KR102217225B1 - Method for intra-prediction, and apparatus thereof - Google Patents

Abstract

The present invention relates to a method and apparatus for performing intra prediction, the method comprising: determining the number of filtering taps (N) applied to each of the plurality of regions by dividing an image to be predicted into a plurality of regions; Generating a prediction pixel by performing interpolation for each of the divided regions using N reference pixels including two adjacent true pixels according to the intra prediction direction; And generating a residual signal using the generated prediction pixel.

Description

TECHNICAL FIELD [0001] Method for intra-prediction and apparatus

The present invention relates to a video encoding/decoding method and apparatus, and more particularly, to a method of performing intra prediction using interpolation filtering during encoding and decoding.

In general, in video coding, a residual signal is generated using intra prediction and inter prediction. The reason for obtaining the residual signal is that when coding is performed with the residual signal, the amount of data is small, so the data compression rate is high, and the better the prediction, the smaller the value of the residual signal.

In the intra prediction method, data of a current block is predicted using pixels surrounding 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 increases from 9 prediction modes used in the existing H.264/AVC to 35 prediction modes as shown in FIG. 1 and further subdivides the prediction (however, the planar prediction mode and the DC prediction mode are shown in FIG. Not visible in 1).

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

As described above, intra prediction and inter prediction are further subdivided to reduce the amount of data in the residual signal, and a video encoding and decoding method with a small amount of computation is required without deteriorating codec performance by 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 transform coding process of a video codec, and an apparatus therefor.

However, the technical problems to be achieved by the embodiments of the present invention are not limited to the technical problems as described above, and other technical problems may exist.

As a technical means for achieving the above technical problem, the intra prediction method according to an embodiment of the present invention divides an image to be predicted into a plurality of regions, and the number of filtering taps applied to each of the plurality of regions (N ) Determining; Generating a prediction pixel by performing interpolation for each of the divided regions using N reference pixels including two adjacent true pixels according to the intra prediction direction; And generating a residual signal using the generated prediction pixel.

In addition, an intra prediction apparatus according to an embodiment of the present invention may include: a tap number determination unit configured to determine the number of filtering taps (N) applied to each of the plurality of regions by dividing an image to be predicted into a plurality of regions; A prediction pixel generator configured to generate a prediction pixel by performing interpolation for each of the divided regions using N reference pixels including two adjacent true pixels according to the intra prediction direction; And a residual signal generator that generates a residual signal using the generated prediction pixel.

Meanwhile, the intra prediction method may be implemented as a computer-readable recording medium in which a program for execution in a computer is recorded.

According to the present invention, when prediction for generating a residual signal according to each prediction direction (mode) is performed, an optimal filtering method is determined to obtain a prediction value, thereby minimizing the size of the residual signal to improve compression performance. Can be improved.

In addition, when performing interpolation in prediction in various directions applied in the intra prediction method, coding performance is performed by varying the number of filtering taps used for interpolation for each region through changes in a specific region or pixel change in the image when performing interpolation. Can improve.

1 is a diagram illustrating examples of intra prediction modes.
2 is a diagram illustrating an example of image coding units.
3 is a diagram illustrating an example of an interpolation method performed for intra prediction.
4 is a diagram for explaining a first embodiment of an intra prediction method according to the present invention.
4 is a diagram for explaining a first embodiment of an intra prediction method according to the present invention.
5 is a diagram for explaining a second embodiment of an intra prediction method according to the present invention.
6 is a diagram for explaining a third embodiment of an intra prediction method according to the present invention.
7 is a diagram for explaining a fourth embodiment of an intra prediction method according to the present invention.
8 and 9 are diagrams for explaining a case for sync filtering.
10 to 12 are block diagrams illustrating embodiments of a configuration for performing intra prediction by adjusting the number of filtering tabs.
13 and 14 are block diagrams illustrating embodiments of a configuration for performing intra prediction by adjusting the number of filtering taps according to transformation of pixel values.
15 is a block diagram showing the configuration of an encoding apparatus according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art may easily implement the present disclosure. However, the present application may be implemented in various different forms and is not limited to the embodiments described herein. In addition, in the drawings, parts not related to the description are omitted in order to clearly describe the present application, and similar reference numerals are attached to similar parts throughout the specification.

Throughout this specification, when a part is said to be "connected" with another part, this includes not only the case that it is "directly connected", but also the case that it is "electrically connected" with another element interposed therebetween. do.

Throughout this specification, when a member is positioned “on” another member, this includes not only the case where a member is in contact with another member, but also the case where another member exists between the two members.

Throughout the specification of the present application, when a certain part "includes" a certain component, it means that other components may be further included rather than excluding other components unless specifically stated to the contrary. The terms "about", "substantially", etc., to the extent used throughout this specification are used at or close to the numerical value when manufacturing and material tolerances specific to the stated meaning are presented, and the understanding of the present application To assist, accurate or absolute figures are used to prevent unfair use of the stated disclosure by unscrupulous infringers. As used throughout the specification of the present application, the term "step (to)" or "step of" does not mean "step for".

In the entire specification of the present application, the term "combination of these" included in the expression of the Makushi format refers to one or more mixtures or combinations selected from the group consisting of components described in the expression of the Makushi format, and the component It means to include one or more selected from the group consisting of.

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

The present invention relates to a video encoding/decoding method and an intra prediction method of an apparatus. In the case of intra prediction in each direction performed in video encoding/decoding, a residual signal according to each prediction direction (mode) When performing prediction for generating a, in order to obtain an accurate prediction value, an optimal filtering method is determined to obtain a prediction value, thereby minimizing the size of the residual signal and improving the compression performance.

Specifically, in prediction according to various directions applied in the intra prediction method, when prediction for generating a residual signal according to each prediction mode (Prediction mode), in order to obtain an accurate prediction value, DCT-based or sink (Sync) This is a method of improving compression performance by applying function-based filtering to obtain accurate prediction values.

2 is a diagram for describing an example of image coding units.

In HEVC, CTB (Coding Tree Block) is used as a video coding unit, and in this case, CTB is defined in various square shapes. The CTB is called a coding unit (CU).

Referring to FIG. 2, the coding unit (CU) is in the form of a quad tree, and when the largest coding unit LCU (Largest Coding Unit) having a size of 64×64, the depth is set to 0. The coding is performed by recursively finding the optimal prediction unit until is 3, that is, the 8×8 coding unit (CU).

A prediction unit that performs prediction is defined as a PU (Prediction Unit), and each coding unit (CU) performs prediction in a unit divided into a plurality of blocks, and performs prediction by being divided into square and rectangular shapes.

According to the HEVC standard prepared for encoding/decoding video data, it is a method to reduce the spatial correlation of the residual signal in a block and increase the energy compression rate after performing Inter/Intra Prediction. The transformation method for (Transform Unit) is used. The signal converted according to the conversion unit is finally generated as a bitstream through entropy coding.

Meanwhile, intra prediction considers a total of 34 directions, and is applied to all square PUs of 4x4, which is the smallest prediction unit, and 64x64, which is the maximum prediction unit. The predicted value of the block boundary used for each prediction creates a 1/32 linear interpolation (interpolation) prediction pixel in relation to the distance between the two pixels for prediction in each direction, which considers only the values of the two pixels, so that the prediction sample is a boundary block. The change of several pixels, which is the edge of, is not considered at all.

Particularly, in the case of a case in which the image change is severe or in the case of a pixel located at the boundary of an object, a prediction method using these two pixels has a problem that the efficiency of the conventional method is further lowered.

FIG. 3 shows an example of an interpolation method performed for intra prediction, and shows a method of predicting a pixel for prediction modes 2 to 34 having directionality among 34 prediction methods.

Referring to FIG. 3, a direction is positioned between the reconstructed pixel on the left and the reconstructed pixel on the top according to each direction, and a predicted pixel is generated by using the values of the two pixels applied to this direction. .

For example, in mode 32, prediction for pixel a may be performed by calculating weights of pixels A and B according to distances. In this case, since prediction is performed through two pixels, it is not efficient at the boundary where the image value changes rapidly.

According to an embodiment of the present invention, in prediction according to various directions applied in an intra prediction method, when prediction for generating a residual signal according to each prediction mode (Prediction mode) is performed, in order to obtain an accurate prediction value , By applying DCT-IF filtering to obtain an accurate prediction value, compression performance can be improved.

In order to solve this problem, as shown in FIG. 4, a prediction pixel may be generated through DCT-based filtering using four pixels, for example, Q, A, B, and C pixels.

For example, the DCT-based filtering coefficient can be expressed using a type-2 DCT as shown in Equation 1 below.

In this case, DCT is first performed, and a coefficient f(x) according to each position is generated through inverse transformation of the DCT. Referring to the case shown in FIG. 4, f(0)=Q, f(1)=A, f(2)=B, f(3)=C, and N=4.

N: number of samples (if N=4, it becomes 4-point Inverse DCT f(x))

If N=4 (i.e., using 4-point DCT, IDCT), in the case of prediction mode 30 in FIG. 4, x = 1+1/2 (= N/2 + 1/2), and accordingly An interpolation (interpolation) value of 1+1/2 sample position can be generated using Equation (2) of Equation 1.

Meanwhile, in the case of prediction mode 29 in FIG. 4, x = 1+13/32 (= N/2 + 13/32), and accordingly, 1+13/ using Equation (2) of Equation 1 above. Interpolation (interpolation) value of 32 sample positions can be created.

And, in the case of prediction mode 32 in FIG. 4, x = 1+26/32 (= N/2 + 26/32), and accordingly, 1+26/32 using Equation (2) of Equation 1 Interpolation (interpolation) value of sample position can be created.

Meanwhile, the number of filter taps used in the DTC-based interpolation may be set to not only 4 but also various numbers, and the number of taps is signaled by a decoder, or surrounding information (for example, edge information or mode information Etc.).

In the example of the present invention, type-2 DCT and Inverse DCT (IDCT) were used, but other types of DCT and IDCT are also available, and various other types of DST (Discrete Sine Transform) and IDST pairs are available. Includes all methods.

5 shows an example of generation of prediction pixels in three direction modes in which k is predicted for prediction modes in 34 prediction directions.

Referring to FIG. 5, when a value applied to a direction corresponding to a specific intra prediction mode does not exist in an accurate direction, a prediction pixel may be generated through a linear filtering method using values of two pixels on both sides. .

For example, mode 28 of k performs prediction on mode 28 by calculating weights of pixels C and D according to distance. In the 19th mode, Q and A, in the 8th mode, M and N are applied equally to determine the predicted pixel of k.

Since prediction is performed through only two pixels on both sides, it is not efficient at the boundary where the image value changes rapidly. To solve this problem, each prediction pixel is predicted through DCT-based (DCT-based) filtering using four pixels around it, such as (B,C,D,E), (L,M,N,O). You can create pixels.

6 shows an example of a method of generating a prediction pixel using 4-Tap DCT-IF filtering.

Referring to FIG. 6, the case of mode prediction in the direction 4 of i and the mode prediction in direction 32 of i using a 4-Tap DCT-IF filter is between A and B using 4 pixels of Q, A, B, and C. Here is an example of two pixel predictions that generate the 4th mode prediction pixel of, and generate the 32nd mode prediction pixel between C and D using 4 pixels L,M,N,O, where the filtering method is 4-Tap This is how to use the DCT-IF filter.

Here, the number of taps can be converted into not only four, but also the size of N-Tap, and the size of the tap can be determined through signaling by a decoder or by surrounding information (edge information, mode information, etc.).

FIG. 7 is a diagram for explaining an example of a method of performing intra prediction using filters with different tap numbers for the horizontal and vertical directions, in which the horizontal direction is 8-Tap and the vertical direction is 4-Tap DCT-IF filtering It shows a method of generating a predicted pixel by using.

In the case of FIG. 7, unlike FIG. 6, the number of taps can be determined differently, such as using 8-Tap at the top and 4-Tap at the left according to the characteristics of the image. This is N-Tap. All of this can be possible.

As shown in FIG. 7, when performing prediction of a pixel, when performing the left mode 4, the prediction pixel is located between M and N, which is applied to the prediction pixel of mode 4 through 4-Tap DCT-IF filtering. A corresponding prediction pixel can be predicted, and when the prediction mode is a mode in the direction of 32 in the pixel at the i position, an example of predicting through the value of the predicted pixel through 8-Tap DCT-IF filtering at the top is shown.

In addition, the filter-related information as described above includes both a method capable of decoding a filtering pixel with a different number of taps through signaling or a method that is possible without signaling through surrounding information.

Since the generated interpolation coefficient value is composed of a decimal point, the symmetric interpolation filtering coefficient value normalized to an integer value can be obtained as follows.

Table 1 below shows an example of interpolation coefficient values according to the intra prediction method of 4-point (4-tap) filtering.

For example, when the 32nd prediction mode is determined for the prediction pixel a in FIG. 4, the position value may be calculated as in Equation 2 below by applying the filtering coefficient value of the table above.

In this way, when a prediction pixel is generated through the DCT-based interpolation coefficient for each location of each mode, a more accurate prediction pixel can be generated than that of generating a prediction pixel for each location by considering only the existing two surrounding pixels. to be.

Here, the DCT-based interpolation filter represents one example and includes all methods that can selectively apply various filtering.

A video encoding/decoding method with higher compression ratio by generating a residual signal that takes into account changes in surrounding images through filtering the signal used for each prediction through a filtering method that improves performance, and Device.

In the above example, the method of deriving the interpolation filter coefficient from the case of N=4 and using it as a prediction sample was exemplified, but N=2n,n=1,2,3,4,... In all cases of this, interpolation filters can be derived and used.

In addition, although type-2 DCT and Inverse DCT (IDCT) were used in this example, other types of DCT and IDCT can also be used, and various other types of DST (Discrete Sine Transform) and IDST pairs can also be used. It can improve performance.

On the other hand, when a prediction pixel is obtained from the top, it may be effective to use a small number of filtering taps when there is an edge between two pixels located at the top (for example, when a change in value is large).

Conversely, when there is no edge (e.g., when the value is small), it may be effective to use a large number of filtering taps to bring a lot of influence from the surrounding pixels, which is the pixel value at the top and left. The same can be applied to all predictions of

That is, by adaptively applying a method of increasing or decreasing the number of taps according to changes in neighboring pixels (eg, edge information or size between pixels), accurate prediction pixels can be generated, resulting in overall encoding/decoding performance. .

According to another embodiment of the present invention, when prediction for generating a residual signal according to each prediction mode in prediction according to various directions applied in an intra prediction method, an accurate prediction value is obtained. In order to obtain it, it is possible to improve compression performance by applying sync filtering to obtain an accurate prediction value through interpolation.

For example, in the intra prediction method described with reference to FIGS. 4 to 7, a prediction pixel may be generated by performing interpolation using a Sync filter in place of a DCT-based filter or in addition to a DCT-based filter. .

8 and 9 are diagrams for explaining a case for sync filtering.

8 shows a normalized sync function, and a coefficient of each 4-tap can be obtained through the sync function as shown.

Through this, as interpolation is performed, each prediction pixel can be obtained according to the method described with reference to FIGS. 4 to 7. In addition, all methods applicable to N-tap as well as 4-tap may be included.

All the images currently viewed through video equipment are values converted from analog signals to digital signals through sampling-restore theorem. Therefore, if the digital signal x[k] exists indefinitely, the most ideal analog signal can be restored through Equation 3 below.

In Equation 3 above, t is time, Ts is a sampling period, and x[kTs] is a digital signal. When the sampling period Ts is defined as 1, the graph may be as shown in FIG. 8.

Substituting the value of the digital signal in Equation 3 above, the analog signal x(t) can be restored.

For example, prediction pixels between integer pixels may be obtained using the restored analog signal x(t). Filter coefficients may be obtained through Equation 4 below according to the number of referenced integer pixels and the location of the prediction pixels.

In Equation 4 above, α is the predicted pixel position and N is the number of referenced integer pixels.

For example, when the number of referenced integer pixels is 8 (N = 8), filter coefficients can be obtained according to the predicted pixel positions as shown in the following table.

Since the above filter coefficient is a decimal arithmetic operation and has high computational complexity, it can be scaled to obtain the integer filter coefficient as shown in Table 3 below.

In a similar way, all filter coefficients can be obtained according to the values of α and N.

According to an embodiment of the present invention, when performing interpolation, in selecting the number of taps by varying the number of filtering taps used for horizontal and vertical interpolation through edge information of an image to improve performance, The number of taps can be predicted when transmitting to decoding through signaling or performing decoding using surrounding information.

As described above, in a method of finding a motion vector (MV), interpolation can have a great influence on performance. In particular, when prediction through precise interpolation is performed, the performance of subsequent transformation and quantization, scanning, and entropy encoding/decoding is affected. In other words, if accurate interpolation through interpolation is performed, it has a very great effect on the performance improvement of the entire codec.

An embodiment of the present invention is an interpolation method that improves overall encoding/decoding performance by varying the number of filtering taps according to information according to an edge direction of an image for a more effective method than the conventional interpolation method.

Hereinafter, embodiments of a configuration for performing intra prediction by adjusting the number of filtering tabs will be described in detail with reference to FIGS. 10 to 12.

10 is a diagram for explaining an example of a method of determining the number of taps for filtering, and illustrates a method of analyzing an edge of an image and determining the number of taps in the horizontal and vertical directions.

Referring to FIG. 10, after the edge of the image is analyzed and detected, the tap size (number of taps) of the filter is determined according to the detected edge, and then different number of taps in the vertical direction and the horizontal direction according to the determined number of taps. Interpolation can be performed using a filter of.

For example, as illustrated in FIG. 7, interpolation using a 4-tap filter may be performed in the horizontal direction, and interpolation using an 8-tap filter may be performed in the vertical direction.

Here, the number of filtering taps may be transmitted by signaling from an encoder to a decoder for decoding, or may include all methods of distinguishing without signaling by using a certain characteristic.

FIG. 11 shows an example of 2-fold extension interpolation using a 4-tap filter and an 8-tap filter, and shows an example in which a frame or picture is predicted by 1/2 pixel of an image used as a reference.

Interpolation is performed with the tap size according to the horizontal and vertical edges with the tap size determined by the method described with reference to FIG. 10.

Step 1 predicts through 4-tap filtering in case of horizontal interpolation, and in Step 2, pixel prediction using 8-tap in case of vertical interpolation.

The size of the tap of the present invention is not limited to the above number, and includes all methods of configuring N-taps, and the coefficient of tap can be applied regardless of the size of the horizontal and vertical. This is applied differently depending on the edge characteristics of the image.

In addition, it is possible to determine both the size of the tap according to the size and direction of the tap through signaling, or even through a complex determination method of edge direction and image change (MV change, pixel change amount, etc.)without signaling. Includes all predictable methods.

FIG. 12 shows an example in which interpolation of various methods can be applied, and is shown to explain various interpolation methods that can be applied in the case of application of 4-fold interpolation.

Referring to Figure 12. Four interpolation methods can be applied in both horizontal and vertical directions while going through a total of Step 4.

As described above, the present invention refers to an interpolation method in which not only one interpolation technology but also N interpolation methods can be adaptively changed according to the characteristics and performance of the N-Tap channel image, which is decoded without signaling according to the change of the image. This is a method that includes all possible methods or methods that can be decoded through signaling in some cases.

On the other hand, if there is an edge or there is a large change in the image, using a small number of taps of filtering is an interpolation method that saves the edge, and when there are few edges and there is little change in pixels, it is effective to use the number of filtering taps. I can.

For example, if the edges are distributed horizontally, it is effective to increase the number of taps for horizontal filtering and reduce the number of taps for vertical filtering. If the edges are distributed vertically, increase the number of taps for vertical filtering and use horizontal filtering. It is effective to reduce the number of taps.

Alternatively, it involves using both methods and selecting a method with high performance through signaling.

In the case of finding and predicting an MV in inter prediction, double interpolation refers to a method of predicting a 1/2 pixel position, and a quadruple interpolation refers to a method of predicting a quarter pixel position.

According to another embodiment of the present invention, when performing interpolation, performance can be improved by varying the number of filtering taps used for interpolation for each area through a change in a specific area or pixel change in an image, and the number of taps is selected. In doing so, it is possible to predict the number of taps in decoding by using signaling or by using surrounding information.

In order to be more effective than the conventional interpolation method, the number of filtering taps may be changed according to a change in a pixel value in units of regions or blocks, thereby improving the performance of the entire encoding/decoding.

For example, by detecting a specific object, A-tap filtering is performed on the object area and B-tap filtering is performed on the other area. Interpolation can be performed by adaptively different filtering coefficients.

13 and 14 are block diagrams illustrating embodiments of a configuration for performing intra prediction by adjusting the number of filtering taps according to transformation of pixel values.

13 shows an example of a method of varying taps of filters used for interpolation for each region in one frame.

Referring to FIG. 13, the number of taps may be differently determined for various areas within one frame, and interpolation method includes all cases of interpolation with various number of taps rather than a method of using the same number of taps in one frame.

Determining the number of taps is a method of interpolation with various number of taps in one frame as shown in FIG. 10 through detection of an object or change of pixels in units of blocks (areas) and changes in adjacent blocks (areas). to be.

Here, the number of taps includes all methods in which signaling is performed by decoding or the same decoding is possible through changes in surrounding pixels and regions without signaling.

FIG. 14 shows an example of the division of the interpolation tap by region and the division of the vertical and horizontal taps, and shows an example of a method in which the vertical and horizontal taps can be determined differently than the case shown in FIG. .

Referring to FIG. 14, by applying a change in the number of taps for each region and a change in width and height, an optimal interpolated pixel value according to the characteristics of an image may be obtained, thereby improving performance in overall encoding/decoding.

Here, the vertical and horizontal taps and the taps on the region are a method including both a method of decoding by signaling and a method capable of decoding without signaling.

For example, if a region is divided within one frame and many edges are distributed, it is effective to determine and use a small number of filtering taps to preserve the edges, and to use a large number of filtering taps for areas with no edges. I can.

In detail, in FIG. 13, the area using 8-Tap interpolation is an area with few edges, and interpolation is performed using a large number of filtering taps. In the case of 4-Tap, in order to preserve the edge as an area where many edges are distributed. The entire image can be interpolated using a small number of filtering taps.

In addition, in FIG. 14, as shown in FIG. 13, the number of taps of the divided image is specifically changed according to the direction of the edge, and the number of vertical and horizontal filtering taps of each region is different.

This may be the same as applying a method of varying the number of filtering taps according to vertical and horizontal as described in FIGS. 10 to 12 above.

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

Typically, the encoding apparatus includes an encoding process and a decoding process, and the decoding apparatus includes a decoding process. The decoding process of the decoding device is the same as that of the encoding device. Therefore, in the following description, the encoding device will be mainly described.

As shown in FIG. 15, the video encoding apparatus according to an embodiment of the present invention includes coding units and structures, inter prediction, intra prediction, interpolation, filtering, and transformation. ) Method and other new algorithms.

Referring to FIG. 15, the video 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 transform encoding/quantization unit 140, and entropy encoding. A unit 150, an inverse quantization/transformation/decoding unit 160, a deblocking filtering unit 170, a picture storage unit 180, a subtraction unit 190, and an addition unit 200 are included.

The encoding mode determiner 110 analyzes the input video signal, divides the picture into coding blocks having a predetermined size, and determines an encoding mode for the divided coding blocks having a predetermined size. The coding mode includes intra prediction coding and inter prediction coding.

A picture is composed of a plurality of slices, and a slice is composed of a plurality of largest coding units (LCU). The LCU may be divided into a plurality of coding units (CU), and the encoder may add information (flag) indicating whether to be divided to the bitstream. The decoder can recognize the location of the LCU using the address (LcuAddr). When partitioning is not allowed, the coding unit (CU) 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) can be divided into a plurality of partitions. In addition, the prediction unit PU may be composed of a plurality of transform units (TUs).

The encoding mode determiner 110 transmits the image data to the subtraction unit 190 in block units (eg, PU units or TU units) having a predetermined size according to the determined encoding mode.

The transform encoding/quantization unit 140 converts the residual block calculated by the subtraction unit 190 from the spatial domain to the frequency domain. For example, a two-dimensional discrete cosine transform (DCT) or discrete sine transform (DST) based transform is performed on the residual block.

Further, the transform coding/quantization unit 140 determines a quantization step size for quantizing the transform coefficient, and quantizes the transform coefficient using the determined quantization step size. A quantization matrix may be determined according to the determined quantization step size and coding mode.

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

The inverse quantization/transformation decoding unit 160 inverse quantizes the quantized coefficients quantized by the transform encoding/quantization unit 140. In addition, the inverse quantization coefficient obtained by inverse quantization is inversely transformed. Accordingly, the residual block converted into the frequency domain can be restored to the residual block in the spatial domain.

The deblocking filtering unit 170 receives inverse quantization and inverse transformed image data from the inverse quantization/transform encoder 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 stores the image in units of pictures. The picture may be a frame-based image or a field-based image. The picture storage unit 180 includes 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 called reference pictures.

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

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

The motion compensation unit 130 corresponds to a block to be encoded from a reference picture used for motion estimation among a plurality of reference pictures stored in the picture storage unit 180 according to motion data input from the motion estimation unit 131 The predicted block is extracted and output.

The motion compensation unit 130 determines filter characteristics of an adaptive interpolation filter required for motion compensation with fractional precision. The filter characteristics are, for example, information indicating the filter type of the adaptive interpolation filter, information indicating the size of the adaptive interpolation filter, and the like.

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 is an adaptive interpolation filter and may determine any one of a separable type and a non-separated type adaptive filter. Then, the determined number of taps of the adaptive interpolation filter and the value of each filter coefficient are determined. The value of the filter coefficient may be determined differently for each position of the fractional pixel relative to the integer pixel. In addition, the motion compensation unit 130 may use a plurality of non-adaptive interpolation filters having fixed filter coefficients.

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

Accordingly, in a predetermined processing unit, the same filter characteristics are used, so the motion compensation unit 130 includes a memory temporarily maintaining the filter characteristics. This memory maintains filter characteristics, filter coefficients, etc. as needed. For example, the motion compensation unit 130 may determine a filter characteristic for each I picture and determine a filter coefficient in a slice unit.

The motion compensation unit 130 receives a reference picture from the picture storage unit 180 and applies filter processing using the determined adaptive interpolation filter, thereby generating a prediction reference picture with decimal precision.

Then, based on the generated reference image and the motion vector determined by the motion estimation unit 131, a prediction block is generated by performing motion compensation with precision of a few pixels.

The subtraction unit 190 receives a block in a reference picture corresponding to the input block from the motion compensation unit 130 when performing inter-picture prediction encoding on an input block to be encoded, and performs a difference operation with the input macroblock to obtain a residual signal. (residue signal) is output.

The intra prediction unit 120 performs intra prediction coding by using reconstructed pixel values within a picture on which prediction is performed. The intra prediction unit receives a current block to be predicted and encoded and performs intra prediction by selecting one of a plurality of preset intra prediction modes according to the size of the current block. The intra prediction unit 120 determines an intra prediction mode of the current block using previously coded pixels adjacent to the current block, and generates a prediction block corresponding to the determined mode.

Among the regions included in the current picture, previously encoded regions are decoded again to be used by the intra predictor 120 and are stored in the picture storage unit 180. The intra prediction unit 120 generates a prediction block of the current block using pixels adjacent to the current block or pixels that are not adjacent but applicable in a previously encoded region 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, information indicating whether or not to filter may be transmitted in the encoder. Alternatively, filtering may be determined based on the intra prediction mode of the current block and size information of the current block.

The prediction type used by the video encoding apparatus depends on whether the input block is encoded in an intra mode or an inter mode by the encoding mode determiner.

Switching between the intra mode and the inter mode is controlled by an intra/inter switching switch.

The entropy encoding unit 150 entropy-encodes the quantization coefficient quantized by the transcoding/quantization unit 140 and motion information generated by the motion estimation unit 131. In addition, the intra prediction mode, control data (eg, quantization step size, etc.) may be encoded. Also, the filter coefficients determined by the motion compensation unit 130 are 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. 15, for example, the reverse of the encoding process as described with reference to FIG. 15. An image can be decoded by performing the process.

The above-described method according to the present invention may be produced as a program for execution in a computer and stored in a computer-readable recording medium. Examples of computer-readable recording media include ROM, RAM, CD-ROM, and magnetic tape. , Floppy disks, optical data storage devices, and the like, and also include those implemented in the form of a carrier wave (for example, transmission through the Internet).

The computer-readable recording medium is distributed over a computer system connected through a network, so that computer-readable codes can be stored and executed in a distributed manner. In addition, functional programs, codes and code segments for implementing the method can be easily inferred by programmers in the art to which the present invention belongs.

In addition, although the preferred embodiments of the present invention have been illustrated and described above, the present invention is not limited to the specific embodiments described above, and the technical field to which the present invention belongs without departing from the gist of the present invention claimed in the claims. In addition, various modifications can be implemented by those of ordinary skill in the art, and these modifications should not be individually understood from the technical spirit or prospect of the present invention.

Claims (13)

In the video decoding method using intra prediction,
Determining an intra prediction direction of the current block;
Generating a prediction pixel by applying a 4-tap interpolation filter to four consecutive reference pixels adjacent to a position determined according to the intra prediction direction; And
And generating a prediction block of the current block by using the generated prediction pixel,
The step of generating a prediction pixel by applying the interpolation filter is performed when the intra prediction mode of the current block is a directional prediction mode,
The consecutive reference pixels are pixels adjacent to the current block,
When a position determined according to the intra prediction direction is located at the upper end of the current block, the four consecutive reference pixels are determined as four consecutive reference pixels located adjacent to the upper end of the current block,
When the position determined according to the intra prediction direction is located on the left side of the current block, the four consecutive reference pixels are determined as four consecutive reference pixels located adjacent to the left side of the current block. Video decoding method. The method of claim 1, wherein generating the prediction pixel comprises:
An image decoding method using DCT (Discrete Cosine Transform) or DST (Discrete Sine Transform) based filtering.
The method of claim 2,
The type of the interpolation filter is an image decoding method transmitted from an encoding device.
delete delete delete delete delete delete delete delete In the video encoding method using intra prediction,
Determining an intra prediction direction of the current block;
Generating a prediction pixel by applying a 4-tap interpolation filter to four consecutive reference pixels adjacent to a position determined according to the intra prediction direction; And
And generating a prediction block of the current block by using the generated prediction pixel,
The step of generating a prediction pixel by applying the interpolation filter is performed when the intra prediction mode of the current block is a directional prediction mode,
The consecutive reference pixels are pixels adjacent to the current block,
When the position determined according to the intra prediction direction is located at the upper end of the current block, the four consecutive reference pixels are determined as four consecutive pixels located adjacent to the upper end of the current block,
When the position determined according to the intra prediction direction is located on the left side of the current block, the four consecutive reference pixels are determined as four consecutive pixels located adjacent to the left side of the current block Encoding method. A non-transitory computer-readable storage medium comprising a bitstream used in an image decoding apparatus,
The bitstream,
Contains information on the intra prediction direction of the current block,
The information on the intra prediction direction of the current block causes the image decoding apparatus to generate a prediction pixel of the current block,
In the video decoding apparatus,
The prediction pixel is generated by applying a 4-tap interpolation filter to four consecutive reference pixels adjacent to a position determined according to the intra prediction direction,
When the intra prediction mode of the current block is a directional prediction mode, a prediction pixel is generated by applying the interpolation filter,
The consecutive reference pixels are pixels adjacent to the current block,
When a position determined according to the intra prediction direction is located at the upper end of the current block, the four consecutive reference pixels are determined as four consecutive reference pixels located adjacent to the upper end of the current block,
When the position determined according to the intra prediction direction is located on the left side of the current block, the four consecutive reference pixels are determined as four consecutive reference pixels located adjacent to the left side of the current block. Storage medium.

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