JPH07143480A - Picture transmitter-receiver and picture transmission reception system - Google Patents

Abstract

PURPOSE:To realize in which error recovery at video decoding is attained through simple processing with excellent quality when a transmission error such as loss of a cell or the like takes place with respect to the picture transmitter-receiver using an ATM network to attain video conference or video image distribution or the like. CONSTITUTION:A picture is coded by dividing the picture in the unit of blocks having a layer structure and a coded bit stream 5 with a header added in each unit thereto is outputted. The header is detected from the coded bit stream 5 to generate a flag representing a transmission content and a 1st flag indicating the transmission content of a current packet and a 2nd flag representing the transmission content of a packet sent just before are added in a transmission packet 9 and the resulting packet is sent to an ATM network 15. When an error takes place in the transmission packet received from the ATM network 15, a type of a coded bit stream causing the transmission error is informed to a picture decoding section 14 with the 1st flag or the 2nd flag reached next to attain recovery depending on a noticed error type.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a TV using an ATM network.
The present invention relates to an image transmission / reception device and an image transmission / reception system capable of transmitting a video signal with good quality and with a simple structure even when a transmission error such as a cell loss occurs in a device capable of a conference or video distribution.

[0002]

2. Description of the Related Art When a video signal is transmitted using an ATM network, cell loss may occur and data may be lost. Therefore, an error recovery method such as cell interleaving is used. In addition, the bit (bi
t) There is a method in which a stream is transmitted and a decoder processes the identification of the missing portion in the encoded bit stream without using the information indicating the error generated in the transmission path.

[0003]

In the method of recovering an error by using cell interleaving or the like, error data can be recovered, but it is necessary to buffer encoded data for interleaving, so that an irregular interval is required. When applied to an image coding device that generates indefinite amount of coded data, there is a problem that the delay time cannot be guaranteed in the face-to-face type video transmission that emphasizes the real-time property.

Further, in the case of transmitting a bit stream without cell interleaving, if a decoder alone is used to identify a missing portion in a coded bit stream without using information indicating an error generated in a transmission path. However, there is a problem that the processing time for that becomes long.

The present invention has been made in order to solve the above-mentioned problems. Even when a transmission error such as a cell loss occurs in an ATM network, the error recovery operation at the time of video decoding can be performed by a simple process. The purpose is to realize a device that enables it.

[0006]

In order to solve the above-mentioned problems, an image transmitting apparatus of the present invention divides an image into blocks having a hierarchical structure and encodes them, and a header that becomes a delimiter for each hierarchy and each block is provided. An image coding unit that outputs the added coded bit stream, a header is detected from the coded bit stream output from the image coding unit to generate a flag indicating the content of transmission information, and a code for each block Packet bit stream and a first flag indicating the transmission content of the current packet and a second flag indicating the transmission content of the packet transmitted immediately before, and a transmission packet generation unit that configures the transmission packet, and transmits the transmission packet to the ATM network. And an ATM network interface section.

Further, the image receiving device receives a transmission packet from the ATM network, and when an error occurs in the transmission packet, an ATM network interface section capable of clearly detecting the error and valid information of the transmission packet, and a transmission error. If the first flag indicating the content of the current transmission packet is valid information, the type of the encoded bitstream in which the transmission error has occurred is notified to the image decoding unit by the first flag, and If the first flag is invalid, the arrival of the next packet is waited for, and the second flag indicating the content of the previous packet described in the next arriving transmission packet causes the transmission error to occur in the encoded bitstream. A reception packet processing unit that notifies the image decoding unit of the type and a reception packet processing unit that decodes the encoded bit stream transmitted from the image transmission device. Characterized in that it comprises an image decoding unit can perform a recovery operation in response to the error type notified from the processing unit.

[0008]

According to the present invention, the means for displaying the output timing of the header which is added to the encoded bit stream and is output to the image encoding unit facilitates the generation of the flag indicating the type of transmission information. Furthermore, by setting the transmission packet unit to the image block unit, the range in which the cell loss is affected even when the cell is lost in the transmission path is limited.

Further, in order to enable the recovery operation by a simple process by notifying the image decoding unit of the type of information of the part which is missing in the transmission path, the transmission packet generation unit stores the contents of the current transmission packet. If the first flag shown and the second flag showing the content of the packet transmitted immediately before are written and transmitted together with the data entity, and an error occurs in the reception packet processing unit, the first flag showing the content of the current transmission packet , Or waiting for the arrival of the packet immediately after, and looking at the second flag indicating the content of the previous packet, the type of lost information is identified, and the image decoding unit receives an error-free coded bit stream or lost data. By transmitting only the identification code that indicates the type of information, it is possible to recover from an error with a simple configuration.

[0010]

1 is a block diagram of an embodiment of the present invention.
In the figure, 1 is an image transmitting device, 11 is an image receiving device, and 15 is an ATM network.

In the image transmitting apparatus 1, the reference numeral 2 divides an image to be transmitted into blocks having a hierarchical structure and encodes the same, and outputs an encoded bit stream 5 to which a header as a delimiter is added for each layer and block. , An image coding unit having means for transmitting the timing of outputting the header to the transmission packet generation unit 3, and 3 detects the header from the coded bit stream 5 output from the image coding unit 2 and transmits the transmission information. Of the encoded bit stream 5 for each block, the first flag 10 indicating the transmission content of the current packet, and the second flag 1 indicating the type of the transmission content of the packet transmitted immediately before.
A transmission packet generation unit that forms a transmission packet 9 with 0 ',
Reference numeral 4 represents an ATM network interface unit for transmitting the transmission packet 9 to the ATM network 15.

Further, 5 is a coded bit stream, and 6 is a video (Vi) showing a delimiter of layered coded data.
deo) header, 7 represents layered encoded data, and 8 represents a header timing signal indicating the output timing of the video header 6 from the image encoding unit 2 to the transmission packet generation unit 3. Reference numeral 9 is a transmission packet transmitted over the ATM network 15, 10 is a first flag indicating the type of the encoded bitstream 5 transmitted in the current packet, and 10 'is the encoded bitstream transmitted in the immediately preceding packet. 5 represents a second flag indicating the type.

In the image receiving device 11, 4'is an ATM
When a transmission packet is received from the network 15 and an error occurs in the transmission packet, an ATM network interface unit capable of detecting an error and clearly indicating valid information of the transmission packet, and 12 when the transmission error occurs If the first flag 10 indicating the content is valid information, the type of the encoded bitstream 5 in which a transmission error has occurred is notified to the image decoding unit 14 according to the type of the first flag 10, and the first
If the flag 10 is invalid, the arrival of the next packet is waited for, and the second bit 10 'indicating the contents of the previous packet described in the next transmission packet 9 causes the transmission error to occur in the encoded bit. A reception packet processing unit for notifying the contents of the stream 5 to the image decoding unit 14, 13 is an error identification signal indicating the type of lost information, and 14 is for decoding the encoded bit stream 5 generated by the image encoding unit 2. When the received packet processing unit 12 notifies the type of the transmission error, the image decoding unit performs a recovery operation according to the error type.

FIG. 2 shows an example of a hierarchical structure of encoded data when an image is encoded, the encoded bit stream 5 is hierarchized and a header is added. In the figure, 21 is a video sequence / GOP header (Video Sequence) indicating information necessary for decoding and a group of a plurality of screens.
/ GOP Header), 22 is a GOP (Group of Pic) which is the substance of encoded data of a plurality of screens.
, 23 is a picture header (Picture Header) indicating the division of one screen, and 24 is 1
Picture (Pi) which is the substance of the encoded data of one screen
, 25 is a slice header (Slice Header) that indicates a delimiter of a slice (Slice) which is a unit of an image block in one screen, and 26 is a slice (Slic) which is the entity of encoded data in the slice unit.
e) Represents unit encoded data.

The operation of the image transmitting / receiving apparatus according to the embodiment of the present invention will be described below with reference to FIGS. When the coded bitstream 5 of an image is transmitted from the image transmission device 1 to the image reception device 11 via the ATM network 15, the coded bitstream 5 is output from the image coding unit 2 in accordance with the hierarchical structure shown in FIG. To be done. Coded bitstream 5
Indicates various headers 21, 23, 25 and slice-unit coded data 2 indicating the delimiters of each layer as shown in FIG.
When the video header 6 is output, a header timing signal 8 indicating the output timing of the video header 6 is transmitted to the transmission packet generation unit 3.

The transmission packet generation unit 3 detects the contents of the video header 6 in synchronization with the header timing signal 8 and generates a flag indicating the contents of the transmission information, and at the same time the coded bit stream 5 for each block and the current packet. The transmission packet 9 is composed of the first flag 10 indicating the transmission content of the above and the second flag 10 ′ indicating the type of the transmission content of the packet transmitted immediately before.

In the case of this embodiment, the contents of the transmission packet 9 may be various video headers, slice headers and encoded data entities. Specifically, for example, the type of the transmission packet 9 includes a packet of a video sequence header,
There are GOP header packets, picture header packets, and packet types consisting of slice headers and slice-unit encoded data. The first flag 10 is composed of a bit string, an identification number, or the like indicating which one of these is the encoded bitstream 5 in the current transmission packet 9. Similarly, the second flag 10 'also indicates which of the above-mentioned packets the packet transmitted immediately before. Of course, the configuration of the bitstream included in one transmission packet may be other than the above, and in that case, the first flag can be identified so that it can be identified according to the type of each content. 1
The configurations of 0 and the second flag 10 'may be determined.

At the time of transmitting the transmission packet header, the ATM network interface unit 4'of the image receiving apparatus 11 receives the transmission packet 9 from the network, and if there is no error, the reception packet processing unit 12 is the transmission packet header. The encoded bit stream 5 is transmitted to the image decoding unit 14 by removing the flag 10 of 1 and the second flag 10 ′. ATM network 1
When an error such as a cell loss occurs at 5, the ATM network interface unit 4'of the image receiving apparatus 11 notifies the received packet processing unit 12 of the occurrence of the error. Received packet processing unit 1
2 indicates that when a transmission error occurs, when the first flag 10 indicating the content of the current transmission packet 9 is valid information, the type of the encoded bitstream in which the transmission error has occurred is image-decoded according to the type of the flag. When the first flag 10 is invalid, the second packet 10 is notified, the second packet 10 waits for the arrival of the next packet, and the second flag 10 indicating the content of the previous packet described in the next arriving transmission packet 9 '. The image decoding unit 14 is notified of the type of the coded bitstream 5 in which a transmission error has occurred due to ".

The image decoding unit 14 receives the error identification signal 13
In addition to recognizing the lost information, the recovery operation such as freezing of the decoding operation and replacement of an erroneous image block is controlled by the type of the lost information, the encoding method of the screen including the lost information, and the like.

When replacing the lost image, the image decoding unit 14 determines the position of the lost image block by referring to the blocks before and after the decoding process. When the image is encoded with the hierarchical structure shown in FIG. 2, the replacement unit is the slice unit 26.

When an encoding method combining interframe encoding and intraframe encoding is used as the encoding method, the lost image block is interframe encoded or intraframe encoded. It is determined from the picture header 23 whether it is a real one. When the lost image is inter-frame coded, it is replaced with the intra-frame coded image used for the prediction of the current frame, and when it is intra-frame coded. In the case of the hierarchical structure shown, the last GOP 22 is replaced with the image used as the reference image for the last inter-frame coding.

In the example of the encoded data shown in FIG. 2, when the picture header 23 is lost, the lost header can be estimated from the picture headers 23 of the preceding and following frames by the encoding algorithm. On the other hand, when the video sequence / GOP header 21 is lost, the information necessary for decoding is described in this header, so that the screen is frozen up to the next video sequence / GOP header 21.

Further, in the image transmitting / receiving apparatus according to the present invention, the image receiving apparatus 11 notifies the image transmitting apparatus 1 of the probability of occurrence of the transmission error counted by the reception packet processing unit 12, and the image transmitting apparatus 1 causes the probability of occurrence of the transmission error. It is also possible to easily control the block size and the transmission packet size, which are coding units, according to

[0024]

As described above, according to the present invention,
Even if a transmission error occurs on the line, the decoder can receive only a coded bitstream that is guaranteed to be error-free or a specific identification code that indicates the type of information that is missing. There is an effect that the time recovery operation can be easily realized.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a hierarchical structure of encoded data according to an embodiment of the present invention.

[Explanation of symbols]

1 image transmission device 2 image encoding unit 3 transmission packet generation unit 4 ATM network interface unit 5 encoded bit stream 6 video header 7 encoded data 8 header timing signal indicating output timing of video header 9 transmission packet 10 current transmission packet First flag 10 'indicating the content Second flag indicating the content of the packet transmitted immediately before 11 Image receiving apparatus 4'ATM network interface section 12 Received packet processing section 13 Error identification signal indicating the type of lost information 14 Image decoding unit 15 ATM network

Claims (3)

[Claims] 1. An image encoding unit that divides an image into blocks having a hierarchical structure and encodes them, and outputs an encoded bit stream to which a header that serves as a delimiter is added for each layer and block, and the image encoding unit. The header is detected from the encoded bit stream output from the unit to generate a flag indicating the content of the transmission information, and the first bit indicating the transmission content of the encoded bit stream for each block and the current packet and immediately before An image transmitting apparatus comprising: a transmission packet generation unit that configures a transmission packet with a second flag that indicates the transmission content of the transmitted packet; and an ATM network interface unit that transmits the transmission packet to an ATM network. 2. An ATM network interface unit which receives a transmission packet from an ATM network and can detect error and clearly indicate valid information of the transmission packet when an error occurs in the transmission packet; When a transmission packet including a first flag indicating the transmission content of the packet and a second flag indicating the transmission content of the packet transmitted immediately before is received and a transmission error occurs, when the first flag is valid information Notifies the image decoding unit, which will be described later, of the type of the coded bitstream in which a transmission error has occurred by the first flag, waits for the arrival of the next packet if the first flag is invalid, and then The type of the encoded bitstream in which a transmission error has occurred is indicated by the second flag indicating the content of the preceding packet described in the incoming transmission packet. Of the received packet processing unit for notifying the image decoding unit, and decoding the encoded bit stream in the received transmission packet, and when a transmission error occurs, the error type notified by the reception packet processing unit An image receiving apparatus, comprising: an image decoding unit that performs a corresponding recovery operation. 3. An image transmission / reception system comprising the image transmission device according to claim 1 and the image reception device according to claim 2.