JPS6130888A - Picture communication system between multipoints - Google Patents

Abstract

PURPOSE:To prevent a picture from deteriorating by setting the number of encoded bits corresponding to periods of segmenting a video signal in correspondence to an encoding system constant and executing the time division multiplex by means of the encoded signal as it is. CONSTITUTION:After analog video signals from video cameras 12A, 12B and 12C of video terminals 1A, 1B and 1C are subjected to the frequency compressing and encoding by video encoders 2A-2C and are transmitted for a long distance, they are transmitted to a communications controller between multispots 16, where the time division multiplex is executed by the encoded signal as it is. The multiplexed video signal is again transmitted to the encoders 2A-2C through an exchange 3.

Description

Detailed Description of the Invention "Field of Industrial Application" This invention is a video conference in which three or more points are connected simultaneously for mutual communication, in which the transmitting side time-division multiplexes image signals from multiple destinations, and the receiving side The present invention relates to a multipoint image communication system that separates the multiplexed signal and simultaneously reproduces image signals from multiple locations.

"Prior Art" Conventionally, as a method of multipoint video conferencing in which three or more points are connected and a conference is held while viewing multiple parties at the same time, multiple points are used to transmit video from multiple other points to one point. It is possible to prepare a line. This case has the disadvantage of requiring a large number of expensive video lines. Furthermore, as another method for multipoint video conferencing, it is conceivable to use digital transmission over long distances and use time division multiplexing technology. That is, as shown in FIG. 7, video terminals IA, IB, and IC each include a video camera, a frame memory, and a monitor.
are accommodated in a switch 3 through video encoding devices 2A, 2B, and 2C, respectively, and a point-to-point communication control device 4 is connected to the switch 3. Point-to-point communication control device 4
is a video encoding device 5A connected to the exchange 3;

5B, 5C, and the synchronization/multiplexing device 6 connected thereto. In order to transmit video signals (image signals) over long distances, it is necessary to use digital transmission in terms of quality and economy. Therefore the video terminal IA.

Analog video signals output from IB and IC are digitized by video encoding devices 2A, 2B and 2C, and then transmitted over long distances. At this time, if the analog video signal is simply PCM encoded, approximately 100
Since a transmission capacity of Mb/s is required, the bandwidth is usually compressed by intraframe coding or interframe coding.

This band-compressed digital video signal is exchanged by the exchange 3 and input to each point-to-point communication control device 4. For example, the video signals from the video terminals IB and IC are time-division multiplexed (field or frame multiplexing) before being sent out. At this time, since the video signals from each point are not synchronized, time division multiplexing cannot be performed as is. In addition, in the above-mentioned band compression encoding methods, in order to improve image quality, the number of encoding bits corresponding to one frame is often variable, and if the signal is band compression encoded, it is time-divided. I can't. For these reasons, the video encoding device 5
After decoding into PCM signals or analog video signals by A, 5B, and 5C, it is necessary to synchronize the video signals of each destination in the synchronization/multiplexing device 6, and then perform field or frame multiplexing.

The field or frame multiplexed signals are sent to video terminals IA, IB, and IC, and after being demultiplexed at each video terminal, they are written into the corresponding frame memories, and by playing back the continuous video signals. Obtainable.

"Problems to be Solved by the Invention" In the method shown in FIG. No extra encoding devices 5A, 5B, 5C are required, and
This method has drawbacks such as cascading the encoding devices, which may cause deterioration of lipids.

The object of the present invention is to provide video signal separation periods (
By keeping the number of encoded bits constant (for example, one frame period or one field period) and performing time-division multiplexing on the encoded signal, it is economical and reduces image quality deterioration. The object of the present invention is to provide an image communication system between a small number of points.

[Means for Solving the Problems] According to the present invention, in an inter-point image communication system in which three or more points are connected simultaneously to mutually communicate video (image) signals, the video signal from the terminal is transmitted in one frame. Means for band compression encoding while keeping the number of encoded bits constant per predetermined fixed period such as one frame period or one field period, and a means for band compression encoding a plurality of video signals as band compression encoded signals. and means for decoding the time-division multiplexed signal and displaying it simultaneously on a plurality of display devices.

Embodiment FIG. 1 shows an embodiment of the present invention, in which parts corresponding to those in FIG. 7 are given the same reference numerals. Video terminal IA, IB
, ICs are video cameras 12A and 12B, respectively.
.

12C1 video monitor 13A, 13A', 13
B, 13B', 13C.

13C'. Each point-to-point communication control device 16 is connected to the exchange 3.

Video terminal IA, IB, IC video camera 1
2A.

The analog video signals from 12B and 12C are band compression encoded by video encoding devices 2A, 2B and 2C, respectively, and after being transmitted over long distances as band compression encoded digital signals, they are sent to each point via an exchange 3. The data is sent to the intercommunication control device 16. Point-to-point communication control device 16
Then, the encoded video signal is time-division multiplexed, and the multiplexed video signal is again sent to each video encoding device 2A, 2B, 2C via the exchange 3, where it is demultiplexed and decoded, and sent to a video terminal. IA, IB.

Multiple video monitors 13A, 13A' of the IC,
13B, 13B'.

Displayed simultaneously on 13C and 13C'.

FIG. 2 shows an example of the configuration of the video encoding devices 2A, 2B, and 2C assuming an interframe encoding method. A video signal from a terminal is encoded by an interframe encoder 21 and sent to a transmission path. A control signal is detected by the control signal detection section 22 from the signal from the transmission path, and based on the control signal, the control circuit 23 controls the demultiplexing section 24 to demultiplex the signal from the transmission path, and the respective interframe decoding sections The data is decoded at 25 and 26 and sent to the terminal.

FIG. 3 shows video signals of each part in FIG. 2. trench, 2nd
The operation will be explained by taking as an example the case where the device shown in the figure is a video encoding device 2A. A video signal (FIG. 3(a)) from the camera 12A of the video terminal IA is input to the interframe encoding section 21. When compression-encoding is performed as a normal continuous signal, the difference between adjacent frames is sent out as shown in Fig. 3). In this case, the encoding bit length for one frame is constant. Note that if the resolution and motion are comparable to those of a video conference, even if the encoding bit length is constant, the image quality will not be affected that much. Considering the case where camera outputs from two points are time-division frame multiplexed using compressed encoded signals,
Frames will be dropped every other frame. Therefore, in Figure 3(b), the interframe difference signal (A3-A2) is discarded, and the signal (A4A3) is sent next to (A2 Al), which prevents normal decoding on the receiving side. .

Therefore, for example, when frame multiplexing two signals, predictive coding is performed using the signal two frames before,
It is necessary to send out a differential signal as shown in FIG. 3(c). Which frame difference is taken during encoding depends on this and the number of video signals to be multiplexed. The number of video signals to be multiplexed is
6 is embedded in the image signal and sent to the video encoding device 2A. The signal is extracted by the control signal detection section 22 and notified to the interframe encoding section 21 via the control circuit 23. The encoding unit 21 determines a differential frame interval according to the number of video signals to be multiplexed.

The signal compressed and encoded by two video encoders as shown in FIG. 3(c) is transmitted through a transmission line and further through an exchange 3 to a frame memory 31A in each point-to-point communication control device 16 (FIG. 4). written to. Similarly, video terminal I
B. The video signal from the IC is sent to the video encoder 2.
A and 2B are compressed and encoded as shown in FIGS. 4(d) and 4(e), respectively, and then sent to the multipoint communication control device 16.
and written into frame memories 31B and 31C, respectively. These video signals are shown in Figure 3(c).
, (d), and (e), frame multiplexing cannot be performed as it is because synchronization is not achieved. Therefore, by commonly performing reading from the frame memories 31A, 31B and 31C using the clock from the signal generator 32, the results shown in FIGS.
) Match the synchronization of the video signals from each point as shown in K.

The video signals read out from the frame memories 31A, 31B, 31C are sent to the multiplexing switches 33A, 33.
The video signals are time-division frame multiplexed by the video signals B and 33C, and control signal insertion units 34A and 3 are inserted into the multiplexed video signals, respectively.
4B and 34C insert a control signal indicating the number of multiplexing points from the control unit 35, and from there, the control signal is sent via the exchange 3 to the video encoding devices 2A, 2B, and 2C.

In addition, the control signal insertion devices 34A, 34B, 34
C is synchronized with the clock from the signal generator 32. Also, a multiplexing switch 33A.

33B and 33C perform time-division frame multiplexing according to instructions from the control unit 35. For example, the output of the multiplexing switch 33A is sent to the terminal IB as shown in FIG. 3(11)K.
.

A video signal is obtained by multiplexing the video signals from the IC, and this video signal is sent to two video encoding devices. The number of multiplexing points is notified from the exchange 3 to the control unit 35.

The time division multiplexed video signal in which the control signal from the exchange 3 is embedded is branched into the control signal detection section 22, the control signal is extracted and sent to the control circuit 23, and the time division multiplexed video signal is separated. 24.

The separation section 24 separates the video signal for each point according to instructions from the control circuit 23 and sends it to the interframe decoding sections 25 and 26. The control circuit 23 instructs the interframe decoding units 25 and 26 whether to perform normal interframe encoding or predictive encoding using the value of two frames before, and perform decoding according to this instruction. conduct. When the interframe decoding section 25 decodes the video signal from the video terminal IB, the decoded video signal becomes as shown in FIG. 3(i). The video signals decoded by the decoding units 25 and 26 are sent to the video terminal IA and displayed on the monitors 13A and 13A', respectively.

In the above explanation, it is assumed that the two video encoding apparatuses have interframe decoding units 25 and 26 corresponding to the number of multiplexing units, but there is only one interframe decoding unit, and the video encoding apparatus 2A and A time-division frame multiplexed signal without band compression may be transmitted to the terminal IA, and the video terminal IA may be provided with a frame memory corresponding to the number of multiplexed signals.

FIG. 5 shows an example of the configuration of the video encoding device 2A in this case. The operation of compressing and encoding the video signal in the interframe encoding section 21 is the same as in the case of FIG. Next, the operation when decoding a time division multiplexed video signal that has been band compression encoded will be described. A control signal detecting section 22 extracts the control signal from the time division multiplexed video signal in which the control signal is embedded, and sends it to the control circuit 23, and the one time division multiplexed video signal is input to the addition circuit 41. Addition circuit 41
Then, the input time division multiplexed video signal is transferred to the switching section 45.
is added to the video signal from and written to the frame memory 42. Therefore, since the sum of the video signal of the previous frame and the sent difference signal is written into the frame memory 42, the video signal before being encoded is decoded and written. The video signal read from the frame memory 42 is sent to the frame memory 43 and the switching section 45.

The switching unit 45 is switched under the control of the control circuit 23, and in the case of normal interframe encoding, the readout signal of the frame memory 42 is time-division multiplexed with signals at two points, and prediction is performed using the signal of two frames before. When transmitting and receiving error signals, a read signal from the frame memory 43 is outputted from the switching section 45. Note that the readout signal of the frame memory 44 is used when signals at three points are time-division multiplexed. Therefore, the switching unit 45 outputs a video signal that has been subjected to interframe decoding and time division multiplexed in the form of a PCM signal. Note that a control signal indicating the number of time-division multiplexed points is embedded in the video signal by the switching unit 45 according to instructions from the control circuit 23.

FIG. 6 shows an example of a configuration of a video terminal having multiple memories. The PC from the video encoding device 2A shown in FIG.
The time division multiplexed signal decoded into the M signal is sent to the video terminal IA.
The sixth example shows how to separate the images and display them on multiple monitors at the same time.
As shown in the figure. PC time-division multiplexed with separation circuit 51A
A control signal indicating the number of multiplexing points is extracted from the M signal, and based on this, the PCM signal for each ground is stored in the frame memory 50.
A and frame memory 50A'. From the frame memories 50A, 50A', if the video signal of the previous frame is repeatedly read out for the missing frame, a continuous video signal is obtained, and the monitor 13A,
13A', images of different locations are simultaneously displayed.

As described above, according to the system shown in FIGS. 5 and 6, only one line is required from the video encoding devices 2A, 2B, and 2C to the video terminals LA, IB, and IC. Devices 2A, 2B, 2
If C can be installed at the nearest station and shared by multiple users, an economical system can be constructed. In addition, PCM
Digital-to-analog conversion of the signal is performed, and video encoding devices 2A, 2B, 2C and video terminals IA, IB
, and an IC may be used for analog transmission.

In the above, we assumed an interframe encoding method as the video encoding method, but even if an intraframe encoding method is used,
Assuming that the encoding bit length for one frame is constant, a multipoint-to-other point image communication system can be constructed in which the band-compressed signal is time-division multiplexed in the same way as the interframe encoding system. I can do it. In this case, the interframe encoding section 21 and interframe decoding sections 25 and 26 in FIG. 2 may be replaced with an intraframe encoding section and an intraframe decoding section, respectively.

At this time, a configuration may be adopted in which only one intra-frame decoding unit is used to output a time-division multiplexed video signal in the form of an intra-frame decoded PCM signal. The output video signal can be received by the video terminal shown in FIG.

Further, in the above description, in order to simplify the explanation, the image communication between three points is described, but the same configuration can be made even in the case of four or more points by increasing the number of multiplexing. Further, although the delimiting period of the signal corresponding to the encoding method is set to one frame, it can be constructed in the same manner even if it is one field.

``Effects of the Invention'' As explained above, when band compression encoding a video signal, the number of encoded bits corresponding to one frame or one field of the video signal is kept constant, and multiple points can be used in communication between key points. The video signal is time-division field or frame multiplexed as it is as a band-compression encoded signal, and then decoded on the receiving side. This method has the advantage that it is possible to perform image communication between points, which is economical since there is no need for encoding, and with little deterioration in image quality.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the overall configuration of an embodiment of the present invention, FIG. 2 is a block diagram showing a specific example of the video encoding device in FIG. 1, and FIG. 3 is a block diagram showing an example of the video signal of each part. 4 is a block diagram showing a specific example of the inter-point communication control device 16 in FIG. 1, FIG. 5 is a block diagram showing another example of the configuration of the video encoding device, and FIG. FIG. 7 is a block diagram showing an embodiment of a video terminal corresponding to FIG. 5, and FIG. 7 is a block diagram showing the configuration of a multipoint video conference using conventional time division multiplexing technology. IA, IB, IC...Video terminal, 2A, 2
B, 2C... Video encoding device, 3... Exchange, 4
...Each point-to-point communication control device, 5A, 5B, 5C...
Video encoding device, 6... synchronization/multiplexing device, 12A
, 12B, 12C...video camera, 13A
, 13A', 13B, 13B', 13
C, 13C'...video monitor, 16...inter-point communication control device, 21...interframe coding unit, 22...
- Control signal detection unit, 23... Control circuit, 24... Separation unit, 25, 26 - Interframe decoding unit, 31A
, 31B, 31C...frame memory, 32.
...Signal generation section, 33A, 33B, 33C...
・Multiplex switch, 34A, 34B, 34C・
...Control signal insertion unit, 35...Control unit, 41...Addition circuit, 42, 43.44...Frame memory, 45
...Switching unit, 50A, 50A'...Frame memory, 51A...Separation circuit.

Claims (1)

[Claims] In a multipoint image communication system that connects three or more points at the same time and performs mutual image communication, means for band compression encoding an image signal from a terminal while keeping the number of encoded bits per predetermined period constant. and a means for time-division multiplexing a plurality of image signals as band compression encoded signals, and a means for decoding the time-division multiplexed signal and displaying it simultaneously on a plurality of display devices. Characteristic multipoint image communication method.