JPH04246933A - Multi-sites picture connection control system - Google Patents

Abstract

PURPOSE:To shorten a time required for freezing a received picture at the time of switching a distributed picture. CONSTITUTION:A picture communication terminal 1 at a site 1 operates an inter-freeze encoding transmission by turning off a picture freeze releasing signal in picture data, until the execution of a switching, and the picture of the side 1 is received by a site 3, and displayed by a display device. And also, a freeze request requiring the freeze of the received picture is transmitted from multi-site picture connector 3 to the site 3, before the switching. After this control, a changeover switch SW is switched to a site 2 side in the multi-site picture connector 3. At that time, the indication of the turning-on of the freeze releasing signal is given to the site 1, and the control signal of an in-frame encoding indication is transmitted. A picture communication terminal 2 at the site 2 adds the turning-on of the freeze releasing signal to the picture data by the in-frame encoding, and transmits it in the same way. A terminal 4 at the site 3 releases the freeze, and the picture of the site 2 is displayed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multipoint image connection control system. In recent years, communication has come to be performed while viewing images using image communication terminals installed at multiple locations distant from each other, such as in TV conferences. In order to realize this multipoint connection communication, a multipoint image connection device is provided, and it performs switching control to select one or more images from among the images transmitted from each image communication terminal and distribute it to the downlink. Is going.

[0002] In multipoint image communication, in order to make the most effective use of the capacity of a transmission path, the image band is usually compressed by using interframe coding. However, after transmission of an interframe-encoded signal starts, the difference between the interframe-encoded signal and the previous frame is basically always encoded. For this reason, even if the interframe code is switched to be distributed and received on the downlink from the middle, the image communication terminal that receives it cannot decode it into the original image. Conventionally, in order to decode a normal image during this switching,
It was necessary to perform controls such as performing intraframe encoding.

0003

2. Description of the Related Art FIG. 4 is a diagram showing a connection switching state by a conventional multipoint image connection device. Figure 4(a)
, (b), an image communication terminal is provided at each of five points, points 1 to 5, and is equipped with one or both of an image transmitting mechanism and an image receiving mechanism, and the image communication terminal at each point is connected to a multipoint image connection. Device (MCU: Multipoint Con
Trol Unit). The state of (a) in FIG. 4 shows a state in which the image of point 1 is distributed to all the remaining points, and the images transmitted from point 1 are being received at points 2 to 5. (b) in Figure 4
) shows a state in which switching is performed in the multipoint image connection device and the connection form changes from state (a), and the image of point 2 is distributed to all remaining points instead of point 1.

FIG. 5 shows an operation sequence of a conventional image communication terminal and multipoint connection device. This figure shows (a) in Figure 4.
The sequence when the connection changes as shown in (b) is shown. The configuration shown in the upper part of FIG.
0, 51, 53 are multipoint image connection devices (displayed as MCU)
52 by a line. Each image communication terminal 50, 51, 53 and multipoint image connection device 52
Transmission and reception of data (encoded image data) and communication of control signals are performed between the two via lines. The operation sequence of connection switching executed by this configuration will be explained. However, in this explanation, the reception point is only point 3, and an image is displayed on the display device 54 at point 3.

[0005] ■ Speaker control performed by detecting the point where the voice is generated in a video conference, etc. (selecting an image of the point where the caller is, etc.), or request control from any receiving point (selecting a specific point) The MCU 52 starts a connection switching operation from the point 1 image distribution state to the point 2 image distribution state by control corresponding to the request to receive the image of the point 1 (control corresponding to the request to receive the image of the point 2).

[0006] The image encoding device (not shown) at point 1 turns off the image unfreezing signal in the image data.
) and performs interframe coded transmission, and point 3 receives the image of point 1 and displays it on the display device 54. Note that the freeze release signal OFF is a control signal that instructs not to release the freeze state, and is added to the image transmitted from point 1 and transmitted. ■Point 3 from MCU52
However, in order to prevent the received data from being corrupted and the received image to be distorted due to connection switching, the received image is frozen (the image is fixed and the display content is not changed by the image signal received after that). A "freeze request" is sent as a control signal.

(2) In the MCU 52, the switch SW, which had previously selected the image from point 1, is switched to select the image from point 2, and the image is transmitted to point 3. ■At this time, the image coding transmission at point 2 is performed by interframe coding transmission with the image unfreezing signal in the image data turned off, and point 3 receives the image at point 2, but the unfreezing signal is It is in a waiting state. Therefore, the image at point 1 is still displayed as a frozen image. ■MCU
52 instructs point 2 to perform intraframe encoding through control communication.

(2) The image encoding device at point 2 turns on the unfreeze signal in the image data in response to an instruction from the MCU and performs intraframe encoding transmission. When point 3 receives an image signal with the image unfreeze signal on, point 1
Unfreeze the image at point 2 and start displaying the image at point 2. ■The image encoding device at point 2 freezes the image around the time when point 3 receives the image unfreeze signal (usually set to a value greater than or equal to the maximum delay time of control communication calculated by the system). Interframe encoding is performed with the cancellation signal turned off.

[0009]

[Problem to be Solved by the Invention] According to the connection control method in a multipoint image connection unit (MCU) for realizing multipoint connection communication by an image encoding device using the conventional interframe coding described above, The procedure for switching the connection is complicated, and the image freeze time and the processing time required for the switching are long, and there is a problem that it takes time to obtain a new image due to the switching. SUMMARY OF THE INVENTION An object of the present invention is to provide a multipoint image connection control system that can shorten the time during which received images are frozen when images to be distributed are switched.

0010

[Means for Solving the Problems] FIG. 1 is a diagram illustrating the principle of the present invention. In the figure, 1 is the image communication terminal at point 1, 2
is the image communication terminal at point 2, 3 is the multipoint image connection device, and 4 is the image communication terminal at point 2.
1 is an image communication terminal at point 3, and 5 is a display device of image communication terminal 4. The principle of the present invention is illustrated by the mutual operation sequence of each part. The present invention transmits an interframe coded image in a steady state from an image communication terminal that does not distribute an image as a received image, and when the image is switched to be distributed as a received image, the intraframe code remains as it is for a certain period of time. The image communication terminal at the point where the signal is no longer distributed due to switching is instructed to perform intraframe encoding.

[0011]

[Operation] In the first state of the sequence shown in FIG. 1, it is assumed that the image of the image communication terminal 1 at point 1 is selected by the changeover switch SW of the multipoint image connection device 3 and distributed to point 3. At this time, the image communication terminal at a point other than point 1 (image communication terminal 2 in this example) sends an intra-frame encoding instruction (11 in FIG. 1) to the multi-point image when its own image is no longer distributed to the receiving points. Since it is received from the connection device 3, an intraframe encoded signal is transmitted. After this,
Control for switching the distributed image from point 1 to point 2 is started by speaker control or by a request from receiving point 3 (12).

[0012] Until the switching is executed, the image communication terminal 1 at point 1 turns off the image unfreeze signal in the image data and performs inter-freeze coded transmission, and the image communication terminal 1 at point 3
receives the image of point 1 and displays it on the display device (13). In addition, before switching, the multipoint image connection device 3 sends a freeze request (control signal ) (14). After this control, the changeover switch SW in the multipoint image connection device 3 is switched to the point 2 side (step 15). At this time, an instruction is given to point 1 to turn on the freeze release signal (17). Also, a control signal instructing intra-frame coding is sent to point 1, which is no longer distributed as a receiving point due to switching (18).
.

[0013] The image communication terminal 2 at point 2 transmits the intra-frame encoded image data by adding the freeze release signal ON as before (17). Upon receiving this, the image communication terminal 4 at point 3 unfreezes and displays the received image data for point 2. The image communication terminal 2 at point 2 waits for the time when point 3 receives the image unfreeze signal (after a predetermined time T), turns off the image unfreeze signal, and switches to interframe encoding to transmit the image data. Send (19th). In this way, the image communication terminal 4 at the point 3 can receive the interframe encoded data after obtaining the entire data of one frame using the first intraframe encoded data, and the image communication terminal 4 at the point 3 can receive the interframe encoded data. The data can be decrypted.

[0014]

Embodiment FIG. 2 is a block diagram of the first embodiment, and FIG. 3 is a block diagram of the second embodiment. In FIG. 2, 20 is an image communication terminal equipped with a mechanism for transmitting images, 21 is a camera, 22 is a preprocessing unit, 23 is an image encoding device, 24 is a control unit, and 25 is an intraframe encoding and interframe encoding 26 is a multi-point image connection device (
MCU), 27 is an encoding mode instruction section, 28 is a control section,
29 is a connection switching unit, 30a is a control communication path for transmitting control signals, and 30b is a data transmission path for transmitting data such as images. The data transmission path can transmit not only image data but also encoded audio data. Further, in this embodiment, only the image communication terminal 20 equipped with an image transmission mechanism is shown, and the image communication terminal equipped with an image reception mechanism has the same configuration as the conventional one and is omitted from illustration.

To explain the configuration of the first embodiment shown in FIG.
The control unit 28 of the U 26 transmits an intra-frame encoding instruction to the image communication terminal 20 to which the image is not distributed to the receiving point via the control communication path 30a when the image is switched from the distributed state to the non-distributed state. It will be done. Image communication terminal 2
When the control unit 24 of the image encoding device 23 of No. 0 receives this, it outputs an encoding control signal to the encoding unit 25 to perform intra-frame encoding. As a result, the encoding unit 25 transfers the intra-frame encoded image data to the data transmission path 30.
Send to b. When the multi-point image connection device 26 switches the currently distributed image to an image of another point due to a request from a receiving point, etc., it sends a freeze request to the receiving side to freeze the image, as shown in FIG. Thereafter, the control unit 28 switches the image from the image communication terminal 20 to the distributed image. At this time, the image communication terminal 20 is instructed to turn on the freeze release signal.

In response to this instruction, in the image communication terminal 20, the control unit 24 of the image encoding device 23 controls the encoding unit 25 to turn on the unfreeze signal, and the encoding unit 25
sends the image data including the intra-frame encoded freeze release signal ON to the multipoint image connection device 26. This image data is transferred to the connection switching unit 2 of the multipoint image connection device 26.
9 to an image communication terminal at a receiving point (not shown). The image encoding device 23 of the image communication terminal 20 performs interframe encoding on the encoding unit 25 after a certain timing from when the control unit 24 starts transmitting the image data with the freeze release signal turned on. Outputs an encoding control signal that performs the following.

The multipoint image connection device 26 controls an intraframe encoding instruction from the encoding mode instruction section 27 to the image communication terminal that has been switched from the distributed state to the non-distributed state by switching the connection switching section 29. Communication channel 30
Send to a. This makes it possible to reduce the time required to complete processing when switching connections by controlling to always perform intra-frame encoding at points where the image is not distributed to any point.

Next, the configuration of the second embodiment will be explained with reference to FIG. 20 to 30 in FIG. 3 correspond to circuits or devices with the same reference numerals shown in FIG. 2 above. In this configuration, in addition to a normal quantizer 250, a coarse precision quantizer 251 is provided as a quantizer used for intra-frame encoding provided in the encoding unit 25. In this case, fineness/coarseness of quantization means the quantization step width and the number of quantization bits (long/short). When a signal quantized by a normal quantizer 250 is intra-frame encoded, the amount of data becomes large because the data compression rate is lower than that of inter-frame encoded data, but this coarse quantizer 250
If 51 is used for intraframe encoding, the amount of data can be reduced (if the data rate is the same, the transmission time can be shortened).

In the configuration of this second embodiment, the image communication terminal 2
When an image of 0 is no longer distributed to any point and an intra-frame encoding instruction is received from the encoding mode instruction section 27 of the multi-point image connection device 26, encoding control is performed from the control section 24 of the image encoding device 23. A quantization control signal is generated together with the signal (intraframe encoding) and the encoding circuit 2 is switched to use the coarse quantizer 251 as a quantizer.
52. Therefore, after this coarse quantizer 2
51, the image data obtained by intra-frame encoding of the quantized signal is output to the data transmission path 30b.

After this, when the multipoint image connection device 26 is switched to distribute the image data of the image communication terminal 20 to the receiving points, the image data encoded intra-frame by coarse quantization is sent to the receiving points. Therefore, the image communication terminal on the receiving side can receive one frame of image data at a higher speed than intraframe-encoded image data using a normal quantizer. Thereafter, the image communication terminal 20 on the transmitting side is switched to the image data transmission mode using interframe encoding.

[0021]

[Effects of the Invention] According to the present invention, in a multipoint image connection control system, it is possible to shorten the image freezing time on the receiving side when switching the connection of images, improve the serviceability for the person viewing the images, and improve the serviceability of the image viewers. It is possible to shorten the time from the start to the completion of the connection switching process of the point image connection device, making it possible to improve the efficiency of the process. Furthermore, by using a coarse quantizer, it becomes possible to transmit newly distributed intra-frame encoded image data in a short time when images are switched.

[Brief explanation of the drawing]

FIG. 1 is a diagram explaining the principle of the present invention.

FIG. 2 is a configuration diagram of Example 1.

FIG. 3 is a configuration diagram of a second embodiment.

FIG. 4 is a diagram showing a connection switching state by a conventional multipoint image connection device.

FIG. 5 is an operation sequence of a conventional image communication terminal and a multipoint connection device.

[Explanation of symbols]

1 Image communication terminal at point 1 2 Image communication terminal at point 2 3 Multipoint image connection device 4 Image communication terminal at point 3

Claims (2)

[Claims] Claim 1: In a multipoint image connection control method in which images selected by a multipoint image connection device connected to each image communication terminal installed at multiple points via a transmission path are transmitted to a plurality of image communication terminals, Image communication terminals at points that are not distributed transmit image data using intra-frame encoding according to instructions from the multipoint image connection device, and the image data is newly distributed to the downlink by connection switching in the multipoint image connection device. A multi-point image connection control system characterized in that the image communication terminal switches the encoding operation from the intra-frame encoding state to the inter-frame encoding state after a predetermined period of time. 2. In claim 1, in the plurality of image communication terminals, the image encoding device is equipped with a quantizer with coarser precision than usual, and the image communication terminals that are not distributed to the downlink are equipped with a quantizer with coarser precision than usual. Perform intra-frame encoding by
A multipoint image connection control method characterized by reducing encoded information within a frame.