KR20140129418A - Method for intra-prediction using residual transform, and apparatus thereof - Google Patents

Abstract

The present invention relates to an intra-prediction apparatus and an intra-prediction method comprising: a step of generating a residual signal according to an intra-prediction mode; a step of performing the residual transform by applying pixel unit DPCM in a first direction to the residual signal; and a step of performing a cross residual transform by applying pixel unit DPCM in a second direction to the residual signal which is residual transformed.

Description

[0001] The present invention relates to an intra prediction method and an apparatus using residual transformation,

The present invention relates to an image encoding / decoding method and apparatus, and more particularly, to a method of performing intra prediction using residual transformation in 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 intra prediction method comprising: generating a residual signal according to an intra prediction mode; Performing residual transformation by applying a pixel-by-pixel DPCM in a first direction to the residual signal; And performing cross-residual transformation by applying a pixel-by-pixel DPCM in the second direction to the residual-transformed residual signal.

According to another aspect of the present invention, there is provided an intra prediction apparatus comprising: a residual signal generator for generating a residual signal according to an intra prediction mode; A residual transformation performing unit for performing residual transformation by applying a pixel-by-pixel DPCM in a first direction to the residual signal; And an intersection residual transformation performing unit for performing an intersection residual transformation by applying a pixel-based DPCM in a second direction to the residual-transformed residual signal, and the intersection residual transformation is selectively performed.

Meanwhile, the intraprediction method may be embodied as a computer-readable recording medium on which a program for execution in a computer is recorded.

According to the embodiment of the present invention, the residual signal is selectively minimized by performing a residual transform and a crossed residual transform instead of the existing intra prediction, thereby improving the compression performance .

1 is a diagram showing examples of intra prediction modes.
2 is a diagram showing an embodiment of a method of performing residual transformation.
3 is a diagram illustrating an embodiment of a residual signal in which intraprediction is performed.
4 is a diagram showing an embodiment of the result of performing the residual transformation.
5 is a block diagram showing a configuration of an encoding apparatus according to an embodiment of 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).

An embodiment of the present invention relates to a video encoding / decoding method and apparatus, and more particularly, to a video encoding / decoding method and apparatus for improving coding performance by reducing a residual signal in coding / decoding of a block-based lossless intra prediction method.

According to an embodiment of the present invention, a residual transform and a crossed residual transform are selectively performed instead of the existing intra prediction. The present invention is applied only to the vertical or horizontal direction and existing prediction can be applied to other directions.

Here, the residual transformation is performed by using pixel-based DPCM in the prediction direction using the residual signal as a result of intra prediction, with reference to FIG.

FIG. 2 is a diagram for explaining an embodiment of a method of performing pixel-by-pixel DPCM on a residual signal, and shows a case of a vertical direction (mode 26) intraprediction of HEVC (High Efficiency Video Coding).

Referring to FIG. 2, l and q are used as reference pixels to predict pixel p in the current block.

The difference between the pixel in the current block and the reference pixel is obtained in accordance with the prediction direction to obtain the residual signal, and the equation for obtaining the residual signal of the first column is expressed by Equation 1 below.

In Equation (1), r denotes a residual signal and can be expressed as shown in FIG.

In the lossless intra prediction, since the conventional prediction method is not transformed and quantized when the conventional method is applied, the residual signal becomes large and the compression rate is low.

In order to solve this problem, a pixel-based DPCM used as a reference pixel in a current block can also be used.

That is, the residual transformation in the present invention is a method of maintaining a block-based processing structure during decoding while performing pixel-by-pixel DPCM in a prediction direction using a residual signal as a result of intraprediction, and a block of HEVC (High Efficiency Video Coding) Unlike a prediction based on a current block, a pixel within a current block to be predicted is used as a reference pixel to generate a residual signal between adjacent pixels in a prediction direction (intra prediction mode), thereby minimizing the residual signal.

On the other hand, in the case of the pixel-by-pixel DPCM, since the pixel-unit DPCM must be restored in pixel units, it may violate the block unit process. However, when restoration is performed using the residual transformation as shown in the following Equation 3, the pixel-by-pixel DPCM can be used while maintaining the block unit processing.

As a concrete example, the encoder applies the pixel-by-pixel DPCM (applying the residual transformation) in the same way as the intra prediction direction in the existing HEVC, and then calculates the residual signal as shown in Equation 3 to decode the residual signal at the decoder side Inverse residual transform is used to decode block-based processing structure.

Since lossless intra compression does not go through transformation and quantization unlike lossy intra compression, the residual signal occupies the largest part of the coding efficiency. Therefore, the adjacent pixel having the most similar value to the current pixel is used as the reference pixel It is advantageous in compression.

In addition, the present invention has an advantage that it is not in violation of the block-based structure of the existing HEVC since it is restored by using the residual signal r 'which is known information transmitted from the encoder to the decoder without the restoration delay which is a disadvantage of the pixel-based DPCM .

In encoding, the residual signal obtained by applying the residual transform (pixel-by-pixel DPCM) as shown in Equation 2 is represented by r 'and can be expressed as shown in FIG.

The residual transformation is the horizontal direction in the existing intra prediction (mode 10). It can be applied to the vertical direction (mode 26) in the same way as above, and it can be applied in all other modes.

According to an embodiment of the present invention, the cross-residual transform may be selectively performed after the residual transform as described above is performed.

In the present invention, the crossover residual transform is a process of applying the residual transform described above to the intra prediction direction to obtain the residual signal r 'and then applying the residual transform to the residual signal r' in a direction intersecting the intra prediction direction again To obtain the residual signal r ".

After performing the above residual transform, it is a crossed residual transform to perform the residual transform opposite to the prediction direction, and it can be expressed by the following equation (4).

On the other hand, the above-described cross-residual transformation can be selectively applied. For example, if the residual transform is vertical, the cross residual transform is applied horizontally, and if the residual transform is horizontal, the cross residual transform can be applied vertically.

After performing the above-mentioned cross-residual transform, the frequency domain transform and the quantization process are omitted because they are lossless compression methods, and the entropy process can be the same as the conventional intra-video compression method (such as HEVC).

In the decoding process, the above process is reversed. In the coding process, the prediction is performed in the vertical direction. Then, the block subjected to the residual transformation and the cross-residual transformation is subjected to block-based inverse cross- (Inverse Crossed Residual Transform) is applied and can be expressed by Equation (5) as follows.

The result r 'obtained after performing the inverse intersection residual transformation (horizontal direction) as shown in Equation (5) above can be decoded in the vertical direction in the same manner as the restoration process of the block-based residual transformation described above.

The residual transform and the residual residual transform according to the present invention can be selectively applied. When residual transform is applied during encoding, the inverse residual transform is applied during decoding. When the residual transform is applied during encoding, The cross residual transform is applied.

According to the embodiment of the present invention, the selective execution of the residual transform and the crossed residual transform as described above is applied only to the vertical or horizontal direction, and the existing prediction method Can be applied.

The choice of residual and crossover residual transforms in the present invention is based on rate-distortion optimization (RDO), which selects two methods in the encoder and calculates the bit rate and distortion degree (RD-Optimization) And the case where only one method is used through the option setting in the header.

In the case of the rate-distortion optimization (RDO) process, after applying both the residual transformation and the cross-residual transformation, the rate-distortion optimization method selects a method with a lower cost.

To distinguish the selected method from the decoder, the encoder adds a signaling bit of 0 or 1 when the mode is transmitted.

On the other hand, in the case of setting an option in the header, the header further includes a bit for determining on / off of using the cross residual transform. On indicates that the two methods are selected through the rate-distortion optimization described above. If it is off, only the residual transformation is used without additional signaling bits.

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

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.

As shown in FIG. 5, 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.

5, 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. Accordingly, 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.

As described above, the configuration of the image decoding apparatus according to an embodiment of the present invention can be derived from the configuration of the image encoding apparatus shown in FIG. 5, and for example, the inverse of the encoding process as described with reference to FIG. 5 So that the image can be decoded.

Meanwhile, in the lossless prediction according to an embodiment of the present invention, a filtering process such as a conversion and quantization process and a deblocking filter as described with reference to FIG. 5 may be omitted.

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 (9)

A method for performing intra prediction,
Generating a residual signal according to an intra prediction mode;
Performing residual transformation by applying a pixel-by-pixel DPCM in a first direction to the residual signal; And
And performing cross-residual transformation by applying a pixel-by-pixel DPCM in a second direction to the residual-transformed residual signal. The method according to claim 1,
Wherein the first direction is the same as the direction corresponding to the intra prediction mode. The method according to claim 1,
Wherein the first direction and the second direction are directions perpendicular to each other. The method according to claim 1,
And a direction corresponding to the intra-prediction mode is a vertical or horizontal direction. The method according to claim 1,
Wherein the cross-residual transform is selectively performed. The method according to claim 1,
And transmitting information on whether the cross-residual transformation is performed to a decoding apparatus. An apparatus for performing intra prediction, the apparatus comprising:
A residual signal generating unit for generating a residual signal according to the intra prediction mode;
A residual transformation performing unit for performing residual transformation by applying a pixel-by-pixel DPCM in a first direction to the residual signal; And
And an intersection residual transformation performing unit for performing an intersection residual transformation by applying a pixel-by-pixel DPCM in a second direction to the residual-transformed residual signal,
Wherein the cross-residual transform is performed selectively. 8. The method of claim 7,
Wherein the first direction is the same as the direction corresponding to the intra prediction mode and the second direction is perpendicular to the direction corresponding to the intra prediction mode. 8. The method of claim 7,
And the direction corresponding to the intra-prediction mode is a vertical or horizontal direction.

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