JP3599661B2 - Image communication terminal - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a communication device for transmitting and receiving image signals, and more particularly to an image communication device having a multipoint communication function.
[0002]
[Prior art]
An international standard for compressing a television signal from a transmission rate of 64 kb / s to 2 Mb / s has been established by the ITU-TSS. 261 is assigned. This standard assumes that one-to-one communication is performed, and in order to connect a plurality of terminals at the same time and perform multipoint communication, a multipoint control device is separately prepared and the multipoint control device is used. Communication between multiple terminals via the Internet.
[0003]
[Problems to be solved by the invention]
In the conventional method, when performing multipoint communication, a multipoint control device is required in addition to a standard normal terminal, so that there has been a problem that the cost of the entire system increases.
[0004]
Accordingly, an object of the present invention is to provide a high-performance image communication terminal capable of economical multi-point communication that minimizes the cost increase of the entire image communication system. An object of the present invention is to realize a loop-type multipoint transmission function by making the most of a function inherent in a compliant moving picture coding apparatus and adding a small-scale circuit. That is, a plurality of terminals are connected in a loop through a line, and each terminal is connected to a small screen HEADER number (hereinafter, referred to as a GOB number) which is a feature of the standard described in Japanese Patent Application Laid-Open No. 05-22321. A simple circuit is used to realize a multipoint function by transferring and deleting a signal transmitted from the upper direction in the required GOB small screen unit in the lower direction using the required GOB small unit or by modifying the GOB number. An image communication terminal is provided.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, in a high-efficiency moving image encoding apparatus, means for connecting three or more terminals in a loop via a line such as ISDN, and a method for converting an encoded signal received from another terminal into a moving image A transmission error correction is performed through a transmission error correction circuit prepared in advance in the image decoding apparatus, and an image start code is selected from signals after removing an error correction signal (for example, a parity signal) used for a transmission error. (Hereinafter referred to as PSC), a means for detecting a small screen start code (hereinafter referred to as GOB HEADER), a means for detecting a GOB number indicating a position of a small screen arriving after the small screen start code, a method for detecting the small screen Means for deleting only a required small screen according to the number of the picture, means for correcting the GOB number according to a predetermined rule, an image start code or a small picture from a coded signal of a moving image. Means for detecting a surface start code, means for detecting a GOB number arriving after a small screen start code, means for replacing the GOB number with a different number based on predetermined means, image start in a received signal Means for transferring a received signal until a code arrives, and for switching to an encoded output signal of a moving image encoding device when the image encoding start code arrives, and a transfer signal prepared for moving image encoding; Means for input to the error correction coding circuit.
[0006]
Further, by adding the loop type multi-point voice coding method to a voice coding apparatus which is means for realizing a voice coding method which is also used in ordinary one-to-one communication, the same software is switched by switching only software. The terminal has a configuration in which the voice coding device can code one-to-one and loop-type multi-point voices and communicate with images.
[0007]
[Action]
A high-performance multipoint TV conference that displays a plurality of screens can be realized only by adding an image insertion / deletion process in GOB units.
[0008]
【Example】
Hereinafter, embodiments of the high-performance image encoding apparatus according to the present invention will be described in detail with reference to the drawings.
[0009]
First, the operation of the moving picture coding apparatus will be briefly described with reference to FIG. 1 so that the contents of the present invention can be easily understood.
[0010]
(1) A television signal captured by the television camera 1 is subjected to analog / digital conversion by an analog / digital converter 2 and stored in an encoded frame memory 3 for moving images.
[0011]
(2) Next, the television signals stored in the encoding frame memory 3 and the reference frame memory 4 are read out, and the correlation between the two television signals is calculated by the motion amount calculation circuit 5, and the motion of the subject is accordingly calculated. The amount of movement is determined.
[0012]
(3) The signal of the reference frame memory 4 at the position where the above-mentioned amount of motion has been compensated is read and becomes a predicted value. The prediction value and the television signal value read from the encoding frame memory 3 are subtracted by a subtraction circuit 6 to calculate a prediction error.
[0013]
(4) The prediction error is obtained by encoding the value quantized by the quantization circuit 7 and the above-mentioned amount of motion by the variable-length encoding circuit 8,
(5) As a modification of the processing of (4), the above-described prediction error is orthogonally transformed by an orthogonal transformation circuit 9 by, for example, a method such as discrete cosine transformation, and then quantized by a quantization circuit 7 to perform variable length coding. Or encoded by the circuit 8.
[0014]
From the quantized signal, the original prediction error is reproduced by the inverse quantization circuit 14 and the inverse orthogonal transform circuit 15, added to the prediction value by the addition circuit 17, and stored in the reference frame memory 4.
[0015]
(6) The coding result is added with a correction bit by an error correction bit adding circuit 10 for transmission error correction, transmitted to the transmission path 11 and transmitted to the receiving side.
[0016]
(7) The decoding device on the receiving side restores the original television signal by means reverse to the above. That is, the transmission error correction circuit 12 corrects the transmission error using the error correction bit, removes the error correction bit used for the error, and transfers the error to the decoding circuit 13. The decoding circuit 13 decodes the signal encoded by the variable-length encoding circuit 8 to obtain a quantized signal, a motion amount, and the like. The quantized signal is inversely quantized by the inverse quantization circuit 14, and the original prediction error value is calculated by the inverse orthogonal transform circuit 15 as necessary.
[0017]
(8) Further, the television signal of the reference frame stored in the reference frame memory 16 is read as a predicted value. However, the reading position is a position where the motion amount detected on the transmission side is compensated. As a result, the same predicted value as that of the transmitting side is obtained.
[0018]
(9) The prediction error value obtained in (7) and the prediction value obtained in (8) are added by the adder circuit 17 and stored in the display frame memory 18 and the reference frame memory 16. The television signal stored in the reference frame memory 16 is read out by switching two switches 19 for selecting inputs on different sides in the next frame, and a predicted value is generated.
[0019]
(10) The television signal stored in the display frame memory 18 is read out, restored to an analog signal through the digital / analog converter 20, and displayed on the monitor 21.
[0020]
(11) Further, on the receiving side, in order to generate the same predicted value on the transmitting side as on the receiving side, a prediction error is obtained by using an inverse quantization circuit 14 and an inverse orthogonal transform 15 on the orthogonally transformed and quantized signal. The result obtained by adding the prediction value read from the reference frame memory 16 by the adder 17 is stored in the frame memory 16 serving as the reference frame memory in the next frame.
[0021]
Next, a method for realizing the loop type multipoint function according to the embodiment of the present invention will be described.
[0022]
The following two types of functions are assumed as loop-type multipoint functions.
[0023]
(1) One screen mode Only one terminal has a transmission right and transmits a moving image or a still image. This terminal is called a one-screen mode terminal. The other terminal receives the transmitted signal, decodes and displays the signal, and transfers the transmitted signal to the next terminal as it is.
[0024]
This terminal is called a through mode terminal.
[0025]
(2) Split screen mode A plurality of terminals (for example, five terminals) have a transmission right, and receive signals are decoded and displayed as they are.
[0026]
From the transferred signals, only the signal generated by the own terminal is deleted, and instead, the signal generated by the own terminal is inserted and transmitted to the lower terminal. Also, a signal transmitted from a terminal other than the inferior terminal is transferred to the inferior terminal after processing such as changing the position in the screen as necessary.
[0027]
This terminal is called a split screen mode terminal.
[0028]
Hereinafter, an embodiment of the present invention that realizes the above operation will be described with reference to FIG. Note that blocks given the same figure numbers as those in FIG. 1 realize the same functions.
[0029]
A signal in which a transmission error has been corrected by the transmission error correction circuit 12 mounted for a normal moving image and the parity bit for error correction has been deleted is output by the PSC detection circuit 26 or the GOB HEADER detection circuit 27 to the PSC or GOB HEADER is detected.
[0030]
At a timing independent of this, one mode among one screen, through, and split screen terminals set manually via the man-machine I / F 28 is set in the flip-flop 29. According to the above PSC detection signal, the mode of the flip-flop 29 is transferred to the next flip-flop 30, and the mode of the terminal is switched.
[0031]
The control circuit 31 performs the following operation according to the terminal mode and the GOB number.
[0032]
(1) One-screen mode terminal: Tilt the switch 32 upward to delete all GOBs and encoded image data except PSC. This PSC is used for setting the mode for the next flip-flop 33.
[0033]
(2) Through mode terminal: The switch 32 is tilted downward to allow all PSC, GOB, and image encoded data to pass therethrough, and write the data into the FIFO 34.
[0034]
(3) Split mode terminal (when five terminals including itself are connected): The following two processes are performed.
[0035]
(A) When the GOB detection circuit 27 detects the GOB HEADER of the GOB numbers 1, 3, and 5, the switch 32 is tilted upward to remove the GOB HEADER and the subsequent encoded image data. In other cases, the switch 32 is moved down to write the data in the FIFO 34.
[0036]
(B) In accordance with the GOB number detected by the GOB detection circuit 27, the GOB number replacement circuit 35 replaces the GOB number as follows.
[0037]
GOB numbers 2, 4, and 6 are replaced with GOB numbers 1, 3, and 5, respectively, GOB numbers 7, 9, and 11 are replaced with GOB numbers 2, 4, and 6, and GOB numbers 8, 10, and 12 are replaced with GOB numbers 7 and 9, respectively. , Replaced with 11.
[0038]
Next, the operation of the control circuit 36 for reading from the FIFO 34 will be described. The control circuit 36 first instructs to read a codeword from the FIFO 34. Next, the PSC detection circuit 37 detects the PSC. When the PSC is detected, the multipoint mode signal stored in the flip-flop 30 is written to the flip-flop 33. The control circuit 36 performs the following control triggered by the multipoint mode and the detection of the PSC by the PSC detection circuit 37.
[0039]
(1) One-screen mode terminal: issues an encoding start command to the variable-length encoding circuit 8 and starts encoding at the terminal itself. At the same time, the switch 38 is tilted upward, and the PSC, GOB, and image encoded data generated by the variable length encoding circuit 8 are transmitted to the downstream transmission line 11 via the transmission error correction bit adding circuit 10. At this time, the reading from the FIFO 34 is continuously performed, and the mode of the terminal is switched upon this occasion.
[0040]
(2) Through mode terminal: Releases the coding start command to the variable length coding circuit 8 and stops the coding. At the same time, a read command is issued to the FIFO 34 to read out PSC, GOB, and image encoded data. At the same time, the switch 38 is moved downward to allow the above PSC, GOB and coded data to pass therethrough and transfer it to the transmission error correction bit adding circuit 10.
[0041]
(3) Split mode terminal: The following two processes are performed.
[0042]
(A) When the PSC detection circuit 37 detects a PSC in the signal read from the FIFO 34, it issues an encoding start command to the variable length encoding circuit 8 and at the same time, flips the switch 38 upward to generate a code generated by its own terminal. Coded data is transmitted to the transmission path via the transmission error correction bit addition circuit.
[0043]
(B) The GOB number replacement circuit 39 removes the PSC from the signal generated by the variable length coding circuit 8 and replaces the GOB number as follows.
[0044]
Replaced GOB numbers 1, 3, and 5 with GOB numbers 8, 10, and 12, respectively.
[0045]
When the encoding end signal is received from the variable length encoding circuit 8, the encoding start command to the variable length encoding circuit 8 is released, and the encoding is stopped. At the same time, the code is read out from the FIFO 34, the switch 38 is turned down, and transmitted to the transmission line 11 via the error correction bit adding circuit 10.
[0046]
In the above description, the case where the split mode has five terminals including itself has been described. However, as illustrated in FIG. 3, a plurality of screens are simultaneously displayed by the same processing in the case of three terminals or four terminals. I can do it. In this case, the replacement of the GOB number replacement circuit 35 is equivalent to the above. The replacement in the GOB number replacement circuit 39 is as shown in FIG.
[0047]
Further, an embodiment in which the speech coding apparatus is switched between one-to-one and loop-type multipoint will be described with reference to FIG.
[0048]
A signal for identifying the one-to-one / loop switching specified by the man-machine I / F 28 is stored in the flip-flop 41. The DSP 42 monitors the above-mentioned identification signal at regular intervals, and switches the switch 43 in accordance with the signal, and switches the switch 43 to a ROM (READ ONLY MEMORY) 44 in which a one-to-one encoding algorithm is stored or a ROM 45 for a loop type. And encodes a signal obtained by digitally converting the audio signal sent from the microphone 46 by the A / D converter 47 and sends the encoded signal to the transmission line 11. Similarly, the DSP 42 restores the signal transmitted from the transmission line 11 to the original audio signal according to the encoding algorithm read from either the ROM 44 or the ROM 45, and converts the signal into an analog signal by the D / A converter 48. Later, the sound is transmitted from the speaker 49 as sound.
[0049]
As another embodiment of the present invention, transmission control when transmitting an image or sound to the transmission line 11 will be described.
[0050]
In the case of transmitting audio and images on a single digital transmission path, a multiplexing / separating circuit is required to multiplex and separate the audio and image signals, and the transmission path generally uses ITU-TSS. International standard H. 221 is often used for multiplex separation. In this standard, an audio signal is normally assigned to B1 which is the first B channel, and an image signal is assigned to B2 which is the second B channel. However, in some cases, the B channel is further subdivided, and audio and video are transmitted through one B channel. The B1 and B2 channels are combined into one signal by the multiplexing circuit and flow on the line, separated into the original B1 and B2 channels by the separation circuit, and further separated into audio and image signals as necessary. . Using this demultiplexing function, a specific method of transmitting video and audio signals between multi-point terminals connected in a loop form by using video and audio signals (connection of lines to form bidirectional loops) The method will be described below with reference to FIG.
[0051]
As is well known, in an ISDN having 2B, B1 is connected first, and then B2 is connected. Therefore, when calls are sequentially connected in a clockwise direction from the chair terminal, the lines B1 and B2 of each terminal are connected as shown in FIG. By the way, in a normal one-to-one communication, an audio signal is connected via the B1 line and an image is connected via the B2 line. Therefore, when the connection is made as shown in FIG. It will be connected incorrectly.
[0052]
Therefore, as shown in FIG. 7, immediately after the separation circuit 50 for separating the signal input from the line into B1 and B2, the signal type identification circuit 52, which is a feature of the present invention, identifies whether the signal is an audio signal or an image signal. Based on this, the cross switch 51 outputs mutually different input signals, and the audio signal is input to the audio DSP 42, the image signal is input to the moving image transmission error correction circuit 12, and the correct image and audio are received. .
[0053]
【The invention's effect】
As described above, by adding a simple circuit to the video encoding circuit, a loop-type multipoint conference function can be realized, so that the practical effect is large.
[Brief description of the drawings]
FIG. 1 is a block diagram of an image communication terminal (high-definition still image transmission / reception) according to the present invention.
FIG. 2 is a block diagram of an image communication terminal (loop-type multipoint communication) according to the present invention.
FIG. 3 is a diagram showing an example of a screen for simultaneously displaying a plurality of screens.
FIG. 4 is a diagram showing a GOB number replacement example when terminals are simultaneously connected at multiple points.
FIG. 5 is a block diagram of a voice encoding unit of the image communication terminal according to the present invention.
FIG. 6 is a connection diagram when the image communication terminals of the present invention are connected in a loop.
FIG. 7 is a block diagram of a control unit of the image communication terminal according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... TV camera, 2 ... Analog / digital converter, 3 ... Frame memory for encoding, 4, 16 ... Frame memory for reference, 5 ... Motion amount calculation circuit, 6 ... Subtraction circuit, 7 ... Quantization circuit, 8 ... Variable length coding circuit, 9 orthogonal transform circuit, 10 transmission error correction bit addition circuit, 11 transmission line, 12 transmission error correction circuit, 13 decoding circuit, 14 inverse quantization circuit, 15 inverse orthogonal transform Circuit, 17 addition circuit, 18 display frame memory, 19, 23, 25, 32, 38 switch, 20 digital / analog converter, 21 monitor, 22, 24 still image frame memory, 26, 37: PSC detection circuit, 27: GOB HEADER detection circuit, 28: Man-machine I / F, 29, 30, 33: flip-flop, 31, 36: control circuit, 34: FIFO, 35, 39 ... GOB number replacement circuit.

Claims (3)

In an image communication terminal connected to a transmission path such as ISDN formed in a loop and including at least first, second, and third terminals,
Each of the terminals,
Encoding means for encoding an image signal from a camera to generate an image start code, a small-screen start code, and encoded data; and means for selecting encoded data and adding a transmission error correction bit to the encoded data. Switching means for selecting the coding means of its own terminal or coding data from another terminal and supplying it to the transmission error correction bit adding means, and transmitting the output data of the transmission error correction bit adding means to the ISDN or the like. receiving means for sending to the end end you located downstream side via the road, the coded signal supplied through a transmission path such as the ISDN from the end edge you located on the upstream side, the encoded Transmission error correction means for performing transmission error correction on a signal and outputting coded data; decoding means for receiving coded data from the transmission error correction means, decoding and supplying the decoded data to a monitor; And the transmission path And a loop-type multipoint circuit is provided between the contact point of the transmission error correcting means and fine said decoding means,
The loop-type multipoint communication circuit,
Remove the transmission error correction signal from the encoded signal from said upstream side terminal, the image start code (PSC), small screen start code (GOB HEADER ), a transmission error correction circuit that outputs a signal including encoded data and a GOB number indicating the position of a small screen that arrives after the small screen start code ,
A first PSC detection circuit for detecting the image start signal (PSC) from an output signal of the transmission error correction circuit;
And GOB HEADER detecting means for detecting the GOB number representing the position of the small screen coming successively from the output signal of the transmission error correction circuit to the small screen start code (GOB HEADER) and said small screens start code,
First GOB number replacement means for replacing the GOB number corresponding to the encoded data of the output signal of the transmission error correction circuit with a different number based on a predetermined rule,
A switch circuit that is located between the transmission error correction circuit and the first GOB number replacement unit and disconnects a signal between them ;
The switch circuit and the first GOB number replacing means are controlled in accordance with the detected GOB number of the GOB HEADER detecting means, and the output signal of the transmission error correction circuit is supplied to the first GOB number replacing means or First control means for controlling the supply so as to prevent the supply or to replace the GOB number supplied to the first GOB number replacement means ;
The image start code ( PSC ) and the small screen start code ( GOB ) corresponding to the GOB number replaced by the first GOB replacement means HEADER ), storage means for storing the encoded data ,
A second PSC detection circuit for detecting an image start code (PSC) from a signal stored in the storage means;
When the second PSC detection circuit detects an image start code (PSC), the image start code (PSC) generated by the encoding means based on the image start code (PSC) and the multipoint mode setting by the mode setting means. PSC ), small screen start code ( GOB HEADER ), second control means for controlling the switching means so that encoded data can be transmitted to the transmission path of the lower terminal via the transmission error correction bit adding means ,
An image communication terminal comprising: The image communication terminal, the image communication terminal according to claim 1, comprising the undistorted speech coding method for transmitting and receiving the undistorted sound with still images. 3. The image communication terminal according to claim 1, wherein the image communication terminal further comprises a means for connecting a moving image and an audio signal simultaneously in both loops.

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