JPS6245293A - Image transmission system - Google Patents

Abstract

PURPOSE:To sent the four channels share of NTSCTV signals in time-division multiplexing to one transmission line by multiplexing time-divisionally a spurious NTSC signal and a luminance difference signal obtained by the time base compression of a horizontal scanning period with each other. CONSTITUTION:The channel signal of channel A among the four channels of NTSC signals is inputted to a terminal 1 and is A/D-converted and is Y/C- separated 3, the horizontal time base of which is compressed to 1/6 through an LPF4, a 1H delay line 5, a subtraction circuit 6, an LPF10 and a time base compression circuit 11. Meanwhile, a signal C is made as the spurious NTSC signal through a decoder 7, a vertical filter 8 and an encoder 9 and the horizontal time base is compressed to 1/3. The same processes are performed against channels B-D. At a multiplexing circuit 50, the output of each time base compression and a synchronizing signal and a burst signal from a generator 49 are read out with a prescribed timing setting two horizontal periods as a unit, to multiplex each signal time-divisionally.

Description

TECHNICAL FIELD The present invention relates to an image transmission system, and more particularly to a multiplex transmission system for television image signals based on the NTSC system.

BACKGROUND ART As a method for multiplexing and transmitting NTSC television image signals, there is a method in which both image signals for two channels are sent through a transmission line for one channel. In this method,
Since only information for two channels is sent, it is impossible to send information for more than two channels.

Purpose of the Invention Therefore, the present invention provides NT for four channels on one transmission path.
The object of the present invention is to provide an image transmission system in which SC television signals are time-division multiplexed and transmitted.

Composition of the Invention According to the present invention, the subcarrier frequency of the color signal that is quadrature-modulated in the NTSC signal is quadrature-phase modulated using a lower frequency to compress the horizontal scanning period to 1/3 of the time axis. The pseudo NTSC signal of one horizontal scan obtained by this process is obtained, and the difference in luminance signal component of the NTSC signal between the horizontal scanning line of this pseudo NTSC signal and the next horizontal scanning line is obtained, and the horizontal scanning time is reduced to 1/6. The luminance difference signal obtained by axial compression is generated for each of four channels of NTSC signal information, and the pseudo NTSC signal and the luminance difference signal for four channels are time-shared with each other in units of two horizontal scanning periods. An image transmission system characterized by multiplexing is obtained.

Example Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a block diagram of a transmitting side according to an embodiment of the present invention. A channel NTSC input terminal 1 has 4 channels N
The A channel signal, which is the first channel of the TSC signals, is input, and the A/D (analog/digital) converter 2 samples it with a clock of 4 x fsc (fsc is the color subcarrier frequency). /, i and A/D
converted. This A/D converted signal is sent to a Y/C separation circuit 3 where the luminance component and color component of the NTSC signal are separated from each other. The luminance signal separated by the Y/C separation circuit 3 is filtered by a low-pass filter 4 to prevent aliasing noise that occurs when it is sampled later with a 2 x rsc clock.
Bandwidth limited to frequencies below sc.

The luminance signal that has passed through the low-pass filter 4 is delayed by one horizontal scanning period by a 1H delay line 5, and the difference between this delayed output and the output of the low-pass filter 4 is outputted by a subtraction circuit 6. This makes it possible to determine the difference in luminance signals between two adjacent lines. This difference signal is supplied to a low-pass filter 10 for limiting the band to below the fsc/2 band so that it can be sampled with the fsc clock, and is written to the memory in the time axis compression circuit 11 with the fsc clock. By reading with a clock of 6 fsc, the horizontal time axis is compressed to 1/6.

On the other hand, the color signal separated by the Y/C separation circuit 3 is decoded into I and Q signals by the decoder 7. And the color signal is
Since it will be transmitted later every other line, it is filtered in the vertical direction on the screen in advance by a vertical filter 8. Then, the 1 and Q signals are quadrature-phase modulated using a subcarrier of 1/3 fsc (however, the frequency may be changed depending on the transmission band of the transmission line) and added to the luminance signal output from the one-day delay line 5. Possibly encoder 9
A pseudo NTSC signal is created by At this time, the phase of the subcarrier is inverted every two lines so that Y/C separation can be performed later. And time axis compression circuit 1
2, write to memory with 2 fsC clock 6
The horizontal time axis is set to 1 by reading with the fsc clock.
/3.

Further, a B channel NTSC signal is input to the B channel NTSC input terminal 13, and the circuits 14 to 24 perform the same processing as the signal operation of the first channel.

Further, C and D channel signals supplied to C channel NTSC input terminal 25 and D channel NTSC input terminal 37, respectively, are similarly processed by circuits 26-36 and 38-48.

In the multiplex circuit 50, each time axis compression circuit 11,
The outputs of 12, 23, 24. 35, 36, 47° 48 and the synchronization signals and burst signals output from the four synchronization signal generators are each output at each timing as shown in FIG. 3 in units of two horizontal scanning periods. The signals are read out and multiplexed by switching them in a time-division manner. In FIG. 3, 108 is a horizontal synchronizing signal, 109 is a burst signal, 110, 111, 1
14, 115 are pseudo NTSC signals for each channel of Δ, B, C, and D, and 112, 113, 115, and 116 are line difference signals of luminance signals for each channel of A, B, C, and D, respectively. The switching output is Δ/D converted by the D/A converter 51, outputted from the 4-channel signal output terminal 52, and transmitted to the transmission path as a multiplexed signal of 4-channel signals.

FIG. 2 is a block diagram of a receiving side according to an embodiment of the present invention. A 4-channel signal output from the transmitting side of the 4-channel image transmission apparatus shown in FIG. 1 is input to a 4-channel signal input terminal 53 via a transmission path. And A/D
The converter 54 performs A/D conversion by sampling with a 6 fsc clock. Then, in order to match the phases of the pseudo NTSC signal and the line difference signal of the luminance signal in a later circuit, the one-day delay line 55 is extended by 1HM.

The output of the 1H delay line 55 is sent to a time axis expansion circuit 56, where the line difference signal 112 portion of the A channel luminance signal shown in FIG. The time axis is expanded by six times, and a line difference signal of the A channel luminance signal with a time magnification equal to that of the original horizontal period is obtained. Then, by interpolating with the horizontal interpolation circuit 57, f
2 fsc clock data is created from the SC clock data.

On the other hand, from the output of the A/D converter 54, the time axis expansion circuit 5
8, the A channel pseudo NTSG signal 11 shown in FIG.
The 0 part is written to the memory with a clock of 6fsc and read out with a clock of 2rsc, thereby performing a three-fold time axis expansion and obtaining an A channel pseudo NTSC signal with a time magnification equal to the original horizontal period. . Since this signal is output every other line, a comb-shaped filter is created with the signals separated from the two lines, and the luminance signal and chrominance signal of the A channel are separated from each other by five Y/C separation circuits. The separated luminance signal is input to the addition circuit 60 and added to the line difference signal of the luminance signal output from the time axis expansion circuit 56. Since the luminance signal separated by the Y/C separation circuit 59 is missing for each line, the luminance signal of the missing line is created by this addition process.

In the switching circuit 61, the Y-C separation circuit 59
The luminance signal separated by , and the luminance signal reproduced by the adder circuit for the missing line are switched and selected for each line, and the original A-channel luminance signal is reproduced. Then, the horizontal interpolation circuit 63 interpolates the 2 fsc clock data and converts it into 4 fsc clock data.

On the other hand, the color signal separated by the Y/C separation circuit 59 is sent to the decoder 62 as 1. It is converted into a Q signal and then passed through the horizontal and vertical interpolation circuit 64.
．． 65, the signals for all lines are created by interpolating the 1 and Q signals that are missing every other line, and by horizontally interpolating the clock data of 2 rsc, it becomes the clock data of 4 fsc. Convert. Then, the A channel luminance signal from the horizontal interpolation circuit 63 and the A channel I signal and Q signal from the horizontal and vertical interpolation circuits 64 and 65, which have become clock data of 4 rsc, are input to the encoder 66 and encoded. and converted to A channel NTSC data. Then, it is D/A converted by the D/A converter 67 to the original A channel NT.
The SC signal is output from the A channel NTSC output terminal 68.

Next, by the operation processing by each circuit 69 to 80, D
An NTSG signal of the channel is obtained.

In addition, by the operation processing by each circuit 82-93, C
The NTSC of the channel is obtained and similarly circuits 95-10
By performing the processing up to step 6, a D channel NTSC signal can be obtained.

DETAILED DESCRIPTION OF THE INVENTION As described above, the present invention converts the subcarrier frequency of a color signal that is quadrature modulated into an NTSC
．． A pseudo NTSC signal of one horizontal scan in which the color signal is quadrature modulated at a frequency lower than 58 MHz and the horizontal scanning period is compressed to 1/3, and the horizontal scanning line of this pseudo NTSC signal corresponds to the next horizontal scanning line. The difference signal between the luminance components of the NTSC signal is calculated, the horizontal scanning time is reduced to 1/6, and the information of the NTSC signal for 4 channels is divided into 2.
The corresponding pseudo NTSC of 4 channels per horizontal scanning period
The signal and the difference signal of the time-axis compressed luminance signal component are time-division multiplexed and transmitted.

Therefore, the frequency band in the horizontal axis direction of the reception screen of each channel can be transmitted up to 1/3 of the transmission line band, and the resolution of the reception screen in the vertical axis direction can also be received without much deterioration. This has the effect that four channels of NTSC signals can be transmitted without much deterioration in image quality if there is a transmission line with approximately 6 MH2 band or more.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a transmitting side according to an embodiment of the present invention, FIG. 2 is a block diagram of a receiving side according to an embodiment of the present invention, and FIG. 3 is a diagram showing a state of multiplexing of 4-channel signals. Explanation of symbols of main parts

Claims (1)

[Claims] One horizontal scan obtained by quadrature modulating the subcarrier frequency of the color signal of the NTSC signal using a lower frequency to compress the horizontal scan period to 1/3. Pseudo NTSC signal and this pseudo NTSC signal
NT between horizontal scanning line of C signal and next horizontal scanning line
Obtain the difference between the luminance signal components of the SC signal and reduce the horizontal scanning time by 1/
The luminance difference signals obtained by time axis compression are generated for each of four channels of NTSC signal information, and the pseudo N
An image transmission system characterized in that a TSC signal and the luminance difference signal are time-division multiplexed with each other.