JPH0287789A - Video telephone conference system and coder and decoder - Google Patents

Abstract

PURPOSE:To prevent deterioration in picture quality attended with changeover of reception picture by providing an in-frame frame memory for prediction coding corresponding to a video telephone conference participant in a video telephone conference device. CONSTITUTION:A frame memory 33i is provided for each information channel 31i. A control circuit 42 receiving reception picture designation information from a video telephone terminal set via a signal channel 32 uses an access control circuit 44i to read an in-frame prediction coding picture signal by one picture frame including the reset instruction information and the inter-frame prediction coding picture signal from the information channel 31i corresponding to the readout is sent to the information channel 31i connecting to a video telephone terminal set being a destination of received picture designation information via a matrix switch 40 as each succeeding frame picture signal. Thus, the deterioration in the picture quality attended with the received picture is prevented in the this way.

Description

[Detailed Description of the Invention] [Table of Contents] Overview Industrial Field of Application Conventional Technology Problems to be Solved by the Invention Means for Solving the Problems Effects of the Invention [(Already Needed)] Based on the stator measurement method Regarding the TV conference system using the interframe predictive coding method and the encoder and decoder, the aim is to prevent image quality deterioration due to switching of received images while reducing the scale of the equipment. A TV teleconference comprising an access control circuit for a memory and the frame memory, an information channel and a matrix switch for outputting a signal from the frame memory to any of the information channels, and a control circuit connected to the signal channel. The control circuit having the apparatus and receiving the received image designation information via the signal channel transmits the access control circuit to one image frame containing the reset instruction information.
The intra-frame predictively encoded image signal is read from the frame memory, and then the inter-frame predictively encoded image signal from the information channel corresponding to the reading is matrix-switched to the above corresponding to the received image designation information. It was configured to send to the information channel.

[Industrial application field]

The present invention relates to a TV teleconferencing system and an encoder and decoder.

A TV teleconferencing system is being developed that provides a more realistic feeling than the conventional audio-only teleconferencing system. This system has the problem of how to send the image signal to each participating TV telephone terminal and how to switch the image signal as necessary. In particular, when switching image signals, depending on the format of encoding and decoding, it is essential to completely synchronize the start point of the encoding operation in the encoder and the start point of decoding in the decoder. .

[Conventional technology]

In a video conference system such as the one described above, if the transmission capacity of the communication path is sufficiently large, the images of users participating in the conference may be reduced2 using a conference device installed within the communication network (at a telephone office), for example. By combining and displaying on each terminal,
A video conference system can be realized.

On the other hand, in order to realize a video conferencing system more economically, it is desirable that the transmission capacity between the conference device and the user terminal be a normal audio band (64 bits/second).

In this case, a code/decoder (CODEC) using a large bandwidth compression technique for the image is required. However, as the number of users participating in a conference increases, the amount of information to be encoded increases, requiring the adoption of more complex bandwidth compression technology, resulting in an increase in the price of terminals that include image C0DEC. Put it away.

Therefore, instead of reducing and combining the images of each user in the conference device, each user is limited to a single image (for example, an image of the person speaking), and each user By making it possible to arbitrarily select an image (an image of the other party), it is possible to create a conference system that is relatively economical and more effective than an audio-only conference.

[Problem to be solved by the invention]

As described above, the interframe prediction method as shown in FIG. 7 is often used as an encoding technique for image C0DEC in a video conferencing system in which the transmission capacity is, for example, about 64 bits/second.

At this time, the predictor including the frame memory becomes a cyclic filter with a feedback loop, and the past history (all frame information) is affected, so the start point of the encoding operation in the encoder and the The decoding start points must be completely synchronized. For this reason, for example, at the start of encoding, the encoder and decoder are reset, and the encoder and decoder are reset.
It is necessary to completely match the internal states of the decoders.

When using an image C0DEC with such an inter-frame prediction function in the conference system, when multiple users receive images of - people from any time, the following inconvenient situation may occur. arise.

For example, as shown in the timing diagram of FIG.
At terminal C, which was receiving the image of
When receiving a screen of Other terminals (
In this example terminal B) also needs to be reset. The reset terminal performs encoding using only intraframe 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 (interframe predictive encoding). In general, interframe prediction has a higher data compression effect when it comes to moving images with little movement, such as video conference calls, so if resets occur frequently, interframe prediction will not be executed effectively and the overall image quality will deteriorate. deterioration is expected.

Therefore, as shown in Figure 9, the conference device is equipped with a number of encoders and decoders corresponding to the number of users participating in the conference, and the conference device decodes the image code sent from each user. If an attempt is made to encode the data again, there is a drawback that the scale of the conference device increases.

The present invention was created in view of such problems, and provides a TV teleconference system, an encoder, and a decoder that can prevent image quality deterioration due to switching of received images while reducing the scale of the device. Its purpose is to provide.

[Means to solve the problem]

FIG. 1 shows a block diagram of the principle of the first invention.

As shown in this figure, the present invention provides a TV teleconference device with:
Frame memory 33 for each information channel 3 Is (i=1.2, . . . n). and the frame memory 33. access control circuit 44. and information channel 31j
(j=one of i) and frame memory 33.
A signal from an arbitrary output information channel 31k (k is j
In a TV teleconference device having a matrix switch 40 for outputting data to one of i other than When an intra-frame predictive encoded image signal is input to the information channel 31□, the access control circuit 44 in response to the reset signal outputs the intra-frame predictive encoded image signal for one image frame including the reset instruction information. The control circuit 42 stores in the frame memory 33 and receives the received image designation information from the TV telephone terminal device via the signal channel 32, and the control circuit 42 causes the access control circuit 44 to display one image including the reset instruction information. The intra-frame predictive encoded image signal for a frame is read out, and the information channel 3 corresponding to the readout is used as the image signal of each subsequent frame.
1. The interframe predictively encoded image signal from the matrix switch 40 is sent to the information channel 31. to which the TV phone terminal device to which the received image designation information is sent is connected.
The present invention is configured so that the information is sent to. This first
Since the essential constituent elements of the second and third inventions used in the implementation of the invention are the same as the constituent elements shown in FIGS. 2 and 5 described later, the constituent elements in these two figures are the same. The attached reference numerals are also used for each component of the second and third inventions, and the figures thereof are omitted.

[For production]

Each frame memory buffer 33 of the TV teleconference device has a T
The intra-frame predictive encoded image signal for one image frame transmitted when the V-telephone terminal device was reset is stored (for details, please refer to the explanation in FIG. 2). The participating TV telephone terminal device is connected to the participating TV telephone terminal device via a matrix switch 40 that is switched by the control circuit 42 based on received image designation information given to the control circuit 42 from the signal channel 32. The image signal designated by the received image designation information is received from among the interframe predictive coding image signals inputted via the information channel 31i to which the (This is an intra-frame predictive coding image signal.) If it is desired to switch the received image during the TV conference, the received image designation information (j) specifying the received image is sent to the control circuit via the signal channel 32. Give to 42.

The control circuit 42 causes an access control circuit 44° to read out one image frame worth of intra-frame predictive encoded image signal including the reset instruction information from the frame 33J, and transfers this to the received image specifying information via the matrix switch 40. (j) Send it to the information channel 31 to which the destination TV phone terminal device is connected, and from the next frame on, send the interframe predictively encoded image signal to the information channel 31, which has already been formed in the matrix switch 40. The information channel 31. sent to.

Then, in the TV phone terminal device that receives the image signal switched in this way and transmits the received image designation information (j), in response to the reset signal, intra-frame predictive coding is performed for one image frame including the reset signal. The signal is sent out as it is as a decoded signal, and is also stored for interframe decoding. From the next frame onward, the interframe decoded signal is used for image reproduction (details are in Section 5).
See figure legends. ) [Embodiment] An embodiment of the present invention will be described with reference to FIGS. 2 to 5. 2 and 3 show an encoder and a decoder for a TV conference image CODEC provided in a TV telephone terminal device, respectively, and FIG. 4 shows a TV conference device.

In Figure 2, 2 is a subtracter, and its subtracted input is T.
A digitized input image signal output from a TV camera constituting the V-telephone terminal device is input. 4 is a quantizer that receives the output of the subtracter 2; Reference numeral 6 denotes a frame memory, which is used to output, for each frame of the digitized image signal output from the TV camera, a prediction signal for encoding the image signal for that frame.

Reference numeral 8 designates a first selector 8 which supplies a signal of 0 when reset, and a predicted signal for one frame in the frame memory 6 when not reset, to the subtraction input (-) of the subtracter 2. 12
is a second selector that applies the output signal of the frame memory 6 to the input of the frame memory 6 when not reset, and the output signal of the quantizer 4 to the input of the frame memory 6 when reset. Reference numeral 14 denotes an intraframe encoder for further performing intraframe predictive encoding processing on the output signal of the interframe encoder (output signal of the quantizer 4). The output signal of the intraframe encoder is multiplexed with the output signal from a speech encoder (not described here) and is used as an information channel (B
channel) is transmitted to a TV conference device, which will be described later.

In FIG. 3, 20 is an intraframe decoder that implements decoding processing for intraframe predictive coding on the encoded image signal transmitted from the TV conference device via the information channel in the 15DN channel. be. The output signal of the intraframe decoder 20 is applied to the addend input of the adder 22. A frame memory 24 is used to output a prediction signal for decoding an interframe encoded image.

26 is a first selector that supplies the "OI+" signal at the time of reset, and the predicted image signal in the frame memory 24 at the time of non-reset to the addition input of the adder 22.28 is the output signal of the intra-frame decoder 20 at the time of reset. is also a second selector that applies the output signal of the intra-frame memory 24 to the input of the frame memory 24 when not reset.Adder 2
The output signal 2 is a decoded signal of a predictively encoded image signal that has been transmitted to each subscriber participating in the TV conference in the TV conference device, and this decoded signal is a decoded signal of the predictively encoded image signal that is transmitted to each subscriber participating in the TV conference. The signal is transferred to a display device, and an image corresponding to the decoded signal is displayed on the display screen. Although the audio decoding system is not shown in FIG. 3 as in FIG. 2, it is omitted because it is not related to the gist of the present invention.

In FIG. 4, 30 is a line interface connected to terminal devices (for example, A, B, and C) via the 15DN, and an information channel (B channel) for image signal transmission, corresponding to each terminal device, Separation of information channel (B channel) for voice signal transmission, signal channel (D channel) for transmission of line control, TV telephone terminal control information, etc.
Perform multiplexing, etc. 31, (i-1, 2,..., n)
indicates each of the information channels (for example, one B channel of 2 B+D channels) for transmitting and receiving image signals that are multiplexed at the line interface. 32 is a separated D
Indicates the channel. 33. is information channel 31. ．． 31□
, . . . 31.1, and is a frame memory connected to the corresponding information channel of 31.1, and is connected to the corresponding information channel 31.1 when the encoder of the subscriber terminal connected to the T■ telephone conference participating in the TV conference is reset. The access control circuit 44i responds to the reset information transmitted via the access control circuit 44i, and stores one image frame's worth of intra-frame predictively encoded image signals. The reset information is placed in the encoding control information section at the beginning of the frame in which the reset information is inserted (see FIG. 6). 4° is a matrix switch, and 42 is its control circuit, which performs read control of the access control circuit 441 and switching of the matrix switch 40.

FIG. 5 shows the access control circuit 44 of FIG. This figure shows the reset signal generation circuit. 50 is a shift register that shifts in the encoded image signal input via the corresponding information channel 31 in response to the clock; 52 is a flag pattern detection circuit; and 54 is a shift register that shifts in the output of the quantizer 4 in response to the clock. A serial/parallel conversion circuit converts into parallel bits, 56 is an output unit that outputs command data corresponding to encoding control information for only intra-frame prediction, 5th 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.

The image signal among the signals transmitted from each TV phone terminal device (via SDN to the TV conference device) is encoded by the encoder and transmitted.

The encoder enters a reset state when transmission of an image signal starts, and at that time, it outputs 0°' via the first selector 8. Therefore, a signal component substantially equal to the input image signal is input from the quantizer 4 to the intra-frame predictor 14, and the intra-frame predicted image signal is transmitted to the TV conference equipment via the 15DN. Further, the frame memory 6 stores the output of the quantizer 4 that has passed through the second selector 12.

After the start of transmission, the next frame image and subsequent frames are stored in frame memory 6.
The difference signal between the output result (prediction signal) and the input image signal is quantized by the quantizer 4 and sent to the intraframe predictive encoder 14 and rsDN as an image signal for interframe predictive coding.
is transmitted to the TV conference device via.

The reset signal indicating the above-mentioned reset state is generated from the circuit shown in FIG. Furthermore, regarding the output result of the intraframe encoder 14, flag pattern information and encoding control information are placed at the beginning of one image frame, as shown in FIG. Based on the encoded control information, a reset signal is generated using the circuit shown in FIG. The flag pattern information is for bit synchronization in the encoder/decoder, and the encoding control information indicates whether the image signal is interframe predictive encoding or intraframe predictive encoding (reset state). This is to make a distinction.

The encoded image signal multiplexed with the audio signal and transmitted via the 15DN is separated at the line interface 30 of the TVV conference terminal shown in FIG.
=1.2,...n) is sent on. If the encoding control information placed at the beginning of the frame of the image signal in the TV telephone terminal device that transmitted the image signal indicates intra-frame prediction (reset state), the code of the image signal The intra-frame predictively encoded image signal for one image frame including the encoding control information is stored in the frame memory 335 under the control of the access control circuit 44, and is input to the matrix switch 40.

The matrix switch 40 has a line interface 3
Under the control of a control circuit 42 which receives received image commands (information) separated by 0 and transmitted via the D channel 32, the input image designated by each participating TV telephone device of each input image signal is Switch notching is performed so that the signal is forwarded to the TV telephone device. As a result, each participating TV
The subscriber of the V-talk terminal device receives the image signal while watching the TV.
Teleconferences can be held.

During the video conference, if any participant among the video conference participants wants to change the image of the other participant that they have been viewing until then to the image of another participant, the received image of the image signal The command to specify the TVV talk terminal and l5D
D formed between the TV conference device and the TV conference device via N
Send through a channel. The control circuit 40 that responded to the received image command via the line interface 30 controls the memory access control circuit 42 . (j is one of i, representing the correspondence to the received image command), reads the intra-frame predictive encoded image signal for one image frame including encoding control information from the frame memory 33°, and calculates the frame period. After the elapse of time, the interframe predictively encoded image signal from the channel 31J is input to the matrix switch 40. The read intra-frame predictively encoded image signal for one image frame and each subsequent inter-frame predictively encoded image signal are transmitted to the channel 31k (to which the TV telephone terminal device C to which the received image command is sent is connected) k causes the matrix switch 40 to perform switching to send the signal to one of i other than j).

The image signal for the TV telephone terminal device A switched as described above is encoded by the encoding control information (see FIG. The image signal inputted via the intra-frame predictive coding decoder 20 (FIG. 3) by the reset signal derived from (B)) is directly provided for image display as a decoding result, and The data is also stored as is in the frame memory 24 via the selector 28.

Each frame subsequent to this frame is decoded using the prediction signal in the frame memory 24, and the decoded image signal is provided for image display. When entering this interframe decoding period, the reset signal disappears and the frame memory 2
The predicted signal for one image frame of 4 is read out for each frame, and is supplied to the addition input of the adder 22 via the first selector 26, and is again sent to the frame memory 28 via the second selector. Stored.

In this way, the TV phone terminal device C that issued the screen switching request can participate in the video phone call while viewing the image of the participant on the other side.

〔Effect of the invention〕

As described above, according to the present invention, a fixed-frame interframe prediction method is used to transmit moving images for a TV conference, and a frame memory for intra-frame predictive coding is stored in a TV conference device. Since the configuration is adapted to accommodate participants in a teleconference, it is possible to prevent deterioration in image quality due to screen switching without increasing the circuit scale of the TV conference device.

[Brief explanation of drawings]

FIG. 1 is a principle block diagram of the first invention, FIG. 2 is a diagram showing an encoder embodiment of the second invention, FIG. 3 is a diagram showing a decoder embodiment of the third invention, and FIG. 5 is a diagram showing the TV conference device, FIG. 5 is a reset signal generation circuit diagram, FIG. 6 is a timing diagram explaining the operation of the TV conference device, and FIG. 7 is a diagram showing the TV conference device.
The figure shows an interframe predictive image encoder, Figure 8 is a timing diagram of a conventional TV conference system, and Figure 9 is a diagram of a conventional T
It is a figure showing an example of a V conference device. 24.31i is frame memory, 12.26.28 is selector, 0.22 is adder, 4 is intraframe encoder, 0 is intraframe coding decoder, O is line interface, 1 is information channel, 2 3 is a signal channel, 3 is a frame memory, 0 is a matrix switch, 2 is a control circuit, and 41 is an access control circuit. In Figures 1 to 4, 2 is a subtracter, 4 is a quantizer, Hanged Shinkan 11 Shishi Figure 2 Figure 2 Sai 4 Matsuri Tsuki/)h-t<Fukozu 7th Figure 1 +) 9yl -t S 5'l; i a SkFig. Figure promotion V %2gsa4 sweetfish rice fillerfin ξin7゛ku akio. TV Golden Candlework 1st evening q

Claims (3)

[Claims] (1) Information channel (31_i) (i=1, 2,...
n) frame memory (33_i) and an access control circuit (44_i) for the frame memory (33_i).
) and the signals from the information channel (31_j) (j=one of i) and the frame memory (33_j) to any said information channel (31_k) (k is one of i other than j). It has a TV teleconference device having a matrix switch (40) for outputting and a control circuit (42) connected to a signal channel (32), and the frame memory (33_j) stores one image including reset instruction information. Intra-frame predictive encoded image signals for frames are stored, and received image designation information is transmitted from the TV phone terminal to the signal channel (3).
2), the control circuit (42) causes the access control circuit (44_j) to read out the intra-frame predictive encoded image signal for one image frame including the reset instruction information, and reads out the intra-frame predictive encoded image signal for each subsequent frame. The matrix switch (4
0), the information channel (31_k) to which the TV phone terminal device to which the received image designation information is sent is connected.
A TV teleconference system characterized by transmitting to. (2) A subtracter (2) that receives an image signal encoded as an input to be subtracted; a quantizer (4) that receives the output of the subtractor (2); and stores a prediction signal for one image frame. a frame memory (6); a first selector (8) that applies "0" when reset and the output of the frame memory (6) when not reset to the subtraction input of the subtracter (2); The output of the frame memory (6) is output from the quantizer (
a second selector (12) that supplies the output of the quantizer (4) to the input of the frame memory (6);
An encoder characterized in that the output of the encoder is an encoded output. (3) An adder (22) that receives a predictively encoded image signal to be decoded as an addend input; a frame memory (24) that stores a predictive signal for one image frame; a first selector (26) that applies the output of the frame memory (24) to the addition input of the adder (22) when reset; and a first selector (26) that applies the output of the frame memory (24) to the addition input of the adder (22) when reset; The predictively encoded image signal is stored in the frame memory (24
), the decoder comprising a second selector (28) that is applied to the input of the adder (22), and the output of the adder (22) is used as the decoded output.