JPH04227388A - Data transmitter - Google Patents

Abstract

PURPOSE: To transmit digital data at the rate of a digital data one bit per each color burst without affecting color demodulation. CONSTITUTION: Digital data are read from a shift register 62 in response to a horizontal synchronizing pulse generated at a transmitter, and used as a control signal for controlling a switch 64. A bit to be transmitted depends on '0' or '1', and a burst flag pulse is generated at a reference position or a shifted position. The burst flag pulse is used for inserting a color burst into the back porch of a horizontal flyback interval. The position of each color burst is judged, and transmitted data are reproduced in a receiver.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for transmitting digital data using color bursts of color television signals.

0002

BACKGROUND OF THE INVENTION In television systems, it may be desirable to transmit supplemental information in addition to normal television information in order to reproduce images and associated audio responses. Various techniques have been proposed for transmitting data superimposed on a television signal.

A color television system disclosed in US Pat. No. 3,723,637, issued to Fujio et al. on March 27, 1973, includes means for transmitting supplemental information. This supplementary information signal is encoded to form an encoded digital signal consisting of pulses having the same frequency and phase as the color burst signal of the color television picture signal. This encoded digital signal is superimposed on the color television signal in place of the original suppressed color burst signal.

US Pat. No. 4, granted to A. Campioni on January 9, 1979.
, 134,127 includes means for transmitting supplemental information, the supplementary information modulating an additional carrier having a frequency (Fa) to provide bursts of supplemental information. Form. This supplemental information burst replaces the normal color burst during the selected line period.

On September 21, 1982, T.J.
U.S. Pat. No. 4,350,999 to T. J. Mortimer discloses a method for transmitting digital information in a color television signal by transmitting a color burst signal for a different number of cycles. has been done. Different cycle numbers represent different digital values. For example, if a 2-bit word is to be transmitted, code 00 is transmitted by transmitting 8 cycles of the color burst signal. Similarly, code 0
1, 10, and 11 are transmitted by transmitting 9 cycles, 10 cycles, and 11 cycles of color burst signals, respectively.

US Pat. No. 4,783,669, issued to A.D. Depaul on November 8, 1988, teaches A technique for adding information to a signal is disclosed.

It would be desirable to provide a technique by which digital information can be transmitted within a color television signal such that the resulting television signal is compatible with the signal processing used in standard television receivers. Therefore, methods for superimposing digital information onto regular television signals include changing the width, frequency, or amplitude characteristics of the color burst, changing the synchronization pulse, or using automatic color control (ACC) circuitry within the television receiver. It must not have any influence. Furthermore, the method for encoding this digital information must be such that it can be reliably decoded within the receiver. Thus, for example, although the technique described in the Mortimer patent of transmitting different numbers of burst cycles to represent each digital value is theoretically compatible with the transmission standard used in the United States (NTSC), in practice may cause problems in operations such as ACC. This is because the number of cycles of the color burst, and therefore the energy of the color burst, changes from line to line. Moreover, since the number of cycles in a transmitted burst is uncertain, it is difficult in practice to accurately decode digital data. This is partly due to the unavoidable presence and counting of noise components, and partly due to the shape of the extracted burst signal, e.g. due to low-pass filtering, so that the counting cycle It becomes unreliable.

[0008]

SUMMARY OF THE INVENTION One aspect of the present invention relates to an encoding method and apparatus for superimposing digital data onto a color television signal by modulating the position of color burst components. Another feature of the invention relates to a decoding method and apparatus for demodulating position modulated color burst components to recover transmitted data.

More specifically, this encoding method is
transmitting a color burst of the television signal at a first location to represent a first digital value (e.g., a logical "0"); transmitting a color burst of a television signal at a location remote from the location of the television signal. Preferably, the first position corresponds to the standard or nominal position of the color burst.

The encoding device consists of a burst position modulator that generates an output control signal consisting of burst flag pulses. Each burst flag pulse consists of a first position indicating a first digital value, or a second position separated by a predetermined time from the first position to indicate a second digital value. A device for inserting a predetermined number of cycles of a color subcarrier signal generated by a conventional color subcarrier oscillator is responsive to each burst flag pulse and is transmitted at a time determined by each burst flag pulse. Inserting a color burst into a composite color television signal.

The invention will be better understood from the following detailed description, taken in conjunction with the accompanying drawings and claims.

0012

[Example] The television transmission system used in most countries around the world has three main formats: NTSC (
National Television System
temCommittee) standard, PAL (Phase
Alternating Line) standard or SECAM (Sequential Color Wi
th Memory) standards. N.T.
The SC standard uses 525 lines per frame to form a television image. On the other hand, PAL standard and SECA
The M standard uses 625 lines per frame. During the line scan process, blanking pulses are provided to the picture tube during the blanking period to ensure that the blanking line is not visible. The application of the present invention to the PAL standard is illustrated in FIGS. 1 and 2. It will be appreciated that the invention is equally applicable to the NTSC and SECAM standards.

Referring to FIG. 1, a blanking period 20 as used in the PAL standard is shown. The leading edge 22 of the blanking period 20 precedes the leading edge 24 of the horizontal sync pulse 26. Leading edge of blanking period 22 and horizontal sync pulse 26
The area between the leading edges 24 of is called the "front pouch" and
Trailing edge 28 of the horizontal sync pulse 26 and trailing edge 3 of the blanking period
The area between 0 and 0 is called the "back porch". A television in which a color burst consisting of eight or more cycles (depending on the transmission standard used) of a color subcarrier signal at a predetermined reference position is placed in the "back porch" and used for color demodulation. Synchronize the color subcarrier oscillator of the receiver. At the transmitter, a line frequency gate pulse (not shown) is applied for an appropriate number of cycles (e.g., 10±1 cycles for PAL, 8 cycles for NTSC).
Cycle or more) to get a color burst.

Referring to FIG. 2, the blanking period 20 of FIG. 1 is shown with the color burst 32 shifted in time by a predetermined amount in accordance with the present invention. More specifically, when the transmitter gate pulse (later referred to as the burst flag) is moved by a time interval T relative to the horizontal sync pulse 26, the sampled color burst 32 is also moved by a time interval T. and can be used to transmit digital data, as described below. The shifted color burst 32 retains the phase and frequency information provided by the transmitter-generated color subcarrier signal and has no effect on color demodulation as long as the temporal shift is within certain limits. Not affected. Color demodulation involves, among other things, extracting a color burst from a composite television signal in response to a color burst gate pulse generated within the receiver, and converting the phase and frequency of a color subcarrier signal generated by a color oscillator to this extracted color burst. The amplitude of the chrominance component of the composite television signal is synchronized to the color burst and controlled according to the amplitude of the extracted color burst (referred to as automatic color control or ACC). The gating pulses generated within the receiver are positioned with respect to the standard or reference position of the color burst and are relatively wide, but narrow enough to exclude image and synchronous components. Therefore, it is only necessary to limit this temporal movement sufficiently to ensure that the transmitted color burst falls within the color burst gate pulses generated within the receiver. If this temporal movement is not so limited, color demodulation functions such as ACC will be adversely affected. For example, a time shift of 400 nanoseconds (ns) has been found suitable for both NTSC and PAL standards. Regarding the number of color subcarrier cycles, 40
0 ns corresponds to approximately 1.7 cycles in the PAL standard, and N
According to the TSC standard, this corresponds to approximately 1.4 cycles.

In accordance with features of the invention, for example, to transmit digital data in a PAL television signal,
At t=0, the color burst 32 is transmitted at its reference position (5.6 μs after the leading edge 24 as shown in FIG. 1) to generate a first digital data signal (e.g., a logic "0"
) and shifted by t=T to represent a second digital data signal (eg, a logic value "1"). The temporal movement of the color burst 32 illustrated in FIG. 2 is 0.4 μs (400
ns) is used to represent the logical value "1". Such burst position modulation techniques can use each color burst to synchronize a subcarrier reference oscillator within the receiver and to transmit digital data at a rate of one bit of digital data for each color burst 32. . The PAL standard television signal has 607 bursts per frame and 25 frames per second, allowing digital data to be sent at a rate of 15.175 Kbits/second.

Referring to FIG. 3, a block diagram of a burst modulator 60 for generating burst flag pulses used to position modulate the color bursts of a television signal as shown in FIGS. 1 and 2 is shown in the dashed rectangle. and for transmitting digital data in such color bursts in accordance with features of the present invention. The burst modulator 60 has a simple configuration and consists of a shift register 62, a switch element 64, and a delay element 66. FIG. 4 shows typical signal waveforms at various locations within the burst modulator shown in FIG.

In operation, "bits" of digital data to be transmitted are placed into shift register 62. By way of example, such digital data may be in the form of non-return-to-zero (NRZ) encoded data. For convenience of explanation, assume that the digital data is an 8-bit word 11101101. These bits of digital data are coupled in parallel fashion (from left to right) to inputs 68 of shift register 62. Load pulses are coupled to load input 70 of shift register 62 at predetermined time intervals to place parallel data bits at input 68 into shift register 62 . For the illustrated 8-bit digital data word, one load pulse is generated for every eight consecutive horizontal sync pulses provided to clock input 69 of shift register 62. A typical load pulse sequence for an exemplary 8-bit digital data word is shown in the second column from the top of FIG. For example, due to the leading edge of the leftmost load pulse,
The illustrated digital data word 11101101 is placed into shift register 62.

The speed of shift register 62 is determined by the speed of the horizontal synchronization pulses applied to clock input 69 of register 62. These horizontal sync pulses are gated to correspond only to lines of the television image signal that contain color bursts that can be used to transmit digital data. A typical sequence of horizontal sync pulses coupled to clock input 69 of shift register 62 is shown in the first column of FIG. In the case of PAL television signals, the color burst is omitted during the vertical retrace interval, so that the horizontal simultaneous pulse is Removed during vertical blanking period. However, in the case of NTSC television signals, color bursts are not omitted during the vertical retrace interval and can therefore be used to transmit data.

A horizontal sync pulse at input 69 of shift register 62 causes the stored data word to be shifted out of the right side of shift register 62 one bit at a time in a serial NRZ sequence. The NRZ sequence at the output of shift register 62 for an exemplary 8-bit digital data word 11101101 is shown in the third column from the top of FIG. The bit sequence is synchronized to the leading edge of the horizontal sync pulse provided to input 69 of shift register 62. This bit sequence is applied as a control input signal to switch element 64.

Switch element 64 has a first input that receives an undelayed burst flag signal, a second input that receives a burst flag signal delayed by 400 ns in the illustrated case at delay element 66 , and a control input signal from shift register 62 . and one output. The undelayed burst flag signal coupled to the first input of switch element 64 is shown in the fourth column from the top of FIG. The delayed burst flag signal coupled to the second input of switch element 64 is shown in the fifth column from the top of FIG. The switch element 64 is, for example, a NOR gate,
It can be implemented with high speed CMOS analog switches or other suitable switching elements. The output signal of switch element 64 provides a sequential position modulated burst flag pulse. Each of these position modulated burst flag pulses is used to generate a color burst with a fixed number of cycles (depending on the television standard) over a period of time defined by the respective burst flag (
position) into a composite color television signal containing luminance and chrominance components. More specifically, the output signal of switch element 64 is coupled to a gating circuit (not shown) which in response to the burst flag pulses combines the output signal of the color subcarrier oscillator (not shown) with a combining circuit. selectively passed through a net (not shown). A combining circuitry combines the position modulated color burst with a composite television signal that includes a luminance component, a chrominance component, and a synchronization component. The gating circuit, color subcarrier oscillator and combining circuitry are not shown as they are common elements of a color television transmitter. It is noted that in the present invention, the number of cycles and phase of the inserted color subcarrier signal (except for the line-by-line phase inversion used in the PAL standard) is the same for each line.

In operation, the burst flag pulses generated at the output of switch element 64 are position modulated in accordance with a serial digital data control signal from shift register 62. Switch element 64 selects the delayed burst flag signal present at its first input whenever a logic value "1" appears at the output of shift register 62 and places a logic value "0" at the output of shift register 62. `` selects the undelayed burst flag signal present at its second input each time it appears. Illustrated 101 from shift register 62
The modulated output burst flag signal from switch element 64 for the 10111 data output sequence is shown in FIG.
Shown in the bottom row. More specifically, the leftmost modulated burst flag signal, in the bottom row of FIG.
ns delayed and represents the first bit (e.g., a logical "1") of the data sequence from shift register 62, and the second modulated flag signal is not delayed and represents the second bit of the data sequence from shift register 62. bits (for example, the logical value “
The burst position modulator 60 uses a phase-corrected shaping filter and data synchronization information (
eg, required when transmitting teletext on a PAL television signal). This is because line synchronization is already available within the television receiver and can be used to provide timing reference information.

Referring to FIG. 5, shown within the dashed rectangle is a block diagram of a burst demodulator 80 in accordance with features of the present invention for use in a television receiver. Burst demodulator 80 is used to decode position modulated color burst signals generated by a transmitter using a burst modulator, such as burst modulator 60 of FIG. FIG. 6 shows typical signal waveforms obtained at various locations within burst demodulator 80.

The composite video signal containing the position modulated color burst produced by a video demodulator (not shown) is processed by video signal processing that processes the luminance, chrominance and sync components of the composite video signal in a conventional manner. (not shown) and is further coupled to a first input of a switching or gating element 82 of a burst demodulator 80 . A typical composite video signal waveform received at the first input of switch element 82 is shown at the top of FIG.
6 and a blanking period 20 including a position modulated color burst 32.

[0024] First one-shot
Circuit 84 generates a first window signal including pulses of a predetermined width in response to horizontal synchronization pulses generated by the signal processing section of the television receiver. The waveform of the window signal is shown in the second column from the top of FIG. One-shot circuits are also known as monostable multivibrators. A trigger signal (such as the trailing edge of a horizontal sync pulse) drives the multivibrator circuit into an unstable state, and the multivibrator circuit remains in that state for a predetermined period of time before returning to a stable state. The first window signal pulse coupled to the input of switch element 82 is sufficiently wide in width to encompass the entire duration of the color burst in the first or reference position or the color burst in the second position. The output signal of switch element 82 contains a sequenced color burst without image information or synchronization information. A typical waveform of the output signal of the switch element 82 is shown in the third column from the top of FIG. An automatic gain control (AGC) amplifier 86 is used to adjust the amplitude of the color burst produced at the output of switch element 82. This is because the amplitude of the received color burst depends on several factors (e.g. antenna response, tuner IF
This is because it differs depending on the response, fine tuning conditions, etc.).

The output signal of AGC amplifier 86 is coupled to a first input (eg, "+" input) of analog comparator 88 and is connected to a reference voltage VR (
(having the level shown in the third column from the top of FIG. 6) is the comparator 8
8 (e.g., the "-" input). The output signal of comparator 88 is a TTL compatible pulse train;
The positive portion of each cycle of the burst component is clipped at the TTL level to form a respective pulse. A typical waveform of the output signal of comparator 88 is shown in the fourth column from the top of FIG.

A second one-shot circuit 92 responds to the horizontal sync pulse and generates a second window signal. Second
The second window signal includes pulses, the width of which is selected such that the falling edge of this second window signal approximately coincides with the edge of the unmodulated color burst. The waveform of the second window signal is shown in the fifth column from the top of FIG. A third one-shot circuit 94 is triggered by the falling edge of the second window signal pulse and generates respective narrow window signal pulses having a predetermined width (eg, about 500 ns). A typical narrow window signal waveform is shown in the sixth column from the top of FIG.

The narrow window signal produced by third one-shot circuit 94 and the output signal of comparator 88 are coupled to respective inputs of AND gate 96 . The output signal of AND gate 96 is low for an unmodulated color burst representing a logic "0" value. However, if the color burst is shifted to represent a logical "1", then almost the last two cycles of the color burst will be at the AND gate 9.
Pass 6. A typical waveform of the output signal of AND gate 96 is shown in the seventh column from the top of FIG.

A filter 98 (shown within the dashed rectangle) is used to low pass filter the output signal from AND gate 96;
Eliminate spikes that may pass through the AND gate in the case of transmission of a color burst representing a logical value "0". Filter 98 comprises a suitable circuit such as the RC circuit shown in FIG. The fourth one-shot circuit 100 has a logic value “
1" is transmitted. The resulting pulse width at the output of the fourth one-shot circuit 100 is one-half the duration of the video line (
For example, in the case of a PAL television signal, it is selected to be approximately equal to 32 μs). One shot circuit 10
The output signal of 0 is already demodulated serial data, but
It has a return-to-zero (RZ) code format. A typical waveform of the output signal of the one-shot circuit 100 is shown in the eighth column from the top of FIG.

Latch circuit 102 receives at a first input the first window signal from first one-shot circuit 84, receives at a second input the output signal from fourth one-shot circuit 100, and receives the output signal from fourth one-shot circuit 100. NRZ format serial data is generated. Latch circuit 102
is "clocked" by the trailing edge of the first window signal. A typical waveform of the output signal of latch circuit 102 is shown in the bottom row of FIG. Shift register 104 receives NRZ encoded serial data from latch circuit 102 . Shift register 104 is clocked by horizontal sync pulses. In the illustrated embodiment, the data words are 8
The data in the shift register is "read out" at the end of eight horizontal sync pulses.

003
Referring to FIG. 7, shown within the dashed rectangle is another configuration of burst demodulator 120 in accordance with features of the present invention. FIG. 8 shows typical signal waveforms within burst demodulator 120. The composite video signal is received at a first input of a switching or gating element 122 of burst demodulator 120 . A typical waveform of a composite video signal is shown in the top row of FIG. First one-shot circuit 1
24 generates a first window signal pulse in response to each horizontal sync pulse. The first window signal is coupled to an input of a second one-shot circuit 126. The typical waveform of the first window signal is shown in Figure 8 from the top 2.
Shown in column. The second one-shot circuit 126 is triggered by the falling edge of each pulse of the first window signal. The falling edge of each pulse of the first window signal should be within a position modulated color burst representing a logical "1" value, preferably near the middle of the color burst. the second one-shot circuit 1 in response to the trigger signal;
26 generates a second window signal at its output. The second window signal consists of several pulses, the width of which is selected to include the remainder of the color burst component, but exclude image information. A typical waveform of the second window signal is shown in the third column from the top of FIG.

When a composite video signal is provided to a first input of switch element 122 and a second window signal (serving as a control signal) is provided to a second input of switch element 122, the output of switch element 122 The signal consists of one portion of each color burst that is position modulated. The waveform of the output signal (referred to as a burst signal) of the switch element 122 is shown in FIG.
It is shown in the fourth column from the top. As shown in FIG. 8, the number of cycles in each burst portion at the output of switch element 122 differs depending on whether a logic "0" or a logic "1" is transmitted for the respective line.

The amplitude of the burst in the output signal of switch element 122 is adjusted by AGC amplifier 128 . Envelope detector 130 (e.g., consisting of a diode, resistor, and capacitor as shown in the dashed rectangle) is connected to amplifier 128.
in response to an amplified burst from the oscilloscope and generates an output signal that includes an envelope of the burst. A typical burst envelope signal is shown in the fifth column from the top of FIG. 8 for a logic value "0" and a logic value "1".

Analog comparator 132 receives the burst envelope (shown in the fifth column of FIG. 8) from envelope detector 130 at its "+" input and receives a predetermined reference from voltage source 133 at its "-" input. Receive voltage VR. Comparator 132 converts the envelope portion into a width modulated pulse. This width modulated pulse is shown in the last column of FIG.
It is amplitude compatible with L logic circuit. If a logic value “0” has a pulse width equal to T, a logic value “1” has a pulse width equal to T+40
It has a pulse width equal to 0ns. Here, T is approximately one-half of the burst width, and in the case of a PAL television signal, takes a value of, for example, approximately 1 μS.

[0034] Start-Stop
p) Oscillator 134 (shown within the dashed rectangle) is activated by each pulse occurring at the output of analog comparator 132. The oscillator 134 includes first and second oscillators connected in series.
It is illustrated as consisting of a NAND gate and an LC resonant circuit. However, it should be understood that a suitable circuit could be used that would only oscillate when the output signal from analog comparator 132 goes "high". The frequency of each burst at the output of oscillator 134 depends on the width of each pulse produced by analog comparator 132, i.e., whether each color burst represents a logic "0" or a logic "1". It really depends. As an example, a start-stop oscillator 134 having a frequency of 20 MHz may have a frequency of 20 MHz for a logic "0".
It oscillates for every cycle (1 μs÷5ns), and when the logic value is “1”, it oscillates for 28 cycles.

Counter 136 counts the number of cycles received from oscillator 134 when the second window signal from second one-shot circuit 126 is in a "high" state, and otherwise in a "reset" state. is maintained. Counter 136 during each "high" period of the second window signal.
The number of cycles counted by is stored in latch 138 when triggered by the falling edge of the second window signal. The count stored in latch 138 is compared to a reference count in digital comparator 140. For the example 20 MHz oscillator, the reference count value may be 24, which corresponds to the intermediate range of values (logic "0" and logic "
24 (i.e., 11
000) is sent to the digital comparator 14.
0 second input. A safety margin of ±4 cycles is used to account for possible jitter in the output signal of analog comparator 132 or drift in the frequency of start-stop oscillator 134. The output signal of digital comparator 140 is demodulated serial data. This is because the output is in a "low" state for each count value of 24 or less, and the output for a count value of 24 or more is in a "high" state. Shift register 142 has one of its inputs coupled to the output of digital comparator 140 and is used to convert serial data from digital comparator 140 to parallel data. shift register 14
2 is clocked by horizontal sync pulses.

The present invention provides that the frequency, phase and amplitude states of the color burst are unaffected by positional movement and do not adversely affect the normal operation of the color television receiver, so that supplementary data can be transmitted along with the color television signal. has advantages over other technologies for transmitting In this regard, it is noted that the small time shift does not require any modification of existing color burst gating circuits, so that conventional color demodulators can be used without modification. Moreover, the encoder is of very simple construction and the decoding process is very reliable. Furthermore, the shape of the color burst is not critical, for example due to low-pass filtering.

The present invention relates to data transmission within a television signal using position modulated color bursts.
Conditions under which the program is available (such as proper payment or identification)
There are numerous applications in pay TV networks and perhaps private or government communications systems to make them available to a satisfied audience. For example, consider a pay TV system that essentially has two parts. The first part scrambles the video signal at the transmitter so that if the program is received by unauthorized viewers, it cannot be viewed. The second part descrambles the video signal within the receiver according to the "key" signal required to "unleash" the scrambled program. For example, a predetermined number of TV lines in each field may be reversed. The order of reversing the lines is continuously and randomly changed. In accordance with a feature of the invention, the key signal required to unscramble to identify scrambled lines is provided by the location of the color burst. For example, a burst is moved in time (
If the logic value is "1"), the next line is reversed. Another application is the transmission of service information used by cable operators. This information is normally transmitted on an extra channel, but channels can be saved by using position modulation of color bursts for data transmission in accordance with the present invention.

It should be understood that the specific embodiments described above are only intended to illustrate the invention. Various modifications can be readily made by those skilled in the art in accordance with the principles of the invention. For example, although in the preferred embodiment the position of the first color burst is not moved and thus corresponds to a standard or reference position, this position could also be moved.

[Brief explanation of the drawing]

FIG. 1 shows standard PAL (phase
(alternating line) indicates a blanking period located within a television signal that includes a color burst used to display a first logical value (eg, "0");

FIG. 2 depicts the blanking period of FIG. 1 including a color burst that is position modulated (moved in time) to represent a second logical bit (e.g., "1") in accordance with features of the present invention; show.

FIG. 3 shows a block diagram of a burst modulator used within a transmitter to generate the blanking period shown in FIGS. 1 and 2, in accordance with features of the invention.

FIG. 4 shows exemplary waveforms occurring at various points in the burst modulator of FIG. 5;

FIG. 5 shows a block diagram of a burst demodulator according to features of the invention used in a receiver to recover digital data encoded by the burst modulator of FIG. 3;

6 shows exemplary waveforms occurring at various points in the burst demodulator of FIG. 5; FIG.

FIG. 7 shows a block diagram of another demodulator according to features of the invention used in a receiver to recover digital data encoded by the burst modulator of FIG. 3;

8 shows exemplary waveforms occurring at various points in the burst demodulator of FIG. 7; FIG.

[Explanation of symbols]

82 Switch element 84 First one-shot circuit 86 AGC amplifier 88 Analog comparator 92 Second one-shot circuit 94 Third one-shot circuit 98 Filter 122 Switch element 124 First one-shot circuit 126
Second one-shot circuit 128 AGC amplifier 130 Envelope detector 132 Analog comparator 134 Start-stop oscillator 136
Counter 140 Digital comparator

Claims (1)

[Claims] 1. A receiver for receiving a composite television signal comprising color bursts that are position modulated for each horizontal synchronization pulse in each horizontal line to transmit digital data, comprising: extraction means for extracting from each horizontal line a portion of the color burst transmitted in a first position and representing a first digital value for each horizontal sync pulse; transmitted at a second position moved by a predetermined time from the reference position;
and determining means for determining whether or not the digital value is represented.