JP3045108B2 - Videophone equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video telephone apparatus, and more particularly to a video telephone apparatus for compressing a digital moving image by using a correlation between preceding and following frames.

[0002]

2. Description of the Related Art FIG. 9 is a block diagram showing an example of a conventional video telephone. This conventional videophone device is a videophone device described in Japanese Patent Application Laid-Open No. 8-195947, which includes a camera unit 101, a video circuit unit 102, a video processing unit 103, a video display unit 104, and an NCU unit. 1
05, audio processing unit 106, CPU unit 107, modem unit 108, key / LED 109, remote controller 110
And so on.

[0003] A camera unit 101 captures a user's image in this conventional videophone device and supplies it to a video circuit unit 102 as a video signal. Video circuit section 102
Converts the video signal supplied from the camera unit 101 and the video signal supplied from the external input terminal IN with the remote controller 11
Switching is performed based on the instruction from 0, the synchronization signal, the luminance signal, and the chrominance signal are separated from one of the video signals and supplied to the video processing unit 103. The video circuit unit 102
Sends the video signal (analog signal) supplied from the video processing unit 103 to the image output terminal OUT.

[0004] The video processing unit 103 includes a video circuit unit 10.
2 is converted into a digital signal (hereinafter, referred to as image data), while the image data from the video display unit 104 is converted into an analog video signal and supplied to the video circuit unit 102. . The video processing unit 103 stores the image data supplied from the video circuit unit 102 based on an instruction from the CPU unit 107 and, for example, JPEG (Joint Photographic coding).
It has a memory for storing compressed image data obtained by compression-encoding the above-mentioned image data by an Experts Group algorithm or the like, and a memory for storing expanded image data obtained by decoding and expanding the compressed image data.

[0005] The video display unit 104 converts the image data into a CP.
On the basis of the instruction from the U unit 107, the video processing unit 103
The video processing unit 103 receives the image data and the decompressed image data read from the memory in the video processing unit 103, performs interpolation, thinning-out processing, and the like according to the display, and synthesizes a character according to a command from the CPU unit 107. Output to

[0006] The NCU unit 105 synthesizes a voice input signal from a telephone, an external voice input, and a microphone input signal, and supplies the synthesized signal to the voice processing unit 106. Also, the NCU unit 105
The output audio signal supplied from the audio processing unit 106 is sent to the telephone and the audio output terminal.

[0007] The audio processing unit 106 converts the audio signal (analog signal) from the NCU 105 into a digital signal. Conversely, the digital audio data that has been decoded and decompressed is converted into analog audio data and supplied to the NCU 105. The audio processing unit 106 converts the digital audio data into, for example, CELP (Code-Excited Linear Predictio).
n) Compress or decompress by algorithm or the like.

[0008] A CPU unit 107 controls each unit of the conventional video telephone apparatus. The CPU unit 107 converts the video signal supplied from the camera unit 101 or the external input terminal IN into a digital signal,
Compressed image data stored in a memory in the voice processing unit 106 and compressed image data stored in a memory in the voice processing unit 106, and voice signals from a telephone, an external voice input, and a microphone input are digitized, compressed, and encoded. Is multiplexed with
It is supplied to the modem unit 108. Also, the CPU unit 107
After the video / audio data multiplexed and transmitted from the other party's videophone device is demodulated by the modem unit 108, the video / audio data is separated and processed by the video processing unit 1.
03 and the voice processing unit 106.

The modem unit 108 functions as a modulator that converts the compressed image / audio data multiplexed by the CPU unit 107 into a transmission signal (analog signal) that can be transmitted through a communication line and transmits the signal. Conversely, the transmission signal (analog signal) sent via the communication line is
It has a function as a demodulator (demodulator) for returning to a digital signal readable by the CPU unit 107 again.
The communication line used by the NCU unit 105 can be used on a general subscriber line.

Next, the operation of the transmitting side of the conventional video telephone will be described with reference to the flowchart of FIG. First, the total number of bytes of image data for one screen to be transmitted is transmitted to the receiving side, and a variable x indicating a packet number to be transmitted is set to "0" (step S10). Next, it is determined whether a retransmission request REQ has been received (step S11). This retransmission request REQ indicates a transfer error (C
The occurrence frequency of the RC error is a predetermined value (for example, 1 every 10 seconds).
Only when the number of times is greater than the number of times, a transmission error is transmitted from the receiving-side videophone to the transmitting-side videophone. Then, the retransmission request R
If the EQ has not been received, the process proceeds to step S12, and the image data packet (x) indicated by the variable x is transmitted.

On the other hand, when the retransmission request REQ is received, the process proceeds from step S11 to step S13, where the image data packet corresponding to the retransmission request REQ is transmitted again.

Next, when the processing in step S12 or S13 is completed, the flow advances to step S14 to determine whether or not transmission of all packets has been completed. And
If the transmission of all packets has not been completed yet, the variable x is incremented by “1” (step S1).
5) Return to step S11. Hereinafter, steps S11 to S11
The process of step S15 is repeatedly executed, and image packet data for one screen is transmitted.

In the above-described image data packet transmission process, when transmission of all packets is completed, step S14 is performed.
Then, the process proceeds to step S16, and it is determined whether or not the all-packet completion notification END from the receiving-side videophone device has been received. This all-packet completion notification END indicates the retransmission request RE.
Similarly to Q, only when the frequency of occurrence of transfer errors (CRC errors) exceeds a predetermined value (for example, once every 10 seconds), when the reception of all packets is completed, Is transmitted from to the transmitting-side videophone device.

In step S16, if the all-packet completion notification END has not been received, the retransmission request REQ
Is determined (step S17). Here, it is determined whether or not the retransmission request REQ has been received. If the next image data is transmitted before receiving the all-packet completion notification END, the retransmission request REQ for the previous image data is generated. This is because, at this time, there is a possibility that the receiving videophone device receives the next image data packet before receiving the image data packet.

If the retransmission request REQ has been received, the process proceeds from step S17 to step S18, where the image data packet corresponding to the retransmission request REQ is transmitted again to the videophone device on the receiving side, and then the process returns to step S16.
On the other hand, if the retransmission request REQ has not been received, the process returns from step S17 to step S16 without doing anything. Hereinafter, steps S16 and S17, or steps S16 and S17, until all packet completion notification END is received.
S18 is repeatedly executed.

Upon receiving the all-packet completion notification END from the video telephone on the receiving side, the process returns from step S16 to the first step S10. At this point, transmission of image data for one screen is completed. Hereinafter, step S
Steps S18 to S18 are repeatedly executed to transmit the next image data in packet units.

Next, the operation of the receiving side of the conventional videophone device will be described with reference to the flowchart of FIG. The receiving-side videophone device first receives the total number of bytes transmitted from the transmitting-side videophone device, and sets the variable x to “0” (step S20). Next, the image data packet (x) indicated by the variable x is received (step S2).
1) In order to determine whether or not the received image data packet (x) has been normally received, it is determined whether or not a CRC error has occurred (step S22).

If a CRC error has occurred, a retransmission request REQ is transmitted to the transmitting-side videophone device so as to retransmit the image data packet (x) in which the CRC error has occurred (step S23). Note that this retransmission request REQ is, as described above, a transfer error (C
It is transmitted only when the frequency of occurrence of (RC) exceeds a predetermined value (for example, once every 10 seconds).

When the processing in step S23 is completed,
Proceed to step S24. On the other hand, if no CRC error occurs, the process directly proceeds to step S24 without doing anything.
In step S24, it is determined whether or not reception of all packets has been completed. If the reception of all the packets has not been completed, the variable x is incremented by "1" (step S25), and the process returns to step S21 to receive the next image data packet. Thereafter, the processes of steps S21 to S25 are repeatedly executed until the reception of all the packets is completed, and the image data packet for one screen is received.

In the above-described image data packet receiving process, when the reception of all the packets is completed, an all-packet completion notification END indicating that all the packets have been received is transmitted to the transmitting-side videophone device (step S26). It returns to the first step S20. At this point, the reception of the image data for one screen has been completed. Hereinafter, the processing of steps S20 to S26 is repeatedly executed to receive the next image data in packet units.

[0021]

However, in the above-mentioned conventional video telephone apparatus, image data is efficiently compressed by using the correlation between the preceding and succeeding frames such as the MPEG system. When image data is transmitted, even if all packets of one frame can be received correctly, the frame cannot be decompressed at all, and the effective data amount transferred may be reduced, or noise may be included in the decompressed image data. There is a problem that it is expensive.

The reason is that if a key frame (I or P picture in the MPEG system) required for decompression of the preceding and following frames is lost, a frame (P or B picture in the MPEG system) requiring information of the preceding and following frames is required. )
This is because, even if all of the packets have been received, it is impossible to expand the frame, or even if the frame is expanded, the expanded image data contains an error.

The present invention has been made in view of the above points,
A videophone device that expands an image without error without reducing the amount of transferred effective data even when transmitting compressed image data by a method that efficiently compresses image data by using the correlation with the preceding and following frames. The purpose is to provide.

[0024]

In order to achieve the above object, according to the present invention, an image signal obtained by efficiently compressing an image signal by using a correlation between the preceding and succeeding frames is converted into an audio signal. A transmitting-side telephone device that packetizes and generates the compressed audio data together with the audio data, transmits the generated image data packet, restores the original image signal, and expands the received audio data packet to restore the original image signal. In a video telephone device comprising a receiving telephone device for restoring an audio signal, a transmitting telephone device determines whether or not there is a retransmission request, and when there is a retransmission request, retransmits an image data packet of a designated key frame. Frame retransmission means
And key frame images required to expand the previous and next frames
The retransmission rate of the data packet is determined, and the
If the retransmission rate is higher than the preset value,
Between keyframes that make the frame interval longer than the current value
The reception-side telephone device includes: an error determination unit that determines whether an error has occurred in the received image data packet; and the reception image data packet determined to have an error by the error determination unit includes a key frame. When it is an image data packet, retransmission request means for transmitting a retransmission request designating the image data packet of the key frame to the transmitting telephone device is provided.

According to the present invention, when a received image data packet determined to have an error in the receiving telephone device is a key frame image data packet, a retransmission request specifying the key frame image data packet is made and transmitted. Since the side telephone device retransmits the image data packet of the key frame, it is possible to prevent the loss of the key frame necessary for decompression of the preceding and succeeding frames, and to increase the retransmission rate and increase the image of the key frame. De
As the number of data packets increases, the data transfer volume increases.
May be too long, but increase keyframe interval
So that the increase in data transfer volume can be reduced.
You.

[0026]

[0027]

[0028]

[0029]

Next, the operation of the embodiment of the present invention will be described. FIG. 1 shows a block diagram of a telephone device on a transmitting side and a receiving side according to a first embodiment of the present invention. In the first embodiment of the present invention, image data obtained by efficiently compressing an image signal by using the correlation with the preceding and succeeding frames is generated by packetizing the audio signal together with the audio data obtained by compressing and encoding the audio signal. A television comprising a transmitting telephone device for transmitting and a receiving telephone device for expanding a received image data packet to restore an original image signal and expanding a received audio data packet to restore an original audio signal. In the telephone device, each of the transmitting-side telephone device and the receiving-side telephone device has a configuration as shown in the block diagram of FIG.

The telephone apparatus according to the first embodiment shown in FIG. 1 includes an input device 1 such as a keyboard, a data processing device 2 operated by a program operation, and a storage device 3 for storing information such as images and sounds. An image input device 4 for inputting an image such as a video camera, an audio input device 5 for inputting audio such as a microphone, an image output device 6 such as a display, an audio output device 7 such as a speaker, and a communication device such as a modem. 8 is included.

The data processing device 2 includes an image processing unit 20
Voice processing means 21 and key frame retransmission means 22
, Key frame interval adjusting means 23 and communication processing means 2
4 is provided. The image processing means 20 includes:
The image data from the image input device 4 is compressed using the correlation with the preceding and succeeding frames, and the compressed image data is sent from the communication device 8 to the receiving side through the communication processing unit 24. On the receiving side, the image processing means 20 receives the compressed image data received by the communication device 8 through the communication processing means 24, decompresses the image data, and sends it to the image output device 6 to display the image.

The voice processing means 21 compresses voice data from the voice input device 5 on the transmission side, and
From the communication device 8 to the receiving side. Voice processing means 2
On the receiving side, the receiving side receives the compressed audio data received by the communication device 8 through the communication processing means 24, decompresses it, sends it to the audio output device 7, and reproduces the audio.

The key frame retransmitting means 22 requests the transmitting side to retransmit when the packet of the image data of the key frame necessary for decompression of the preceding and succeeding frames cannot be received due to an error. The key frame retransmitting means 22 retransmits an error packet to the receiving side when the transmitting side receives a retransmission request from the receiving side.

The key frame interval adjusting means 23 adjusts the key frame interval on the transmitting side according to the packet retransmission rate to the receiving side. The communication processing unit 24 packetizes the compressed image data and audio data and controls the communication device 8 to perform transmission and reception.

Next, referring to FIG. 1, FIG. 2 and FIG.
The operation of the first embodiment of the present invention will be described.

FIG. 2 is a flowchart for explaining the operation of the data processor 2 on the transmitting side according to the first embodiment of the present invention.
Here, transmission of one frame of an image will be described.

The image processing means 20 compresses the image data from the image input device 4 by one frame (step A1).
At this time, the image processing means 20 compresses a key frame that becomes a reference frame at the time of expansion of the preceding and succeeding frames at a constant interval. This interval is adjusted by the key frame interval adjusting means 23 in a subsequent step A6.

The communication processing means 24 transmits the total amount of data to be transmitted to the receiving side, and initializes the image data packet number x to be transmitted to 0 (step A2).

The key frame retransmitting means 22 determines whether there is a retransmission request from the receiving side. If there is a retransmission request, the process proceeds to step A4, and if not, the process proceeds to step A7 (step A3).

If there is no retransmission request, the communication processing means 2
4, after transmitting the image data of the image data packet number x (step A7), updates the image data packet number (step A8).

If there is a retransmission request, the key frame retransmitting means 22 retransmits the packet specified by the receiving side (step A4). When the retransmission request rate becomes equal to or more than a certain value (step A5), the key frame interval adjusting unit 23 changes the key frame interval according to the retransmission rate (step A6).

In the following, the communication processing means 24 performs step A3
To A8 are repeated until transmission of all packets is completed (step A9).

After completing the transmission of all the packets, the communication processing means 24 waits for an all-packet reception completion signal from the transmitting side (step A10). While waiting for the all-packet reception completion signal, the communication processing unit 24 transmits a packet specified by the receiving side (Step A12) when there is a retransmission request from the receiving side (Step A11).

FIG. 3 is a flowchart for explaining the operation of the data processing device 2 on the receiving side according to the first embodiment of the present invention.
Here, reception of one frame of an image will be described.

The communication processing means 24 receives the total amount of data sent from the transmitting side and initializes the received image data packet number x to 0 (step B1).

Next, the communication processing means 24 receives the image data packet sent from the transmitting side (step B).
2), determine whether a reception error has occurred (step B)
3). When a reception error occurs or when the frame currently being received is a key frame (step B4), the key frame retransmitting unit 22 sends a request for retransmission of the current packet to the transmitting side (step B5).

Thereafter, the communication processing means 24 repeats steps B2 to B5 while updating the received packet number (step B7) until all the packets have been received (step B6).

When the reception of all the packets is completed, the communication processing means 24 sends an all-packet reception completion signal to the transmitting side (step B8), and the image processing means 20 decompresses one frame of image data (step B9). ) .

According to the first embodiment of the present invention,
Since key frames required for decompressing other frames are always decompressed, even if all the packets of the frame can be received, the key frames that need to be referred to by that frame are not decompressed, and this causes the transfer. There is an effect that when an error occurs, the effective amount of data transfer does not decrease, and no error is included in the decompressed image.

Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 5 is a block diagram showing a telephone device on the transmitting side and the receiving side according to the second embodiment of the present invention. In the figure, the same components as those in FIG.
The description is omitted. In the telephone device according to the second embodiment of the present invention shown in FIG. 5, the data processing device 9 is different from the data processing device 2 in the first embodiment shown in FIG. Except for this point, a difference is that a frame retransmission unit 92 is provided.

The frame retransmitting means 92 sends a retransmission request to the transmitting side when the packet of the image data has an error and cannot be received on the receiving side. The frame retransmitting means 92 retransmits an error packet to the receiving side when the transmitting side receives a retransmission request from the receiving side.

Next, referring to FIG. 5, FIG. 6 and FIG.
The operation of the second embodiment of the present invention will be described. FIG. 6 is a flowchart for explaining the operation of the data processing device 9 on the transmission side according to the second embodiment of this invention. Here, transmission of one frame of an image will be described.

The image processing means 20 compresses the image data from the image input device 4 by one frame (step C1).
At this time, the image processing means 20 compresses the image as a key frame that becomes a reference frame at the time of expansion of the preceding and succeeding frames at a constant interval. This interval is adjusted by the key frame interval adjusting means 23 in the subsequent step C6.

The communication processing means 24 transmits the total amount of data to be transmitted to the receiving side, and initializes the image data packet number x to be transmitted to 0 (step C2). The frame retransmitting means 92 determines whether there is a retransmission request from the receiving side,
If there is a retransmission request, the process proceeds to step C4, and if not, the process proceeds to step C7 (step C3). If there is no retransmission request, the communication processing unit 24 transmits the image data of the image data packet number x (step C
7) Update the image data packet number (Step C)
8).

When there is a retransmission request, the frame retransmitting means 92 retransmits the packet specified by the receiving side (step C4). When the retransmission request rate becomes equal to or more than a certain value (step C5), the key frame interval adjusting means 23 changes the key frame interval according to the retransmission rate (step C5).
6). Hereinafter, the communication processing unit 24 performs steps C3 to C3.
8 until all packets have been transmitted (step C
9).

After completing the transmission of all the packets, the communication processing means 24 waits for an all-packet reception completion signal from the transmitting side (step C10). While waiting for the all-packet reception completion signal, the communication processing unit 24 transmits a packet specified by the receiving side (Step C12) when there is a retransmission request from the receiving side (Step C11).

FIG. 7 is a flowchart for explaining the operation of the data processing device 9 on the receiving side according to the second embodiment of the present invention. Here, reception of one frame of an image will be described. The communication processing unit 24 receives the entire data amount sent from the transmission side, and initializes the received image data packet number x to 0 (step D1).

Next, the communication processing means 24 receives the image data packet transmitted from the transmission side (step D).
2), determine whether a reception error has occurred (step D)
3). When a reception error occurs, or when the error occurrence rate is equal to or more than a certain value (step D4), the frame retransmission unit 92 sends a request for retransmission of the current packet to the transmission side (step D5).

Thereafter, the communication processing means 24 repeats steps D2 to D5 while updating the received packet number (step D7) until the reception of all the packets is completed (step D6).

When the reception of all the packets is completed, the communication processing means 24 sends an all-packet reception completion signal to the transmitting side (step D8), and the image processing means 20 decompresses one frame of image data (step D9). ) .

[0061]

Next, the operation of one example (first example) of the first embodiment of the present invention will be described in detail. In the first embodiment, MPEG (Moving Picture Exper
tsGroup) method.

In the MPEG system, moving picture data is obtained by motion-compensated inter-frame prediction and DCT (discrete cosine transfection).
orm: discrete cosine transform). In order to perform inter-frame prediction, a still image compression algorithm, for example, JPEG (Joint Photographic c)
Although the compression efficiency is superior to that of the oding expert group, the random access in units of frames cannot be performed because information of the frames before and after the expansion of the frames is required. For this reason, a layer composed of a plurality of image frames called a GOP (Group of Picture) is provided,
Random access is performed in OP units.

The GOP includes an intra-coded frame (I picture) which can be decompressed only by that frame, an inter-frame coded frame (P picture) requiring a previous frame for decompression, and a preceding and succeeding frame for decompression. , And three types of frames, ie, frame interpolation coded frames (B pictures). Generally, when compressed to the same amount of code, the B picture has the highest image quality, followed by the P picture and the I picture. However, when the number of B pictures is increased, the random accessibility deteriorates, and in the case of an image having a lot of motion, the compression efficiency decreases. One GO
P has one or more I pictures and zero or more P pictures and B pictures.

FIGS. 4A and 8A show an example of the GOP structure. The arrow indicates the dependency of the frame required at the time of expansion (when expanding the original frame of the arrow, it is necessary to expand the frame preceding the arrow in advance). If the I picture or P picture cannot be expanded due to a reception error, all the remaining frames of the GOP cannot be expanded. In order to avoid such a situation, in the embodiment of the first embodiment, the key frame retransmitting means 22 is provided so that the I picture or the P picture is always retransmitted.

However, even if the retransmission rate of the packet increases, if the retransmission of all the I and P pictures is continued, the amount of data transfer may become too large. In this case, a key frame interval adjusting means 23 is provided to increase the interval between key frames by increasing the composition ratio of the B pictures of the GOP.

When the number of B pictures is increased, there is a risk that the random access property is reduced and the compression efficiency is reduced in the case of a rapidly moving image, as described above. It doesn't matter.

Hereinafter, the operation on the transmitting side of the embodiment of the first embodiment will be described with reference to FIG.

The image processing means 20 compresses the image data from the image input device 4 by one frame (step A1).
At this time, the image processing means 20 compresses the frame with a predetermined GOP, for example, a GOP configuration as shown in FIG. This GOP configuration is such that when the retransmission rate of image data exceeds a certain value, the key frame interval
3 changes.

The communication processing means 24 transmits the total amount of data to be transmitted to the receiving side, and initializes the image data packet number x to be transmitted to 0 (step A2). The key frame retransmitting means 22 determines whether there is a retransmission request from the receiving side, and if there is a retransmission request, proceeds to step A4, and if not, proceeds to step A7 (step A3).

If there is no retransmission request, the communication processing means 2
4, after transmitting the image data of the image data packet number x (step A7), updates the image data packet number (step A8).

When there is a retransmission request, the key frame retransmitting means 22 retransmits the packet specified by the receiving side (step A4). If the retransmission request rate is equal to or more than a certain value (step A5),
The interval between pictures or P pictures is changed according to the retransmission rate (step A6). For example, first, as shown in FIG. 4B, a P picture in a GOP is changed to a B picture. When the retransmission rate further increases, the length of the GOP is changed to increase the interval between I pictures as shown in FIG.

Hereinafter, the communication processing means 24 executes step A3.
To A8 are repeated until transmission of all packets is completed (step A9). After completing the transmission of all the packets, the communication processing unit 24 waits for an all-packet reception completion signal from the transmitting side (step A10). While waiting for the all-packet reception completion signal, the communication processing unit 24 transmits a packet specified by the receiving side (Step A12) when there is a retransmission request from the receiving side (Step A11).

Next, the operation of the receiving side of the first embodiment will be described with reference to FIG. The communication processing unit 24 receives the entire data amount sent from the transmission side and initializes the received image data packet number x to 0 (step B1).

Next, the communication processing means 24 receives the image data packet transmitted from the transmitting side (step B).
2), determine whether a reception error has occurred (step B)
3). When a reception error occurs, the key frame retransmitting means 22 determines whether the currently received frame is an I picture or a P frame.
If it is a picture (step B4), a request for retransmission of the current packet is sent to the transmitting side (step B5), so that all I and P pictures are reliably expanded.

Thereafter, the communication processing means 24 repeats steps B2 to B5 while updating the received packet number (step B7) until all the packets have been received (step B6). When the reception of all the packets is completed, the communication processing means 24 sends an all-packet reception completion signal to the transmitting side (step B8), and the image processing means 20 outputs
Decompress the image data for the frame.

Next, the operation of one example (second example) of the second embodiment of the present invention will be described in detail. Also in the second embodiment, an example in which the MPEG system is used for image compression will be described.

First, the operation on the transmitting side of the second embodiment will be described with reference to FIG. The image processing means 20 compresses the image data from the image input device 4 by one frame (step C).
1). At this time, the image processing means 20 compresses the frame in a predetermined GOP, for example, a GOP configuration as shown in FIG. This GOP configuration is changed by the key frame interval adjusting means 23 in a subsequent step C6 when the retransmission rate of the image data exceeds a certain value.

The communication processing means 24 transmits the total amount of data to be transmitted to the receiving side, and initializes the image data packet number x to be transmitted to 0 (step C2). The frame retransmitting means 92 determines whether there is a retransmission request from the receiving side,
If there is a retransmission request, the process proceeds to step C4, and if not, the process proceeds to step C7 (step C3).

If there is no retransmission request, the communication processing means 2
4, after transmitting the image data of the image data packet number x (step C7), updates the image data packet number (step C8).

When there is a retransmission request, the frame retransmitting means 92 retransmits the packet specified by the receiving side (step C4). When the retransmission request rate becomes equal to or more than a certain value (step C5), the key frame interval adjusting means 23 changes the key frame interval according to the retransmission rate (step C5).
6). For example, first, as shown in FIG.
Change the picture to an I picture. If the retransmission rate further increases, the ratio of I pictures in the GOP is
The picture is increased as shown in (C), and finally all pictures in the GOP are made I pictures (or the length of the GOP is shortened) as shown in FIG. As a result, even if a picture cannot be expanded due to an error, it is possible to reduce the possibility that expansion of the next frame becomes impossible.

Hereinafter, the communication processing means 24 executes step C3.
To C8 are repeated until transmission of all packets is completed (step C9). After completing the transmission of all packets, the communication processing unit 24 waits for an all-packet reception completion signal from the transmission side (step C10). While waiting for the all-packet reception completion signal, the communication processing unit 24 transmits a packet specified by the receiving side (Step C12) when there is a retransmission request from the receiving side (Step C11).

In the second embodiment, the compression ratio (image quality or data amount) is inferior to that of the first embodiment because the composition ratio of I-pictures is high. However, image data is recorded and reproduced later. This is advantageous in the case of random accessibility in the case of transmitting the image or in the case of transmitting an image with a lot of movement.

[0083]

As described above, according to the present invention,
When the received image data packet determined to have an error in the receiving side telephone device is a key frame image data packet, a retransmission request specifying the image data packet of the key frame is made, and the key frame is transmitted from the transmitting side telephone device. The retransmission of the image data packet prevents the loss of key frames required for decompression of the preceding and succeeding frames. Therefore, for example, the image data is reconstructed by using the correlation with the preceding and succeeding frames such as the MPEG method. When image data compressed by a method of efficiently compressing is transmitted, it is possible to prevent an error from being included in a decompressed image due to a missing key frame without reducing the amount of transferred effective data.

According to the present invention, when the retransmission rate increases and the number of key frame image data packets increases, the data transfer amount may become too large, but the key frame interval is increased. Therefore, an increase in the data transfer amount can be reduced.

[0085]

[Brief description of the drawings]

FIG. 1 is a diagram showing a first example of each of a telephone device on a transmitting side and a telephone device on a receiving side according to the present invention.
It is a block diagram showing an embodiment.

FIG. 2 is a flowchart for explaining an operation on a transmission side according to the first embodiment of the present invention.

FIG. 3 is a flowchart for explaining the operation of the receiving side according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram for explaining an operation of the key frame interval adjusting means 23 according to an example of the first embodiment of the present invention.

FIG. 5 is a diagram showing a second example of each of the telephone devices on the transmitting side and the receiving side according to the present invention.
It is a block diagram showing an embodiment.

FIG. 6 is a flowchart for explaining an operation on the transmission side according to the second embodiment of this invention.

FIG. 7 is a flowchart illustrating an operation of a receiving side according to the second embodiment of this invention.

FIG. 8 is an explanatory diagram for explaining the operation of a key frame interval adjusting means 23 according to an example of the second embodiment of the present invention.

FIG. 9 is a block diagram of an example of the related art.

FIG. 10 is a flowchart for explaining the operation of a conventional transmitting-side telephone device.

FIG. 11 is a flowchart for explaining the operation of the conventional receiving-side telephone device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 input device 2 data processing device 3 storage device 4 image input device 5 audio input device 6 image output device 7 audio output device 8 communication device 9 data processing device 20 image processing means 21 audio processing means 22 keyframe retransmission means 23 keyframe interval Adjustment means 24 communication processing means 92 frame retransmission means

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N ⁷ /14-7/173 H04N 7/24-7/68 H04L 1/16 H04M 11/06

Claims (1)

(57) [Claims] 1. A transmitting telephone for generating and transmitting image data obtained by efficiently compressing an image signal by using a correlation with a preceding and succeeding frame together with audio data obtained by compressing and encoding an audio signal. A video telephone device comprising: a device and a receiving telephone device that expands a received image data packet to restore an original image signal and expands a received audio data packet to restore the original audio signal. The transmitting side telephone device determines whether or not there is a retransmission request, and when there is a retransmission request, retransmits the image data packet of the designated key frame, and the key frame required for decompressing the preceding and following frames. Image of
The retransmission rate of the data packet is determined, and the image data packet
If the packet retransmission rate is higher than the preset value,
Keyframe to increase the interval between keyframes longer than the current value
An error determining unit that determines whether an error has occurred in a received image data packet; and a receiving image data packet that is determined to have an error by the error determining unit. A video telephone device comprising: a retransmission request unit that transmits the retransmission request specifying the image data packet of the key frame to the transmitting telephone device when the image data packet is the key frame image data packet.