KR20140129409A - Method for encoding and decoding image using transform, and apparatus thereof - Google Patents

Abstract

A method and an apparatus for encoding / decoding an image according to the present invention, the encoding method comprising the steps of transforming a residual signal into a transform coefficient by applying an Hadamard transform; Quantizing the transform coefficient; Scanning the quantized transform coefficients based on the location where the quantized transform coefficients are present; And performing entropy coding on the scanned transform coefficients.

Description

TECHNICAL FIELD The present invention relates to a method and apparatus for encoding / decoding images using a transform,

The present invention relates to an image encoding / decoding method and apparatus, and more particularly, to a method of performing a transform using a transform having +1 and -1 during encoding and decoding.

Generally, in video coding, intra prediction and inter prediction are used to generate a residual signal. The reason why the residual signal is obtained is that when the data is coded with the residual signal, the amount of data is small, so that the data compression rate is high, and the better the prediction, the smaller the value of the residual signal is.

The intraprediction method predicts the data of the current block by using the pixels around the current block. The difference between the actual value and the predicted value is called a residual signal block. In the case of HEVC, the intra prediction method is increased to 35 prediction modes as shown in FIG. 1 in nine prediction modes used in the existing H.264 / AVC, and is further segmented and predicted (the planar prediction mode and the DC prediction mode 1).

In the case of the inter prediction method, the current block is compared with the blocks in the neighboring pictures to find the closest block. At this time, the position information (Vx, Vy) of the found block is referred to as a motion vector. The difference between the intra-block pixel values of the current block and the prediction block predicted by the motion vector is called a residual-signal block (motion-compensated residual block).

In this way, intra prediction and inter prediction are further subdivided so that the amount of data of the residual signal is reduced, and a video coding and decoding method with a small amount of computation is required without degrading the codec performance using an efficient transform.

An embodiment of the present invention provides a video encoding and decoding method having good performance with a small amount of computation in a transcoding process of a video codec and an apparatus therefor.

It is to be understood, however, that the technical scope of the present invention is not limited to the above-described technical problems, and other technical problems may be present.

According to an aspect of the present invention, there is provided an image encoding method including transforming a residual signal into a transform coefficient by applying an Hadamard transform to the residual signal; Quantizing the transform coefficients; Scanning the quantized transform coefficients based on a location where the quantized transform coefficients are present; And performing entropy coding on the scanned transform coefficients.

According to an aspect of the present invention, there is provided an image encoding apparatus including: a transform unit configured to apply a transform matrix to a residual signal to form a transform coefficient; A quantization unit for quantizing the transform coefficient; A scanning unit that scans the quantized transform coefficients based on a position where the quantized transform coefficients exist; And an entropy coding unit for performing entropy coding on the scanned transform coefficients.

According to another aspect of the present invention, there is provided a method of decoding an image, the method comprising the steps of: constructing a quantized residual signal block by performing inverse scanning according to information transmitted from an encoder; Performing inverse quantization on the quantized residual signal block; And performing inverse transform using the Hadamard transform on the inversely quantized residual signal block.

Also, an image decoding apparatus according to an embodiment of the present invention includes an inverse scanning unit configured to perform quantized residual signal blocks by performing inverse scanning according to information transmitted from an encoding apparatus; A dequantizer for dequantizing the quantized residual signal block; And an inverse transformer performing an inverse transform using the Hadamard transform on the inverse quantized residual signal block.

Meanwhile, the image encoding and decoding method may be embodied as a computer-readable recording medium on which a program to be executed by a computer is recorded.

According to the present invention, it is possible to provide a video encoding and decoding method having a good performance with a small amount of computation in the process of transform coding a video codec, and an apparatus therefor.

In addition, the video coding efficiency can be further improved by applying different scanning procedures and methods to the Hadamard transform.

1 is a diagram showing examples of intra prediction modes.
2 is a block diagram showing a configuration of an encoding apparatus according to an embodiment of the present invention.
3 is a view for explaining a first embodiment of a scanning method suitable for a transform according to the present invention.
4 is a view for explaining a second embodiment of a scanning method suitable for a transform according to the present invention.
5 is a view for explaining a third embodiment of a scanning method suitable for a transform according to the present invention.
6 is a view for explaining a fourth embodiment of a scanning method suitable for a transform according to the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. It should be understood, however, that the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In the drawings, the same reference numbers are used throughout the specification to refer to the same or like parts.

Throughout this specification, when a part is referred to as being "connected" to another part, it is not limited to a case where it is "directly connected" but also includes the case where it is "electrically connected" do.

Throughout this specification, when a member is " on " another member, it includes not only when the member is in contact with the other member, but also when there is another member between the two members.

Throughout this specification, when an element is referred to as "including " an element, it is understood that the element may include other elements as well, without departing from the other elements unless specifically stated otherwise. The terms "about "," substantially ", etc. used to the extent that they are used throughout the specification are intended to be taken to mean the approximation of the manufacturing and material tolerances inherent in the stated sense, Accurate or absolute numbers are used to help prevent unauthorized exploitation by unauthorized intruders of the referenced disclosure. The word " step (or step) "or" step "used to the extent that it is used throughout the specification does not mean" step for.

Throughout this specification, the term " combination thereof " included in the expression of the machine form means one or more combinations or combinations selected from the group consisting of the constituents described in the expression of the machine form, And the like.

As an example of a method of encoding an actual image and its depth information map, the Moving Picture Experts Group (MPEG) and the Video Coding Experts Group (VCEG) having the highest coding efficiency among the video coding standards developed so far jointly standardize Encoding can be performed using HEVC (High Efficiency Video Coding).

The image encoding and decoding method according to the embodiment of the present invention can apply a transform having a kernel of +1 and -1 to the residual block.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning method applied when a Hadamard Transform is used in a transform method that is a technique applied to moving picture encoding / decoding.

In detail, the scanning order and method are applied differently according to the characteristics of the Hadamard transform, and it is predicted by using a decoding / decoding method and neighboring mode information, And can include all methods that can be decoded without signaling.

In HEVC, interpolation is performed using a DCT-based interpolation filter (DCT-IF) when interpolating sub-sample values for color difference signals. The reason for this is that in order to further reduce the residual signal, the motion prediction using an 8-point FIR filter in units of sub-integer pixels, which is finer than the motion prediction compensation of an integer pixel, (For chroma blocks, motion prediction compensation is performed using a 4-point FIR filter of 1/8 pixel unit in YUV 4: 2: 0 color format).

Also, 1/8 or 1/16 interpolation can be used for Luma for more sophisticated motion prediction and compensation.

Currently, intraprediction and inter prediction are further subdivided to reduce the amount of residual signal data, and more sophisticated prediction methods are being tried. Therefore, the video encoding and decoding method according to an embodiment of the present invention uses a transform having kernels of + 1 / -1 rather than using an existing integer transform using DCT or DST . There is no difference in the performance of the codec, and the use of kernels of + 1 / -1 reduces the amount of computation compared to other kernels.

An example of a transform of k + 1 / -1 kernels is the Hadamard Transform. Hadamard transform is a matrix of +1 and -1. The Hadamard transform form is constructed as shown in Equation 1 below.

Equation (1) means a one-dimensional forward Hadam transform and an inverse Hadamard transform. Because Hadamard transforms are separable transforms, 2D transforms can be easily implemented by applying one-dimensional transforms horizontally and then vertically (or vertically applying them horizontally).

The following equation (2) represents a one-dimensional 4-point, 8-point Hadamard transform (N = 4,8).

Equation (2) represents an orthogonal vector in which each row (base vector) is denoted by an inner product. That is, A-1 = AT. Also, the kernels are made up of +1 and -1 except for constants.

The order of the rows can be changed to 0-4-6-2-3-7-5-1 (order of arrangement of basis vectors), or used as is.

In the equation (2), the value of N can be scaled only after (N = 4, 8 in equation (2)). The above example is an example of transform application for 4x4 residual block and 8x8 residual block, but the proposed transform can be applied to 16x16, 32x32 residual block as above (N = 2n, n is a positive integer) .

According to an embodiment of the present invention, when a transform having kernels of + 1 / -1 is used in a transcoding process in a video codec, a good performance can be achieved with a small amount of calculation.

FIG. 2 is a block diagram illustrating a configuration of an image encoding apparatus according to an embodiment of the present invention. Referring to FIG.

Generally, the encoding apparatus includes an encoding process and a decoding process, and the decoding apparatus has a decoding process. The decoding process of the decoding apparatus is the same as the decoding process of the encoding apparatus. Therefore, the encoding apparatus will be mainly described below.

2, an image encoding apparatus according to an exemplary embodiment of the present invention includes an encoding unit and structure, Inter prediction, Intra prediction, Interpolation, Filtering, Transform ) Method and so on.

2, the image encoding apparatus includes an encoding mode determination unit 110, an intra prediction unit 120, a motion compensation unit 130, a motion estimation unit 131, a transcoding / quantization unit 140, A dequantization / conversion decoding unit 160, a deblocking filtering unit 170, a picture storage unit 180, a subtracting unit 190, and an adding unit 200. The dequantization /

The encoding mode determination unit 110 analyzes an input video signal to divide a picture into a predetermined size of an encoding block, and determines a coding mode for the divided predetermined size of the encoding block. The encoding mode includes intraprediction encoding and inter prediction encoding.

The picture is composed of a plurality of slices, and the slice is composed of a plurality of maximum coding units (LCU). The LCU can be divided into a plurality of coding units (CUs), and the encoder can add information indicating whether or not to be divided to a bit stream. The decoder can recognize the position of the LCU by using the address (LcuAddr). The coding unit CU in the case where division is not allowed is regarded as a prediction unit (PU), and the decoder can recognize the position of the PU using the PU index.

The prediction unit PU may be divided into a plurality of partitions. Also, the prediction unit PU may be composed of a plurality of conversion units (TUs).

The encoding mode determination unit 110 sends the image data to the subtraction unit 190 in units of blocks of a predetermined size (for example, in units of PU or TU) according to the determined encoding mode.

The transform coding / quantizing unit 140 transforms the residual block calculated by the subtracting unit 190 from the spatial domain to the frequency domain. For example, two-dimensional discrete cosine transform (DCT) or discrete cosine transform (DST) -based transform is performed on the residual block.

In addition, the transcoding / quantization unit 140 determines a quantization step size for quantizing the transform coefficient, and quantizes the transform coefficient using the determined quantization step size. The quantization matrix can be determined according to the determined quantization step size and encoding mode.

The quantized two-dimensional transform coefficients are transformed into one-dimensional quantized transform coefficients by one of the predetermined scanning methods. The transformed one-dimensional sequence of quantization transform coefficients is supplied to the entropy encoding unit 150.

The inverse quantization / conversion decoding unit 160 dequantizes the quantization coefficients quantized by the transcoding / quantization unit 140. Further, the inverse quantization coefficient obtained by inverse quantization is inversely transformed. Thus, the residual block transformed into the frequency domain can be restored into the residual block in the spatial domain.

The deblocking filtering unit 170 receives the inverse quantized and inverse transformed image data from the inverse quantization / inverse transform coding unit 160 and performs filtering to remove a blocking effect.

The picture storage unit 180 receives the filtered image data from the deblocking filtering unit 170 and restores and restores the image in picture units. The picture may be a frame-based image or a field-based image. The picture storage unit 180 has a buffer (not shown) capable of storing a plurality of pictures. A plurality of pictures stored in the buffer are provided for intra prediction and motion estimation.

The pictures provided for intra prediction or motion estimation are referred to as reference pictures.

The motion estimation unit 131 receives the at least one reference picture stored in the picture storage unit 180 and performs motion estimation to output motion data including an index indicating a motion vector and a reference picture and a block mode do.

In order to optimize the prediction precision, a motion vector is determined with a fractional pixel precision, for example, 1/2 or 1/4 pixel accuracy. Since the motion vector can have a fractional pixel precision, the motion compensation unit 130 applies the interpolation filter for calculating the pixel value of the fractional pixel position to the reference picture so that the pixel value of the fractional pixel position .

The motion compensation unit 130 is configured to perform motion compensation on a block to be coded from a reference picture used for motion estimation among a plurality of reference pictures stored in the picture storage unit 180 according to the motion data input from the motion estimation unit 131 And outputs the extracted prediction block.

The motion compensation unit 130 determines a filter characteristic of the adaptive interpolation filter necessary for motion compensation with a decimal precision. The filter characteristic is, for example, information indicating the filter type of the adaptive interpolation filter and information indicating the size of the adaptive interpolation filter.

The size of the filter is, for example, the number of taps, which is the number of filter coefficients of the adaptive interpolation filter.

Specifically, the motion compensation unit 130 may determine either a separate type or a non-separable type adaptive filter as an adaptive interpolation filter. Then, the number of taps of the determined adaptive interpolation filter and the value of each filter coefficient are determined. The value of the filter coefficient can be determined differently for each position of the fractional pixel relative to the integer pixel. Also, the motion compensation unit 130 may use a plurality of non-adaptive interpolation filters with fixed filter coefficients.

The motion compensation unit 130 can set the characteristics of the interpolation filter in a predetermined processing unit. For example, it can be set in a fractional pixel unit, a coding basic unit (encoding unit), a slice unit, a picture unit, or a sequence unit. In addition, one characteristic may be set for one video data.

Therefore, since the same filter characteristic is used in a predetermined processing unit, the motion compensation unit 130 has a memory that temporarily holds the filter characteristic. This memory maintains filter characteristics, filter coefficients, and the like as needed. For example, the motion compensation unit 130 can determine the filter characteristic for each I picture and determine the filter coefficient for each slice.

The motion compensation unit 130 receives a reference picture from the picture storage unit 180 and applies a filter process using the determined adaptive interpolation filter to generate a prediction reference picture of a decimal precision.

Then, based on the generated reference picture and the motion vector determined by the motion estimation unit 131, motion compensation is performed with a small number of pixels to generate a prediction block.

The subtractor 190 receives the block in the reference picture corresponding to the input block from the motion compensator 130 and performs a difference operation with the input macroblock in the case of performing inter picture prediction coding on the input block to be coded, and outputs a residue signal.

The intraprediction unit 120 performs intraprediction encoding using the reconstructed pixel values in a picture to be predicted. The intra prediction unit receives the current block to be predictively encoded and performs intra prediction by selecting one of a plurality of intra prediction modes preset according to the size of the current block. The intra predictor 120 determines the intra prediction mode of the current block using the previously coded pixels adjacent to the current block, and generates a prediction block corresponding to the determined mode.

The previously encoded region of the current picture is decoded again for use by the intra prediction unit 120 and stored in the picture storage unit 180. [ The intra prediction unit 120 generates a prediction block of a current block using pixels neighboring the current block or non-adjacent but applicable pixels in the previously coded area of the current picture stored in the picture storage unit 180. [

The intra prediction unit 120 may adaptively filter adjacent pixels to predict an intra block. For the same operation in the decoder, it is possible to transmit information indicating whether or not filtering is performed in the encoder. Or the intra-prediction mode of the current block and the size information of the current block.

The prediction type used by the image coding apparatus depends on whether the input block is coded in the intra mode or the inter mode by the coding mode determination unit.

The switching between the intra mode and the inter mode is controlled by the intra / inter selector switch.

The entropy encoding unit 150 entropy-codes the quantization coefficients quantized by the transcoding / quantization unit 140 and the motion information generated by the motion estimation unit 131. [ Also, an intra prediction mode, control data (e.g., quantization step size, etc.), and the like can be coded. Also, the filter coefficient determined by the motion compensation unit 130 is encoded and output as a bit stream.

Referring to FIG. 2, the encoder according to an exemplary embodiment of the present invention may perform a transform of an 8 × 8 DCT, a 16 × 16 DCT, a 32 × 32 DCT, or a 4 × 4 DST, which is used in a transform process of a conventional HEVC encoder, It is configured using the proposed transforms with configured 4x4, 8x8, 16x16, 32x32 kernels.

Also, when the proposed transform is applied to the encoder, the decoder applies the inverse transform (A-1 = AT) with the proposed kernels of + 1 / -1 in the process of inversion of the transform.

Here, when the transformer proposed in the encoding apparatus according to FIG. 2 is used, the inverse transform proposed in the decoding process is applied.

As another example, when using a transform proposed by any video encoder, the proposed inverse transform is applied to the decoding process.

As described above, the configuration of the image decoding apparatus according to the embodiment of the present invention can be derived from the configuration of the image encoding apparatus shown in FIG. 2, and for example, the inverse of the encoding process as described with reference to FIG. 2 So that the image can be decoded.

An embodiment of the present invention relates to a scanning method applied when a Hadamard Transform is used in a transform (Transform) method which is a technique applied to moving image encoding / decoding.

In detail, the scanning order and method are applied differently according to the characteristics of the Hadamard transform, and it is predicted by using a decoding / decoding method and neighboring mode information, And all methods that can be decoded without signaling.

The coefficients using Hadamard Transform are quantized and bitstreams are generated through entropy coding according to the scanning method. Here, we can perform the scanning through the Hadamard Transform as shown in the following example.

FIG. 3 is a view for explaining a first embodiment of a scanning method suitable for a transform according to the present invention, and shows an example of a scanning method for an 8x8 block. This can be applied to various block sizes.

As shown in FIG. 3, the method includes a scanning method from the upper left to the lower right and a scanning method from the lower right to the upper left, and scanning can be applied in various methods according to the mode information.

The above four scanning methods are simple examples, and the scanning methods in various orders can be equally applied to coding and decoding.

Since the prediction performance is improved, the Hadamard transform will have fewer transformed coefficients in quantization than the existing integer type DCT and integer type DST. Hadamard transform can use a kernel composed of 1, -1 The amount of computation can be reduced.

That is, the Hadamard Transform can have similar characteristics as the integer DCT and DST, and thus has the characteristics of being divided into DC and AC, but the reason for using the Hadamard transform is that the predicted value is very small To eliminate multiply operations and to use the improved transforms.

When the residual signal is small, the transformed coefficients may be distributed in a very small number. In this case, it is necessary to select an optimal scanning method by varying the scanning methods applied in entropy coding through various scanning methods.

For example, in the intra block, the best scanning method is determined in terms of vertical scanning in the horizontal prediction mode, horizontal scanning in the vertical prediction mode, and rate-distortion in the vertical prediction mode, and the information about the scanning method can be signaled to the decoder have.

4 shows an example of a method of dividing the inside of the 8x8 block into four scanning methods.

This method also includes a method of transmitting a form by signaling with a decryptor / decoder or a method of scanning in a promised form using peripheral information.

FIG. 5 is a diagram for explaining an embodiment of a method of dividing the inside of a block of 8x8 into four sub-blocks and scanning. In the case where a coefficient exists at a position as shown in FIG. 5, An example of dividing a block into 4 blocks and performing 4x4 scanning is shown below.

The distribution point in FIG. 5 indicates the positions where the transformed and quantized coefficients are present. When the coefficients are distributed from the upper left corner to the coefficients from the upper left corner, the scanning is performed by the dividing method, The performance can be improved.

In this case, the entropy coding plays a very important role in the performance.

FIG. 6 shows a case where all the coefficients are distributed in the upper left corner. In this case, when the entire block size is scanned to 8x8 without dividing the block, the performance is improved or the performance is better than the dividing method Includes all of the options you can use selectively.

That is, the present invention refers to a method of improving performance through a scanning method that does not divide or divide according to the distribution of coefficients.

The present invention relates to a scanning method which can be applied when a Hadamard transform is used. As described above, all the scanning methods include a method of transmitting information to a decoder / decoder through signaling, Information, MV information, and the like).

The method according to the present invention may be implemented as a program for execution on a computer and stored in a computer-readable recording medium. Examples of the computer-readable recording medium include a ROM, a RAM, a CD- , A floppy disk, an optical data storage device, and the like, and may also be implemented in the form of a carrier wave (for example, transmission over the Internet).

The computer readable recording medium may be distributed over a networked computer system so that computer readable code can be stored and executed in a distributed manner. And, functional programs, codes and code segments for implementing the above method can be easily inferred by programmers of the technical field to which the present invention belongs.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, It should be understood that various modifications may be made by those skilled in the art without departing from the spirit and scope of the present invention.

Claims (13)

A method of encoding an image,
Transforming the residual signal by applying an Hadamard transform to the transform coefficient;
Quantizing the transform coefficients;
Scanning the quantized transform coefficients based on a location where the quantized transform coefficients are present; And
And performing entropy coding on the scanned transform coefficients. 2. The method of claim 1, wherein the scanning step
Wherein the order is set differently according to the characteristics of the Hadamard transform. 2. The method of claim 1, wherein the scanning step
And dividing the residual signal block into a plurality of sub-blocks and performing scanning for each divided sub-block. The method of claim 3,
Wherein at least one of the division into the sub-blocks and the number of sub-blocks to be divided is determined according to a position where the quantized transform coefficient exists. 2. The method of claim 1, wherein the scanning step
And applying the scanning order to the quantized transform coefficients differently according to the intra prediction mode. The method according to claim 1,
And signaling information on a scanning scheme performed on the quantized transform coefficients to a decoding apparatus. An apparatus for encoding an image, the apparatus comprising:
A transform unit for applying a Hadamard transform to the residual signal to construct a transform coefficient;
A quantization unit for quantizing the transform coefficient;
A scanning unit that scans the quantized transform coefficients based on a position where the quantized transform coefficients exist; And
And an entropy coding unit for performing entropy coding on the scanned transform coefficients. 8. The apparatus according to claim 7, wherein the scanning unit
And divides the residual signal block into a plurality of sub-blocks and performs scanning for each divided sub-block. 9. The method of claim 8,
Wherein at least one of the division into the sub-blocks and the number of sub-blocks to be divided is determined according to a position where the quantized transform coefficient exists. A method for decoding an image,
Performing inverse scanning according to information transmitted from an encoding device to construct a quantized residual signal block;
Performing inverse quantization on the quantized residual signal block; And
And performing inverse transform using the Hadamard transform on the inverse quantized residual signal block. 11. The apparatus of claim 10, wherein the information transmitted from the encoder
Wherein the residual signal block exists for each of a plurality of sub-blocks divided. 12. The apparatus of claim 11, wherein the information transmitted from the encoder
And dividing the sub-blocks into sub-blocks and information on at least one of the number of sub-blocks to be divided. An apparatus for decoding an image, the apparatus comprising:
An inverse scanning unit configured to perform inverse scanning according to information transmitted from an encoding device to construct a quantized residual signal block;
A dequantizer for dequantizing the quantized residual signal block; And
And an inverse transformer for performing an inverse transform using the Hadamard transform on the inverse quantized residual signal block.

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