JPS6282894A - Video transmission system - Google Patents

Abstract

PURPOSE:To transmit two video signals through only one transmission line by dividing the frequency band of a luminance signal into four bands and executing prescribed processing to reduce the bands of a video signal, compress a horizontal scanning period and multiplex two video signals with time division. CONSTITUTION:A luminance signal in a video signal inputted from an input terminal 1 is separated into different signals YL, YM1, YM2, YH in four bands by filters 4-7. The signal YM2 is modulated with prescribed times the horizontal scanning frequency and only one band is extracted by an LPF 10. The signal YH is also similarly processed. On the other hand the chroma signals, I and Q signals are modulated with two rectangular phases by decoders 31, 32 and modulated in an area C. Respective signals YM1, YM2, YH through combline filters 14-17 are added to the signal YL by an adder 18. A video signal inputted from an input terminal 20 is similarly processed and the two video signals are multiplexed with time division by an MPX circuit 39 through time axis compressing circuits 19, 38 and outputted as an analog signal.

Description

TECHNICAL FIELD The present invention relates to a transmission system for television video signals, and more particularly to a video transmission system for transmitting two-channel video signals through one transmission path.

Prior Art Conventionally, in this type of two-channel video signal transmission system, the horizontal scanning time of each video signal is compressed to 172, and the two video signals are time-division multiplexed within one horizontal scanning period.

In the conventional two-channel video transmission system described above, each horizontal scanning time is compressed to 1/2, so there is a drawback that the frequency band to be transmitted is doubled. Furthermore, if the transmission path band is limited to the frequency band for one channel, there is a drawback that the horizontal resolution deteriorates.

OBJECTS OF THE INVENTION An object of the present invention is to provide a video transmission system that can transmit two video signals on one transmission path without increasing the frequency band or degrading the horizontal resolution.

Structure of the Invention The video transmission system according to the present invention separates each video signal into a luminance signal and a chrominance signal, divides the frequency band of the luminance signal into four, and among the four divided luminance signals, the low frequency band is The remaining three luminance signals and chrominance signals with different frequency bands are calculated as nfH, (n+1/4) fH, (n+1/2) in a band higher than the low frequency signal of the luminance signal.
) fil, (n+3/4)fll (n is an integer,
fH is the horizontal scanning frequency) By multiplexing the frequency spectrum with different frequency offsets, the frequency band of the video signal is reduced and the horizontal scanning time is halved, thereby converting the two video signals into one horizontal This is a configuration in which two-channel video signals are transmitted through one transmission path by time-division multiplexing during the scanning time.

Example Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of a transmitter of a two-channel video transmission apparatus that is an embodiment of the present invention. The NTSC signal input terminal 1 receives the first channel of the two-channel NTSC signals sent by the two-channel video transmission device. This signal is converted from an analog signal to a digital signal by an A/D (analog/digital) conversion circuit 2, and then converted into a Y
/C (luminance signal/chrominance signal) separation circuit 3 separates the signal into a luminance signal and a chroma signal. The separated luminance signal is passed through a YL filter 4. Y old filter 5. The YH2 filter 6 and the YI+ filter 7 provide YL and Y)11. as shown in FIG. 3(a), respectively. '12. Yll is separated into signals in four scale frequency bands. Signal YH2 is the modulation circuit 8
and f2 = (f!+1/4)・fH (R is an integer, f
H is the horizontal scanning frequency), and the low-pass filter 10 extracts only one sideband of the modulated wave.

By doing this, the signal of YH2 becomes Y) in Fig. 3(b).
Shift the frequency to 12 regions.

Further, the signal Yl+ separated by the YH filter 7 is multiplied by the signal CO32πf3 having a frequency of f3 = (n+3/4)-fH (n is an integer) in the modulation circuit 9, and the signal Yl+ separated by the YH filter 7 is multiplied by the signal CO32πf3 having a frequency of f3 = (n+3/4)-fH (n is an integer). is taken out. In this way, the frequency of the YH signal is shifted to the YH region of FIG. 3(b).

On the other hand, the chroma signal separated by the Y/C separation circuit 3 is decoded by the decoder 12 into an I signal and a Q signal. Then, in the encoder 13, fl-(m+f/2)-
By quadrature two-phase modulating the ■ signal and the Q signal with a modulated wave having a frequency of fH (m is an integer), C in Fig. 3(b) is obtained.
modulated into the region of

By doing this, each signal YH1, YH2, Yll
.

In case C, the signals overlap in the same frequency band as shown in FIG. 3(b).

However, the signal YH from the Y old filter 5 is K・fl(
K is an integer), and has a frequency spectrum centered around the spectrum of YHl in FIG. 3(C). In addition, the signal Y by the low-pass filter 10
Since n2 is modulated by l) +1/4) -fll, it has a spectrum with <1/4 fH offset like YH2 in FIG. 3(C). Furthermore, the signal Yl+ from the low-pass filter 11 is (n+3/4)-fl
Since it is tail modulated, it has a spectrum with an offset of <3/4f11 as shown in YH in FIG. 3(C). Furthermore, the chroma signal of the encoder 13 is (m+
1/2) -fHT: Because it is modulated, 1/2f
It has a spectrum with H offset.

As shown in FIG. 3(C), each signal YH1, YH2, YH,
Since C has a spectrum spread, comb-shaped filters 14, 15, 16, 1 are used to prevent interference with each other.
7, each spectrum is processed to limit its width. Then, in the adder circuit 18, YL, YH, YH2, YH, C
By adding the respective signals, it becomes possible to create a signal with approximately 1/2 the frequency bandwidth of the signal in the frequency band shown in Fig. 3(a) as shown in Fig. 3(b). .

On the other hand, the NTSC signal input terminal 20 is connected to the second channel of the NTSC signal sent by the two-channel video transmission device.
The channel signal is input.

This second channel signal is inputted in synchronization and phase with the first channel signal inputted to the NTSC signal input terminal 1. The operation from the mA/D conversion circuit 21 to the addition circuit 37 converts the first channel signal into
The same processing as that performed from the /D conversion circuit 2 to the addition circuit 18 is performed.

The band-compressed first and second channel signals output by the adder circuit 18 and the adder circuit 37 are sent to the time compression circuit 19.
．． In 38, the horizontal scanning period is compressed to 172 using a memory, and the readout time of both channel signals is shifted.
By time-division multiplexing in the PX circuit 39, a signal as shown in FIG. 4 is obtained. At this time, both channel signals are 1/2
Because the time axis has been compressed, the frequency band has doubled, and the two tunnel signals, which had been band-compressed by the adding circuit 18.37, have almost the original signal band as shown in Figure 3(d). It will be the same. Furthermore, in the three MPX circuits, a synchronization signal and a burst signal are inserted into the blanking period. Then, the digital signal is converted into an analog signal by the D/A conversion circuit 40, and the two-channel video signal is sent to the transmission line for one channel from the two-channel video signal output terminal 41.

FIG. 2 is a block diagram of a receiver of a two-channel video transmission apparatus which is an embodiment of the present invention.

A 2-channel video signal is input to a 2-channel video input terminal 42 from a transmission path, and an A/D conversion circuit 43 converts the analog signal into a digital signal.

The time axis expansion circuit 44 converts the first channel signal of the two-channel video signal shown in FIG.
This is doubled to create a signal corresponding to the signal of the adder circuit 18 of the transmitter. This signal has the frequency arrangement shown in FIG. 3(b). From this signal, each signal YL, YHI, YH2, Y
H and C are separated and returned to each frequency arrangement shown in FIG. 3(a) as follows.

A low-pass filter 45 separates the signal YL.

Bypass filter 46 separates each signal YHI, YH2, Y)
l.

Take out C. Since this signal has a comb-shaped frequency spectrum as shown in FIG. 3(C), only the signal YH is extracted by the comb-shaped filter 48. In addition, the bypass filter 47 outputs signals Y81, YH2, YH, C
Take out. This signal also has a comb-shaped frequency spectrum as shown in Figure 3 (C), so each 1/4
Each signal fH is processed by comb-shaped filters 49, 50, and 51 with offsets of
2. Take out C and Yll.

The signal YH2 extracted by the comb filter 49 is multiplied by the signal CO32πf2 having a frequency of f2 = <1 + 1/4)·f II in the modulation circuit 52, and by extracting only one sideband of the modulated wave in the bypass filter 54. , YH2 signals are shifted in frequency to the YH2 region of FIG. 3(a). Further, the signal y++ extracted by the comb-shaped filter 50 is sent to the modulation circuit 53 as f3 = (n+3/
4) A signal with a frequency of -fH is multiplied by cos2π'3, and only one sideband of the modulated wave is extracted by the bypass filter 55, and the frequency of the YH signal is shifted to the Yll region in FIG. 3(a).

Further, the chroma signal separated by the comb-shaped filter 51 is decoded by the decoder 56 into an I signal and a Q (i @), and then by the encoder 13
) The I signal and Q signal are quadrature two-phase modulated using a modulated wave having a frequency of fll.

Then, in the adder circuit 58, the signal Y of the low-pass filter 45 is
L, signal YH1 of the comb filter 48, signal Y82 of the bypass filter 54. Signal Y1 of bypass filter 55
1. By adding the chroma signals of the encoder 57, the luminance signal becomes NT having the frequency band shown in FIG. 3(a).
Create SC signal. In addition, a blanking processing circuit 59 adds HBL (horizontal blanking) and VBL (I direct blanking) synchronization signals and burst signals, and a D/A conversion circuit 60 converts the digital signal into an analog signal.
NTS of the first channel from the NTSG signal output terminal 61
Outputs C signal.

Further, the time axis expansion circuit 62 of the A/D transformation circuit 43 doubles the horizontal scanning time of the second channel signal of the two-channel video signal shown in FIG. Create. The 13 operations from the time axis expansion circuit 62 to the NTSG signal output terminal 79 are performed in the same way as those from the time axis expansion circuit 44 to the NTSC signal output terminal 61.

As a result, the second channel NTSG signal is output to the NTSC signal output terminal 79.

The time axis compression circuit 19.38 and MPX circuit 39 in Fig. 1 are brought before the Y/C separation circuit 3.22, and the operations from the Y/C separation circuit 3.22 to the addition circuit 18.37 are combined into one. The circuit configuration can be simplified by time-sharing the circuit. However, in that case, it is necessary to double the operating speed of the circuit from the Y/C separation to the adder circuit.

Similarly, in the block of Fig. 2, the time axis expansion circuit 44°62
By placing the circuit after the adder circuit, it is possible to have a single circuit configuration from after the time base expansion circuit to the adder circuit.

In addition, although each comb-shaped signal spectrum in FIG. 3(C) is the spectrum before time axis compression, the circuit may be configured so that the spectrum in FIG. 3(C) is obtained after time axis compression. . This cutting signal C is (227+1/2) f
If you make it l+ and get J3, 2 chi 1? channel video signal to NTS
C receivers can receive color signals.

As described in detail, the present invention has four frequency bands for a luminance signal.
The three luminance signals with different frequencies excluding the low frequency region signal from the four luminance signals are divided into four luminance signals, and the color signal is transferred to a frequency offset 1 in a band higher than the low frequency region signal of the luminance signal. By reducing the frequency band of the image signal and compressing the horizontal scanning time to 1/2, the two video signals can be time-divided into one horizontal scanning time by multiplexing them at different frequencies. By multiplexing, it is possible to transmit two video signals on one transmission path without degrading the horizontal resolution.Also, the vertical resolution does not deteriorate.However, the resolution in diagonal directions on both sides deteriorates. , since the resolution in the diagonal direction is not visually noticeable, it does not pose much of a problem.

[Brief explanation of drawings]

Claims (1)

[Claims] For each of the two-channel video signals, the luminance signal and chrominance signal are separated, the frequency band of the luminance signal is divided into four, and the frequency bands of the four divided luminance signals excluding the low-frequency region signal are separated from each other. Different residual luminance signals and the chrominance signal are multiplexed so as to have frequency spectra in which frequency offsets are set differently in frequency bands higher than the low frequency region, and the horizontal scanning time is reduced to 1/2. A video transmission system characterized in that the video signals of the two channels are time-division multiplexed within one horizontal scanning time.