JP2862249B2 - TV teleconference system, interframe encoder and composite device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Table of Contents] Overview Industrial application Field of the Invention Prior Art Problems to be Solved by the Invention Means for Solving the Problems Action Embodiment Effects of the Invention [Summary] Inter-frame prediction code by fixed prediction method Video-telephone conferencing system and inter-frame coder and decoder using a video coding method, with the aim of enjoying the prevention of image quality deterioration due to received image switching while reducing the scale of the device. , Each at reset
An inter-frame encoder that generates an encoded image signal of a frame based on intra-frame prediction, and generates an encoded image signal of each frame based on inter-frame prediction after non-reset, and is connected to a video conference device. A decoded image signal generated from the image signal received from the information channel is generated based on intra-frame prediction in one frame at reset,
Each of the frames at the time of non-reset is provided with a decoder that generates a frame based on inter-frame prediction. The video telephone conference device includes a frame memory provided for each information channel, an information channel to which the video telephone terminal device is connected, and a A matrix switch for outputting an image signal from a frame memory corresponding to the information channel to an information channel to which an arbitrary video telephone terminal device other than a certain video telephone terminal device is connected; and a matrix switch provided for each frame memory. When the encoding control information included in the image signal received from the information channel to be executed indicates intra-frame prediction, storing the encoded image signal for one frame together with the corresponding encoding control information in the frame memory; The image coded signal for one frame is received from the frame memory together with coding control information indicating intra-frame prediction. An access control circuit for performing output to the read matrix switch, and when connecting the matrix switch between the transmitting videophone terminal device and the receiving videophone terminal device according to the received image designation information received from the signal channel, A control circuit for generating an output command, causing the matrix switch to select an image signal from the frame memory first, and then selecting an image signal from the corresponding information channel is provided.

[Industrial applications]

The present invention relates to a video conference system and an inter-frame encoder and decoder.

Video teleconferencing systems that are more realistic than conventional teleconferencing using only voice are being developed. This system has the problem of how to send an image signal to each participating videophone terminal, and how to switch the image signal as needed. In particular, in the switching of the image signal, it is necessary to completely synchronize the start time of the encoding operation in the encoder and the start time of the decoding in the decoder, which is indispensable depending on the form of encoding and decoding. .

[Conventional technology]

In the video conferencing system as described above, if the transmission capacity of the communication path is sufficiently large, for example, a conference device installed in a communication network (at a telephone office) is used to reduce the image of a user who participates in the conference. By synthesizing and displaying on each terminal, a video conference system can be realized.

On the other hand, in order to realize a video conference system more economically, it is desirable that the transmission capacity between the conference device and the user terminal be in a normal voice band (64 kbit / sec).
In this case, a codec / decoder (CODEC) using a significant band compression technique for the image is required. However, as the number of users participating in the conference increases, the amount of information to be encoded increases, and it becomes necessary to employ more complicated band compression technology.
As a result, the price of the terminal including the image CODEC increases.

Therefore, instead of reducing and synthesizing the image of each user in the conference device, the image received by each user is limited to a single image (for example, an image of the person speaking), and the image received by each user (the partner's image) An image can be arbitrarily selected to realize a more economical conference system that is relatively economical and more effective than a conference using only audio.

[Problems to be solved by the invention]

As described above, an inter-frame prediction method as shown in FIG. 6 is often used as an image CODEC encoding technique in a video conference system having a transmission capacity of, for example, about 64 kbit / sec.

At this time, the predictor including the frame memory becomes a recursive filter having a feedback loop, and the past history (all frame information) is affected. The decoding start time must be completely synchronized. For this reason, it is necessary to reset the encoder and decoder at the start of encoding, for example, so that the internal states of the encoder and decoder completely match.

When an image CODEC having such an inter-frame prediction function is used in the conference system, when a plurality of users receive one user image from an arbitrary time, an inconvenient state occurs as follows. .

For example, as shown in the timing diagram of FIG. 7, in the terminal C that has received the image of the user D, when the screen of the user A is received on the way, the sender side (the encoder of the terminal A) and the receiver side When resetting in order to match the predictors at the (decoder of terminal C), the other terminal (terminal B in this example) receiving the image of terminal A also needs to be reset. Therefore, the entire system is frequently reset. The reset terminal performs encoding by only intra-frame prediction, and after transmitting one frame, encodes and transmits a difference signal between the image signal of the previous frame and the image signal to be transmitted (inter-frame prediction encoding). Generally, TV
Inter-frame prediction has a higher data compression effect for moving images with less movement, such as in a telephone conference, so if resetting is performed frequently, inter-frame prediction will not be executed effectively, and overall image quality will deteriorate. is expected.

Therefore, as the conference device, as shown in FIG. 8, a number of encoders and decoders corresponding to the users participating in the conference are prepared, the image code transmitted from each user is decoded in the conference device, and the code is renewed. However, there is a disadvantage that the scale of the conference apparatus increases.

The present invention has been created in view of such problems,
It is an object of the present invention to provide a video conference system, an inter-frame encoder and a decoder capable of enjoying image degradation due to received image switching while reducing the scale of the apparatus.

[Means for solving the problem]

The invention according to claim (1) provides a large number of videophones that encode a TV image signal, transmit the encoded image signal to an information channel of a communication line, and restore the TV image signal from the encoded image signal received from the information channel of the communication line. In a video-phone conference system comprising a terminal device and a video-phone conference device for controlling a connection between the many video-phone terminal devices via a communication line to realize a video conference, Respectively generates an encoded image signal of one frame at the time of reset based on intra-frame prediction, and generates an encoded image signal of each frame at the time of non-reset after that based on inter-frame prediction, The coded image signal of each frame to be coded by the inter-frame coder is connected to the video conference device by adding coding control information indicating which prediction the coded image signal is based on. Means for transmitting an image signal to an information channel connected to the video conference device, and a reset signal for generating a reset signal when encoding control information included in the image signal received from the information channel connected to the video conference apparatus indicates intra-frame prediction. Generating means for generating a decoded image signal generated from an image signal received from an information channel connected to the video conference apparatus, in one frame when the reset signal is generated, based on intra-frame prediction; A decoding unit for generating a video signal based on inter-frame prediction for each frame, and output means for outputting received image designation information designating a receiving party to the video conference device using a signal channel; The device is the TV
A frame memory provided for each information channel to which the telephone terminal device is connected, an information channel to which a certain video telephone terminal device is connected, and an image signal from the frame memory corresponding to the information channel, A matrix switch for outputting to an information channel to which any video telephone terminal device other than the device is connected, and encoding control information provided for each frame memory and included in an image signal received from the corresponding information channel, being a frame. Storing the encoded image signal for the one frame in the frame memory together with the corresponding encoding control information when indicating the intra prediction;
An access control circuit for receiving an output command, reading out an image coded signal for one frame from a frame memory together with coding control information indicating intra-frame prediction, and outputting the read out signal to the matrix switch, and the reception received from the signal channel When connecting the matrix switch between the transmitting side videophone terminal apparatus and the receiving side videophone terminal apparatus according to the image designation information, generating the output command in response to receiving the received image designation information, A control circuit for causing a switch to select an image signal from the frame memory first, and thereafter to select an image signal from a corresponding information channel is provided.

The inter-frame encoder according to claim 1 includes a subtractor that receives an image signal encoded as an input to be subtracted, a quantizer that receives an output of the subtractor, and a prediction signal for one image frame. Frame memory to be stored and “0” at reset,
A first selector for providing the output of the frame memory to the subtraction input of the subtractor at the time of non-setting, and the output of the quantizer at the time of reset, and the output of the frame memory at the time of non-reset. A second selector for providing an input, wherein the quantizer outputs an intra-frame predictive coded image signal at reset, and outputs an inter-frame predictive coded image signal at non-reset thereafter. I do.

The decoder according to claim 1, wherein the intra-frame decoder receives a predicted coded image signal to be decoded, an adder receives an output of the intra-frame decoder at an input to be added, and outputs a signal for one image frame. A frame memory for storing the prediction signal of
A first selector for providing "0" when a reset signal is generated, an output of the frame memory to an addition input of the adder for non-reset, and an output of the intra-frame decoder for reset, A second selector for providing an output of the frame memory to an input of the frame memory, wherein the adder outputs an intra-frame prediction decoded image signal when a reset signal is generated, and an inter-frame prediction when a non-reset is performed thereafter. It is characterized by outputting a decoded image signal.

[Action]

In the video conference call system of the present invention, the inter-frame encoder in the video telephone terminal device on the transmitting side receives the system reset at the start of the video conference call, etc.
A coded image signal of a frame is generated based on intra-frame prediction, and a coded image signal of each frame at the time of non-reset is subsequently generated based on inter-frame prediction. The encoded image signal is transmitted to an information channel connected to the video conference phone, with encoding control information indicating which prediction the encoded image signal is based on added.

In other words, the transmitting-side videophone terminal device resets the 1
The frame is an intra-frame prediction, and each subsequent non-reset frame generates encoded data by an inter-frame prediction,
Control information indicating whether the request is a reset request (coding control information indicating intra-frame prediction or inter-frame prediction) is added to the predicted coded image signal of each frame and transmitted.

On the other hand, in the videophone terminal device on the receiving side, the output means outputs the received image designation information designating the receiving party to the videophone conference device using the signal channel. That is, a reception request is output.

In a video conference call, the access control circuit
When the encoding control information included in the image signal received from the information channel to which the video telephone terminal is connected indicates intra-frame prediction, the encoded image signal for one frame is stored in the frame memory together with the corresponding encoding control information. Store.
On the other hand, when the control circuit receives the reception image designation information, the control circuit sends the transmission signal to the matrix switch according to the reception image designation information.
A connection is made between the video telephone terminal device and the receiving video telephone terminal device, and an output command is output to the access control circuit. The access control circuit receives the output command, reads out an image coded signal for one frame from the frame memory together with coding control information indicating intra-frame prediction, and outputs the signal to the matrix switch. The matrix switch is
Under the control of the control circuit, first, an image signal from the frame memory is selected, and thereafter, an image signal from the corresponding information channel is selected.

In other words, the video teleconferencing device relays the received image signal to the video phone terminal device that has issued the reception request. At this time, the video teleconferencing device predicts the coded image signal of the frame based on intra prediction (the first one frame). The encoded image signal) is stored in a frame memory together with encoding control information (reset request) indicating intra-frame prediction. Then, the video teleconference device transmits an image signal for one frame (an image signal for one frame with a reset request) from the corresponding frame memory to the video telephone terminal device which has issued the reception request, and then transmits the image data to the transmission destination. The output result of the inter-frame encoder of the video telephone terminal is delivered as it is to the video telephone terminal that issued the reception request.

In the videophone terminal device that has issued the reception request, the reset signal generation means generates the reset signal when the coding control information included in the image signal received from the information channel connected to the videophone conference device indicates intra-frame prediction. Occur. The decoder generates a decoded image signal generated from an image signal received from the information channel connected to the video conference device, in one frame when the reset signal is generated, based on intra-frame prediction, and in a subsequent non-reset state. Are generated based on inter-frame prediction.

When the receiving-side videophone terminal device outputs the received image designation information for which the receiving party has been changed, the videophone conference device first takes out the image signal with intra-frame prediction from the corresponding frame memory and transmits it, and then transmits it. The relay station directly transmits the transmission image signal of the video telephone terminal device on the side. As a result, the reset process by reception switching is performed only by the decoder of the videophone terminal device whose reception partner has been changed. In addition, the video telephone terminal device whose reception partner has been changed can easily synchronize and decode the image signal.

As described above, according to the present invention, intra-frame prediction is only one frame at the time of system reset, and inter-frame prediction is effectively performed in each subsequent frame, so that deterioration of image quality is suppressed as a whole. become. Also,
In the videophone terminal device, the reset processing of the inter-frame encoder is uniformly performed only once by a system reset at the start of a conference or the like, and the decoder can be individually reset. The time can be reduced and the synchronization control can be easily performed. In addition, since the video conference device has a frame memory for intra-frame predictive encoding for video conference participants, the image quality associated with reception switching can be reduced without increasing the circuit size of the video conference device. Reduction can be prevented.

〔Example〕

One embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a configuration example of a video conference call system, and FIG.
FIG. 3, FIG. 3 and FIG. 4 show an inter-frame encoder, a decoder and a timing generation circuit of a video conference image CODEC provided in the video telephone terminal device, respectively.

In FIG. 1, in the video telephone conference system according to the present embodiment, a large number of video telephone terminal devices (for example, A, B, C) and the video telephone conference device 46 are connected via ISDN which is a communication line.

First, the configuration of the video conference device 46 will be described with reference to FIG. 30 is a video telephone terminal device (A, B, C) via ISDN
Is the line interface connected to The line interface 30 is used for transmitting information channels (B channels) for transmitting image signals, information channels (B channels) for transmitting audio signals, line control, videophone terminal control information, etc. for each terminal device. Signal channel (D channel)
Separation / multiplexing.

31i (i = 1, 2,..., N) is the line interface 3
0 indicates each of information channels (for example, one B channel of 2B + D channels) for image signal transmission / reception separated / multiplexed. 32 indicates the separated D channel. 33i
(I = 1, 2,..., N) and 44 _i (i = 1, 2,.
n) is a frame memory and an access control circuit connected to the corresponding information channel among the information channels 31 ₁ , 31 ₂ ,..., 31 _n , respectively.

The access control circuit 44 _i, when an image signal came transmitted from the TV conference call participant subscriber terminal comes connected during TV telephone conference via the information channel 33i includes a reset request, 1 including the reset request The intra-frame prediction coded image signals for the image frames are stored in the corresponding frame memory 31i. The interframe encoder of the conference participant terminal performs a system reset at the start of a video conference call, etc., and starts transmitting a predicted coded image signal. At this reset, an intra-frame predicted coded image signal is output. Then, at the time of non-reset, an inter-frame prediction coded image signal is output. Then, to the image signal to be transmitted, encoding control information for distinguishing between the signal at the time of reset and the signal at the time of non-reset is added (see FIG. 5A). This encoding control information (intra-frame prediction) is a reset request, and the frame memory
(See the left half of FIG. 5B) 40 is a matrix switch, and 42 is a control circuit thereof. The control circuit 42 performs read control of the access control circuit 44i and switching of the matrix switch 40.

In FIG. 2, the reset signals inputted to 8, 8 and 14 from the outside are generated by a control system (not shown), and become high level (at the time of reset) when a system reset is performed at the start of a conference or the like. Thereafter, when the system reset is released, the level becomes low (during non-reset) (see the reset signal in FIG. 5). Numeral 2 denotes a subtracter, to which a digitized input image signal output from a TV camera constituting the video telephone terminal device is input. 4 is a subtractor 2
Is a quantizer receiving the output of. Reference numeral 6 denotes a frame memory, which is used for outputting, for each frame of the digitized image signal output from the TV camera, a prediction signal for encoding the image signal of the frame.
Reference numeral 8 denotes a first selector 8 which supplies a signal of "0" at the time of reset and a prediction signal of one frame in the frame memory 6 to the subtraction input (-) of the subtractor 2 at the time of non-reset. Reference numeral 12 denotes a second selector which supplies the output signal of the frame memory 6 to the input of the frame memory 6 at the time of reset and the output signal of the quantizer 4 at the time of reset. Reference numeral 14 denotes an intra-frame encoder for further performing an intra-frame predictive encoding process on an output signal of the inter-frame encoder (output signal of the quantizer 4). The intra-frame encoder 14 adds the above-described encoding control information to the image signal of each frame output from the quantizer 4 according to a reset signal. Specifically, as shown in FIG. 5A, at the time of reset, coding control information indicating “intra-frame prediction” is added, and at the time of non-resetting, coding control information indicating “inter-frame prediction” is added. Add.
An output signal of the intra-frame encoder is multiplexed with an output signal of a speech encoder (not shown), and an ISDN such as 2B + D formed in a digital integrated service network (ISDN).
The signal is transmitted to the above-described TV conference device connected to the information channel (B channel) in the channel.

In FIG. 3, reference numeral 20 denotes an intra-frame decoder that implements a decoding process for intra-frame prediction encoding on an encoded image signal transmitted from the video conference device via the information channel in the ISDN channel. is there. In-frame decoder 20
Is supplied to the adder input of the adder 22. Reference numeral 24 denotes a frame memory, which is used to output a prediction signal for decoding an inter-frame coded image. 26 from outside
The reset signal to be input to the control signals 28 and 28 is generated by the timing generation circuit shown in FIG. 4 described later in accordance with the received coding control information. Reference numeral 26 denotes a first selector which supplies a signal of "0" at the time of reset and a predicted image signal in the frame memory 24 to the addition input of the adder 22 at the time of non-reset. Reference numeral 28 denotes a second selector which supplies the output signal of the intra-frame decoder 20 to the input of the frame memory 24 at the time of reset and the output signal of the frame memory 24 at the time of non-reset. The output signal of the adder 22 is a decoded signal of the predicted coded image signal transmitted to each TV conference participant in the TV conference apparatus. The image corresponding to the decoded signal is transferred to the telephone display device and displayed on the display screen. This third
In the figure, as in FIG. 2, the speech decoding system is not shown, but is omitted because it does not relate to the gist of the present invention.

FIG. 4 shows a reset signal generation circuit. In FIG. 4, reference numeral 50 denotes a shift register that shifts in an encoded image signal input from the video conference device via an information channel in the ISDN information channel in response to a clock, 52 denotes a flag pattern detection circuit, and 54 denotes a video conference. A serial / parallel signal which changes to a parallel bit in response to a clock on an encoded image signal transmitted from a device via an information channel in the ISDN information channel.
A parallel conversion circuit, an output section for outputting command data corresponding to encoding control information for only intra-frame prediction;
Is a comparison circuit, and 60 is a D-FF circuit.

The image signal switching operation under the above system configuration will be described below.

Among the signals transmitted from each videophone terminal device to the videophone conference device via the ISDN, an image signal is encoded by the encoder and transmitted.

The encoder enters a reset state at the start of transmission of an image signal. At that time, the encoder outputs “0” via the first selector 8. Accordingly, a signal component substantially equal to the input image signal is input from the quantizer 4 to the intra-frame encoder 14, and the intra-frame predicted image signal to which the encoding control information (intra-frame prediction) is added is transmitted via the ISDN. It is transmitted to the TV conference device. The output of the quantizer 4 that has passed through the second selector 12 is stored in the frame memory 6.

After the start of transmission, after the next frame image, the difference signal between the output result (prediction signal) of the frame memory 6 and the input image signal is quantized in the quantizer 4 to generate an intra-frame encoding as an image signal for inter-frame prediction encoding. The inter-frame prediction coded image signal to which the coding control information (inter-frame prediction) is added is transmitted to the video conference apparatus via ISDN.

As described above, the reset signal indicating the reset state is generated when a system reset is performed at the start of a conference or the like. FIG. 5 (A) shows a video signal from a TV telephone terminal device to a TV.
FIG. 5 (B) shows an image signal transmitted from the video conference device to the video telephone terminal device.
This is shown in relation to the reset signal. In-frame encoder
In FIG. 14, as shown in FIG. 5 (A), at the beginning of one image frame, the above-described encoding control information indicating the distinction between reset and non-reset and flag pattern information are added. The decoder of the videophone terminal device generates a reset signal using the circuit shown in FIG. 4 based on the encoding control information. The flag pattern information is for synchronizing bits in the encoder / decoder, and the encoding control information is whether the image signal is inter-frame prediction encoding or intra-frame prediction encoding (reset state). It is for distinguishing.

The coded image signal multiplexed with the audio signal and transmitted via the ISDN is separated by the line interface 30 of the video conference terminal shown in FIG. 1, and the channel 31 _i (i = 1, 2,...)
.., n). TV that transmitted the image signal
When the encoding control information placed at the head of the frame of the image signal in the telephone terminal device indicates the intra-frame prediction (reset state), one image frame including the encoding control information of the image signal is included. The intra-frame prediction coded image signal is stored in the frame memory 33 _i under the control of the access control circuit 44 _i , and the matrix switch 40 _i
Is input to

The matrix switch 40 is connected to the line interface 30
Under the control of the control circuit 42 for receiving the received image command (designated information) separated and transferred through the D channel 32, the input of each of the participating video telephone terminal devices out of the input image signals is controlled. Switching is performed so that the image signal is forwarded to the videophone terminal device. That is, the control circuit 42 includes a memory access control circuit 42i corresponding to the received image command.
Then, an intra-frame prediction encoded image signal for one image frame including the encoding control information (intra-frame prediction) is read out from the corresponding frame memory 33i, and the matrix switch
After the elapse of the frame period, the inter-frame prediction coded image signal from the information channel 31i is input to the matrix switch 40.

At the same time, the control circuit 42 converts the read intra-frame predictive coded image signal for one image frame and each subsequent inter-frame predictive coded image signal into the received video command destination video telephone terminal device. The matrix switch 40 causes switching to be transmitted to the connected information channel 31i. As a result, from the video conference device to the video telephone terminal device to which the received image command is sent,
An image signal of the format shown in FIG. 5 (B) is transmitted.

In the videophone terminal device to which the received image command is sent,
The image signal input via the intra-frame predictive encoder / decoder 20 (FIG. 3) is input to the adder 22 and the first selector 28. On the other hand, as shown in FIG. 4, the reset signal generation circuit forms a reset state in the first frame of the received image signal according to the coding control information included in each frame, and forms a non-reset state in each subsequent frame. I do. At the time of reset, the first selector 26
Outputs "0" to 22. Therefore, the intra-frame predictive coded image signal for the first one image frame is directly provided for image display as a decoding result, and the second selector
The data is also stored as it is in the frame memory 24 via.

Next, at the time of non-reset, the reset signal disappears, the prediction signal for one image frame in the frame memory 24 is read out for each frame, and supplied to the addition input of the adder 22 via the first selector 26. At the same time, it is stored again in the frame memory 24 via the second selector.

That is, inter-frame decoding of each frame is performed using the prediction signal of the frame memory 24. Since the first selector 26 outputs the output of the frame memory 24 to the adder 22, the inter-frame decoded image signal is used for image display. Thereby, the subscriber of each participating video telephone terminal device can hold a video telephone conference while receiving the image signal.

During the video conference, if any of the video telephone participants wants to change the image of another participant who has been watching so far to the image of another participant, the received image of the image signal Is input from the keyboard, and the command is transmitted via the D-channel formed between the videophone terminal device and the videophone conference device via ISDN.
The control circuit 42 responding to the received image command via the line interface 30 performs a memory access control circuit 42 _j (j is one of i, representing the received image command) corresponding to the received image command. Frame memory 33 _j
, An intra-frame prediction coded image signal for one image frame including the coding control information is read out, and after the lapse of the frame period, the inter-frame prediction coded image signal from the channel 31 _j is input to the matrix switch 40. The read prediction image signal for one frame corresponding to the read one image frame and each subsequent inter-frame prediction encoding image signal are transmitted to the channel 31 _k to which the video telephone terminal C to which the received image command is transmitted is connected. (K is one of i other than j) causes the matrix switch 40 to perform switching.

The image signal of the videophone terminal device A switched as described above is encoded control information (see FIG. 6 (B)) added to the head of the intra-frame prediction encoded image signal for the first one image frame. )), The image signal input through the intra-frame predictive encoder / decoder 20 (FIG. 3) by the reset signal is used as it is as a decoding result for image display, and the second selector It is also stored as it is in the frame memory 24 via. Decoding of each frame following this frame is performed using the prediction signal in the frame memory 24, and the decoded image signal is provided for image display. When the inter-frame decoding period starts, the reset signal disappears, and a prediction signal for one image frame in the frame memory 24 is read out for each frame, and is input to the addition input of the adder 22 via the first selector 26. While being supplied, it is stored again in the frame memory 24 via the second selector.

Thus, the videophone terminal device C that has issued the screen switching request can participate in the videophone while watching the image of the other participant.

〔The invention's effect〕

As described above, according to the present invention, in a video conference call system using an inter-frame prediction system of a fixed prediction system for transmission of a moving image for a video conference call, intra-frame prediction is only one frame at reset, Since the inter-frame prediction is effectively executed in each subsequent frame, deterioration of image quality is suppressed as a whole. In addition, in the video telephone terminal device, the reset processing of the interframe encoder is uniformly performed only once by the system reset at the start of the conference, and the decoder can be individually reset. The time can be reduced and the synchronization control can be easily performed.
Since the video conference device has a frame memory for intra-frame predictive encoding for video conference participants, the image quality associated with reception switching can be achieved without increasing the circuit size of the video conference device. Can be prevented from lowering.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a video conference system corresponding to claim (1), FIG. 2 is a diagram showing an embodiment of an interframe encoder corresponding to claim (2), and FIG. FIG. 4 is a diagram showing a decoder embodiment corresponding to item (2), FIG. 4 is a reset signal generation circuit diagram, FIG. 5 is a timing diagram for explaining the operation of the TV conference apparatus, and FIG. FIG. 7 is a timing chart of a conventional video conference system, and FIG. 8 is a diagram showing an example of a conventional video conference system. 1 to 4, 2 is a subtractor, 4 is a quantizer, 6, 24, 31 _i is a frame memory, 8, 12, 26, and 28 are selectors, 10, 22 is an adder, and 14 is a frame. Inner encoder, 20 is an intra-frame encoder / decoder, 30 is a line interface, 31 _i is an information channel, 32 is a signal channel, 33 _i is a frame memory, 40 is a matrix switch, 4
2 is a control circuit, and _44i is an access control circuit.

Claims (3)

(57) [Claims] 1. A number of video telephone terminal devices for encoding a TV image signal, transmitting the encoded image signal to an information channel of a communication line, and restoring the TV image signal from an encoded image signal received from the information channel of the communication line; In a video conference system configured to control a connection between the video telephone terminals through a communication line and realize a video conference, the plurality of video telephone terminals are each reset when reset. An inter-frame encoder that generates an encoded image signal of one frame based on intra-frame prediction, and generates an encoded image signal of each frame at the time of non-reset after that based on inter-frame prediction; An information channel connected to the video teleconference apparatus by adding encoded control information indicating which prediction the encoded image signal is based on to the encoded image signal of each frame to be encoded. Image signal sending means for sending to, a reset signal generating means for generating a reset signal when the encoding control information included in the image signal received from the information channel connected to the video conference device indicates intra-frame prediction, A decoded image signal generated from an image signal received from an information channel connected to the video conference device is generated based on intra-frame prediction in one frame when the reset signal is generated. In the frame, a decoder that generates based on inter-frame prediction, and output means for outputting received image designation information designating a receiving party to the video telephone conference device using a signal channel, the video telephone conference device comprises: A frame memory provided for each information channel to which the video telephone terminal is connected; and an information channel to which a video telephone terminal is connected. A matrix switch for outputting an image signal from a frame memory corresponding to the channel and its information channel to an information channel to which an arbitrary video telephone terminal device other than the certain video telephone terminal device is connected; And when the coding control information included in the image signal received from the corresponding information channel indicates intra-frame prediction, stores the coded image signal for one frame in the frame memory together with the corresponding coding control information. An access control circuit for receiving an output command, reading out an image coded signal for one frame from a frame memory together with coding control information indicating intra-frame prediction, and outputting the read out signal to the matrix switch, The videophone terminal on the transmitting side is connected to the matrix switch according to the received image designation information. When connecting the terminal device and the receiving videophone terminal device, the output command is generated in response to the reception of the received image designation information, and the matrix switch first transmits an image signal from the frame memory. And a control circuit for selecting an image signal from a corresponding information channel thereafter. 2. An interframe encoder according to claim 1, wherein: a subtractor receiving an image signal encoded at an input to be subtracted; a quantizer receiving an output of the subtractor; A first memory for storing "0" at the time of reset, and the output of the frame memory to a subtraction input of the subtractor at the time of non-setting, and a quantizer at the time of reset. And a second selector for providing an output of the frame memory to an input of the frame memory at a non-reset time thereafter, wherein the quantizer outputs an intra-frame prediction coded image signal at a reset time, and An inter-frame encoder that outputs an inter-frame prediction coded image signal at the time of non-reset. 3. The decoder according to claim 1, further comprising: an intra-frame decoder that receives the predicted coded image signal to be decoded; and an adder that receives an output of the intra-frame decoder at an input to be added. A frame memory for storing a prediction signal for one image frame, a first selector for providing "0" when a reset signal is generated, and an output of the frame memory to an addition input of the adder when non-reset, and a reset. A second selector for giving the output of the intra-frame decoder to the output of the intra-frame decoder at the time of non-reset, and the input of the frame memory at the time of non-reset. A decoded image signal, and an inter-frame predictive decoded image signal when not reset thereafter.