KR20130003707A - Method and apparatus for image encoding/decoding using efficient non-fixed quantization - Google Patents

Abstract

PURPOSE: A method and an apparatus for encoding/decoding an image using efficient non-fixed quantization are provided to control the size of the quantization according to the position of a frequency coefficient and to improve compression performance. CONSTITUTION: A converting unit produces a frequency conversion block(S810). The quantization unit selects a scanning method according to the mode information of a block determined by a prediction unit on the frequency conversion block(S820). While the quantization unit performs a determined scanning, it changes the size of the quantization on the frequency conversion block(S830). An encoding unit encodes the quantized frequency conversion block into a bit stream through an entropy coding(S840). [Reference numerals] (AA) Start; (BB) End; (S810) Generating a frequency conversion block by a converting unit(530); (S820) Selecting a scanning order according to the determined block mode information by a prediction unit(510) on the frequency conversion block; (S830) Determining the size of the quantization according to the determined scanning order; (S840) Generating a bit stream using a finished quantization factor

Description

TECHNICAL FIELD [0001] The present invention relates to an efficient encoding / decoding method and apparatus using non-uniform quantization,

The present invention relates to a moving picture encoding / decoding method and apparatus. More specifically, when a frequency transform coefficient block obtained by frequency-transforming a residual signal between an original video signal and a prediction signal is quantized, quantization is performed by varying quantization magnitudes according to positions of respective frequency coefficients, Decoding method and apparatus.

The contents described in this section merely provide background information on the embodiment of the present invention, but do not necessarily constitute the prior art. It also includes both coding and decoding methods and apparatuses similar to the background technology as well as the technology corresponding to the background information.

Moving Picture Experts Group (MPEG) and Video Coding Experts Group (VCEG), formed by experts in video compression technology, formed a joint team of MPEG and VCEG called Joint Collaborative Team on Video Coding (JCT-VC) Standardization of a standard named HEVC (High Efficiency Video Coding), aiming at a new video compression standard which has a compression performance improvement of about 50% with .264 / AVC (Advanced Video Coding), high quality, high performance and high efficiency video compression technology Is in progress. It is aimed at high-quality / high-performance compression technology with improved compression ratio than the existing H.264 / AVC technology. Various coding methods have been adopted and have made a lot of improvements in picture quality and performance improvement than existing standardization technology. Technology development is in progress with the goal of preparing a CD (Committee Draft) in Feb 2012, a Final Draft of IS (FDIS) in January 2013, and an International Standard (IS) in 2013, and the Test Model under Consideration (TMuC) , And the HEVC Test Model (HM1.0) and WD1.0 were completed after the third JCT-VC meeting held in Guangzhou, which ended in October 2010. In addition, HM2.0 and WD2.0 were completed after the 4th JCT-VC meeting held in Daegu in January 2011, and HM3.0 and WD3.0 were held after the 5th JCT-VC meeting held in Geneva, 0 was completed.

1 shows an example of CU (Coding Unit) which is a coding unit of HEVC. HEVC starts with the basic unit of such a coding unit (CU) and has a form of a quad tree. Referring to FIG. 1 in detail, when a depth is set to 0 and a depth is set to 3, that is, an 8 × 8-size coding unit (LU) is selected for a LCU (Largest Coding Unit) CU) in the encoding process.

The basic unit of coding is classified as a basic unit of prediction classified into a lower hierarchy, and is defined as a prediction unit PU (Prediction Unit), and one prediction unit (PU) is divided into a plurality of blocks to perform prediction .

FIG. 2 shows a prediction order of a prediction unit (PU) in one coding unit (CU) and the kind of PU which is a typical prediction unit.

Referring to FIG. 2, after a Skip mode is performed in one coding unit CU having a size of 2N × 2N, an inter 2N × 2N mode, an inter 2N × N mode, an inter N × 2N mode, The intra 2N 占 2N mode, and the intra N 占 N mode. However, prediction is performed on all remaining prediction units (PU) except for the inter N × N mode and the intra N × N mode in all the coding units (CU) except for the coding unit (CU) of size 8 × 8 .

The prediction method is largely classified into an intra prediction coding method for predicting prediction using a prediction value from a block coded in a coding frame and an inter prediction coding method for predicting a block of a current frame by estimating a motion from a previously reconstructed frame can do.

Intra prediction methods include Unified Intra Prediction (Prediction) in which predictions are performed in various directions using pixel values of left, lower left, upper left, upper, and upper right of a previously coded corresponding block .

3 is a diagram showing a direction of a conventional intra prediction mode.

Referring to FIG. 3, there are a total of 35 prediction modes including an DC (Direct Current) mode, a Planar mode, and an angular mode with a total of 33 prediction directions.

Inter-predictive coding of video uses motion compensation to predict the current block by estimating the motion from the previously encoded frame by dividing the image frame.

When one prediction block is created by the intra prediction method or the inter prediction method, a residual signal is generated by calculating a difference value between the original pixel value of the current block and the prediction value of the prediction block. The generated residual signal is subjected to frequency conversion to obtain a frequency transform block and quantized to form a quantized frequency coefficient block. The basic unit of conversion and quantization is called a conversion unit (TU) and entropy coding is performed according to a scanning method determined according to the conversion unit (TU) to generate a bitstream.

FIG. 4 shows a method of scanning a frequency coefficient after conversion and quantization of the predicted unit PU, which has been predicted, through the transform unit (TU).

Referring to FIG. 4, in the intra-frame prediction method, scanning is applied using one of a vertical scanning method, a horizontal scanning method, and a zigzag scanning method. In the inter-frame prediction method, a zigzag scanning method Is used. Various methods can be used for the scanning method. FIG. 4 shows an example of using scanning of three methods, scanning the quantized frequency coefficient block according to a predetermined order, and encoding through the entropy coding method .

In performing the transform and the quantization according to the transform unit (TU), the quantization process quantizes the transformed coefficients to the frequency coefficients, and the determination of the magnitude of the quantization is determined by a quantization parameter. The values of all the coefficients within the transform unit (TU) perform the same quantization according to the quantization size determined through the quantization parameter. However, regardless of the scanning method and the order, all of the conversion units (TU) perform quantization with the same size, which is not effective in the coding performance.

According to an embodiment of the present invention for solving such problems, when a frequency transform coefficient block obtained by frequency-transforming a residual signal between an original image signal and a prediction signal is quantized, the magnitude of the quantization is varied according to the position of each frequency coefficient, Thereby improving the compression performance.

According to an aspect of the present invention, there is provided an apparatus for encoding / decoding an image, the apparatus comprising: a prediction block generation unit that generates a prediction block of a current block, subtracts a prediction block from the current block to generate a residual block, Transforming the quantized frequency transform block to generate a frequency transform block, quantizing the frequency transform block by varying the quantization size according to the position of the frequency coefficient in the frequency transform block, and encoding the quantized frequency transform block into a bit stream through entropy coding ; And decoding the quantized frequency transform block through an inverse entropy process from the bit stream, restoring the frequency transform block by varying the size of the inverse quantization according to the position of the quantized frequency coefficient in the quantized frequency transform block, And a picture decoder for reconstructing a current block by restoring a residual block, generating a predictive block through intra-picture prediction or intra-picture prediction information, and adding the reconstructed residual block and the generated predictive block, Encoding / decoding apparatus.

According to another aspect of the present invention, there is provided an apparatus for encoding an image, the apparatus comprising: a prediction unit generating a prediction block of a current block; A subtracting unit for subtracting a prediction block from the current block to generate a residual block; A transform unit for transforming the residual block to generate a frequency transform block; A quantization unit for quantizing the frequency transform block by varying quantization magnitudes according to positions of frequency coefficients in the frequency transform block; And a bitstream generation unit for encoding the quantized frequency conversion block into a bitstream through entropy coding.

The quantization unit may quantize the frequency conversion block by varying the quantization size according to the distance from the scanning start point.

The quantization unit may have different quantization sizes on the basis of a certain distance at the scanning start point.

The quantization unit may vary the quantization size in each of the intra-block areas of the frequency conversion block.

The quantization unit may vary the quantization size using the scanning information and the scanning information according to the prediction information of the block.

The size of the quantization may be different from the quantization size of the color difference signal and the luminance signal in performing quantization for the frequency conversion block.

According to another aspect of the present invention, there is provided an apparatus for decoding an image, the apparatus comprising: a decoding unit decoding a frequency transform block quantized through an inverse entropy process from a bitstream; An inverse quantization unit for restoring a frequency transform block by varying the size of the inverse quantization according to a position of a quantization frequency coefficient in the quantized frequency transform block; An inverse transformer for inversely transforming the frequency transform block to recover a residual block; A prediction unit for generating a prediction block through intra-picture prediction or intra-picture prediction information; And an adder for adding the reconstructed residual block and the generated prediction block to reconstruct a current block.

The inverse quantization unit may restore the frequency transform block by varying the size of the inverse quantization according to the distance from the start point of the inverse scanning.

The inverse quantization unit may have a different inverse quantization size on the basis of a certain distance at the inverse scanning start point.

The inverse quantization unit may vary the size of the inverse quantization for each in-block area of the frequency conversion block.

The inverse quantization unit may vary the inverse quantization size according to the inverse scanning method according to the extracted prediction information.

The size of the inverse quantization may be different from the size of the inverse quantization of the chrominance signal and the luminance signal in performing the restoration on the frequency transform block.

According to another aspect of the present invention, there is provided a method of encoding / decoding an image, comprising: generating a prediction block of a current block; subtracting the prediction block from the current block to generate a residual block; Transforming the residual block to generate a frequency transform block, quantizing the frequency transform block by varying the quantization size according to the position of the frequency coefficient in the frequency transform block, and quantizing the quantized frequency transform block using a bitstream through entropy coding A video encoding step of encoding; And decoding the quantized frequency transform block through an inverse entropy process from the bit stream, restoring the frequency transform block by varying the size of the inverse quantization according to the position of the quantized frequency coefficient in the quantized frequency transform block, And reconstructing a current block by restoring a residual block, generating a predictive block through intra-picture prediction or intra-picture prediction information, adding the reconstructed residual block and the generated predictive block, And provides a video encoding / decoding method.

According to another aspect of the present invention, there is provided a method of encoding an image, the method comprising: a prediction step of generating a prediction block of a current block; A subtraction step of subtracting a prediction block from the current block to generate a residual block; A transforming step of transforming the residual block to generate a frequency transform block; A quantization step of quantizing the frequency conversion block by varying quantization magnitudes according to positions of frequency coefficients in the frequency conversion block; And a bitstream generation step of encoding the quantized frequency conversion block into a bitstream through entropy coding.

In the quantization step, the frequency conversion block may be quantized by varying the quantization size according to the distance from the scanning start point.

In the quantization step, both sides may have different quantization sizes based on a certain distance at the scanning start point.

The size of the quantization may be different from the quantization size of the color difference signal and the luminance signal in performing quantization for the frequency conversion block.

According to another aspect of the present invention, there is provided a method of decoding an image, the method comprising: a decoding step of decoding a frequency transform block quantized through an inverse entropy process from a bitstream; An inverse quantization step of restoring a frequency transform block by varying the magnitudes of inverse quantization according to positions of quantization frequency coefficients in the quantized frequency transform block; An inverse transform step of inversely transforming the frequency transform block to recover a residual block; A prediction step of generating a prediction block through intra-picture prediction or intra-picture prediction information; And an addition step of reconstructing a current block by adding the reconstructed residual block and the generated prediction block.

In the dequantization step, the frequency conversion block may be restored by varying the size of the inverse quantization according to the distance from the start point of the inverse scanning.

In the dequantization step, both sides may have different inverse quantization sizes based on a certain distance at a start point of the inverse scanning.

The size of the inverse quantization may be different from the size of the inverse quantization of the chrominance signal and the luminance signal in performing the restoration on the frequency transform block.

As described above, according to an embodiment of the present invention, when a frequency transform coefficient block obtained by frequency-transforming a residual signal between an original video signal and a prediction signal is quantized, quantization is carried out by varying the quantization size according to the position of the frequency coefficient The compression performance is improved.

1 is a diagram showing a size of a coding unit (CU) and a quad tree form.
FIG. 2 is a diagram showing the types and order of prediction units (PU) encoded in one coding unit (CU).
3 is a diagram showing a direction of a typical intra mode.
4 is a diagram illustrating a scanning method applied differently according to a prediction method.
FIG. 5 is a block diagram illustrating a video encoding apparatus according to an embodiment of the present invention. Referring to FIG.
FIG. 6 is a block diagram of a video decoding apparatus according to an embodiment of the present invention. Referring to FIG.
7 is a flowchart for explaining prediction unit (PU) determination in a coding unit (CU) according to an embodiment of the present invention.
8 is a flowchart illustrating a process of generating a bitstream from a frequency conversion block.
9 is a flowchart illustrating an image encoding method according to an embodiment of the present invention.
10 is a flowchart illustrating an image decoding method according to an embodiment of the present invention.

The Video Encoding Apparatus and the Video Decoding Apparatus to be described below may be implemented as a personal computer (PC), a notebook computer, a personal digital assistant (PDA), a portable multimedia player (PMP) A portable terminal, a portable multimedia player, a PlayStation Portable (PSP), a wireless communication terminal, a smart phone, a TV, a server terminal such as an application server and a service server, A communication device such as a communication modem for performing communication with various devices or wired or wireless communication networks, a memory for storing various programs and data for inter or intra prediction for encoding or decoding an image, coding or decoding for image, And a microprocessor for controlling It can mean a variety of devices.

In addition, the image encoded by the video encoding apparatus can be transmitted in real time or in non-real time through a wired or wireless communication network such as the Internet, a local area wireless communication network, a wireless LAN network, a WiBro network, a mobile communication network, A serial bus, and the like, and can be decoded and reconstructed into an image and reproduced by an image decoding apparatus.

The moving picture may be generally composed of a series of pictures, and each picture may be divided into a predetermined area such as a frame or a block. In the case where an area of an image is divided into blocks, the divided blocks can be roughly classified into an Intra block, which is an intra-picture prediction method, and an Inter block, which is an inter-picture prediction method, according to a coding method. The intra prediction block refers to a block that is coded using Intra Prediction Coding (Prediction Coding) scheme. The intra prediction coding is a coding method in which a pixel of a block previously coded and decoded and reconstructed in a current picture, A prediction block is generated by predicting the pixels of the current block and a difference value between the current block and the pixel of the current block is encoded. The inter-picture prediction block refers to a block that is coded using Inter Prediction Coding. Inter-prediction coding refers to one or more past pictures or future pictures to predict a current block in a current picture to generate a prediction block And the difference value between the current block and the current block is encoded. Here, a frame to be referred to in encoding or decoding a current picture is referred to as a reference frame.

FIG. 5 is a block diagram illustrating a video encoding apparatus according to an embodiment of the present invention. Referring to FIG.

The image encoding apparatus 500 according to an exemplary embodiment of the present invention generates the quantized frequency transform block by quantizing the frequency transform block of the image according to a predetermined scanning method, A subtractor 520, a transformer 530, a quantizer 540, and an encoder 550, as shown in FIG.

An input image to be encoded is input as a coding unit. In the present invention, a coding unit is an N × N block type and N has a size of 2 ⁿ . The coding unit is in the form of a quad tree and performs inductive encoding from the largest coding unit to a specified depth.

The prediction unit (PU) in the encoder is of the NxM block type, and N and M are each ²ⁿ in size. The prediction unit (PU) in the coding unit is predicted by one prediction unit (Prediction Unit) in one coding unit (CU). The prediction unit PU has four inter prediction units and two intra prediction units PU and performs coding on all the prediction units PU to use the prediction unit PU having the best compression efficiency. In this case, the prediction unit PU is divided into a conversion unit TU, the conversion unit TU is independent of the size of the prediction unit PU, and is equal to or smaller than the size of the coding unit CU. The transform unit is transformed and quantized, and then a bitstream is generated through entropy coding. In this case, the criterion for the compression efficiency is determined by a rate distortion cost including the number of bits necessary for transmission of image information and the difference between the original block and the prediction block.

The prediction unit 510 generates a prediction block using another frame to predict a prediction unit PU of the current coding unit CU or generates a prediction block using the already coded left and top pixel values. That is, in the intra prediction mode, the predicting unit 510 determines the prediction mode using the reconstructed upper and left coding unit (CU) information, and generates a prediction block using the prediction mode In the inter-picture prediction mode, the predicting unit 510 may generate a motion vector through motion estimation in a previous frame that has undergone a coding process, and may generate a prediction block in a motion compensation process using the motion vector. The prediction unit 510 may use an inter-picture prediction method and / or an intra-picture prediction method.

The subtractor 520 calculates the difference between the original pixel value of each pixel of the current block and the predicted value generated by the predictor 510 to generate a residual signal. This is a residual signal generated through the corresponding inter-picture prediction method and intra-picture prediction method in the predicting unit 510, and the residual signal is determined in units of a prediction unit (PU).

The transforming unit 530 transforms the residual signal generated by the subtracting unit 520 into a frequency domain. The transform unit 530 is transformed into a transform unit. The transform unit TU has an N × N block form and N has a size of ²ⁿ . The transform unit 530 transforms the transform unit TU into the transform unit TU immediately after all the predictions are performed on the current prediction unit PU and the size of the transform unit TU corresponds to the size of the corresponding coding unit CU And is independent of the size of the prediction unit (PU). The conversion unit TU is in the form of a quad tree such as a coding unit CU and performs inductive conversion from the size of the coding unit CU to a depth arbitrarily specified. At this time, a split transform flag of the transform unit TU is transmitted to the decoder to transmit information on the size of the transform unit TU having the lowest rate-distortion value RD cost. Here, the transforming unit 530 may use various transform techniques for transforming image signals on a time axis, such as discrete cosine transform (DCT) or wavelet transform, to a frequency axis So that the residual signal can be converted into the frequency domain.

The quantization unit 540 quantizes the frequency transform block made up of the residual signal transformed into the frequency domain by the transform unit 530. Here, it is assumed that the quantization unit 540 not only performs quantization of a frequency coefficient block, but also simultaneously performs quantization and scanning. In this case, when the predicting unit 510 performs prediction using the inter picture prediction method, the quantizing unit 540 scans the frequency coefficient block using a zigzag scanning method and uses the in- Scanning direction, horizontal scanning, vertical scanning, and zigzag scanning in accordance with the prediction direction determined by the prediction unit 510. FIG. For example, the scanning method can be determined in such a manner that the intra-prediction mode has a horizontal direction, the horizontal direction scanning has vertical direction, the vertical direction scanning has a vertical direction, and the zigzag scanning method has a DC mode. , And the method of determining such a scanning method may vary depending on the embodiment.

On the other hand, the quantization unit 540 may perform quantization with different quantization sizes according to the scanning method determined according to the prediction mode and the position of the frequency coefficient, instead of the uniform quantization having the same quantization parameter for all the blocks.

 The scanning method is not limited to the method shown in FIG. 4 and may include all of various scanning methods. Also, various scanning methods may be used according to the embodiment, A detailed description of a method for varying the size of the quantization to be performed will be described later.

The encoding unit 550 encodes the quantized frequency conversion block having the frequency coefficients quantized by the quantizing unit 540 into a bitstream. As such an encoding technique, entropy encoding technology may be used, but various other encoding techniques may be used without being limited thereto.

In addition, the encoding unit 550 may include various information necessary for decoding the encoded bit stream as well as the bit stream obtained by encoding the quantized frequency coefficients in the encoded data. That is, the encoded data includes a field including a coded block pattern (CBP), a delta quantization parameter, and a bit string in which a quantized frequency coefficient is coded and information necessary for prediction (for example, A motion vector in the case of an intra prediction), or the like.

The inverse quantization unit 560 inverse quantizes the transformed and quantized residual block (i.e., the quantized frequency transform block), and the inverse transform unit 570 inversely transforms the inverse quantized transform residual block, And reconstructs the residual block (Reconstruction). In this case, the inverse quantization and inverse transform can be performed by reversing the transformation process performed by the transform unit 530 and the quantization process performed by the quantization unit 540, respectively. That is, the inverse quantization unit 560 and the inverse transformation unit 570 convert the information about the transformation and quantization (for example, information about the transformation and the quantization type) generated and transmitted from the transformation unit 530 and the quantization unit 540, To perform inverse quantization and inverse transform. Here, the inverse quantization unit 560 performs the same inverse quantization according to the quantization method of different sizes according to the scanning method described in the quantization unit 540. [

The addition unit 580 adds the residual block generated by the inverse transform unit 570 to the prediction block generated by the prediction unit 510 to generate a reconstructed block.

The frame memory 590 stores the reconstructed block in the adder 580 and is used as a reference block to generate a predictive block in intra or inter prediction.

The method described in the present invention performs a calculation process as follows in a process of generating a frequency transform block by the transform unit 530 and quantizing the generated block by the quantization unit 540.

In order to convert the prediction block into the frequency block in the transforming unit 530, the transform of the residual block corresponding to the NxN size is performed according to the following equation (1).

Where X represents a residual block generated by a prediction block, A represents a product of a matrix for frequency conversion, T represents a transposed matrix in which rows and columns of the matrix are changed, and Y represents a residual block X represents the transformed residual block that is the result of the transform performed on X.

The Y used in Equation (1) can be expressed in the form of a DCT like the Equation (2). The present invention is not limited to DCT in the conversion but includes all similar frequency conversion methods such as discrete cosine transform. After the frequency conversion process, the transformed residual block is subjected to the following quantization process. The quantization process has a calculation process as shown in Equation (3) below.

In Equation (3), Level represents the elements of the frequency conversion block expressed by a matrix after frequency conversion is performed on the residual block, and Qstep Represents the size of the quantization step.

Equation (4) and Equation (5) can be expressed by expressing the basic quantization operation performed as Equation (3) to be applied to an actual quantization process.

In Equations (4) and (5), Coeff denotes a frequency transform coefficient expressed by a matrix after transforming each residual signal of the residual block, Q is a coefficient determined according to a quantization parameter, It is the determining factor. In H.264 / AVC, Integer Transform is used, and part of the conversion process is replaced by the quantization process. Therefore, Q including a part of the number to be multiplied by the position of the frequency conversion coefficient in the integer type conversion process is applied, and another Q can be used depending on the position of the frequency conversion coefficient. In HEVC that does not use integer type conversion, since the conversion process and the quantization process are separated, the same Q value is applied to the positions of all frequency conversion coefficients at the time of quantization. offset is an element that determines the error due to rounding in the quantization process and the size of the dead zone. Here, a round down operation is performed. M is determined by M = log ₂ N in the case of NxN block depending on the size of the conversion unit (TU). For example, if the size of the conversion unit (TU) is 4x4, then M = log ₂ 4 = 2. In order to support IBDI (Internal Bit Depth Increase), the DB has a pixel value of 8 bits or more per pixel (for example, when the pixel has 12 bits per pixel, it is defined as 4, and when the pixel has 8 bits per pixel, This is the value used.

The present invention uses a method of adjusting the amount of stored frequency conversion coefficients according to the magnitude of Q in Equation (5). In the following description, Q is defined as a Q value, and the size of the quantization can be determined according to the change of the Q value. That is, if the Q value is large, the quantization size is reduced. If the Q value is small, the quantization size can be increased.

The position of the transform block is classified according to the scanning method used in the intra-prediction and the inter-image prediction determined in FIG. 4, and the coefficients close to the scanning start point have a large Q value by adjusting the Q value according to the scanning position, And the quantization scale is determined to be large by making the coefficients in the far distance in the scanning order have a small Q value. FIG. 7 is a diagram illustrating a change in Q value for a transformation according to an embodiment of the present invention. FIG.

In FIG. 7, Q values are changed according to the scanning method determined in FIG. 4. In FIG. 7, the Q value is relatively large in the white coefficient position, and the quantization size is adjusted to be small so that values close to the starting point of the scanning In FIG. 7, the position of the gray portion (hatched portion) is divided by the distant value in the order of scanning, and the Q value of the corresponding coefficient is adjusted to be smaller than the size of the quantization To make the value of the coefficient after the quantization is made small.

In FIG. 7, it is also shown that the quantization coefficient can be changed by dividing the frequency coefficient block into a certain area. For example, the quantization coefficients of the left two lines (or the top two lines) of the frequency coefficient block may be different from the quantization coefficients of the pixels of the remaining lines. The case where the quantization coefficients are divided into the regions and the quantization coefficients are different can also be determined depending on the scanning method. That is, in the case of the horizontal direction scan, the quantization coefficients may be different by a method in which the quantization coefficients of the upper two rows are different from the quantization coefficients of the remaining rows.

The inverse quantization unit 560 and the inverse transformation unit 570, which perform inverse calculation of the transform unit 530 and the quantization unit 540, are as follows.

The inverse quantization is performed in the same manner as the quantization process of the present invention and the inverse transformation is performed in the same manner as the conversion process. In particular, in the inverse quantization process, the same inverse quantization process as the quantization process according to the previous scanning method is performed. The transform coefficients after the quantization process can obtain the residual blocks of the original values through the following inverse quantization process and inverse transform process.

The inverse quantization is calculated as shown in Equation (6).

Equation (6) represents a basic dequantization operation. IQ is a coefficient determined according to the inverse quantization parameter, and is an element for determining the size of the inverse quantization.

Equation (7) indicates that the product of Q and IQ can be represented by 20 powers of 2, and after inverse quantization, the inverse transform is performed. The inverse transform is expressed by Equation (8) .

In Equation (8), X represents a residual block reconstructed by multiplying the transformed residual block Y by a matrix A for integer transformation and a transpose matrix, which is a matrix in which rows and columns of the A matrix are changed.

By applying the above-described transform and quantization, transformation and quantization can be performed according to various transformation and quantization types such as NxN block size conversion and quantization such as 4x4 block size conversion and quantization, 16x16 block size conversion and quantization . This uses the same method as the video decoding apparatus and method described later.

8 is a flowchart illustrating a process of generating a bitstream from a frequency transform block according to an exemplary embodiment of the present invention.

The transform unit 530 generates a frequency transform block (S810), and the transform process may have a DCT or other transform as shown in Equations (1) and (2). In addition, the conversion can be applied differently depending on the color difference signal and the brightness signal.

The quantization unit 540 performs in-picture prediction according to the mode information of the block determined through the predicting unit 510 for the frequency transform block for which the transform is completed, or in the vertical direction according to the prediction direction in the inter picture prediction, Zigzag scanning, and the like, and selects a scanning method (S820). At this time, quantization using a Q value having a different quantization size using Equations 3 to 5 is performed while performing the determined scanning (S830). The Q value described above may be a method of using a fixed value depending on a region. However, a method of calculating a Q value using a fixed value or a method that varies depending on a position can be used. It can also be applied. In this embodiment, the quantization coefficient is determined to be smaller than a value closer to the order of scanning. The entropy coding of the encoding unit 550 is performed by varying the quantization size according to the scanning order in operation S840 so that the performance of the entire image encoding apparatus can be improved by more effectively generating the bitstream.

That is, the method of varying the quantization size according to the order of the scanning method and the position of the coefficient described in the embodiment of the present invention may vary the quantization method and size in the method described in the embodiment, Which means that it can be applied in various forms. Here, the various forms are different from the quantization method, not only the number of the scanning method applied to the prediction direction of the block and the change of the Q value in performing the quantization, and the method of varying the quantization size according to the scanning Quot; means a video encoding apparatus including all of them.

6 is a block diagram illustrating a configuration of an image decoding apparatus according to an embodiment of the present invention.

6, an apparatus 600 for decoding an image according to an exemplary embodiment of the present invention may perform a decoding process by omitting a process of dequantizing and inverse-converting a signal using a quantized frequency-converted signal of a current prediction unit block of an image, And includes a decoding unit 610, an inverse quantization unit 620, an inverse transformation unit 630, an addition unit 640, and a prediction unit 650.

The decoding unit 610 decodes the bit stream and extracts the quantized frequency conversion block.

The decoding unit 610 can decode or extract information necessary for decoding as well as the quantized frequency conversion block by decoding the encoded data. The information necessary for decoding refers to information necessary for decoding an encoded bit stream in encoded data (i.e., a bit stream). For example, information on a block type, information on a motion vector, information on a transform and a quantization type And may be various other information.

That is, the decoding unit 610 decodes the bitstream, which is the data encoded by the image encoding apparatus 500, and extracts the quantized frequency conversion block including the pixel information of the current block of the image, And transfers necessary information to the predicting unit 650.

The prediction unit 650 can predict a current block in the same manner as the prediction unit 510 of the image encoding apparatus 500 using information required for prediction transmitted from the decoding unit 610. [

The prediction unit 650 generates prediction values for the current block by using the inter picture prediction method or the intra prediction method using the information necessary for prediction extracted by the decoding unit 610. [ The prediction unit 650 predicts a prediction unit using the information obtained through the decoding unit 610 through the bitstream in the same manner as the prediction method according to the division of the prediction unit determined by the prediction unit 510 of the image coding apparatus 500 And generates a predicted value.

The predicting unit 650 of the image decoding apparatus 600 according to an embodiment of the present invention uses the information of the extracted prediction mode and prediction unit to perform the same processing as the predicting unit 510 of the image encoding apparatus 500 Thereby generating a prediction block. Therefore, further detailed description thereof will be omitted in order to avoid redundant description.

The inverse quantization unit 620 dequantizes the quantized frequency transform block extracted from the bit stream by the decoding unit 610. [ This is the same as the scanning method described in the quantization unit 540 in the image encoding apparatus 500 and the method of varying the quantization size according to the scanning position, and a detailed description thereof will be omitted in order to avoid redundant description. Here, it is assumed that the information about the scanning method according to the prediction mode and the position of the point where the quantization coefficient is changed in the scanning method is promised to use the same value as the image coding apparatus 500. Therefore, if the prediction mode is extracted without additional information, the scanning method and the point at which the magnitude of the quantization coefficient is changed can be known, so that inverse scanning and dequantization can be performed using the point. Here, it is assumed that the inverse quantization unit 620 performs inverse scanning and inverse quantization together. Therefore, the scanning method used in the quantization unit 540 corresponds to the inverse quantization method of the inverse quantization unit 620, and the quantization size used in the quantization unit 540 corresponds to the inverse quantization size of the inverse quantization unit 620.

The inverse transformer 630 inversely transforms the frequency transform block inversely quantized by the inverse quantizer 620 into a time domain to recover the residual block.

The adder 640 restores the original pixel value of the current block by adding the residual signal reconstructed by the inverse transform unit 630 and the predicted pixel value generated by the predictor 650. [

The current block restored by the addition unit 640 or the prediction unit 650 is transmitted to the frame memory 660 and can be used for predicting another block in the prediction unit 650. [

The frame memory 660 stores the reconstructed image to enable generation of an intra prediction block and an inter prediction block.

The image encoding / decoding apparatus according to an embodiment of the present invention may be configured by connecting the bit stream output end of the image encoding apparatus 500 of FIG. 6 to the bit stream input end of the image decoding apparatus 600 of FIG.

According to an embodiment of the present invention, there is provided an apparatus for encoding / decoding an image, the apparatus comprising: a prediction block generation unit for generating a prediction block of a current block, subtracting a prediction block from the current block to generate a residual block, To generate a frequency transform block, to quantize the frequency transform block by varying the quantization size according to the position of the frequency coefficient in the frequency transform block, and to encode the quantized frequency transform block into a bit stream through entropy coding An encoder; And decoding the quantized frequency transform block through an inverse entropy process from the bit stream, restoring the frequency transform block by varying the size of the inverse quantization according to the position of the quantized frequency coefficient in the quantized frequency transform block, And a picture decoder that restores the current block by restoring the residual block, generates a predictive block through inter-picture prediction or intra-picture prediction information, and adds the restored residual block and the generated predictive block.

Here, the image encoder can be implemented by the image encoding apparatus 500 according to an embodiment of the present invention, and the image decoder can be implemented with the image decoding apparatus 600 according to an embodiment of the present invention.

9 is a flowchart illustrating an image encoding method according to an embodiment of the present invention.

That is, the image encoding apparatus 500 includes a prediction step 910 of generating a prediction value using a motion vector value of a luminance component of a current block of an image, a step 910 of calculating a difference value between the original pixel value and the prediction pixel value of the current block, A transforming step 930 for transforming the generated residual signal into a frequency domain using DCT or wavelet transform, a quantization step 940 for quantizing the residual signal transformed into the frequency domain, , And determines an optimal quantized frequency transform residual signal and encodes it into a bitstream through an encoding step 950 to encode the image.

Here, the prediction step 910 corresponds to the function of the predicting unit 510, the subtraction step 920 corresponds to the function of the subtractor 520, the transform step 930 corresponds to the function of the transform unit 530, 940 correspond to the functions of the quantization unit 540 and the encoding step 950 corresponds to the functions of the encoding unit 550, detailed description thereof will be omitted.

10 is a flowchart illustrating an image decoding method according to an embodiment of the present invention.

The video decoding apparatus 600 receives and stores a bitstream of an image through a wired / wireless communication network or a cable, and stores the current block of the video as a motion vector value And decodes and restores the original pixel value image obtained by adding the inversely quantized and inverse transformed residual signal only when the quantized frequency conversion coefficient exists.

To this end, the image decoding apparatus 600 comprises a decoding step 1010 of decoding a bit stream and extracting a quantized frequency transform residual signal representing information on a pixel value of a current block of an image, a quantization step of transforming the quantized frequency transform residual signal into a predetermined An inverse quantization step 1020 for inversely quantizing the quantized values according to the positions of respective coefficients according to the scanning method, an inverse transform step 1030 for inversely transforming the inversely quantized frequency transform residual signal into a time domain, An adding step 1050 of restoring the original pixel value of the current block by adding the residual signal of the current block restored in step 1030 and the predicted pixel value of each pixel of the current block predicted in step 1040, And decodes the transmitted bitstream.

Here, the decoding step 1010 corresponds to the operation of the decoding unit 610, the dequantization step 1020 corresponds to the operation of the dequantization unit 620, and the inverse transformation step 1030 corresponds to the operation of the inverse transformation unit 630 And the prediction step 1040 corresponds to the operation of the predicting unit 650 and the addition step 1050 corresponds to the operation of the adder 640, and thus a detailed description thereof will be omitted.

An image encoding / decoding method according to an embodiment of the present invention can be realized by combining an image encoding method according to an embodiment of the present invention and an image decoding method according to an embodiment of the present invention.

According to an aspect of the present invention, there is provided a method for encoding / decoding an image, comprising: generating a prediction block of a current block, generating a residual block by subtracting a prediction block from the current block, transforming the residual block, An image encoding step of quantizing the frequency transform block by varying quantization magnitudes according to positions of frequency coefficients in the frequency transform block and encoding the quantized frequency transform block into a bitstream through entropy coding; And decoding the quantized frequency transform block through an inverse entropy process from the bit stream, restoring the frequency transform block by varying the size of the inverse quantization according to the position of the quantized frequency coefficient in the quantized frequency transform block, And reconstructing a current block by reconstructing a residual block, generating a prediction block by inter-picture prediction or intra-picture prediction information, and adding the reconstructed residual block and the generated prediction block.

Here, the image encoding step may be implemented as an image encoding step according to an embodiment of the present invention, and the image decoding step may be implemented as an image decoding step according to an embodiment of the present invention.

Although all of the constituent elements constituting the embodiment of the present invention can be implemented by one independent hardware, some or all of the constituent elements may be selectively combined to perform some or all of the functions combined in one or a plurality of hardware As a computer program having a program module for performing the functions described herein. The codes and code segments constituting the computer program may be easily deduced by those skilled in the art. Such a computer program can be stored in a computer-readable storage medium, readable and executed by a computer, thereby realizing an embodiment of the present invention. As the storage medium of the computer program, a magnetic recording medium, an optical recording medium, a carrier wave medium, or the like may be included.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

As described above, according to the embodiment of the present invention, when a frequency transform coefficient block obtained by frequency-converting a residual signal between an original video signal and a prediction signal is quantized, quantization is performed by varying the quantization size according to the position of the frequency coefficient, It is a very useful invention because it has the effect of improving the performance.

Claims (22)

An apparatus for encoding / decoding an image, the apparatus comprising:
A residual block is generated by subtracting the prediction block from the current block, and the residual block is transformed to generate a frequency transform block, and the quantization size is varied according to the position of the frequency coefficient in the frequency transform block An image encoder for quantizing the frequency transform block and encoding the quantized frequency transform block into a bit stream through entropy coding; And
The frequency transform block is decoded from the bitstream through the inverse entropy process, the frequency transform block is restored by varying the size of the inverse quantization according to the position of the quantization frequency coefficient in the quantized frequency transform block, An image decoder for restoring a current block by restoring a residual block, generating a prediction block through inter-picture prediction or intra-picture prediction information, adding the reconstructed residual block and the generated prediction block,
And an image encoding / decoding device for decoding the image.
An apparatus for encoding an image, the apparatus comprising:
A prediction unit for generating a prediction block of a current block;
A subtracting unit for subtracting a prediction block from the current block to generate a residual block;
A transform unit for transforming the residual block to generate a frequency transform block;
A quantization unit for quantizing the frequency transform block by varying quantization magnitudes according to positions of frequency coefficients in the frequency transform block;
A bitstream generation unit for encoding the quantized frequency conversion block into a bitstream through entropy coding,
And an image encoding unit for encoding the image.
3. The method of claim 2,
Wherein the quantization unit comprises:
And quantizes the frequency conversion block by varying the quantization size according to the distance from the scanning start point.
The method of claim 3,
Wherein the quantization unit comprises:
Wherein the first and second quantization units have different quantization sizes based on a predetermined distance at a scanning start point.
3. The method of claim 2,
Wherein the quantization unit comprises:
Wherein a size of the quantization is made different for each intra-block area of the frequency conversion block.
3. The method of claim 2,
Wherein the quantization unit comprises:
Wherein the scanning method is different according to the prediction information of the block and the quantization size is changed using the scanning information.
3. The method of claim 2,
The size of the quantization may be,
Wherein a quantization size of a color difference signal and a luminance signal are different in performing quantization on the frequency conversion block.
An apparatus for decoding an image, the apparatus comprising:
A decoding unit that decodes a quantized frequency transform block through an inverse entropy process from a bit stream;
An inverse quantization unit for restoring a frequency transform block by varying the size of the inverse quantization according to a position of a quantization frequency coefficient in the quantized frequency transform block;
An inverse transformer for inversely transforming the frequency transform block to recover a residual block;
A prediction unit for generating a prediction block through intra-picture prediction or intra-picture prediction information; And
An adder for adding the reconstructed residual block and the generated prediction block to reconstruct a current block,
And an image decoding unit for decoding the image.
9. The method of claim 8,
Wherein the inverse-
And reconstructs the frequency transform block by varying the size of the inverse quantization according to the distance from the start point of the inverse scanning.
10. The method of claim 9,
Wherein the inverse-
Wherein the quantizer has a different inverse quantization size on the basis of a certain distance from the start point of the inverse scanning.
9. The method of claim 8,
Wherein the inverse-
Wherein the size of the inverse quantization is made different for each of the in-block areas of the frequency conversion block.
9. The method of claim 8,
Wherein the inverse-
Wherein the inverse quantization method is different from the inverse quantization method according to the extracted prediction information.
9. The method of claim 8,
The size of the inverse quantization may be,
Wherein the inverse quantization magnitudes of the chrominance signal and the luminance signal are different in performing restoration of the frequency transform block.
A method of encoding / decoding an image,
A residual block is generated by subtracting the prediction block from the current block, and the residual block is transformed to generate a frequency transform block, and the quantization size is varied according to the position of the frequency coefficient in the frequency transform block An image encoding step of quantizing the frequency transform block and encoding the quantized frequency transform block into a bit stream through entropy coding; And
The frequency transform block is decoded from the bitstream through the inverse entropy process, the frequency transform block is restored by varying the size of the inverse quantization according to the position of the quantization frequency coefficient in the quantized frequency transform block, An image decoding step of restoring a current block by restoring a residual block, generating a prediction block through intra-picture prediction or intra-picture prediction information, adding the restored residual block and the generated prediction block,
And decoding the encoded image.
A method of encoding an image,
A prediction step of generating a prediction block of a current block;
A subtraction step of subtracting a prediction block from the current block to generate a residual block;
A transforming step of transforming the residual block to generate a frequency transform block;
A quantization step of quantizing the frequency conversion block by varying quantization magnitudes according to positions of frequency coefficients in the frequency conversion block;
A bitstream generation step of encoding the quantized frequency conversion block into a bitstream through entropy coding;
Wherein the image encoding method comprises:
16. The method of claim 15,
In the quantization step,
Wherein the frequency conversion block is quantized by varying a quantization size according to a distance from a scanning start point.
17. The method of claim 16,
In the quantization step,
Wherein the quantization step has a different quantization size with respect to a certain distance at a scanning start point.
16. The method of claim 15,
The size of the quantization may be,
Wherein quantization magnitudes of the color difference signal and the luminance signal are different in performing quantization on the frequency conversion block.
A method for decoding an image,
A decoding step of decoding a quantized frequency conversion block through an inverse entropy process from a bitstream;
An inverse quantization step of restoring a frequency transform block by varying the magnitudes of inverse quantization according to positions of quantization frequency coefficients in the quantized frequency transform block;
An inverse transform step of inversely transforming the frequency transform block to recover a residual block;
A prediction step of generating a prediction block through intra-picture prediction or intra-picture prediction information; And
An addition step of adding the reconstructed residual block and the generated prediction block to reconstruct a current block;
And decoding the decoded image.
20. The method of claim 19,
In the inverse quantization step,
Wherein the frequency transformation block is reconstructed by varying the size of the inverse quantization according to the distance from the start point of the inverse scanning.
21. The method of claim 20,
In the inverse quantization step,
Wherein the inverse quantization step has a different inverse quantization size with respect to a certain distance at a start point of the inverse scanning.
20. The method of claim 19,
The size of the inverse quantization may be,
Wherein the inverse quantization magnitudes of the chrominance signal and the luminance signal are different in performing restoration of the frequency transform block.

Images