KR20140129420A - Method for intra-prediction using residual transform, and apparatus thereof - Google Patents

Abstract

A method and apparatus for performing intraprediction of the present invention includes generating a residual signal according to an intra prediction mode corresponding to a first direction, Performing a residual transformation on a residual signal by applying a pixel-by-pixel DPCM in a second direction intersecting with the first direction; And performing a transform and quantization process on the residual-transformed signal.

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 corresponding to a first direction; Performing a residual transformation on the residual signal by applying a pixel-by-pixel DPCM in a second direction intersecting with the first direction; And performing a transform and quantization process on the residual-transformed signal.

According to another aspect of the present invention, there is provided an intra prediction apparatus including: a residual signal generating unit generating a residual signal according to an intra prediction mode corresponding to a first direction; A residual transformation performing unit for performing residual transformation on a pixel-by-pixel DPCM in a second direction intersecting with the first direction with respect to the residual signal; A transform unit for transforming the residual-transformed signal to output transform coefficients; And a quantization unit for performing quantization on the transform coefficients.

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 an embodiment of the present invention, a residual transform and a crossed residual transform are selectively performed for all intra modes, such as vertical, horizontal, and diagonal directions, instead of the existing intra prediction, So that the compression performance can be improved.

In addition, by applying the crossover residual transform in the lossy intra coding, the residual signal can be reduced, and the coding efficiency expected from the transform and quantization can be further increased.

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 showing an embodiment of the result of performing the residual transformation.
4 is a block diagram showing a configuration of an encoding apparatus according to an embodiment of the present invention.
5 to 7 are block diagrams showing embodiments of the configuration of a decoding apparatus 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 embodiment of the present invention selectively performs a residual transform and a crossed residual transform instead of the existing intra prediction.

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.

Referring to FIG. 2, it is an example of a vertical direction (26th mode) intra prediction of a conventional HEVC (High Efficiency Video Coding). We use l and q as reference pixels to predict the 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 the above equation, r 'denotes the residual signal and can be expressed as shown in FIG.

That is, at the time of encoding, the residual signal obtained by applying the residual transform as shown in Equation (1) is expressed as 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.

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 (2).

Cross-residual transformations are optionally applicable. (In the present example, the cross-residual transform is applied horizontally if the residual transform is vertical. If the residual transform is horizontal, the cross-residual transform is applied vertically)

After performing the above cross residual transform, a frequency domain transform and a quantization process are applied, and the entropy process is the same as that of the existing 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 (3) as follows.

The result r 'obtained after performing the inverse intersection residual transformation (horizontal direction) as shown in Equation (3) above can be decoded in the vertical direction in the same manner as in 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.

According to another embodiment of the present invention, a residual transform and a crossed residual transform can be selectively performed in place of the existing intra prediction for the selected region.

Here, the selection region means that a divided region such as an object or a block is designated according to a specific purpose or characteristics of an image.

Also, in order to decode the residual transform or the residual residual transform applied to the selected region, the signaling bit is transmitted to the selected region during encoding.

For signaling bit transmission for decoding, n bits can be used. In addition, various methods can be applied such as a method in which only the residual transformation is applied to the selected region, a method in which only the cross residual transformation is applied, and a method in which residual transformation and cross residual transformation are selectively applied.

Meanwhile, the selection region is divided into regions based on existing object classification, extraction method, segmentation, ROI, etc., and can be classified into various methods in addition to the above-described method.

In the case of designation of the block selection area, it is possible to arbitrarily select it or select it through a specific algorithm. For example, the designation of the selection area in the present invention can be divided into object designation and block designation.

First, in the case of the object designation, residual transformation and intersection residual transformation are applied only to a specific portion displayed by an object map in a state where an object is divided through an object map. 0 and 1, respectively.

That is, when the object is represented by 1 in the object map, it is possible to apply the technique of the present invention without additional signaling bits.

In addition, if the technique of the present invention is applied only to the inner area determined by the start position and the end position, no additional signaling bit is required.

In the case of block designation, on / off signal bits for the technique of the present invention are transmitted to arbitrarily selected LCU, CU, and PU blocks.

For example, 0 means that the general coding is applied, and 1 means that the residual transform and the residual residual transform are applied.

The selective use of the residual transformation and the crossover residual transformation as described above can be applied to all the intra prediction modes such as the diagonal direction as well as the vertical and horizontal directions.

4 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.

4, 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.

4, 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. 4, and for example, the inverse of the encoding process described with reference to FIG. 4 So that the image can be decoded.

The difference between the present invention and the application of cross residual transform in lossless intra coding is that the filtering process, such as transform and quantization and deblocking filters, remains intact. By reducing the residual signal by applying cross residual transform in lossy intra coding, the coding efficiency expected from the transform and quantization can be further increased.

For example, the compression process such as transformation, quantization, and entropy after performing the above-mentioned cross-residual transformation may all be the same as the intra-image compression scheme according to the existing HEVC.

That is, in the decoding process, the above process is performed inversely. In the case where the horizontal direction cross-residual transform is performed after the vertical direction prediction in the encoding process, the inverse frequency-domain (inverse integer transform using DCT or DST, (Inverse Crossed Residual Transform) (horizontal direction) is applied to r '' that has been subjected to the transform process and can be expressed by Equation (3) as described above.

On the other hand, in the lossless prediction, a filtering process such as the conversion and quantization process and the deblocking filter as described with reference to FIG. 4 may be omitted.

In the loss prediction and the lossless prediction, although the applied residual transformations are different from each other, the method of the cross residual transform may be the same, and the difference between applying the loss coding and the lossless coding in applying the module Can be.

That is, in the case of lossy coding, a residual transformer (a module in which a residual transform and an intersection residual transform is performed) is added to the transform unit in the configuration of the decoding apparatus as shown in FIGS. 5 to 7, Quantization, and the like. In case of lossless coding, the residual transformer may be added in the case of the transformer, the quantizer, the inverse quantizer, and the inverse transformer without the inverse transformer (general lossless coding) .

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 (10)

A method for performing intra prediction,
Generating a residual signal according to an intra prediction mode corresponding to a first direction;
Performing a residual transformation on the residual signal by applying a pixel-by-pixel DPCM in a second direction intersecting with the first direction; And
And transforming and quantizing the residual-transformed signal. 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,
Wherein the first direction is vertical or horizontal. The method according to claim 1,
Wherein the residual transformation is selectively performed. The method according to claim 1,
And transmitting information on whether the cross-residual transformation is performed to a decoding apparatus. The method according to claim 1,
Wherein the residual transformation is performed on a selected region based on a particular object or block. 7. The method of claim 6,
Wherein at least one of the plurality of objects is classified in the object map of the image. An apparatus for performing intra prediction, the apparatus comprising:
A residual signal generator for generating a residual signal according to an intra prediction mode corresponding to the first direction;
A residual transformation performing unit for performing residual transformation on a pixel-by-pixel DPCM in a second direction intersecting with the first direction with respect to the residual signal;
A transform unit for transforming the residual-transformed signal to output transform coefficients; And
And a quantization unit for performing quantization on the transform coefficients. 9. The method of claim 8,
Wherein the first direction and the second direction are perpendicular to each other. 9. The method of claim 8,
Wherein the first direction is vertical or horizontal.

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