r' is output from the OR gate 11, i.e., the signal C3 of that part of A3 which differs from A2 is read from the buffer memory 7A. This process is then repeated. The OR gate 10 passes the output signal from either buffer memory 7A or 7B, the OR gate 11 mixes the output signal from the OR gate 10 and the code signal output from the code signal generator 6, forming the signals 201, 202, and '202 in Fig. 3. To explain the process whereby 202, and '201 are formed, the horizontal scanning area outside of tq4-tq5 in 202 and '202 may be either black or white, but is gray (an intermediate value) herein. This level can be set and easily changed by clamping the output of the OR gate 10 and changing the clamp level. Furthermore, as shown by '202, the position of the signal in tq4 - tq5 may be shifted from tq3, and the distance of the shift may be varied at every horizontal scanning period. The code signal indicating the distance between tq3 - tq4 may be inserted between tq1 - tq2. It is also possible to insert and transmit a separate digital or analog signal (tq11 - tq12) at some position other than tq3 - tq4. In addition, while the signal processing becomes somewhat more complex, multiple signals Cn1, Cn2 may be used for those parts which differ in An and An-1, and the position'information for Cn1, Cn2... may be encoded and inserted to the signal for a single horizontal scanning period as shown in Fig. 4. In Fig. 4, tn4 - tn5 is the position of Cn1, and tn14 - 1n15 is that of Cn2. The code signal indicating the original position of the Cn1 signal in An is inserted to tn'4 - tn4, the code signal indicating the original position of the Cn2 signal in An is inserted to tn'14 - tn14, and the receiver uses these code signals to insert Cn1 and Cn2 at the appropriate positions in the original An signal. This is controlled by the timing control circuit 5; in this case the timing control circuit 5 shall contain an MPU. The code signal for a signal indicating difference is described below with reference to Fig. 5 for that case in which there is one code signal in a single horizontal scanning period. In Fig. 5, tn1 and tn2 correspond to tq1 and tq2, respectively. If the signal for one horizontal scanning period is sampled with a 4fsc clock signal, there will be 910 samplings. Even if the sync signal burst signal is excluded, the number of samplings in the horizontal scanning periods from tq3 - tq6 will be 512 or greater, thus requiring a 10-bit address signal. As shown in Fig. 5, the ten bits a0 - a9 express the position of tq4 in 201, and the ten bits b0 - b9 express the position of tq5 in 201. The six bits c0 - c6 indicate the position of tq4 in '202 in 16 clock units of the 4fsc. Specifically, as shown by '202, when the signal at tq4-tq5 is time shifted, because no problems arise for practical utility even at the roughness of 16 clock units of the 4fsc (approx. 1.1 µsec.), only six bits are used here in order to reduce the number of bits. Adding one start and stop bit before and after, respectively, a0 - c5 results in a total 28 bits. If the width of one bit is 1/fsc ≒ 139.7 nsec, then 28 x 139.7 ≒ 3.92 µsec. Thus, most of the NTSC sync signal can be apportioned to these 28 bits, and as shown in Fig. 5 a horizontal sync trigger can be inserted to tn1 - tn8. The sync signal and burst signal may be consecutively transmitted before and after a0 - c5 from the code signal generator 6. In Fig. 4, tn'4 - tn4 is unnecessary, and the 28 bits may be inserted at tn'14 - tn14. Thus, if the difference between the signals for the previous horizontal scanning period and the current horizontal scanning period is transmitted and received and the remaining common portion of the signals is not transmitted, other signals may be inserted to tq11 - tq12 as shown by '202 in Fig. 3 for a significant portion of the horizontal scanning periods in one field. Because a typical television signal contains a significant amount of common signals, those signals which do not need to be synchronized can be transmitted during tq11 - tq12 in '202 in Fig. 3. These additional signals can be generated by an additional signal generator circuit (not shown) controlled by the output of the timing control circuit 5, and supplied to the OR gate 11 for transmission. While this signal format cannot be received by a common home receiver, it is a convenient means of sending and receiving signals in which the sender and receiver correspond one-to-one as in satellite communications and CATV. For example, if a specific algorithm is applied to the bits in a0 - a9, b0 - b9, and c0 - c5 in Fig. 5, and a discrete algorithm is used by each receiver to decode the received signal, the confidentiality of communications can be maintained. Furthermore, information relating to the algorithm can also be inserted to tq11 - tq12 for transmission and reception. Thus, by applying the signal processor according to the above embodiment, the transmitter can compress the amount of transmission data for the television signal using a delay line, the receiver can reproduce the original signal with a virtually identical circuit construction, and the circuit construction can thus be simplified. In addition, the transmission contents can be encoded so that they can be understood only by one specified receiving party and not understood by other parties. Moreover, other digital and analog signals can also be easily transmitted together with the television signal (video). Thus, using the signal processing circuit shown in Fig. 1, the television signal which has been compressed and to which has been added other data signals is frequency converted and transmitted at a level compatible with satellite communications, CATV, and similar broadcasting formats. For example, if satellite broadcasting is used, the signal could be transmitted as a 27-MHz bandwidth, 36-MHz Ku band signal, or a 100-MHz bandwidth Ka band signal. The receiver which is used to receive the television signal broadcast from the above transmitter is described hereinbelow. The broadcast signal is converted from the Ku band or Ka band frequency, for example, if broadcast by satellite, to the frequency level of the original UHF or VHF signal, and input to the receiver shown in Fig. 6. Fig. 6 is a block diagram of the television receiver according to a first embodiment of the present invention. In Fig. 6, 21 is a video detector circuit and 22 is an A/D convertor. The television signal input to the video detector circuit 21 is, as shown by '202 in Fig. 3, a compressed video signal from which those parts of the video signal in one field which are the same as parts of the video signal for the one previous field are removed. Furthermore, as shown by '202 in Fig. 3, a code signal indicating the position in signal A2 during the original horizontal scanning period q of the video signal C2 differing at period tq4 - tq5 is inserted at time tq1-tq2. A code signal indicating the timing at which the video signal for tq4 - tq5 in this signal '202 is also inserted to period tq1 - tq2. As described above, the television signal comprising the compressed video signal and the code signal is supplied from the video detector circuit 21 to the synchronous separation circuit 23 and chroma subcarrier (fsc) regenerator 24; the horizontal sync signal (drive signal) HD and the vertical sync signal (drive signal) VD are output from the synchronous separation circuit 23, and the chroma subcarrier fsc is output from the fsc regenerator 24. The horizontal and vertical sync signals HD and VD, and the chroma subcarrier fsc are all input to the control logic circuit 28 as will be described below. Note that the synchronous separation circuit 23 and the fsc regenerator 24 are devices of common knowledge, and further detailed description thereof is thus omitted below. The television signal output from the video detector circuit 21 is converted to a digital signal by the A/D convertor 22, and output to the first and second line memories 26, 27. This digital television signal is input to the data processing circuit 29, where the code signal for one field is extracted and sent to the control logic circuit 28. Thus, as stated above, the horizontal and vertical sync signals HD and VD from the synchronous separation circuit 23 and the chroma subcarrier fsc from the fsc regenerator 24 are input to the control logic circuit 28 with the code signal from the data processing circuit 29; the control logic circuit 28 outputs a control signal to controllers 30, 31 so that the write clock and the read clock are output from the write controller 30 and the read controller 31, respectively; the write clock and read clock are the triggers for writing and reading the video signal to the first, second, and third line memories 26, 27, 25, respectively, based on the timing information, the timing clock reference of which is the horizontal sync signal HD. In Fig. 6, 32, 33, 36, and 37 are AND gates, 34 and 38 are OR gates, 35 and 39 are inverters, 40 is a regeneration circuit which comprises a D/A convertor for digital-analog conversion of the digital television signal output from the OR gate 14, and 41 is a cathode ray tube (CRT) on which is displayed the regenerated output television signal from the D/A cenverter-regeneration circuit 40. The operation of a receiver according to the preferred embodiment of the present invention as thus described is described hereinbelow with reference to Fig. 7 and Fig. 8. In Fig. 7 and Fig. 8, 0H (horizontal scanning period 21H) in the reception signal is preceded by the vertical blanking period (VBL), and the video signal begins from pH (22H). Note that this video signal is shown to compare with the video signal from the transmitter as shown in Fig. 3. The signal for 21H in the video signal input to the video detector circuit 21 is first written to the line memory 25, at which time the video signal from the A/D convertor 22 is supplied to the line memory 26. A code for zero is written to the line memory 25 indicating that the signal component for period t3 - t6 in 21H, or the video signal component from the control logic circuit 28 is not present. A code signal indicating the timing at which the video signal which differs from the video signal in 21H is inserted in 22H is inserted to period t1 - t2 in the partially compressed signal 301 (201 in Fig. 3) of 22H as described hereinabove with respect to the transmitter in the preferred embodiment of the present invention; this code signal is extracted from signal 301 by the data processing circuit 29, sent to the control logic circuit 28, and a control signal is supplied from the control logic circuit 28 to control the write controller 30 so that a high level signal (write clock) causing a write operation to be performed to the line memory 26 during t3 - t6 in 22H is output from the write controller 30. The result is that the 22H video signal component (period t3 - t6) 301 is written to the line memory 26 at 22H as shown in Fig. 7. Note that period t1 - t3 is a 1-bit 8 τ long code signal when τ = 1/4 fsc. Also at 22H, a control signal is supplied from the control logic circuit 28 to the read controller 31 to start a drive state, and a read clock is supplied from the read controller 31 to the line memory 25. Furthermore, the AND gate 32 is opened by the output from the read controller 31, and AND gate 33 is closed by the inverted output of the inverter 35. Thus, the output of the OR gate 34 is zero because the contents of the line memory 25 are output during 22H, and zero data is newly written through the feedback loop. Note that the write clock is supplied from the write controller 30 to the line memory 25 during period t3 - t6 from 22H to 262H (or 263H). That case in which the signal at 23H (402 in Fig. 8) is received is described next. In this description, however, the phase difference between the output of line memory 26 and the input of the write clock to line memory 25 shall not be considered. The technique whereby a phase difference is provided in the transfer of data from one memory area to another is common knowledge, and further description is omitted hereinbelow. The 23H video signal (402 in Fig. 8) transmitted from the transmitter and indicating the difference component of the 22H video signal and the 23H video signal before compression is put through the video detector circuit 21 and the A/D convertor 22, as was the previous 22H signal, but the video signal component (the t3 - t6 component of 402) is this time written to line memory 27. While the 23H video signal is written to the line memory 27, the video signal (301) written in 22H is read from line memory 26. At this time, the signal in line memory 26 (t3 - t6 in video signal 301) is controlled so that the complete signal is transferred to line memory 25 and output based on the 22H code signal (t1 - t2) stored in the memory area (not shown) of the control logic circuit 28. Specifically, a low level signal (11 in Fig. 6) is supplied from the read controller 31 to the AND gate 32, and the AND gate 32 is thus closed. Also, the output of the inverter 35 becomes the inverse of the 11 signal, i.e., a high level signal, and the AND gate 33 is opened. Similarly, the high level control signal 12 from the read controller 31 is supplied to the AND gate 36, and the AND gate 36 opens. The output of the inverter 39 which inverted signal 12 causes AND gate 37 to close. Therefore, the output of the OR gate 38 becomes the output of the line memory 26 from T230 - T240 in Fig. 7. The read clock is, of course, supplied continuously to the line memory 26 during this period. Thus, the received signal is read in 23H, i.e., the video signal 402 from t3 - t6 in Fig. 8 and the video signal 301 from t3 - t6 from the line memory 26 from T230 - T240 in Fig. 7, from the line memory 26 and input sequentially to AND gate 36, OR gate 38, AND gate 33, and OR gate 34, from which it is input to the D/A convertor-regeneration circuit 40 for conversion to an analog video signal which is output to the CRT 41. At this time, the output of the OR gate 34, i.e., video signal 301 from t3 - t6, passes the feedback loop and is written to line memory 25. It should be noted with respect to Fig. 7 that T230 in Fig. 7 corresponds to time t0 in 23H, but the signal from t0 - t3 is not shown in Fig. 7. This omission has absolutely no bearing on the description of the operation of the preferred embodiment. This is also true for 24H, 25H, and successive periods. The operation when the 24H signal is input as the reception signal is described next. The waveform of the 24H input signal is not shown in the figures. The video signal at 24H (T240 - T250 in Fig. 7) is written to the line memory 26 according to the write control of the control logic circuit 28. At this time, the control signal 12 from the read controller 31 is a low level signal. Thus, the low level signal 12 closes the AND gate 36 and opens the AND gate 37 in 24H. The 23H reception signal contains a code signal at t1 - t2 in signal 402 indicating at what timing in 23H the video signal is inserted (in Fig. 7 and Fig. 8 this would be read at 24H). This code signal is interpreted by the data processing circuit 29 as described hereinabove, and as the result, a control signal is input from the control logic circuit 28 to the write controller 30 and the read controller 31, the clocks from these controllers are output to the line memories 25, 26, 27, and the control signal shown in Fig. 7 is output from the read controller 31 to the gates or the inverters 32, 33, 35, 36, 37, and 39. Based on this code signal, a read clock is supplied to the line memory 27 only during T'234 - T'235 in Fig. 7 during 24H, and a read clock is supplied to the line memory 25 from T240 (=T'230) - T250 (=T'240), except during the period T'234- T'235. The control signal 11 during 24H is a high level signal at T240 - T'234 and T'235 - T250, and a low level signal from T'234 - T'235 based on the 23H code signal stored in the memory area of the control logic circuit 28. Thus, during T240 - T'234, the AND gate 32 is open and the AND gate 33 is closed by the control signal 11, and the signal read from the line memory 25 to which the read clock is supplied, i.e., the 301 video signal at t3 - t4 in Fig. 8, is put from the line memory 25 through the AND gate 32, OR gate 34, and D/A convertor-regeneration circuit 40, and output to the CRT 41. Next, during T'234 - T'235, the low level control signal 11 closes AND gate 32 and opens AND gate 33. Thus, the signal read from the line memory 27 to which the read clock is supplied during T'234 - T'235, i.e., the 402 video signal at t4 - t5 in Fig. 8, is put through the AND gate 37, OR gate 38, AND gate 33, OR gate 34, and D/A convertor-regeneration circuit 40, and output to the CRT 41. The signal read from the line memory 27 passes the feedback loop and is written to the line memory 25 as was described for the previous case hereinabove. Next, during T'235 - T'250, the high level control signal 11 opens AND gate 32 and closes AND gate 33; the signal read from the line memory 25 to which the read clock is supplied, i.e., the 301 video signal at t5 - t6 in Fig. 8, is put from the line memory 25 through the AND gate 32, OR gate 34, and D/A convertor-regeneration circuit 40, and output to the CRT 41. The video signal read from the line memory 25 passes the feedback loop and is written to the line memory 25 as was described for the previous case hereinabove. As thus described, the source signal for 23H which differs from the signal received at 22H only with respect to the t3 - t4 component of the 402 signal in Fig. 8 is restored in 24H as shown by 302 in Fig. 8. Note that the content of the line memory 25 at this time is the video signal for t3 - t6 of 301 in Fig. 8 during 23H (the horizontal line portion of T230 - T240 in line memory 25 in Fig. 7), and at 24H, the memory contents at 23H are rewritten with the video signal for t4 - t5 of 402 in Fig. 8 (the area shaded by diagonal lines at T'234 - T'235 in line memory 25 in Fig. 7). The line memory 26, however, is set to the write state as described above, and is written with the 24H reception signal. Thus, the signal indicating the difference between the 23H video source signal and the 24H video source signal (the crosshatch area at 24H in the reception signal in Fig. 7) is written to the line memory 26. The video source signal of 24H is restored at 25H with the same operation used to restore the 23H video source signal at 24H, and by repeating this operation at each horizontal scanning period the original image can be restored and reproduced on the CRT 41. A sample code signal, e.g., the code signal inserted to t1 - t2 in 301 and 402 in Fig. 8, contained in the signal received by the receiver is described below with reference to Fig. 9. In Fig. 9, t1 - t13 is a horizontal sync signal comprising a series of ones and zeroes, and the code signal comprises t13 - t20. Note that t20 in Fig. 9 corresponds to time t2 in Fig. 8. The R1S after t13 is the start bit, which is always a R1.S The next RxS identifies whether that line signal is a signal in which is contained a part of the video source signal (partial signal), or is a signal which contains a complete video source signal (complete signal). For example, a R0S here may indicate a partial signal, and a R1S may indicate a complete signal. In the embodiment described hereinabove, this RxS bit is a 1 for signal 301 in 22H, and is 0 in the received signals of 23H and 24H. The seven bits at a0 - a6 following the RxS bit compose the code identifying the timing at which the beginning of the video signal is positioned in the television signal restored by the receiver, and may be a code expressing, for example, the length from t1 to t4 in 302 in Fig. 8. The seven bits b0 - b6 following the a0 a6 bit code compose the code identifying the timing at which the end of the video signal is positioned in the television signal restored by the receiver, and may be a code expressing, for example, the length from t1 to t5 in 302 in Fig. 8. The six bits c0 - b5 following the b0 - b6 bit code compose the code identifying the timing at which the beginning of the video signal is positioned in the television signal partially omitted by the transmitter, and may be a code expressing, for example, the length from t1 to t4 in 402 in Fig. 8. The six bits d0 - d5 following the c0 - c5 bit code compose the code identifying the timing at which the beginning of another data code signal is positioned in the television signal partially compressed by the transmitter, and may be a code expressing, for example, the length from t1 to t11 in 402 in Fig. 8. The R1S between t19 and t20 is the stop bit. One horizontal scanning period (1H) from t0 to t6 in the television signal shown in Fig. 8 is approximately 63.5 µs in an NTSC signal, and if this is sampled at 4fsc, there will be 910 samplings. Therefore, there will be no problems for practical use even if t1 - t5 is expressed with seven bits, removing the lowest three bits t1 - t6. Also, from t1 - t11, the lowest four of the ten bits are dropped and the highest six bits are determined at (1/4fsc) x 16 ≒ 1.12 µs. While it is preferable to determine t1-t5 and t1 - t6 according to the screen at each sampling point, setting these every eighth sampling unit (approximately 0.56 µs) presents no problems in practical use. Because it is not necessary to precisely identify the position of other data at t11 - t12 and it is sufficient to know the position of t11, this is determined every 16th sampling unit. In the data processing circuit 29 in Fig. 6, the data at t13 - t19 and at t11 - t12 is extracted and processed. The data at t11 - t12 contains either a code indicating the data length, or start and stop bits. It should be further noted that as shown in Fig. 9, t1 - t15 is 32 times t14 - t15, and if t14 - t15 is 1/2 fsc ≒ 139.5 nsec., then 32 x 139.7 nsec. ≒ 4.47 µs, and can thus be held to the width of the NTSC horizontal sync signal. Therefore, even if the color burst is not moved, the horizontal sync signal may be written to t1 - t15 in Fig. 9. The highest frequency component of t13 - t20 is the fsc, and is thus within the transmission band width of the normal NTSC signal (on a normal television the amplitude will be 1/2, but this poses no problems in signal processing). According to the preferred embodiment of the present invention as described hereinabove, even if only a signal containing that part which differs from the preceding line is received, the source image on the transmitting side can be accurately reproduced on the receiving side. Moreover, in this case confidential communications (images) can be transmitted by applying specific processing to the bits a0 - a6, b0 - b6, c0 - c5, and d0 - d5 in Fig. 9 and informing only the intended recipient of the required conversion procedure. The description of the preferred embodiment hereinabove concerned specifically the signal processing as it applied to line units, but it is also possible to replace the line memories in Fig. 6 with field memories or frame memories and apply this same processing in field or frame units, and it is also possible to combined line unit processing with field or frame unit processing. Next, a receiving device which receives the video signal of a signal processing method in which only the difference component is transmitted by frame or field comparison and restores the original image is described below. Fig. 10 is a second embodiment of the television signal receiving device according to the present invention. In Fig. 10, reference number 71 is a video detector circuit which detects a signal in which only the difference component of two input signals compared by frame or field is transmitted, and 72 is an analog/digital (A/D) convertor. The A/D convertor 72 may be, for example, an 8-bit convertor, and output eight lines of parallel data, but in these figures only one line of data is shown. Reference number 73 is a synchronous separation circuit which outputs the horizontal sync signal (drive signal) HD, the vertical sync signal (drive signal) VD, and the frame pulse (FP) (herein this is the same phase as the VD of the field beginning from 1H). Reference number 74 is the chroma subcarrier (fsc) regenerator which is described hereinbelow as an NTSC format signal, though it is not restricted to an NTSC format television signal. The output of the fsc regenerator 74 is input to the control logic circuit 78, and is used for sampling or as a clock. Reference number 75 is a first frame memory with a one frame storage capacity, 76 is a second frame memory, and 77 is a third frame memory 77; 78 is the control logic circuit which controls the drive (writing, reading) of the frame memories 75, 76, 77 by means of the write controller 80 and the read controller 81. Reference number 79 is the data processing circuit which extracts and processes the data signal inserted at t7 - t8 and t17 - t18 in 101 in Fig. 3, and extracts the position information of the video image information (t4 - t5 and t14 - t15 in 101) included at t1 - t2 and t11 - t12 in 101, and outputs this to the control logic circuit 78. Reference numbers 82, 83, 86, and 87 are AND gates, 85 and 89 are inverters, 84 and 88 are OR gates, 90 is an image output circuit which comprises a digital-analog (D/A) convertor, and 91 is a cathode ray tube (CRT). The operation of a television signal receiver as thus comprised is described hereinbelow with reference to Fig. 11 and Fig. 12. Fig. 11 and Fig. 12 are waveform diagrams for the purpose of describing the operation. When the video signal of 22F is input at the null signal state which is present through frame 21 (hereinafter 21F), the components of the image signal at t3 - t6 and t13 - t16 in 22F are completely different from those of the signal at 21F, and the signals at t3 - t6 and t13 - t16 of 100 are written to the second frame memory 76. Note that the description herein ignores the horizontal fly-back period with respect to the video signal. In addition, the operation applied to, for example, the signal at periods t3 - t6 in field 1 and the signal at t13 - t16 in field 2 is repeated thereafter, and the description hereinbelow is therefore restricted to that applied to the signal in field 1. Zero data (a black level video signal) is first written to the first frame memory 75 according to the output from the control logic circuit 78 and the code signal indicating that the signals for t3 - t6 and t13-t16 in 22F inserted in 1H or two or more horizontal scanning periods must be written to t1 - t2 and t11 - t12 in 101, i.e., to the vertical fly-back period, is extracted by the data processing circuit 79 and sent to the control logic circuit 78 in parallel with the writing of the video signal to the second frame memory 76. Specifically, the control logic circuit 78 is drive controlled according to this extracted code signal, and the input signal of 22F is write controlled so that the signals at t3 - t6 and t13 - t16 are written to the second frame memory 76. This write operation is indicated with a RWS (22F) in Fig. 11. At 22F, simultaneous to the writing of the 22F received signal to the second frame memory 76, the video signal for 21F, i.e., the previous frame, is output from the first frame memory 75 according to the control of the control logic circuit 78. More specifically, a control signal is input from the control logic circuit 78 to the read controller 81 to cause the read controller 81 to output a read clock; this read clock enables reading from the first frame memory 75, causes the AND gate 82 to open with a high level signal from the D terminal of the read controller 81, thus setting the output of the inverter 85 to a low level, and closing the AND gate 83. Thus, the black level video signal read from the first frame memory 75 at 22F passes AND gate 82 and OR gate 84, is converted to an analog signal by the D/A convertor circuit 90, and the processed video signal is displayed on the CRT 91. This 22F signal (the 21F video signal) is also passed from the output of the OR gate 84 through the feedback loop connected to the input of the first frame memory 75 and is rewritten to the first frame memory 75. Therefore, with the supply of the read clock to the first frame memory 75, the write clock is supplied according to the control of the control logic circuit 78 from the write controller 80 from 22H to 262.5H and from 284H to 525H corresponding to t3 - t6 and t13 - t16 in 22F. Note that there is actually a phase difference in the read clock to the second frame memory 76 and the write clock to the first frame memory 75, but this phase difference is herein ignored in this description. The method whereby a phase difference is provided for data transfer from memory to memory is one of common knowledge, and further description is therefore omitted. Next in 23F, the signal 101 comprised of the video signal for the difference component in the result of the comparison of the 23F signal on the transmitter side (301 in Fig. 12) and the 22F signal (100 in Fig. 12) is input to the third frame memory 77 via the video detector circuit 71 and the A/D convertor 72. As with the case of 22F described hereinabove, a code signal is inserted to t1 - t2 and t11 - t12 in the 23F signal, and writing of the 23F input signal 101 to the third frame memory 77 is executed according to this code signal. The signal 101 differs from the signal 100 in the previous frame at t4-t5 and t14 - t15, but the signal is controlled here so that all components from t3 - t6 and t13 - t16 are written to the third frame memory 77. Note, however, that selective writing of the differing periods t4 - t5 and t14 - t15 can be easily achieved with this embodiment, and no problems would be caused by so defining the code signal. With the writing of the reception signal to the third frame memory 77 in 23F, the data in the second frame memory 76 is output to the first frame memory 75 and displayed based on the 22F code signal stored in the memory (not shown in the figure) of the control logic circuit 78. Specifically, the AND gate 82 is closed by the low level signal from the read controller 81, thus causing the inverter 85 to output a high level signal which opens AND gate 83. Moreover, the high level signal from the E terminal of the read controller 81 causes the AND gate 86 to open, and the low level signal output from the inverter 89 causes the AND gate 87 to close. With the gates thus set, a read clock is supplied from the read controller 81 to the second frame memory 76 so that the signals for t3-t6 and t13 - t16 in 101 are read. Thus, the 100 video signal in the second frame memory 76 passes the AND gate 86, OR gate 88, inverter 85, AND gate 83, and OR gate 84, is signal processed by the D/A convertor circuit 90, and displayed on the CRT 91. In addition, the video signal for t3 - t6 and t13 - t16 in 100 is written through the feedback loop on the OR gate 84 output side to the first frame memory 75 from T2300 - T2400 in Fig. 17 (corresponding to period t3 - t16 in Fig. 18 with the omission of t6 - t13). A write clock is, of course, supplied to the first frame memory 75 at this time. Note that time T2300 in Fig. 11 corresponds to the t0 in 23F in Fig. 12, but that t0 - t3 are omitted from the figure in Fig. 11. It is to be noted that this has absolutely no affect on the operation of the present invention, and does not degrade the essential quality of the present invention. Next at 24F, the signal 102 (Fig. 11 reception signal T2400 - T2500) comprising the video signal for the difference component based on the comparison result of the 24F signal on the transmitter side (not shown in Fig. 12, stored in the first frame memory 75 in Fig. 11 (T2500-T2600)) and the 23F signal (301 in Fig. 12, stored in the first frame memory 75 in Fig. 11 (T2400 - T2500)) is input to the second frame memory 76. Storage to the second frame memory 76 is controlled according to the code signal as described above with respect to 22F and 23F so that the signal corresponding to the periods t3 - t6 and t13 - t16 in signals 100, 101, and 301 is written to the second frame memory 76. With the writing of the received signal 102 to the second frame memory 76, transfer of the signal in the third frame memory 77 to the first frame memory 75, and switching between the first frame memory 75 and the third frame memory 77 for reading and display are also executed based on the 23F code signal stored in the memory of the control logic circuit 78. Specifically, in order to restore the original image in 23F, the signal is first read from the first frame memory 75 during periods T'2300 (T2400) - T'2340, and the signals must then be read from the third frame memory 77 during the period T'2340 - T'2350, and again from the third frame memory 77 during period T'2341 - T'2351, and from the first frame memory 75 during period T'2351 - T2500 (T'2400). In order to achieve this reading control, a high level signal 11 is output from terminal D of the read controller 81 during periods T'2300 - T'2340, T'2350-T'2341, T'2351 - T'2400, and a low level signal 11 is output during periods T'2340 - T'2350, T'2341 - T'2351, and a low level signal 12 is output from terminal E. Thus, during periods T'2300 - T'2340, T'2350-T'2341, T'2351 - T'2400 the AND gates 82 and 87 are open and the AND gates 83 and 86 are closed; during these periods the output signal from the first frame memory 75 to which the read clock is supplied passes gates 82, 84, the D/A convertor circuit 90, and is displayed on the CRT 91. During the other periods T'2340 - T'2350, T'2341 - T'2351, AND gates 83 and 87 are open and AND gates 82 and 86 are closed; during these periods the output signal from the third frame memory 77 to which the read clock is supplied passes gates 82, 84, the D/A convertor circuit 90, and is displayed on the CRT 91. In this way the original image 301 of 23F is reproduced and displayed on the CRT 91. Note that the write clock is supplied to the first frame memory 75 so that a so-called read-modified-write occurs; the difference component is rewritten so that the signal 301 is formed in the first frame memory 75. This signal stored in the first frame memory 75 becomes as shown during T2400 - T2500 in Fig. 11. At 25F, the signal 103 (reception signal T2500 - T2600) comprised of the difference component based on the comparison result of the 25F source signal on the transmitter side and the 24F signal ((T2500 - T2600) in the first frame memory 75 in Fig. 11) is input to the third frame memory 77. With the writing of the reception signal 103 to the third frame memory 77, transfer of the signal in the second frame memory 76 to the first frame memory 75, and switching between the first frame memory 75 and the second frame memory 76 for reading and display are also executed based on the 24F code signal stored in the memory of the control logic circuit 78. Specifically, in order to restore the original image in 24F, it is necessary to first read the signal from the first frame memory 75 during periods T'2400 (T2500)-T'2440, T'2450 - T'2441, and T'2451 - T'2500 (T2600), and from the second frame memory 76 during the periods T'2440 - T'2450 and T'2441 - T'2451. In order to achieve this reading control, a high level signal 11 is output from terminal D of the read controller 81 during periods T'2400 - T'2440, T'2450 - T'2441, T'2451 - T'2500, and a low level signal 11 is output during periods T'2440 - T'2450, T'2441 - T'2451, and a high level signal 12 is output from terminal E. Thus as the result of this reading control, during periods T'2400 - T'2440, T'2450 - T'2441, T'2451-T'2500 the AND gates 82 and 86 are open and the AND gates 83 and 87 are closed, and the read output signal from the first frame memory 75 is displayed on the CRT 91; during the other periods T'2440 - T'2450, T'2441 - T'2451, AND gates 83 and 86 are open and AND gates 82 and 87 are closed, and the read output signal from the second frame memory 76 is displayed on the CRT 91. In this way the original image of 24F is reproduced and displayed on the CRT 91. Note that the read-modified-write applied to the first frame memory 75 at this time is executed as it is during the 24F. Thereafter, writing occurs alternately to the second frame memory 76 and the third frame memory 77 depending on whether the frame is an odd-numbered frame or an even-numbered frame, reading occurs from the first frame memory 75 and either the second frame memory 76 or the third frame memory 77, the source signal for the one frame preceding the frame of the currently received signal is always reproduced in the first frame memory 75, or is written in its entirety as received, so that the images of one (frame) screen are sequentially reproduced. According to the present embodiment as described hereinabove, it is possible to restore and reproduce a compression processed signal using only three frame memories, thereby making it possible to reduce the cost of the equipment and achieve a more compact reception system. One example of the code signal as referred to in the above description is described below with reference to Fig. 13. In Fig. 13 t1 - t1001 is the vertical sync signal, t1001 - t2 is 1H (or 0.5H) in the vertical blanking period, and may be, for example, the 1H (or 0.5H) following the vertical sync signal. If the period t1001 - t2 is 0.5H (=63.5 µs/2), and a 32-bit signal is therein inserted, 1 bit is equal to approximately 1 µs, thus making electrical signal processing quite simple. Note that in Fig. 11 and Fig. 13 the length of t1 - t2, and therefore the length t1 - t1001 and t1001 - t2, do not match in the figures; this is a problem of graphic representation in the figures, and the operation is not affected whether t1 - t1001 is 1H or 3H, or t1001 - t2 is several H periods. In the code signal shown in Fig. 13, t1001-t1005 consists of the start mark R0101,S t1032 - t2 is the stop bit; the x-bit at t1005 - t1006 is the code indicating whether the present frame signal is a partial signal as shown in 23F and 24F in Fig. 11, or is a complete signal as shown at 22F and 25F, and may be set, for example, as x = 0 for a partial signal or x = 1 for a complete signal. Note that code signals with the same construction and meaning are inserted at t1 - t2 and t11 - t12 in one frame. Note that it is also possible to omit insertion of the code signal at t11 - t12. Furthermore, if the start mark at t1001 - t1005 is changed for every field, field detection will also be facilitated. The seven bits at a0 - a6 identify the length from t1 - t4 in signal 201 in Fig. 12, and the corresponding seven bits in the second field express the length from t11 - t14 in signal 201. The seven bits b0-b6 express the length from t1 - t5 or from t11 - t15 in signal 201 and 301, and c0 - c5 express the length of t1 - t4 or t11 - t14 in 101. The final six bits from d0 - d5 express the length from t1 - t7 or from t11 - t17. Because there are seven bits from a0 - a6, one field can be expressed as 128 components, and the timing of t7 can be obtained every 2H. In the video signal for one field (262.5H), because t1 - t3 normally occupy approximately 21H, the timing of the signal can be expressed by approximately 242H if the field is divided from 22H. If 2H are represented by one bit, seven bits can sufficiently express the timing. It is sufficient to define the length every 4H for the 6-bit data at c0 - c5 and d0 - d5. A preferred embodiment of a television signal receiver according to the present invention which is suited to the signal processing method whereby video signals are compared on the basis of two consecutive fields and the video signal for a given field is a signal for only that part of the signal which differs is described hereinbelow with reference to Figs. 14 to 16. Fig. 14 is a block diagram of a television signal receiver according to the present invention, and Fig. 15 and Fig. 16 are waveform diagrams used to explain the operation of said receiver. These correspond to Figs. 10 to 12 for the second embodiment described hereinabove. As will be known from the block diagram of this third embodiment of the present invention as shown in Fig. 14 , it differs in that the frame memories 75, 76, and 77 are replaced by field memories 75f, 76f, and 77f. Because the screen image comprises one frame of two fields, the video signal which can be omitted is reduced even with still images when compared with the frame method as described with reference to the embodiment hereinabove, but there is no change in the fact that there is a significant reduction in the amount of transmission data for the original image itself. The operation of the third embodiment of the television signal receiver as shown in Fig. 14 corresponds to the description of the first field in the description of frame unit operation in the previous embodiment, and there is no fundamental change in operation in any way. Further detailed description of its operation is therefore omitted. In the second and third embodiment as thus described, if the partial signal (t4 - t5 in the signal 301 in Fig. 16) is transmitted and received in the same frame or field at a position (t4 - t5 in signal 101 in Fig. 16) different from the original image, and the code signal is pre-encoded so that only specific contract parties can decode the code signal, discrete transmission of video and data is possible. Furthermore, if the position of the partial signal is periodically varied, confidential communications which cannot be read by third parties can also be easily achieved. Note while that in the second and third embodiments the descriptions above assumed that the partial signal was positioned at one place in one frame or one field, by slightly increasing the number of bits in the code signal, partial signals may be easily placed at two or more positions with the same basic operation. For example, because in text broadcasts 190-bit information is sent in 1H, it is possible to insert seven sets in the 26 bits from t1006 - t1032 in Fig. 13, thus enabling correspondence with partial signals at seven locations. Next, a fourth embodiment of the television signal receiver according to the present invention is described hereinbelow with reference to the accompanying figures. The major feature of this embodiment is that instead of using three frame memories or field memories, only one frame memory or field memory and two line memories are used to restore the signal transmitted with the difference components obtained from a frame or field comparison to the source image. This embodiment is described with the frame memories 76, 77 shown in Fig. 10 replaced with line memories 76L, 77L. In Fig. 17, those components which differ from the embodiment shown in Fig. 10 include line memories 76L, 77L as described above, control logic circuit 78L, write controller 80L, and read controller 81L, which differ slightly in that the control of these is based on a line unit, and all other components are the same, with like parts identified by like reference numbers. Specifically, the input television signal is detected by the video detector circuit 71, A/D converted, and input alternately to the line memories 76L, 77L according to the code signal inserted, for example, to t1 - t2, at the header position of each horizontal scanning period. The code signal is, as described above, extracted by the data processing circuit 79, processed, and input to the control logic circuit 78L, which thus controls the write controller 80L, read controller 81L, and opens and closes gates 82 - 89 according to the code signal. The operation of the receiver according to this embodiment as it processes a signal corresponding to that at period T2200 - T2400 in Fig. 11 as described hereinabove is described below with reference to Fig. 18 and Fig. 19. As described with the case of the second embodiment above, the signal at the period T2200 - T2300 is controlled and processed so that the complete signal is written to the first frame memory 75 because there was no signal present at 21F. In other words, with respect to T2200 - T2300 in Fig. 25, writing and reading are controlled so that the signal written to one line memory at a given horizontal scanning period (nH) is read at the next horizontal scanning period ((n+1)H), and the signal read from the line memories 76L and 77L passes the AND gates 86, 87, OR gate 88, AND gate 83, and then OR gate 84, wherefrom the signal is output to the D/A convertor circuit 90, and then fed back for the read-modify-write operation to the frame memory 75. Therefore, the output signal 11L at terminal D of the read controller 81L is a low level signal during T2200 - T2300, and the output signal at terminal E changes between a low and high level signal at each 1H. therefore, the read clock from the read controller 81L to the line memories 76L, 77L is also alternately supplied every 1H. The description hereinbelow refers to that case in which a signal to be rewritten from 30H in frame 23 is received. The video signal (t4 - t5) at 30H (T23029-T23030) is written to the line memory 76L, the video signal for 29H in the preceding frame 22F is read from the first frame memory 75, passes the AND gate, OR gate 84, and this 30H is output to the CRT 91. At the next horizontal scanning period 31H, the t4 - t5 signal (the crosshatched area at line memory 77L in Fig. 19) for the difference component at T23030 - T23031 in the received signal for 31H is written to the line memory 77L according to the code signal. Also, following the reading of the video signal for 30H in 22F from the frame memory 75 from t0 - t'4, the signal written to the line memory 76L at 30H is read at t'4 - t'5 in period T23030-T23031, passes the AND gate 86, OR gate 88, AND gate 83, and the OR gate 84, and is then output from the D/A convertor circuit 90 for display to the CRT 91, and the read-modify-write operation is applied to the frame memory 75. Next at 32H, the signal received at 32H is written to the line memory 76L according to the code signal at t4 - t5 in T23031 - T23032. Also, the 31H video signal in 22F is read from the first frame memory 75 at t0 - t'4, followed by the signal (the crosshatched area) written to line memory 77L in 31H being reread from t'4 - t'5. In other words, at t0 - t'4 and t'5 - T23032, AND gates 82, 87 are open, AND gates 83, 86 are closed, the contents of the first frame memory 75 are read, and at t'4 - t'5, AND gates 83, 87 are open, AND gates 82, 86 are closed, and the contents of the line memory 77L are read. Thus, the signal read from AND gates 82, 83 passes the OR gate 84, the D/A convertor circuit 90, and is displayed on the CRT 91, or is fed back to the first frame memory 75 where a read-modify-write is performed. By repeating this signal processing, the video compression applied on the transmission side can be restored to the original signal without error on the receiving side. According to the processing method in this embodiment, it is sufficient to send in horizontal scanning line units only that part of the frame contents which differ, and because those parts of the horizontal scanning lines which are the same can also be omitted, the amount of information in the video signal which must be transmitted can be reduced. Furthermore, the transmission efficiency can be increased because another data signal can be inserted in those open areas of the signal not carrying video signal data. In addition, this method can also be used for confidential communications by comprising the code signal so that it can only be received by specific contract parties. One example of the code signal inserted at each horizontal scanning line unit in this fourth embodiment is described hereinbelow. In Fig. 20, t1 - t'1 is the horizontal sync pulse, t'1 - t14 is the start bit, and the x-bit at t14 - t15 indicates whether the signal for that horizontal line is a partial signal or a complete signal extending across the full band of 1H, and may, for example, contain a R0S to indicate a partial signal and a R1S for a complete signal. The seven bits at a0 - a6 (t15 - t16) are the code identifying, for example, the length from t1 - t'4 when t4 in 30H is t'4 in the source image signal; the seven bits b0 - b6 (t16 - t17) are the code identifying, for example, the length from t1 - t'5 when t5 in 30H is t'5 in the source image signal. The six bits c0 - c5 (t17 - t18) express the length of t1 - t4 in 30H, and the six bits from d0 - d5 (t18 - t19) express the length from t1 - t11. If the signal is a standard NTSC format signal, 1H is approximately 63.56 µs, and there are therefore 910 sampling points when the signal is sampled at 4fsc based on the output of the fsc regenerator 74. Therefore, if there are ten bits, the length from t4 - t5 can be determined at each sampling interval, but when the signal is transmitted including components in which there is no difference, the lowest three bits (8 samples at 4fsc: approx. 560 nsec.) can be dropped with no problems posed for practical use. Therefore, the lowest three bits in a0 - a6 and b0 - b6 may be dropped and the code comprised to express the timing for 8 sampling units. By dropping the lowest four bits for c0 - c5 and d0 - c5, the code can be comprised to express the timing at each 16 samples in 4fsc, i.e., approx. 1.12 µsec. increments. In Fig. 26, t19 - t2 is the stop bit, and t'1 - t2 is thus a 33-bit code including 29 bits and a 4-bit horizontal sync pulse. If 1 bit is 1/2 fsc, approx. 139.7 nsec., 33 bits is 4.61 µsec., sufficient to fit the horizontal sync signal width in the NTSC format, and the code signal can thus be inserted without affecting the color burst. By applying specific encoding to this signal and transmitting the decoding information only to specific contract parties, confidential communications can be achieved. This decoding information may be inserted at various areas, including, for example, the vertical fly-back period. According to the present invention, images are compared by line, frame, or field, and the image signal is processed for transmission of the difference component only of the line, frame, or field, thereby yielding the following effects. (1) It is possible to transmit other information in place of the signal components which are the same, and the transmission efficiency can thus be increased. (2) Even if the image signal in a transmission is received, the complete image cannot be discerned, and this method is therefore suited to confidential communications. (3) By varying the transmission timing of the transmission signal irregularly, and encoding the timing information in the transmission, a communication method with high confidentiality can be achieved. (4) Because this method determines transmission or non-transmission by image data comparison on a simple line or frame basis and does not use an advanced signal compression technique in which a line correlation or frame correlation is detected, the system can be simply constructed.

Claims: A television signal processor having a receiver for receiving a video signal which includes, in one horizontal scanning period, a section of a second horizontal line video signal which differs from a first horizontal line video signal in one previous horizontal scanning period, and a code indicating the position of the section in said one horizontal scanning period, said receiver comprising: a first storage means (25; 75; 75f) for storing a video signal for at least a horizontal scanning period; second storage means (26; 76; 76f; 76L) for storing a video signal for at least a horizontal scanning period; third storage means (27; 77; 77f; 77L) for storing a video signal for at least a horizontal scanning period; and gate means (32-39; 82-89) for gating outputs of said first, second and third storage means; characterized by control means (28; 78; 78f; 78L), which receives said code, for controlling the writing and reading a video signal of one horizontal scanning period and for controlling said gate means such that: the first horizontal line video signal of said one previous horizontal scanning period is stored in said second storage means; the first horizontal line video signal of said one previous horizontal scanning period stored in said second storage means is read and transmitted through said gate means to said first storage means; the section of the second horizontal line video signal of said one horizontal scanning period is stored in said third storage means; and the first horizontal line video signal of said one previous horizontal scanning period stored in said first storage means is read, and simultaneously the section of the second horizontal line video signal of said one horizontal scanning period in said third storage means is read, and by the use of said code, a portion of the first horizontal line video signal from said first storage means is gated and stored in said first storage means in one horizontal scanning period while the section is not present within said one horizontal scanning period, and the section of the second horizontal line video signal from said third storage means is gated and stored in said first storage means while the section is present in said one horizontal scanning period. The television signal processor according to claim 1, wherein each of said first, second and third storage means (25, 26, 27) is a line storage means for storing a horizontal line data. The television signal processor according to claim 1, wherein each of said first, second and third storage means (75, 76, 77) is a frame storage means for storing a frame data. The television signal processor according to claim 1, wherein each of said first, second and third storage means (75f, 76f, 77f) is a field storage means for storing a field data. The television signal processor according to claim 1, wherein said first storage means (75) is a frame storage means for storing a frame data, and each of said second and third storage means (76L, 77L) is a line storage means storing a horizontal line data. The television signal processor according to anyone of claims 1 to 5, wherein said section is shifted from an original position to a shifted position, and said code carries a shifted position data and an original position data.

Inventors: HIRASHIMA MASAYOSHI, HIRASHIMA, MASAYOSHI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1989
Main classification: H04N7
IPC codes: H04N7, G06T9