JP3408104B2 - Encoding device and decoding device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coding apparatus for coding information such as an image and transmitting it to another apparatus via a communication line, and decoding the transmitted coded data to restore the original information. The present invention also relates to a decoding device, and more particularly, to a coding device and a decoding device that communicate encoded data in an environment with a high transmission error rate such as a wireless communication network.

[0002]

2. Description of the Related Art In recent years, PHS (Personal Ha)
An image communication service using a wireless communication network such as an ndyphone system) or a digital cellular system is expected, and is being put into practical use.

At present, these wireless communication networks do not have a large transmission capacity. Therefore, when transmitting multimedia information having a large amount of information such as voice and image, the amount of data to be transmitted is reduced by encoding.

By the way, one of the problems in wireless communication is that the transmission error rate is high. Since the data encoded as described above has various redundancies reduced from the original information, the amount of information per bit is larger than that of the data before encoding, and a small amount of error that occurred during transmission is restored. It can have a significant impact on later quality. Therefore, in image communication using these wireless communication networks, it is very important to take measures to prevent the deterioration of information quality due to this transmission error.

FIG. 4 shows the configuration of an encoding system including an encoder and a decoder used in conventional image communication. The input image signal 41 is encoded by the information source encoding unit 42 to reduce the data amount. Encoded image data 4
3 is sent to the transmission control unit 44, and is sequentially transmitted as encoded data 45 according to the transmission speed of the communication line. On the other hand, the encoded data 45 received from the communication line is the reception control unit 4
6 and the encoded signal 47 from the reception control unit 46.
Are sequentially sent to the information source decoding unit 48 for each unit encoded as. Then, it is decoded by the information source decoding unit 48,
It is output as an image signal 49.

The operation of the encoder (referred to as an encoding device in the following description) in FIG. 4 will be described below with reference to FIGS. 4 and 5. FIG. 5 shows a configuration example of the information source coding unit of FIG. As shown in FIG. 5, the input image signal 41 is sent to the conversion / quantization unit 51 as it is or the difference from the encoded reproduction signal of the previous frame. conversion/
The quantizing unit 51 removes the spatial redundancy of the image signal, and transmits the coded signal 43 to an external buffer or the like and also to the dequantizing / inverse transforming unit 52.

In the inverse quantizing / inverse transforming section 52,
Processing reverse to that of the quantizer 51 is performed to generate a decoded difference signal 53. The decoded difference signal 53 is added to the restoration signal 55 of the previous frame accumulated in the frame memory 54,
It is newly stored in the frame memory 54. The restored image signal 55 stored in the frame memory 54 is used to reduce the temporal redundancy by taking the difference from the input image signal 41 of the next frame.

Further, as shown in FIG. 4, the coded signal 43 from the information source coding unit 42 is sent to the transmission control unit 44. The transmission control unit 44 adds header information indicating an encoding condition and the like to the encoded signal, performs buffering in accordance with the transmission speed of the communication line, and sequentially transmits.

Next, the operation of the decoder (referred to as a decoding device in the following description) in FIG. 4 will be described with reference to FIGS.
Will be described with reference to. As shown in FIG. 4, the received encoded data string is divided into header information and image information by the reception control unit 46, and the image information is sent to the information source decoding unit 48.

FIG. 6 shows a configuration example of the information source decoding unit 48. The coded signal 47 of the received image information is decoded by the inverse quantization / inverse conversion unit 61. The decoded differential signal 62 generated here is added to the restoration signal 64 of the previous frame accumulated in the frame memory 63, is newly stored in the frame memory, and is transmitted to the outside. This output signal 49 is the restored image signal.

As described above, the image signal is coded and transmitted in order to reduce the amount of transmission data, but is usually variable length coded in order to further improve the coding efficiency. When variable length coding is performed, the amount of coded data differs for each frame of an image and is not constant.

Therefore, in order to determine the start position of the image frame on the decoding device side, the encoding device inserts a synchronization word into the encoded data string. This sync word is
A unique code, which is a fixed pattern and does not match other image information codes, is assigned so that there is no detection error. The presence of this synchronization word enables the decoding device to determine the boundary of the image information from the coded data string that is continuously received, and can correctly restore the image signal.

By the way, when encoding an image signal,
In order to reduce the delay of the encoding process, the image signal is divided into blocks and processed. The division unit of the block is shown in FIG. One frame of an image is divided into several GOBs (groups of blocks). The GOB is further divided into some 16-pixel × 16-line macroblocks. The macro block is divided into four luminance signal blocks and two color difference signal blocks. Each block has a size of 8 pixels × 8 lines. A set of macroblocks for one column in the horizontal direction may be referred to as a macroblock line. In the case of FIG. 7, 1
GOB corresponds to one macroblock line.

These encoded data are sequentially transmitted from the upper left to the lower right of the image frame in GOB units, in GOBs in macroblock units, and in macroblocks in block units. At this time, a synchronization word is inserted at the beginning of the frame and at the beginning of each GOB so that the decoding device can specify the positions of the frame and the GOB. The macroblock and the block are identified by the header of the macroblock following the GOB header and the data in the block.

Since the synchronization word is set in this way, if the pattern is searched on the decoding device side,
Even if there is an error in the encoded data on the way, synchronization can always be taken at the beginning of the GOB, so that the influence of the error can be prevented from spreading later.

[0016]

However, on the decoding device side, it is necessary to constantly search for a synchronization word in order to ensure synchronization, which increases the processing overhead. Further, due to a transmission error or the like, there is a possibility that the same pattern may happen to appear even though it is not the beginning of the frame or GOB, or an error may occur in the synchronization word itself and be recognized as another code. In such a case, the subsequent decoding of the code is affected, resulting in a great deterioration of the restored image.

The present invention has been made in view of the above problems, and provides an encoding device and a decoding device that solve the above problems.

[0018]

The invention according to claim 1 of the present application is as follows.
Encoding means for coding the image information in the encoded data from said encoding means, in the coding apparatus and a synchronous word inserting means for inserting a synchronization word indicating the boundary of the image information, the code The synchronization word insertion unit inserts the synchronization word at a boundary position of a macro block in the encoded data, the determination unit determining the data length represented by the number of bits of the encoded data. , The boundary position of the macroblock into which the synchronization word is inserted is set to a position before the data length determined by the determining means.

[0019]

[0020]

According to the second aspect of the present invention, the receiving means for receiving the encoded data including the synchronization word indicating the boundary of the image information and the data length represented by the number of bits of the encoded data are set.
In a decoding device comprising a determining means for determining and a decoding means for decoding the encoded data to restore the original image information, the decoding means is determined by the determining means.
Whether there is a sync word at a position before the specified data length.
If there is no sync word, the data length
The feature is that the preceding and following macroblocks are not decoded .

[0022]

[0023]

[0024]

In the above encoding device, the synchronization word insertion interval selection unit determines an appropriate data length interval of the synchronization word from the transmission speed of the communication line and the condition of the input image signal, and notifies the synchronization word insertion unit. The synchronization word insertion unit counts the data length of the encoded data and inserts the synchronization word according to the data length N notified from the synchronization word insertion interval selection unit. At this time, the data length N is a tentative guide, and the position where the sync word is actually inserted is set to the head of the macroblock. Whether the position of inserting the synchronization word is after or before the data length N is determined in advance, or a condition is determined such that it is determined closer to the data length N. The synchronization word insertion interval determination unit,
The data length interval of the sync word is determined by the same algorithm as that of the sync word insertion interval selection unit and is notified to the sync word detection unit.

Further, the synchronization word detecting unit in the decoding device counts the data length of the encoded data and detects the synchronization word in accordance with the data length N notified from the synchronization word insertion interval determining unit.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. In the following description, the same parts as those in the above-mentioned conventional example will be described with the same reference numerals. Further, in the following description, the encoding device and the decoding device are not limited to those that exist independently, but also include an encoder and a decoder provided in one image encoding system.

FIG. 1 is a block diagram showing the configuration of an encoding device according to the present invention. 10 marks Goka control unit, 11 a synchronization word inserted interval selector, 12 is a synchronization word inserted portion, 4
Reference numeral 2 is an information source encoding unit, and 44 is a transmission control unit.

In the above encoding device, at the start of transmission of encoded data, the synchronization word insertion interval selector 11 determines the approximate size of one macroblock line based on the format and frame rate of the input image signal and the transmission speed of the communication line. The data length N is determined and notified to the synchronization word insertion unit 12.

At this time, the data length N to be determined may be previously statistically determined and stored in a table, or may be calculated when the encoding condition is determined. The conditions necessary for the calculation are also transmitted to the decoding device side at the start of communication.

The synchronization word insertion unit 12 that has been notified of the data length N starts counting the data length from the beginning of each synchronization word, and it is located at the beginning position of the nearest macroblock before and after the position where the data length N has passed. Insert a sync word.

Here, the position where the sync word is inserted is at the beginning of the macro block that appears first after the data length N has passed from each sync word, or the macro that appears last within the range of the data length N from each sync word. Decide on either of the beginning of the block.

FIG. 2 shows a block diagram of a decoding device according to the present invention. 20 decoding control unit, 21 a synchronous word detecting section, 22 synchronization word insertion interval determining unit, 46 a reception control unit, 4 8 are information source decoding unit. In this decoding device, the synchronization word insertion interval determination unit 22 determines the data length N of the approximate length of one macroblock line from the transmission speed of the communication line and the received encoded data, and sends it to the synchronization word detection unit 21. Notice. Data length N determined at this time
May be stored in a table, which is statistically obtained in advance, or may be calculated from the encoding condition notified from the encoding device of the communication destination. Also, the synchronization word insertion interval selection unit 1 on the encoding device side
The same algorithm as 1 is adopted.

The sync word detecting unit 21 notified of the data length N starts counting the data length from the beginning of each sync word, and when the data length N has elapsed, searches for the sync word in the forward or reverse direction. To start. Whether to start the search in the forward direction or the reverse direction may be determined in advance in accordance with the operation of the encoding device, or the search may be performed in both directions and the synchronization which appears at a position closer to the position of the data length N may be determined. It is also possible to adopt words.

In this decoding device, if the synchronization word cannot be detected at the above position, it is considered that a transmission error has occurred. At this time, the decoding device is expected to appear. By not using the preceding and following macroblocks for decoding, it is possible to reduce the influence of the transmission error on the restored image.

FIG. 3 shows an example of a coded data string by the above coding device. The PSC 31 is a picture start code indicating the beginning of the frame. SYNC32 is
In sync words, the distance between sync words is N ± α (α = 1
The data length is within the macro block).

[0037]

As described above, according to the encoding device and the decoding device of the present invention, the synchronization words are inserted into the encoded data at semi-fixed intervals, and at the beginning of the macro block. , It is possible to easily identify the position of the synchronization word on the decoding device side without changing the conventional processing procedure for each block, and it is possible to reduce erroneous detection of the synchronization word due to a transmission error. It is possible to reduce deterioration of a restored image due to an error.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a configuration of an encoding device according to the present invention.

FIG. 2 is a block diagram showing an embodiment of a configuration of a decoding device according to the present invention.

FIG. 3 is a conceptual diagram for explaining a configuration of an encoded data string by the encoding device and the decoding device of the present invention.

FIG. 4 is a block diagram showing a configuration of a conventional encoding device and decoding device.

FIG. 5 is a block diagram showing a configuration of an information source encoding unit in the encoding device.

FIG. 6 is a block diagram showing a configuration of an information source decoding unit in the decoding device.

FIG. 7 is a conceptual diagram for explaining a configuration of a coding block of an image signal.

[Explanation of symbols]

11 Sync Word Insertion Interval Selector 12 Sync word insertion part 21 Sync word detector 22 Sync word insertion interval determination unit 32 sync words

Continuation of front page (56) Reference JP-A-8-331559 (JP, A) JP-A-7-111651 (JP, A) JP-A-8-214301 (JP, A) JP-A-8-265750 (JP , A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04N ⁷ /24-7/68 H04L 1/00 H04L 1/08-1/24

Claims (2)

(57) [Claims] 1. Encoding comprising: an encoding means for encoding image information; and a synchronization word inserting means for inserting a synchronization word indicating a boundary of image information into encoded data from the encoding means. In the device, comprising a determining means for determining a data length represented by the number of bits of the encoded data , the synchronization word insertion means inserts the synchronization word at the boundary position of the macroblock in the encoded data, An encoding apparatus, wherein a boundary position of the macro block into which the synchronization word is inserted is set to a position before the data length determined by the determining means. 2. A receiving means for receiving encoded data including a sync word indicating a boundary of image information, and a data length represented by the number of bits of the encoded data are determined.
Determining means for, in the decoding apparatus and a decoding means for restoring the original image data by decoding said encoded data, said decoding means, determined by the determination means Day
Search whether there is a sync word at a position before the
If there is no synchronization word, the mark before and after the data length is
A decoding device characterized by not decoding a black block .