JPH10271496A - Processing method for coded and decoded image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize deterioration in image quality in the case that processing such as editing/coding is repeated to a decoded image signal in multi-stages that is obtained by decoding a code string resulting from applying high efficiency coding to an image signal. SOLUTION: In the processing method for a coded.decoded image, when a code string 2 that is obtained by applying high efficiency coding to an image signal is decoded by an image decoding section 3, a coded parameter 6 when a processed decoded image 4 is coded is extracted by a coding parameter extract section 5, a coding parameter recording section 7 records the processing of recording the coded parameter 6 to the decoded image signal 4 and provides an output of a recording processing image signal 8. In the case of coding again the image signal 8, a coded parameter detection section 11 reads the coded parameter 6 from the image signal 8, and a re-coding section 12 encodes the recording-processed image signal 8 while referencing the read coded parameter 6 and provides an output of a code string 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for processing an encoded and decoded image, and more particularly, to a multi-stage process of decoding an encoded image, re-encoding the obtained decoded image, and transmitting and storing the decoded image. The present invention relates to a technique which is effective when applied to a method of processing an encoded / decoded image which can control deterioration of image quality.

[0002]

2. Description of the Related Art It is now assumed that a decoded image obtained by high-efficiency encoding and decoding is re-encoded.

In this case, depending on conditions at the time of re-encoding,
It is not always possible to execute a code string obtained by encoding.
It is necessary to perform processing after obtaining a decoded image of the (Pulse Code Modulation) signal.

[0004] Considering a case where an image obtained by encoding and decoding is subjected to editing processing and then transmitted and stored with high-efficiency encoding again, the encoding / decoding is repeated, that is, a situation where multiple stages are connected. Will occur.

[0005] FIG. 4 is a diagram showing an example of the configuration of a multi-stage connection of encoding and decoding according to a conventional method when editing an encoded and decoded image. The PCM image signal 52 input from the input terminal 51 is subjected to high-efficiency encoding in a first encoding unit 53, and a first code sequence 54 is obtained. After the first code string 54 is transmitted or stored, the first decoding unit 55
And a first decoded image 56 of the PCM signal is obtained. An editing process is performed on the obtained decoded image 56 by an image editing unit 57, and an edited image 58 is obtained. Next, the edited image 58 is input to the second encoding unit 59 and subjected to high-efficiency encoding, so that a second code string 60 is obtained. After being transmitted or stored, the second code string 60 is decoded by the second decoding unit 61, and the second code string 60
Is obtained.

[0006]

In the multi-stage connection of the encoding and decoding described above, generally, as the number of stages to be connected increases, the image quality of the obtained decoded image gradually deteriorates. The degree of image quality degradation differs depending on the connection mode, but if there is a difference in the encoding parameter at the time of encoding at each stage of the connection, the degree of degradation will increase.

In the prior art, only the decoded image obtained as a PCM signal is handled irrespective of the coding parameters when the obtained decoded image is coded. When the image is re-encoded, there is a possibility that a mismatch occurs with the encoding parameter used when the unedited image was obtained.

[0008] For example, MPEG (Motion Picture Ex)
pert Group) coding method (ISO / IEC 11172-2, IS
In O / IEC 13818-2), as shown in FIG. 2, the coding type of each frame is set to an I picture to be coded only within the frame, a P picture to be coded using a temporally past frame, Encoding is divided into three types of B pictures, which are encoded using both temporally past and future frames.

In this case, in the multistage connection of the encoding and decoding, when the picture types are matched, the deterioration of the picture quality of the decoded picture can be minimized. However, when the re-encoding is performed using only the decoded picture which has become the PCM signal. Cannot refer to the picture type of the decoded image at the time of re-encoding. Therefore, since the picture type at the time of re-encoding does not match the picture type at the time of the previous encoding, there is a problem that the degree of image quality deterioration becomes large when encoding and decoding are repeated. there were.

It is an object of the present invention to provide a technique capable of making the encoding parameters coincide when encoding and decoding are connected in multiple stages.

Another object of the present invention is to provide a technique capable of controlling image quality deterioration when coding and decoding are repeated.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0013]

According to the present invention, in order to achieve the above object, a decoded image obtained by decoding a code sequence obtained by performing high-efficiency coding is converted from a code sequence into a decoded image. The extracted encoding parameters used during encoding are recorded by processing the decoded image,
When re-encoding the processed decoded image signal, the recorded encoding parameters can be extracted and encoded while referring to them.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments (examples) of the present invention will be described below in detail with reference to the drawings.

In all the drawings for describing the embodiments (examples), those having the same functions are denoted by the same reference numerals, and their repeated description will be omitted.

FIG. 1 is a block diagram for explaining the principle of an embodiment of the present invention, wherein 1 is an input terminal, 2 is a code string, 3 is an image decoding unit, 4 is a decoded image signal, and 5 is an encoding signal. A parameter extraction unit, 6 is an encoding parameter, 7 is an encoding parameter recording unit, 8 is a recorded image signal, 9 is an output terminal, 10 is an input terminal, 11 is an encoding parameter detection unit, and 12 is re-encoding. , 13 is a code string, and 14 is an output terminal.

As shown in FIG. 1, a code string 2 input from an input terminal 1 is decoded by an image decoding unit 3 and
A decoded image signal 4 of the M signal is obtained. On the other hand, the coding parameter extraction unit 5 extracts the coding parameter 6 used when the code string 2 was obtained from the code string 2.

The encoding parameter recording section 7 records the encoding parameter 6 by processing the decoded image signal 4, and outputs the recorded image signal 8 to an output terminal 9.

When performing re-encoding, the encoding parameter 6 is extracted from the processed image signal 8 input from the input terminal 10 by the encoding parameter detecting unit 11. The processed image signal 8 is encoded by the re-encoding unit 12 with reference to the extracted encoding parameters 6 to obtain a code sequence 13.

According to the method described above, the coding parameter used to obtain the code string is obtained by decoding the code string obtained by encoding the image signal with high efficiency into a PCM signal once. When the image is recorded by being processed and the processed image is re-encoded, it is possible to extract the recorded encoding parameters and perform encoding while referring to the extracted encoding parameters. .

In the embodiment of the present invention, a case is considered in which an image encoded and decoded by the MPEG system is encoded again by the MPEG system. As a condition at the time of re-encoding, it is assumed that a frame of a part of the obtained decoded image sequence is re-encoded.

MPEG (Motion Picture Expert Gr)
oup) In the coding method, the coding type of each frame is defined as an I picture that is coded only within the frame, a P picture that is coded using a temporally past frame, and both temporally past and future frames. Is divided into three types of B-pictures to be encoded. However, it is known that when MPEG encoding / decoding is connected in multiple stages, picture quality degradation can be minimized by matching picture types. ing.

As shown in FIG. 2, if there is a sequence S1 of an image code string, and the picture type structure in the first stage of coding / decoding is a P picture for every two frames and an I picture for every six frames. I do. If it is attempted to re-encode a frame subsequent to this decoded image sequence S1 by a time t1 with the same picture type structure as the sequence S1, the frame that was a B picture in S1 will be It will be encoded as a picture. In this case, the encoding start position is adjusted so that the I-picture is re-encoded as an I-picture, the P-picture is re-encoded as a P-picture, and the B-picture is re-encoded as a B-picture, thereby obtaining an image code sequence S2.

FIG. 3 shows a block configuration of the present embodiment.
The image signal S1 input from the first input terminal 21 is encoded by the first MPEG encoding unit 22, and the obtained first code string 23 is transmitted or stored, and the first MPEG decoding is performed. The first decrypted PCM decoded by the unit 24
S1 ′ is obtained as the image signal 25.

The first MPEG decoding unit 24 decodes the code string, and at the same time, extracts picture type (I picture, P picture, B picture) information for each frame from the decoded image signal 25, Decoded image signal 25
Are stored in a first image signal storage memory 26, and the extracted coding parameters (picture type information) 27 are stored in a first coding parameter storage memory 28.

The decoded image signal 25 stored in the first image signal storage memory 26 and the coding parameter (picture type information) 27 of each frame stored in the first coding parameter storage memory 28 are In the coding parameter recording unit 29, picture type information is recorded in the decoded image signal 25 by processing the decoded image signal 25, and the coding parameter (picture type information) 27 of each frame is recorded and processed. S2 is obtained as (PCM image signal) 30 and output from the first output terminal 31.

Coding parameters (picture type information)
27 is a recorded image signal (PCM image signal) 30
When encoding is performed again, the image signal (PCM image signal) 30 in which the encoding parameter (picture type information) 27 is input from the second input terminal 32 is output from the encoding parameter detecting unit 33. At the same time as the encoding parameter (picture type information) 27 is extracted, the encoding parameter (picture type information) 27 is sent to the second encoding parameter storage memory 34, and the image signal (PCM image signal) that has been recorded is processed. 30 is stored in the second image signal storage memory 35.

The encoding start position adjusting unit 36 reads the encoding parameter (picture type information) 27 of each frame from the encoding parameter storage memory, and determines the closest temporally closest position of the designated re-encoding start frame n1. so,
The re-encoding start frame is adjusted so that the picture types match, and n1 'is obtained as the encoding start frame.

In the second MPEG encoding section 37, the encoding start position adjusting section 36 outputs the encoding start frame n1 '.
And the picture type information 38 of the frame after n1 'is read, and the image signal 39 of the frame after n1' is read.
Is read from the second image signal storage memory 35 and encoded. As a result, the picture types can be matched between the encoding in the first MPEG encoding unit 22 and the encoding in the second MPEG encoding unit 37.

As an example of a method of processing the picture type information into the PCM decoded image signal and recording the same, the encoding parameter recording unit 29 converts each frame of the decoded image signal 25 into a block consisting of 8 pixels in both the horizontal and vertical directions. (8
x8), and each block is two-dimensional DCT
(Discrete Cosine Translation) The 1 × 1 high frequency component (highest frequency component) of the obtained coefficient is converted into a coding parameter (picture type information) 27 (I: 0,
P: 1, B; 2), and by performing an inverse DCT transform on the rewritten 8 × 8 DCT coefficient, an image signal (PCM image signal) in which the picture type information of each frame is recorded and processed. ) 30 can be used.

At this time, the pixel values of the PCM decoded image signal 25 and the recorded image signal (PCM image signal) 30 change, but the deterioration of the image quality due to the change is small. PCM image signal) 30
It can be regarded as the M decoded image signal 25.

The effect of this on the image quality of the PCM decoded image signal obtained after the next stage of encoding and decoding is small.
The recorded image signal (PCM image signal) 30, the PCM decoded image signal obtained by decoding the code sequence obtained by re-encoding the picture in the same manner as the preceding stage with the same picture type as the PCM decoded image signal 25. Is more suppressed in image quality than a PCM decoded image signal obtained by decoding a code string obtained by re-encoding without encoding the picture type of the previous stage and the picture type.

Coding parameters (picture type information)
When the image signal (PCM image signal) 30 on which the image signal 27 is recorded is to be encoded again, the encoding parameter detection unit 33 determines whether each frame of the image signal (PCM image signal) 30
The pixel values of each block consisting of 8 pixels in both the horizontal and vertical directions are read, and the read blocks are subjected to DCT conversion, and (I: 0, P: 1, B; 2) ), And extracts the encoding parameter (picture type information) 27 of each frame. At this time, the pixel value of the image signal (PCM image signal) 30 does not change in the encoding parameter detection unit 33.

In the above embodiment, the case where re-encoding is performed with reference to the picture type of the frame has been described. However, adjustment of the quantization step, the encoding bit rate and the motion vector may be similarly considered. be able to.

In the above embodiment, the case where MPEG is used as the high-efficiency coding method has been described. However, other high-efficiency coding methods can be similarly considered.

As described above, the invention made by the present inventor is:
Although specifically described based on the embodiment (example),
The present invention is not limited to the above-described embodiment (example), and it is needless to say that various changes can be made without departing from the gist of the present invention.

[0037]

As described above, according to the present invention, when decoding a code string obtained by performing high-efficiency coding of an image signal, a coding parameter obtained when the code string is obtained is extracted. The extracted encoding parameters are recorded by processing the decoded image, and when re-encoding the processed decoded image, the recorded encoding parameters are separated, and the separated encoding parameters are separated. Can be referenced. With this, when encoding and decoding are connected in multiple stages,
It is possible to make the encoding parameters coincide, and as a result, it is possible to control image quality degradation when encoding and decoding are repeated.

[Brief description of the drawings]

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

FIG. 2 is a diagram for explaining a processing operation in the present embodiment.

FIG. 3 is a block diagram showing a schematic configuration of an embodiment (example) of the present invention.

FIG. 4 is a diagram illustrating a configuration example of a multi-stage connection of encoding and decoding according to a conventional method.

[Explanation of symbols]

1, 10, 21, 32 ... input terminals, 2, 13, 23, 4
0: code sequence, 3: image decoding unit, 4: decoded image signal, 5:
Encoding parameter extraction unit, 6, 27 ... Encoding parameter, 7: Encoding parameter recording unit, 8: Recorded image signal, 9, 14, 31, 41 ... Output terminal, 11 ... Parameter detection unit, 12 ... Re-encoding unit, 22... First MP
EG encoder, 24... First MPEG decoder, 25.
First decoded PCM image signal, 26 ... first image signal storage memory, 28 ... first encoding parameter storage memory, 2
9: coding parameter recording unit, 30: recorded image signal, 33: coding parameter detection unit, 34: second coding parameter storage memory, 35: second image signal storage memory, 36: coding Start position adjustment unit, 37... Second MPEG encoding unit, 38... Picture type information of frames after n1 ′, 39... Image signals of frames after n1 ′.

Claims (1)

[Claims] 1. A method for decoding a decoded image signal obtained by decoding a code sequence obtained by performing high-efficiency coding of a digital image signal on the basis of a code sequence to obtain the code sequence. The extracted encoded parameters are extracted, and the extracted parameters are processed by processing the decoded image signal to perform recording. When the processed decoded image signal is again encoded with high efficiency, the recorded encoding A method for processing an encoded / decoded image, wherein parameters are extracted and referred to.