JPH0720269B2 - Two-channel multiplex transmission system for television signals - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a transmission signal processing technique of a color television signal for transmitting two NTSC color television signals through a one-channel transmission path, and more particularly to a television signal The present invention relates to a sampling method and a color signal multiplexing method.

(Prior Art) In order to transmit two NTSC television signals through a one-channel transmission line, various systems have been proposed and put into practical use.

(1) Line switching system In this system, the transmitting side switches two video channels for each line and sends them, and the receiving side separates each channel, and then the thinned lines are interpolated by line interpolation.

(2) Vertical compression / combining method This method compresses two video channels to 1/2 in the vertical direction on the transmitting side, divides them vertically and combines and sends them, and then doubles them vertically on the receiving side. Restore. On the sending side
For 1/2 compression, scanning lines are thinned out one by one and written in the memory, and information thinned out by line interpolation is interpolated on the receiving side.

(3) Field switching method (Thomson Bidiplex) In this method, the odd field and the even field are alternately switched to transmit 2 channels, and the odd side and the even field are separated on the receiving side, and then the intermediate field is lost by the field interpolation. To store.

(4) Horizontal compression / synthesis method This method is a method of compressing two video channels in the horizontal direction to 1/2 in the horizontal direction on the transmitting side, swaying these to the left and right to create a synthetic signal, and transmitting it. According to the specification of No. 56-52981, the two types of video signals are sampled only in the horizontal direction, and the number of samples is simply thinned to half, and then the time axis is compressed to 1/2. The time-division multiplexed signal is transmitted during the horizontal scanning period, the receiving side separates the two types of signals within the horizontal scanning period, the time axis is expanded only in the horizontal direction, and the missing sample value is interpolated to insert the original image. Restore the signal. Further, prior to the above time axis compression, YC separation is performed, and then the band of the Y signal is limited to about 2 MHz,
For the C signal, a composite signal is produced by modulating with a subcarrier having a frequency half that of the conventional subcarrier frequency Fsc.

(Problems to be Solved by the Invention) In the representative conventional examples described above, with regard to the schemes (1) and (2), the resolution of the received image in the vertical direction is remarkably deteriorated, and the practicability as a broadcast image quality is high. Lacking in. Method (3) is not as bad as the vertical resolution, but
Restoration of a moving image results in dropped frames, and when the camera is panned, the image movement becomes unnatural and causes severe flicker.

In method (4), the Y signal band is as narrow as 2 MHz and the image is blurred.
Since the frequency is 2, there is a drawback that the deterioration of cross color and cross luminance is significantly larger than that of the conventional method.

The object of the present invention is to solve the above-mentioned problems and to solve the problems of the conventional one.
It is intended to provide a two-channel multiplex transmission system that can transmit two programs while maintaining the NTSC standard on the NTSC standard transmission line, reducing the transmission cost by half.

(Means for Solving Problems) In order to achieve this object, 2 of the television signal of the present invention is used.
In the channel multiplex transmission method, two luminance signals of two YC-separated color television signals are subjected to time-axis compression after field or line offset sub-sampling, respectively. The color signals are respectively modulated by the color subcarriers of the NTSC signal, or if the color signals are modulated by the color subcarriers at the time of YC separation, the two color signals are alternately taken out for each field for those. Are multiplexed with the two luminance signals after each time axis compression and transmitted, and a two-channel NTSC color television signal is transmitted through a one-channel NTSC transmission line. .

(Operation) Even if the C signal is alternately transmitted field-sequentially as described above, the deterioration does not pose a problem in view of the spatial and temporal resolution of the visual sense with respect to the color difference signal, and the C signal does not affect the Y signal that is subsampled. However, deterioration due to cross color and cross luminance is small because it is multiplexed in the high frequency range.

These will be described below using the three-dimensional space-time frequency domain.

For the sake of explanation, the band of the transmission path is 4.5 MHz, and points in the three-dimensional space-time frequency domain are expressed by (horizontal frequency (MHz), vertical frequency (CPH), time frequency (Hz)). That is, (0,0,0) indicates a DC component, (3.58,525 / 4,15) indicates a color subcarrier, and (0,525 / 2,30) indicates a carrier by interlacing. For details of this area, see Yuyama, Yano: Low-level family image quality in component coding, Technical Report of the Television Society of Japan, TEBS89-2, May 1983.
It is clear on the 25th of the month.

Fig. 4 shows the signal band of the current NTSC color television system, and the Y signal is A, B, C, D, E, F, G depending on the characteristics of the camera.
It exists in the area 1 surrounded by a solid line. On the other hand, the C signal is N
It exists around the point (3.58,525 / 4,15).

Fig. 5 shows that the Y signal is line-limited by the carrier at the point (4.5,525 / 4,0) after the band is limited to the area 2 surrounded by A, B, C, D, E, F, G. The figure shows how offset subsampling is performed. In this case, half of the 4.5MHz, 2.25MHz and higher components are folded back and exist in the H, I, J, K, D, and G regions.
Information in area 2 can be transmitted even if the bandwidth of the transmission path is limited to 2.25 MHz.

FIG. 6 shows a situation in which the line-offset Y signal is doubled on the time axis and then the C signal is multiplexed. FIG. 7 is a diagram in which FIG. 6 is projected on the horizontal / vertical plane and the horizontal / time plane, and the C signal is multiplexed in the hatched portion. From this figure, if the vertical band of the C signal is limited to 525/8 and line-sequentially multiplexed, 2.25MHz of the original Y signal is obtained.
It can be seen that the following signal components are not affected. As a matter of course, the Y signal can be transmitted up to 4.5 MHz in an image with a small C signal component.

If the same consideration is applied to the field offset subsampling by the carriers of (4.5,525 / 2,0) and (4.5,0.30), it is assumed that they correspond to FIGS. 5 and 7, and FIG.
Figure 9 is obtained. That is, in this case, since the folding of the horizontal high frequency component is separated from the low frequency component in the vertical direction, the Y signal can be transmitted up to 4.5 MHz by band-limiting the C signal in the vertical direction at 525/8.

Further, when the image is a stationary surface or the movement is slow, the Y and C signals can be separated in the time axis direction. That is, the C signal may be field-sequentially transmitted with band limitation in the time direction. In this case, since it is not necessary to limit the band of the C signal in the vertical direction, both the Y and C signals can be transmitted without losing the horizontal and vertical resolutions. Even when the image moves faster, the band is limited to the triangular area in the time / horizontal space as shown in FIG. 9, so there is little crosstalk between Y and C and use is allowed if a slight deterioration is allowed. it can.

(Embodiment) The signal processing system on the transmitting side and the receiving side according to the method of the present invention will be sequentially described below with reference to the drawings according to the embodiment.

FIG. 1A is a block diagram of an example of the signal processing system on the transmitting side. The signals of the two programs 1 and 2 are separated into luminance signals Y1 and Y2 and color signals C1 and C2 by two YC separation circuits 1 and 2, respectively. These luminance signals Y1 and Y2 each have two lines /
Sent to field subsamplers 3, 4. The line / field subsamplers 3 and 4 output the motion detectors 5 and 6 for detecting the motion information of the programs 1 and 2 according to the contents of the output motion modes M ₁ and M _{2 and} are shown in FIG. Luminance signals Y1 and Y2 are selected by selecting either sampling (a) or line offset subsampling (b).
To sample. The outputs of the line / field subsamplers 3 and 4 are respectively sent to the time axis compressors 7 and 8 and compressed by the time axis, and then selected by the switch S1 for one line period (one line is a horizontal scanning period of the NTSC system). Case 63.5
The brightness signal Y is obtained by multiplexing the brightness signals Y1 and Y2 in (μsec). In FIG. 2, O marks are image sample points, X marks are non-sample points, solid lines are odd field lines, and broken lines are even field lines.

Figure 3 shows this relationship on the time axis. The luminance signal Y
The information of the effective scanning period T of 1 and Y2 is T / 2, respectively, T1 and T2
This indicates that the luminance signal Y is time-axis compression-multiplexed with time. The color signals C ₁ and C ₂ are added to the luminance signal Y by switching each field by the switch S2. Further movement mode M1, M2, synchronizing signal, a color burst is added in addition circuit 9 to form an NTSC signal for normal, NT as the signal N _T
It is sent to the SC transmission line. Various methods have been proposed for the motion detection method, and the method is determined by, for example, the integrated value of the difference signal for one frame.

A block diagram of an example of a signal processing system on the receiving side is shown in FIG. In the YC separation section 11 shown in FIG. 1B, the luminance signal Y and the color signal C are separated from the signal _NT . Therefore NTSC
The signal N _{T that} has been A / D converted from the transmission line is the horizontal high-pass filter 1
2 and the delay elements D _v 13, D _t 14. The output of the horizontal high-pass filter 12 is sent to the vertical high-pass filter 15 and the temporal high-pass filter 16. The delay amounts of the delay elements D _v 13 and D _t 14 are respectively adjusted to the delay amounts of the filters 15 and 16 described above. By the mode signals M1 and M2 separated from the transmission signal by the mode signal separator 17, the outputs of the vertical high-pass filter 15, the temporal high-pass filter 16, the delay element D _v 13 and the delay element D _t 14 are switched by the switches S3 and S4. The selected output of the switch S3 is sent to the color signal field interpolating unit 24 as the color signal C. Further, the color signal C is subtracted from the output of the switch S4 to obtain a signal corresponding to the luminance signal Y, which is sent to the sub-sampling interpolating unit 18.

The sub-sampling interpolating unit 18 shown in FIG. 1B is an example of a circuit that restores the original signal from the sub-sampled luminance signal Y by interpolation. Delay element (DL) 19, DL20,
DL21 is 1 field-1 clock, 1 line-1
Clock, delay of 1 clock time. Switch S5 and S6 are controlled by mode signals M1 and M2, and tilted to the top to interpolate for field offset subsampling, and tilted to the bottom to interpolate for line offset and subsampling. Do. The original luminance signals Y1 and Y2 are demodulated by expanding the output of the sub-sampling interpolation unit 18 in the time axis by the time axis expanders 22 and 23.

As for the color signal, the color signal C output of the YC separation unit 11 is sent to the color signal field interpolation unit 24, and the signal delayed by one field time by the field delay element 25 and the signal not delayed are switched by the switches S7 and S8 in field units. By alternately switching, the color signals corresponding to the original color signals C1 and C2 are demodulated by interpolating the color signals of the fields that are not transmitted.

(Effect of the Invention) By implementing the method of the present invention, one-channel NTSC
Two NTSC color programs can be transmitted on the transmission line according to the NTSC standard. Therefore, it is economical to use for a transmission line whose line cost is expensive such as sanitary relay, and because of the space and weight limitations such as aerial photography, two FPUs are used.
If you can't use an (outdoor repeater), you can use one FPU to transmit images from two cameras, which is great for news and program production.

[Brief description of drawings]

FIG. 1 is a diagram showing a signal processing system of a transmitting side (a) and a receiving side (b) according to the present invention method, and FIG. 2 is a field offset (a) and line in a line / field subsampler of the present invention method. Offset (b) Diagram showing each sub-sample as a model, Fig. 3 is a diagram showing waveforms of each part in Fig. 1 (a), Fig. 4 is a diagram showing spectrum of current NTSC system signal, Fig. 5 FIG. 6 is a diagram showing a spectrum of the line offset sub-sampling method, FIG. 6 is a diagram showing a spectrum obtained by time-axis compression after line offset sub-sambling, and FIG. 7 is a spectrum of the spectrum shown in FIG. Horizontal
FIG. 8 is a diagram projected on the time plane, FIG. 8 is a diagram showing a spectrum of the field offset sub-sampling method, and FIG. 9 is a diagram showing the spectrum shown in FIG.
It is the figure projected on the time plane. 1,2 …… YC separation circuit 3,4 …… Line / field subsampler 5,6 …… Motion detector, 7,8 …… Time axis compressor 9 …… Additional circuit, 11 …… YC separation unit 12 ...... Horizontal high-pass filter 13,14 …… Delay element D _v and D _t 15 …… Vertical high-pass filter 16 …… Time high-pass filter 17 …… Mode signal separator 18 …… Sub-sample interpolator 19,20, 21 …… Various delay elements 22,23 …… Time axis expander 24 …… Color signal field interpolator 25 …… Field delay element

Claims (5)

[Claims] 1. Two YC-separated two luminance signals of two color television signals are respectively subjected to time-axis compression after field or line offset subsampling to obtain two colors of the two color television signals. The signal is modulated by the color subcarrier of the NTSC signal, or if the color signal is modulated by the color subcarrier at the time of YC separation, the two color signals are alternately extracted for each field, and these are taken out. A television signal characterized in that it is multiplexed with the two luminance signals after each time axis compression and transmitted, and a two-channel NTSC color television signal is transmitted through a one-channel NTSC transmission path. 2-channel multiplex transmission system. 2. The multiplex transmission system according to claim 1, wherein the two YC-separated color television signals are respectively YC from two NTSC color television signals.
A two-channel multiplex transmission system for television signals, which is obtained separately. 3. The multiplex transmission system according to claim 1 or 2, wherein the switching of the field or line offset subsampling is controlled by motion information. Channel multiplex transmission system. 4. A two-channel multiplex transmission system for television signals according to claim 3, wherein the switching is performed in units of image blocks or fields. 5. The multiplex transmission system according to claim 3 or 4, wherein the information for switching is multiplexed in a horizontal or vertical blanking period. Channel multiplex transmission system.