JPS6127943B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of multiplexing a plurality of types of index signals onto a video signal converted into a narrowband signal.

For example, in a system that transmits a wideband image signal such as a television video signal via an audio magnetic tape or a narrowband transmission medium such as a telephone line, the image signal is converted to a scanning speed in advance to transmit a narrowband image signal. However, when the image signal, such as a television video signal, is composed of an image information signal representing the content of the picture itself and accompanying vertical and horizontal synchronization signals, the above-mentioned method is applied. In order to provide guidelines for correctly restoring the original signal by receiving the scanning speed converted signal in such a system, an index signal similar to the above-mentioned synchronization signal, for example 1, is added to the scanning speed converted image information signal. It is necessary to multiplex various signals such as an index that indicates the start of each image or an index that indicates the start of each horizontal scanning line. Furthermore, if the above-mentioned index signal is incorrectly detected during reception, the restored image will be greatly incorrect in units of one horizontal scanning line or one image.
An important key to the success or failure of this system is a method of multiplexing index signals that can be transmitted stably and faithfully over a narrow band transmission medium having direct current blocking characteristics, such as audio magnetic tape or telephone lines.

The present invention has been made in view of the above points in order to efficiently multiplex an index signal with an image information signal and to transmit it faithfully.

The present invention assigns a plurality of types of burst signals each having a different frequency to one index, so that each of the plurality of types of indexes can be assigned its own during the no-signal period of a video signal converted to a narrow band. It is designed to multiplex the signals so that they are different.

The present invention will be explained below with reference to Examples.

For example, the proprietary band of audio magnetic tape is 60Hz~
The passband of general telephone lines is about 300Hz to 3400Hz, and in order to faithfully transmit signals in a transmission medium that has DC blocking characteristics, for example, Japanese Patent Application Laid-Open No. 49-29928
It is advantageous to use a bipolar pulse train signal in which the image signal is pulse-interval modulated so that the amplitude value of each picture element is proportional to the time interval between adjacent pulses, as disclosed in .

FIG. 1 shows an embodiment of the invention suitable for signals converted into narrowband signals in this manner. Reference numeral 11 is a scanning speed converter which converts the television video signal 20 from the terminal 1 into
29928, by the speed conversion method known in the art, Part 1
This is a device that converts an image information signal in units of one horizontal scanning line into a narrowband image information signal 21 which is sequentially pulse-interval modulated for each horizontal scanning line over an image, and outputs the signal. The start command signal 22 from terminal 2 starts the scanning speed conversion for the image.
It outputs an index control signal 23 that guides the start of that one image, and sequentially guides the start of that one horizontal scanning line each time the speed conversion of that one horizontal scanning line starts. An index control signal 24 is output. Also, this device 1
The narrowband signal 21 from 1 is generated during the period when the control signals 23 and 24 are output, that is, before the scanning speed conversion for one image is started and when the speed conversion for each horizontal scanning line is started. In the period before the signal is output, the signal is output as if the no-signal state continues.

The control signal 23 from the device 11 is directly supplied to the first burst generator 12 and is also supplied to the third burst generator 14 via the gate 15, and the control signal 24 is supplied directly to the first burst generator 12. It is supplied directly to the generator 13 and also to the third burst generator 14 via the OR gate 15. As shown in FIG. 2, these first, second, and third burst generators each have a control signal 2
3 or 24, and generates burst-like bipolar pulse train signals with repetition frequencies _{of 1} , ₂ , and ₃ and repetition cycle numbers of _N1 , _N2 , and _N3, respectively, within the period of the control signal. Gate 15 is device 11
The control signal 23 or 24 from the burst generator is gated to feed the third burst generator. Further, the first, second, and third burst generators 1
The burst signals from 2, 13, and 14 are sent to the adder 16.
supplied to

Therefore, when the control signal 23 is supplied from the device 11, the first and third burst generators 12, 14
operates, and the repetition frequency ₁ and
₃ burst signals are generated and these are added to adder 1.
6 is added to form a composite burst signal of ₁ and ₃ . Similarly, a control signal 24 from the device 11 causes the second and third burst generators 13, 14 to
operates to generate burst signals ₃ and ₃ , which are added to ₂ in adder 16.
This results in a composite burst signal of ₃ . These composite burst signals are band-limited by a filter 17, then added to and multiplexed with the narrowband image information signal 21 from the device 11 by an adder 18, and outputted to the output terminal 3.

The period in which the above composite burst signal is inserted is:
As described above, since it is equal to the no-signal period of the narrowband image information signal 21, this composite burst signal will not alter the quality of the image information. Furthermore, since the index indicating the start of one image and the index indicating the start of each horizontal scanning line are multiplexed on the image information signal with the composite burst signal as described above, such multiplexing is possible. By receiving the signal and accurately detecting its composite burst signal, it is possible to obtain guidelines for correctly restoring the original image. Regarding the above-mentioned narrowband image information signal, as mentioned above, for example,
If the bipolar pulse train signal is transmitted using a pulse interval modulation method such as that known in the 29928, it is possible to faithfully transmit the signal without deteriorating the image quality even on a transmission medium that is cut off from direct current. Since this is nothing but a bipolar pulse train signal that does not have a DC component, it can be transmitted faithfully like an image information signal.

Next, a method for detecting the index signal multiplexed with the composite burst signal as described above will be explained using the embodiment shown in FIG. That is, a composite burst signal with repetition frequencies ₁ and ₃ , and
A multiplexed signal of two types of index signals consisting of composite burst signals of ₂ and ₃ is simultaneously supplied to the first, second, and third single tuning circuits 21, 22, and 23 via the terminal 4. Supplied. These 21, 22, and 23 are ₁ , ₂ , and 23, respectively.
₃ , thus tuning to only a single frequency of ₁ above.
In the _first index signal portion _{consisting of the combined} burst signals of In the second index signal part, only 22 and 23 are active, and from each
_Two and _three single burst signals are extracted.
These first, second and third single tuned circuits 21, 2
Each burst signal extracted singly from 2 and 23 is transmitted to the first, second, and third envelope detectors 3, respectively.
1, 32, 33, and these 3
Each detection output from 1, 32, 33 is passed through the first, second, and third low-pass filters 41, 42, and 33, respectively.
43, and burst frequency components included in each detection output are removed. Furthermore, each output from these 41, 42, and 43 is the first,
The signal is supplied to the second and third threshold circuits 51, 52, and 53, and the level is compared with each of the thresholds, and if the voltage exceeds the respective threshold from each of the circuits 51, 52, and 53, A signal of "1" is output only when

Therefore, in the first index signal portion, since the single burst signals ₁ and ₃ are extracted only from 21 and 23, respectively, as described above, the output levels of the filters 41 and 43 become maximum, and the threshold circuit 51 and 53 thresholds, "1" is extracted from each, and as a result, the first
AND gate 61 opens and “1” is output to terminal 5. On the other hand, in this first index signal portion, 22 does not operate, and therefore "1" is not output from the threshold circuit 52, so the second AND gate 62 is closed and the terminal 6 is is not output. Similarly, in the second index signal portion, _{the second} and _third single burst signals are extracted only from 22 and 23, respectively, and the output levels of the filters 42 and 43 are maximized, so that the threshold circuits 52 and "1" is output only from 53, and "1" is not output from the threshold circuit 51 because 21 is not operated. Therefore, only the second AND gate 62 is open and the terminal 6 “1” is output to the terminal 5, and no output is output to the terminal 5. Thus, only one of the first and second index signals is detected from terminals 5 and 6.

By the way, according to the multiplexing method of the present invention as described above, in the detection method as shown in FIG.
Due to the spectrum of frequencies ₁ , ₂ , and ₃ ,
When each of the single tuning circuits 21, 22, and 23 described above operates, the image information signal portion may also be detected as a burst signal, but if each index is configured with multiple types of burst signals as described above, It is extremely rare for the image information signal portion to have a spectrum with a frequency equal to those of these multiple types of burst signals simultaneously and for a certain period of time. If the detected wave is regarded as an index, the index will not be mistakenly detected in the image information signal portion. Furthermore, the frequency arrangement of the burst frequencies constituting the above image information signal and each index is such that the main spectrum of one of the image information signals is located in the frequency range of the low frequency group, and the main spectrum of the other multiple types of burst signals is located in the frequency range of the low frequency group. If the frequencies are located in the frequency range of the high frequency group, the amplitude of the harmonic spectrum of the image information signal will generally become small. exist at the same time, the thresholds of the threshold circuits 51, 52, and 53 are appropriately selected to set the spectral amplitude of the burst signal as a threshold relative to the amplitude of the harmonic spectrum of the image information signal. By performing value discrimination, it is possible to further reduce index error detection in the image information signal portion.

Next, since the spectrum of the burst signal formed as shown in FIG. 2 has a finite number of repetition cycles, it generally has a certain spread, unlike a line spectrum. If the repetition frequency of the burst signal is ₀ and the number of repetition cycles is N ₀ , the spectrum has a maximum amplitude at the repetition frequency ₀ , and _K = (1 ±K/N ₀ ) ₀ (K = 1, 2, 3, ... ...) (1) Generally, a zero point slot is placed at the Kth position from the center frequency ₀ so that the amplitude is zero at each frequency. has. On the other hand, in the detection method as shown in FIG. 3, the tuning characteristics of the single tuning circuits 22, 22, 23 have a maximum amplitude at the center frequency ₀ as shown in FIG. 5, but generally have a certain spread. When the frequencies of multiple types of burst signals are close to each other, the spectrum of the nearby burst signals falls within the spread of the tuning characteristics, resulting in a false burst signal that is erroneously tuned to the nearby burst signal. This causes the detection of
The interference of adjacent burst signals can be minimized by doing the following.

That is, if the repetition frequency of the adjacent burst signal is ₀ ' and the number of repetition cycles is _N0 ', then
The spectrum of this proximity burst signal is as above,
_{' K} = (1+K/N ₀ ) ₀ ' (K = 1, 2, 3...) which has the maximum amplitude at repetition frequency ₀ ' and is at the Kth position from its center frequency ₀ '.
...(2) It has a zero point slot at the frequency. here,
The above two burst frequencies ₀ and ₀ ′ ( ₀ <
₀ ′), from equations (1) and (2), (1+K/N ₀ ) ₀ = ₀ ′……(3) and (1−K/N ₀ ′) ₀ ′= ₀ ……( 4) If ₀ and ₀ ' are selected so as to satisfy, that is,
(3), (4) If K is removed from both equations and ₀ / ₀ '= _N0 / _N0 ' _is selected so that it satisfies ( ₅ ), then one of the burst frequencies becomes Since the spectrum of the burst signal mixed into one single tuned circuit having a tuning point corresponds to the slot of the peak and zero point, the spectrum mixing at the tuning point and its vicinity is either zero, or even if mixed, it is extremely small. Since the level is small, a false burst signal as described above will not be detected.

As described above, according to the present invention, it is possible to efficiently multiplex a wide variety of other signals such as an index signal different from the image information signal converted into a narrowband image information signal, and also to have DC cutoff characteristics. Furthermore, according to the multiplexing method of the present invention, the signals that are multiplexed with each other can correctly propagate the information without altering the information of each other. You can.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the signal multiplexing method according to the present invention. FIG. 2 is a diagram showing an example of the waveform of a burst signal in the present invention. Third
FIG. 1 is a block diagram showing an example of a circuit for detecting multiplexed signals in the embodiment of FIG. FIG. 4 is a diagram showing the frequency spectrum of the burst signal of FIG. 2. FIG. 5 is a diagram showing an example of the tuning characteristics of the single tuning circuit shown in FIG. 3. 11: Scanning speed converter, 12, 13, 14:
Burst generator, 15: OR gate, 16,1
8: Adder, 17: Filter, 21, 22, 2
3: Single tuning circuit, 31, 32, 33... Envelope detector, 41, 42, 43... Low pass filter, 51, 52, 53: Threshold circuit, 61, 6
2: AND gate.

Claims (1)

[Scope of Claims] 1. Directs the start of scanning speed conversion for each image or for each horizontal scanning line of image information into an image information signal that has been converted into a narrow band bipolar pulse train signal through scanning speed conversion. A signal multiplexing method characterized by time division multiplexing by allocating information signals as multiple types of multipolar pulse train signals each having a different repetition frequency. 2. The signal multiplexing method according to claim 1, wherein the information signal guiding the start of the scanning speed conversion is at least two types of burst-like bipolar pulse train signals with repetition frequencies close to each other;
A signal multiplexing method characterized in that the ratio of each repetition frequency is chosen to be equal to the number of repetition cycles of each.