JPH06276511A - Picture signal coding method and decoding method - Google Patents

Abstract

PURPOSE:To send a CBP value efficiently by providing a CBP VLC table for a luminance signal block and for a color difference signal block so as to encode the CBP in a block in the macro block. CONSTITUTION:An inputted picture signal is inputted to a field memory group 11 and a macro block signal MB being an object of coding is fed to a hybrid coder 12. A motion compensation prediction error signal S2 of an MB layer outputted from the coder 12 is subjected to variable length coding at a VLC device 13. In this case, a CBP code representing whether or not a block in the MB has a non-null DCT to be sent is added to a header of the MB layer and the resulting data are sent. The CBP is generated by a CBP generator 16 based on the signal S2 and obtained as the CBP for a luminance signal block and a CBP for a color difference signal block. Then the VLC device 13 applies coding to the CBP of the luminance and color difference signal blocks by referencing the VLC table. Thus, the CBP is sent efficiently.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a moving picture coding and decoding apparatus.

[0002]

2. Description of the Related Art When a moving image is digitized and recorded and transmitted, the amount of data is enormous, so that data is encoded (compressed). As a typical encoding method, there is MPEG (Moving Picture Expert Group) 1. MPEG1 is ISO (International Organization for Standardization) and IE
C (International Electrotechnical Commission) JTC (Joint TechnicalCom)
mittee) 1 SC (Sub Committee) 29 WG (Worki
ng Group) 11 is a common name for a moving image coding system that has been advanced. MPEG1 employs a hybrid method in which motion compensation predictive coding and DCT (Discrete Cosine Transform) coding are combined.

The motion compensation predictive coding is a method utilizing the correlation of the image signal in the time axis direction, predicts a currently input image from an image signal which has already been decoded and reproduced, and is decoded and reproduced. This is a method of compressing the amount of information required for encoding by moving a known image signal according to the motion of the signal and transmitting the motion information (motion prediction vector) at that time and the prediction error at that time. In MPEG1, one image (picture) is a small block (called MB, macro block, and is composed of 16 lines × 16 pixels).
And the motion-compensated predictive coding is performed for each small block.

The motion compensation prediction error signal at this time is subjected to DCT conversion. In DCT coding, the signal power is concentrated on a specific frequency component by utilizing the two-dimensional correlation in the image of the image signal, and only the distributed coefficient is coded to compress the information amount. It is possible. DC in MPEG1
Multiply T by a block unit composed of 8 lines × 8 pixels.

FIG. 1 shows the relationship between MB and block in MPEG1. In MPEG1, since the image format is a 4: 2: 0 component signal, MB consists of four luminance blocks that are adjacent to each other on the left, right, top, and bottom, and the color difference blocks of Cb and Cr that are at the same position on the image. It consists of 6 blocks. The order of transmission is Y0, Y
1, Y2, Y3, Cb, Cr.

[0006] In MPEG1, when transmitting a motion compensation prediction error signal of this MB layer, a CBP (Coded Block Pattern) indicating whether or not six blocks in the MB have non-zero DCT coefficients to be transmitted. Variable length code called
(VLC, Variable Length Code) is added to the header of the MB layer and transmitted. CBP exists if any of the six blocks in the MB has a non-zero coefficient.

FIG. 4 shows a VLC table at this time. In the block order of (Y0, Y1, Y2, Y3, Cb, Cr), there is a non-zero coefficient for each block "1", none "
As 0 ', the value when arranged in binary notation from MSB (Most Significant Bit) is used as the CBP value, and the VLC code corresponding to each value is given. In decoding, VLC is converted to binary notation from FIG.
Therefore, there is a non-zero coefficient in the block which is "1" in the order of (Y0, Y1, Y2, Y3, Cb, Cr).

For example, the shortest VLC code of "111" indicates that the non-zero coefficient exists only in the blocks of Y0, Y1, Y2 and Y3 (the non-zero coefficient is present in the block of Cb, Cr). not exist). In the CLC VLC table structure for a 4: 2: 0 component signal in MPEG1, a short VLC is assigned when a non-zero coefficient does not exist in a color difference signal block (Cb, Cr block).

In this VLC table, b is
The numbers before that are binary numbers, and the numbers in parentheses are the codes expressed in binary numbers expressed in decimal numbers.

[0010] In recent years, MPEG2 which received after MPEG1
In the above, a method is being considered in which not only the 4: 2: 0 component signal but also the 4: 2: 2 component signal and the 4: 4: 4 component signal are targeted as the image signal to be encoded. In particular, 4: 2: 2 component signals are recommended by CCIR (Recommenda)
This is a format widely known as tion 601 (Rec. 601) and is also widely used as a recording format of image signals used in broadcasting stations and the like, and therefore the trend in MPEG2 is drawing attention.

2 and 3, 4: 2: 2 and 4: 2: 2.
The relationship between MB and block in each case of a 4: 4 component signal is shown. In a 4: 2: 2 component signal, MB has four luminance blocks adjacent to each other on the left, right, top and bottom, and Cb0, Cb1, Cr at the same position on the image.
Each of the color difference blocks of 0 and Cr1 is composed of eight blocks in total. The order of transmission is Y0, Y1, Y2, Y3, Cb0, Cr
0, Cb1 and Cr1.

For a 4: 4: 4 component signal, MB
Are four luminance blocks that are adjacent to the left and right and top and bottom, and Cb0, Cb1, Cb2, Cb3, Cr0, which are at the same position on the image.
The color difference blocks of Cr1, Cr2, and Cr3 are composed of 12 blocks in total. The order of transmission is Y0, Y1, Y2, Y3,
Cb0, Cr0, Cb1, Cr1, Cb2, Cr2, Cb3, Cr3.

[0013]

Problems to be Solved by the Invention 4: 2: 0 and 4:
One of the problems in encoding the 2: 2 and 4: 4: 4 component signals is the handling of the CBP described above. This is because the number of blocks included in the MB differs between the formats, and the MP
The problem is that the VLC table (FIG. 4) for 4: 2: 0 component signals in EG1 cannot be used for 4: 2: 2 and 4: 4: 4 component signals.

In order to solve the above problem, 4: 2: 0
A coding technique for a CBP (Coded Block Pattern) code, which has high coding efficiency for 4: 2: 2 and 4: 4: 4 component image signals and is simple in the coding and decoding apparatus, is required. ing.

Further, in general, when a component image signal is coded by a hybrid coding method, a motion compensation prediction error signal in a macroblock has non-zero coefficients only in a luminance signal block (Y block) and a chrominance signal block. In many cases, there are no non-zero coefficients in (Cb, Cr blocks).

Therefore, in order to encode and decode the CBP code more efficiently, it is necessary to make good use of the above properties.

An object of the present invention is to provide a CBP encoding and decoding technique for 4: 2: 0 and 4: 2: 2 and 4: 4: 4 component image signals in order to meet the above requirements. To do.

[0018]

In order to solve such a problem, the encoding method according to the present invention divides one screen of an input image signal into macroblocks composed of a plurality of pixels,
Predetermined conversion for compression processing is performed in units of each macroblock, and for variable length coding, it is used to represent which of the small blocks into which the macroblock is further divided has a non-zero conversion coefficient. A first VLC table and a color difference signal block for variable-length coding a CBP code of a luminance signal block in an image signal coding method in which a CBP code is added to a header of the macro block to transmit compressed data. And a second VLC table for variable length coding of the CBP code, the VBP code of the CBP code is added to the header of the macroblock according to the type of signal.

Further, in the decoding method according to the present invention, the encoded image signal is inversely VLC'd in units of macroblocks formed by dividing one screen into a plurality of parts, and the compressed image signal and the macroblock are further divided. In the image signal decoding method for separating the compressed image signal on the basis of the CBP code for expressing which one of the small blocks has a non-zero transform coefficient, and decoding the compressed image signal based on the CBP code, First inverse VLC for inverse variable length encoding of CBP code
The table and the second inverse VLC table for inverse variable-length encoding the CBP code of the color difference signal block are referred to, the VLC code of the CBP code is decoded according to the type of the signal, and the decoded CBP code The compressed image data is decoded based on

That is, in the present invention, CLC VLC tables having different properties for the luminance signal block and the color difference signal block are prepared, and the CBP of the luminance signal and color difference signal blocks in the macroblock are respectively set in the VLC tables. The encoding is performed with reference to.

At this time, in order to simplify the encoding and decoding methods, 4: 2: 0 of the component image signal,
VL of CBP for luminance signal block and chrominance signal block regardless of 4: 2: 2, 4: 4: 4 format
Share the C table.

[0022]

According to the encoding and decoding method of the present invention, 4:
In each component image signal of 2: 0, 4: 2: 2, 4: 4: 4, the luminance signal block in the macro block has the same configuration, so the CBP for the luminance signal block has the format of the component image signal. Can be shared regardless of. Therefore, the VLC table (reverse VL
(C table) can be reduced, and the circuit scale can be reduced.

Also, the VL of the CBP for the color difference signal block
By sharing the C table in the 4: 2: 0 and 4: 2: 2 formats, it is not necessary to distinguish between these two formats and use the table in variable length encoding and decoding of the CBP value. It can be processed efficiently. In the case of the 4: 4: 4 format, VLC of CBP for color difference signals is applied twice to efficiently process.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a moving picture coding apparatus having a CBP coding means of the present invention will be described with reference to FIG.

In this encoding apparatus, the input image is shown in FIG.
Encoding is performed based on the data structure in MPEG1 as shown in FIG. Each data layer will be briefly described below.

1. Block Layer The block is composed of, for example, 8 lines × 8 pixels adjacent to each other in luminance or color difference. For example, DCT (Discrete C
(osine Transform) is executed in this unit.

2. MB (Macro Block) Layer The block structure of the MB is as shown in FIGS. 1, 2 and 3. What is used for the motion compensation mode, whether the prediction error need not be sent, and the like are determined in this unit.

3. The slice layer image is composed of one or a plurality of macroblocks that are arranged in the scanning order. At the beginning of the slice, the first macroblock contains data indicating its position in the image, and is designed to be able to recover if an error occurs.
Therefore, the length and starting position of the slice are arbitrary and can be changed depending on the error condition of the transmission path.

4. PICTURE LAYER A picture or each image is composed of at least one or more slices. Then, it is classified into I-picture, P-picture and B-picture according to the encoding method.

5. GOP layer A GOP is composed of one or more I-pictures and zero or more non-I-pictures.

6. Video sequence layer A video sequence is composed of one or more GOPs having the same image size, image rate and the like.

Information for controlling the basic operation of the present encoding device is stored in the memory 18. These are the image frame size, the output bit rate of encoded information, the motion prediction compensation method, and the like. These pieces of information are output as S25.

The moving image to be encoded is the image input terminal 10
Will be entered more. The input image signal is supplied to the field memory group 11. From the field memory group 11, the macroblock signal S1 currently to be encoded is supplied to the hybrid encoder 12.

The hybrid encoder 12 is a hybrid code combining motion compensation predictive coding, which is a typical high-efficiency coding method for moving images, and transform coding such as DCT (Discrete Cosine Transform). Make a change. Since the structure does not affect the main point of the present invention, the description thereof is omitted here.

The MB layer motion-compensated prediction error signal S2 output from the hybrid encoder 12 is variable-length encoded into a Huffman code or the like by the VLC unit (variable-length encoder) 13. At this time, a CBP (Coded B) indicating whether or not the block in the MB has a non-zero DCT coefficient to be transmitted.
A variable length code called a lock pattern) is added to the MB layer header and transmitted. The CBP is transmitted if even one block in the MB has a non-zero coefficient. The CBP receives the input of the motion compensation prediction error signal S2 and is configured by the CBP configurator 16. In the CBP composer 16, CB
P is a value in the luminance signal block and C in the color difference signal block
It is calculated separately for the BP value.

The structure of the MB luminance signal block is 4:
In each of the component image signals of 2: 0, 4: 2: 2, 4: 4: 4, all are the same, and CBP is a block order of (Y0, Y1, Y2, Y3) and has non-zero coefficients for each block. M as "1" with and "0" without
A value obtained by arranging from SB (Most Significant Bit) and displaying it in a 4-bit binary number is a CBP value.

The structure of the MB color difference signal block is 4:
The component image signals of 2: 0, 4: 2: 2, 4: 4: 4 are all different, but here, as in the case of the luminance signal block, the CBP of the chrominance signal block is a 4-bit binary number. Express code as a unit.
That is, in the 4: 2: 0 format, (Cb, Cr, *,
*) Code 4 bits. Here, "*" means Do
It means n't Care, that is, any code is acceptable. In 4: 2: 2 format, (Cb0, Cr0, Cb
4-bit code as (1, Cr1). In 4: 4: 4 format, (Cb0, Cr0, Cb1, Cr1) and (Cb2, Cr2, Cb3, Cr3)
Two 4-bit codes of

VLC for the CBP value of the luminance signal block and the CBP value of the color difference signal block thus obtained
VLC is applied by the instrument 13. The variable length code table at this time is shown in FIGS. Here, regardless of the format of 4: 2: 0, 4: 2: 2, 4: 4: 4 of the component image signal, the CLC VLC tables for the luminance signal block and the color difference signal block are shared. Therefore, in converting the CBP to VLC, the VLC unit 13 is 4:
It is not necessary to distinguish the format difference between the 2: 0 and 4: 2: 2 formats. In the case of the 4: 4: 4 format, CLC VLC for color difference signals is applied twice. Whether it is applied twice or not is determined by the format of the input image signal. In the table above,
The numbers in parentheses are codes expressed in binary numbers and expressed in decimal numbers.

It should be noted here that C of the luminance signal block is
VLC “000000” of BP and C of color difference signal block
Since the combination of VLC "0" of BP is meaningless, it is desirable to prohibit the generation of that pattern.

In the above example, the simplicity of the encoder is given priority, but if the CBP coding efficiency in the 4: 2: 0 format is given the highest priority, the coding efficiency of 4: 2: 0 as shown in FIG. A CBP VLC table for the color difference signal block is prepared.
The table of FIG. 9 is used for the 4: 2: 2 and 4: 4: 4 formats. As described above, CB
Configure P and VLC them.

The variable-length code output from the VLC unit 13 is stored in the buffer memory 14 and then output to the output terminal 15.
The bit stream is transmitted at a constant transmission rate.

Next, a moving picture decoding apparatus corresponding to the above moving picture coding apparatus will be described with reference to FIG.

The bit stream signal input from the input terminal 50 is stored in the buffer memory 51 and then supplied to the inverse VLC unit 52.

As described in the description of the encoding device, the bit stream is composed of six layers (layers), that is, video sequence, GOP, picture, slice, macroblock and block layers. The video sequence, GOP, picture, and slice layers receive a start code indicating that they start at the beginning of each layer, and then receive header information that controls the decoding of the image. When receiving the respective start codes, the inverse VLC unit 52 decodes the header information of each layer and stores the obtained control information for image decoding in the memory 201. These pieces of information are output as S104.

The MB layer motion compensation prediction error signal S80 supplied from the inverse VLC unit is supplied to the hybrid decoder 53. The hybrid decoder 53 performs hybrid decoding that combines motion compensation, which is a typical high-efficiency coding method for moving images, and transform coding such as inverse DCT (Invers Discrete Cosine Transform). Since the structure does not affect the main point of the present invention, the description thereof is omitted here.

At this time, CLC VLC indicating which block in the MB has a non-zero DCT coefficient
Are received in the MB layer header. The CBP is used independently for the luminance signal block and the color difference block, as shown in FIG. 8 and FIG.
It is decrypted by referring to the table.

The structure of the MB luminance signal block is 4:
In the component image signals of 2: 0, 4: 2: 2, 4: 4: 4, all are the same, and CBP is "1" in the block order of (Y0, Y1, Y2, Y3). Has a non-zero coefficient in.

The structure of the MB color difference signal block is 4:
The component image signals of 2: 0, 4: 2: 2, 4: 4: 4 are all different, but here the CBP of the color difference signal block is a 4-bit binary code as in the case of the luminance signal block. Is obtained in units. That is, in the 4: 2: 0 format, (Cb, Cr,
A 4-bit code is decoded as *, *). here"
* "Is Don't Care, that is, an arbitrary code.

In the 4: 2: 2 format, (Cb0, Cr0, C
The 4-bit code is decoded as b1, Cr1). 4: 4: 4
In the format, (Cb0, Cr0, Cb1, Cr1) and (Cb2, Cr2, Cb3,
Two 4-bit codes (Cr3) are decoded. CBP is
This means that there is a non-zero coefficient in the block that is "1" when viewed from the first bit.

According to this method, regardless of the format of component image signals of 4: 2: 0, 4: 2: 2, 4: 4: 4, CBP VLC tables for luminance signal blocks and color difference signal blocks are used. Can be shared.
Therefore, in CBP decoding, the inverse VLC unit 52
It is not necessary to distinguish between these two formats between 4: 2: 0 and 4: 2: 2 formats. In addition,
In case of 4: 4: 4 format, CB for color difference signal
Apply reverse VLC of P twice in succession.

When the VLC table of FIG. 10 is used to convert the CBP value for the 4: 2: 0 color difference signal block into VLC on the encoder side, the inverse VLC unit also corresponds to this. In this case, the table of FIG. 9 is 4:
It is used for color difference signal blocks of 2: 2 and 4: 4: 4 formats. The CBP is decoded as described above.

Based on the CBP, the decoded macroblock layer data S81 is output from the terminal 55. As described above, the image data is restored from the bitstream data.

[0053]

According to the above method, it is possible to efficiently transmit the CBP value for 4: 2: 0 and 4: 2: 2 and 4: 4: 4 component image signals.

In each component image signal of 4: 2: 0, 4: 2: 2, 4: 4: 4, the luminance signal block in the macro block has the same structure, so the CBP for the luminance signal block is It can be shared regardless of the format of the component image signal.

By sharing the CLC VLC table for the color difference signal block in the 4: 2: 0 and 4: 2: 2 formats, the difference between these two formats in the variable length encoding and decoding of the CBP value is performed. There is no need to distinguish between.

The size of the CBP variable length table is MP
It is reduced from 64 entries to 32 entries compared to EG1. Also, the maximum bit length of the variable length code is MPEG1.
The width is reduced from 9-bit width to 7-bit width.

[Brief description of drawings]

FIG. 1 is a diagram showing a block configuration of an MB in a 4: 2: 0 format signal.

FIG. 2 is a diagram showing a block configuration of an MB in a 4: 2: 2 format signal.

FIG. 3 is a diagram showing a block configuration of an MB in a 4: 4: 4 format signal.

FIG. 4 is a VLC table of CBP in MPEG1.

FIG. 5 is a diagram showing a data structure in MPEG1.

FIG. 6 is a block diagram of an encoder in this embodiment.

FIG. 7 is a block diagram of a decoder in this embodiment.

FIG. 8 is a CBP V for a luminance signal block in the present embodiment;
It is an LC table.

FIG. 9 shows V of CBP for color difference signal block in the present embodiment.
It is an LC table.

FIG. 10 is a CLC VLC table for a color difference signal block dedicated to a 4: 2: 0 format.

Claims (13)

[Claims] 1. A screen of an input image signal is divided into macroblocks composed of a plurality of pixels, a predetermined conversion for compression processing is performed in units of each macroblock, and at the time of variable length coding, the macro In the image signal coding method, a CBP code for representing in which of the small blocks the block is further divided, a non-zero transform coefficient exists, is added to the header of the macro block, and compressed data is transmitted. The first VLC table for variable-length encoding the CBP code of the luminance signal block and the second VLC table for variable-length encoding of the CBP code of the color difference signal block are referred to and depending on the type of signal. An image signal coding method, wherein a VLC code of the CBP code is added to a header of the macroblock. 2. The image signal coding method according to claim 1, wherein the CBP code having the same number of bits is used for a luminance signal block and a color difference signal block. 3. The image signal encoding method according to claim 2, wherein when the input image signal is a component image signal of (4: 2: 0) format, the CBP for the color difference signal is obtained.
The code is an image signal coding method, wherein 2 bits out of 4 bits are coded arbitrarily. 4. The image signal encoding method according to claim 2, wherein when the input image signal is a component image signal of (4: 4: 4) format, the CBP for the color difference signal is obtained.
The code consists of an 8-bit code, and the 8-bit C
An image signal coding method, wherein the second VLC table is applied twice to a BP code. 5. The image signal encoding method according to claim 1, wherein the second VLC table differs depending on the format of the input image signal. 6. The image signal coding method according to claim 5, wherein in the second VLC table, a table for a (4: 2: 0) signal format is configured separately from other signal formats. An image signal encoding method characterized by the following. 7. The image signal encoding method according to claim 3, 4 or 6, wherein generation of the CBP code is prohibited when all the conversion coefficients in the luminance block and the color difference block in the macroblock are 0. An image signal encoding method characterized by the above. 8. An inverse VLC of an encoded image signal is performed in units of macroblocks formed by dividing one screen into a plurality of units, and the compressed image signal and the macroblock are each divided into non-zero blocks. In the image signal decoding method for separating the CBP code for representing whether or not the transform coefficient exists and decoding the compressed image signal based on the CBP code, the CBP code of the luminance signal block is subjected to the inverse variable length coding. First inverse VLC table and CB of color difference signal block for
A second inverse VLC table for inverse variable-length encoding of a P code is referred to, the VLC code of the CBP code is decoded according to the type of signal, and the compressed image is based on the decoded CBP code. An image signal decoding method characterized by decoding data. 9. The image signal decoding method according to claim 8, wherein the CBP code having the same number of bits is used for the luminance signal block and the color difference signal block. 10. The image signal decoding method according to claim 9, wherein when the image signal is a component image signal of (4: 2: 0) format, 2 bits out of 4 bits are arbitrary codes for the color difference signal. The image signal decoding method is characterized in that the CBP code is decoded. 11. The image signal decoding method according to claim 9, wherein when the image signal is a component image signal of (4: 4: 4) format, the second inverse VLC table is used twice for the color difference signal. An image signal decoding method, characterized in that the CBP code composed of 8 bits is decoded. 12. The image signal decoding method according to claim 8, wherein the second inverse VLC table is different depending on the format of the image signal. 13. The image signal decoding method according to claim 12, wherein in the second inverse VLC table, a table for a (4: 2: 0) signal format is configured separately from other signal formats. An image signal decoding method characterized by the following.