KR20140072938A - Method and apparatus for adaptive filtering of reference pixels for intra prediction - Google Patents

Abstract

The present invention relates to a method and apparatus for performing adaptive filtering on surrounding reference samples in intra-picture prediction of a video codec. The decoding method includes: deriving a reference sample; Padding a reference sample; Adaptively filtering the reference samples; And performing intra-frame prediction using the filtered reference pixels.

Description

TECHNICAL FIELD The present invention relates to an adaptive reference pixel filtering method and apparatus,

The present invention relates to image processing techniques and, more particularly, to a method and apparatus for improving the performance of intra prediction in video compression techniques.

Recently, as the demand for high resolution and high definition video has increased, there has been a need for a highly efficient video compression technology for the next generation video service. In response to these market demands, MPEG and VCEG, which jointly standardized the MPEG-2 Video and H.264 / AVC codecs, have been jointly standardized on new video compression technologies since 2010. MPEG and VCEG have established Joint Collaborative Team on Video Coding (JCT-VC) for the development of new standard technologies and are now developing next generation video standard technology called HEVC (High Efficiency Video Coding) through JCT-VC. These HEVCs are standardizing to improve compression efficiency by more than 50% compared to H.264 / AVC High profile, which is known to have the highest compression efficiency in the past, and support full-HD and 4K-resolution video .

In the video codec, the intra prediction technique uses decoded pixels located around the block to be encoded. Since the intra-picture prediction uses a pixel to which the in-loop filter such as the deblocking filter or the sample adaptive offset is not applied to the decoded neighboring pixels, the intra-picture prediction performance may be degraded due to the quantization error of the reference pixel .

An object of the present invention is to improve the performance of intra prediction by performing adaptive filtering on decoded reference pixels located in the periphery before performing intra prediction.

According to an aspect of the present invention, there is provided an adaptive reference pixel filtering method and apparatus, comprising: deriving a reference sample; Performing padding on a pixel-by-pixel basis in a reference sample region; Filtering the reference samples adaptively for the reference sample region; And performing in-picture prediction using the reference pixel on which the filtering is performed.

According to an embodiment of the present invention, the performance of the intra prediction can be improved by using the neighboring pixels of the current block to be encoded in the reference sample derivation unit and the reference sample padding unit as prediction values.

Also, according to an embodiment of the present invention, the adaptive reference sample filtering unit can effectively reduce errors in the reference samples by classifying the types of errors in units of pixels and applying filtering differently according to the error characteristics.

FIG. 1 is a block diagram showing a configuration of a video decoding apparatus according to a first embodiment of the present invention.
2 is a conceptual diagram for explaining the derivation range of a sample in the reference sample derivation unit shown in FIG.
3 is a conceptual diagram illustrating a padding method in a case where all the pixels around a block in the reference sample padding unit shown in FIG. 1 are not referable.
FIG. 4A is a conceptual diagram for explaining a padding method in a case where a pixel located at the bottom left of a block in the reference sample padding unit shown in FIG. 1 is not referable.
4B is another conceptual diagram for explaining a padding method in a case where some pixels located at a left boundary of a block in the reference sample padding portion shown in FIG. 1 are not referable.
4C is another conceptual diagram for explaining a padding method in a case where some pixels located at the upper boundary of a block in the reference sample padding portion shown in FIG. 1 are not referable.
5 is a flow chart of the adaptive reference sample filtering unit shown in FIG.
6 is a conceptual diagram for explaining the operation of the edge category judgment shown in Fig.
7 is a conceptual diagram for explaining the operation of the filter selection process shown in FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description of the embodiments of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present disclosure rather unclear.

It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, . In addition, the description of "including" a specific configuration in the present invention does not exclude a configuration other than the configuration, and means that additional configurations can be included in the practice of the present invention or the technical scope of the present invention.

The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component.

In addition, the components shown in the embodiments of the present invention are shown independently to represent different characteristic functions, which does not mean that each component is composed of separate hardware or software constituent units. That is, each constituent unit is included in each constituent unit for convenience of explanation, and at least two constituent units of the constituent units may be combined to form one constituent unit, or one constituent unit may be divided into a plurality of constituent units to perform a function. The integrated embodiments and separate embodiments of the components are also included within the scope of the present invention, unless they depart from the essence of the present invention.

In addition, some of the components are not essential components to perform essential functions in the present invention, but may be optional components only to improve performance. The present invention can be implemented only with components essential for realizing the essence of the present invention, except for the components used for the performance improvement, and can be implemented by only including the essential components except the optional components used for performance improvement Are also included in the scope of the present invention.

FIG. 1 is a block diagram showing a configuration of a video decoding apparatus according to a first embodiment of the present invention.

Referring to FIG. 1, the image decoding apparatus 100 includes a reference sample derivation unit 110, a reference sample padding unit 120, an adaptive reference sample filtering unit 130, and an intra prediction unit 140 do.

The reference sample derivation unit 110 derives a reference sample (pixel) located in the vicinity of a block to be encoded or decoded when intra prediction is performed.

The reference sample padding unit 120 replaces the neighboring pixel values according to a predetermined rule for the samples derived from the reference area using pixels derived from the reference sample derivation unit 110. [

The adaptive reference sample filtering unit 130 separates the edge categories based on the corresponding pixels for each reference sample prepared through the reference sample padding unit 120 and selectively applies a filter for each category to filter .

The intra-frame prediction performing unit 140 performs intra-frame prediction using reference samples to which the filtering is applied via the adaptive reference sample filtering unit 130. [

2 is a conceptual diagram for explaining the derivation range of a sample in the reference sample derivation unit shown in FIG.

Referring to FIG. 2, when the size of a block to be encoded / decoded is N × N (200), the reference sample derivation unit 110 shown in FIG. 1 obtains {2N × 1} (210) And a pixel located in the {1 x (2N + 1)} (220) region. In the reference sample derivation unit 110, if some pixels in the derived region are frame boundaries, the reference sample derivation unit 110 can not derive the pixels of the corresponding region. In addition, if some pixels of the derived region are located in another slice or tile than the block 200 to be encoded / decoded, it is impossible to derive the pixels of the corresponding region.

3 is a conceptual diagram illustrating a padding method in a case where all the pixels around a block in the reference sample padding unit shown in FIG. 1 are not referable.

Referring to FIG. 3, when all the pixels in the sample derivation range around the block 300 to be encoded / decoded can not be referenced 310, the reference sample padding unit 120 sets the half value of the bit depth DC).

FIG. 4A is a conceptual diagram for explaining a padding method in a case where a pixel 400 located at the bottom left of a block in the reference sample padding unit shown in FIG. 1 is not referable.

Referring to FIG. 4A, when a pixel 400 of a reference region located at the bottom of a block to be encoded / decoded is impossible to be referenced, the reference sample padding unit 120 moves And replaces it with the first referenced pixel value 410.

4B is another conceptual diagram for explaining a padding method in a case where some pixels located at the left boundary in the reference sample padding portion shown in FIG. 1 are not referable.

Referring to FIG. 4B, the reference sample padding unit 120 includes a pixel 430 located below the corresponding pixel 420, which is not available for reference, among the pixels 415 located on the left side of the block to be encoded / .

4C is another conceptual diagram for explaining a padding method in a case where some pixels located at the upper boundary of a block in the reference sample padding portion shown in FIG. 1 are not referable.

Referring to FIG. 4C, the reference sample padding unit 120 includes a pixel 450 located on the left side of the pixel 440 that is not available for reference among the pixels 435 located above the block to be encoded / decoded, .

5 is a flow chart of the adaptive reference sample filtering unit shown in FIG.

Referring to FIG. 5, the adaptive reference sample filtering unit 130 determines (510) an edge category for each pixel in the reference area. In the filter selection step 520, a filter is selected according to a predetermined category. After the filter is selected for each pixel, filtering is performed on the pixels of the reference region in the pixel-based filtering step 530.

FIG. 6 is a conceptual diagram for explaining the operation of the edge category judgment 510 shown in FIG.

Referring to FIG. 6, the edge category determination 510 for a pixel in the reference area uses two sets of adjacent pixels in the reference area based on the current pixel 600 to use a pixel set 605 of three pixels in total do. In the pixel set 605, when all the pixels located on the left and right of the current pixel 600 are larger or smaller than the current pixel, it corresponds to the category A 610. Corresponds to category B (620) if the current pixel value is equal to the right pixel value, and is less than or greater than the left pixel. Corresponds to category C (630) if the current pixel value 600 is equal to the left pixel value and is greater than or less than the right pixel value. The category D (640) corresponds to the category A (610), the category B (620), and the category C (630) when determining the edge category based on the current pixel (600).

In the edge category determination process, the lowest left pixel among the pixels of the reference area shown in FIG. 2 does not have a category at the corresponding position since there is no more reference area below. Likewise, a pixel located at the rightmost uppermost pixel among the pixels of the reference region shown in FIG. 2 does not have a category at that position because there is no more reference region on the right side.

FIG. 7 is a conceptual diagram for explaining the operation of the filter selection process 520 shown in FIG.

Referring to FIG. 7, a process 520 of filter selection is performed according to the result of the edge category determination operation of FIG. For example, since the first set of pixels 700 corresponds to category A, the filter coefficient {1,2,1} / 4 is selected. Likewise, the second pixel set 710 corresponds to category A, so the same filter coefficient is selected. In addition, the filter coefficient {1,2,1} / 4 is also selected for a set of pixels not corresponding to categories A, B,

Since the third pixel set 720 and the fourth pixel set 730 correspond to category B, the filter coefficient {2, 1, 1} / 4 is selected. At this time, weights of 2/4, 1/4, and 1/4 are used in turn based on the leftmost pixel of the pixel set.

The fifth pixel set 740 and the sixth pixel set 750 correspond to the category C, so filter coefficients {1,1,2} / 4 are selected. At this time, weights of 1/4, 1/4 and 2/4 are used in turn based on the leftmost pixel of the pixel set.

In the above-described embodiments, methods are described based on a flowchart as a series of steps or blocks, but the present invention is not limited to the order of the steps, and some steps may occur in different orders or in a different order than the steps described above have. It will also be understood by those skilled in the art that the steps depicted in the flowchart illustrations are not exclusive, that other steps may be included, or that one or more steps in the flowchart may be deleted without affecting the scope of the present invention. You will understand.

The above-described embodiments include examples of various aspects. While it is not possible to describe every possible combination for expressing various aspects, one of ordinary skill in the art will recognize that other combinations are possible. Accordingly, it is intended that the invention include all alternatives, modifications and variations that fall within the scope of the following claims.

Claims (1)

A method of performing filtering on a reference pixel when intra prediction is performed in a video codec, the method comprising: deriving a reference sample located around a block to be encoded / decoded; Fitting the sample of the reference region; Determining a category on a pixel-by-pixel basis, selecting a filter for each category, and performing filtering on the reference sample using the selected filter; And performing in-picture prediction using the filtered reference pixels.

Images