KR101373670B1 - Method and apparatus for intra prediction - Google Patents

Abstract

The present invention relates to an intra prediction method and apparatus. According to the present invention, the number of bits of the encoded data indicating the intra prediction mode of the current block is reduced compared to the conventional method, thereby increasing the compression ratio of the image.

Description

Intra prediction method and apparatus {METHOD AND APPARATUS FOR INTRA PREDICTION}

The present invention relates to an intra prediction method and apparatus.

Recently, there is an increasing demand for high definition and high definition video such as HD (High Definition) video and UHD (Ultra High Definition) video in various applications. As the image data becomes high resolution and high image quality, the data amount increases relative to the existing image data. Therefore, when the image data is transmitted using a medium such as a wired / wireless broadband line or stored in an existing storage medium, The cost increases. High-efficiency image compression techniques are required to solve such problems as image data has high resolution and high image quality.

An inter prediction technique for predicting a pixel value included in a current picture from a previous or a subsequent picture of a current picture using an image compression technique, an intra prediction technique for predicting a pixel value included in a current picture using pixel information in the current picture, there are a variety of techniques such as intra prediction technology, entropy coding technique in which short codes are assigned to values having a high appearance frequency, and long codes are assigned to values having a low appearance frequency. It can be compressed and transmitted or stored effectively.

The present invention calculates a difference between pixel values of neighboring pixels adjacent to a current block to be encoded or decoded, and refers to an intra prediction mode of the current block by referring to a mode ranking table corresponding to the type of the current block determined according to the difference. It is an object to provide a prediction method and apparatus.

An intra prediction method according to an embodiment of the present invention includes: calculating a difference between pixel values of neighboring pixels adjacent to a current block to be encoded; Determining a type of the current block based on the difference; Determining an intra prediction mode of the current block; And encoding the intra prediction mode of the current block with reference to a mode ranking table corresponding to the type of the current block.

Intra prediction device according to an embodiment of the present invention, the difference calculation unit for calculating the difference of the pixel value of the adjacent pixels adjacent to the current block to be encoded; A mode determination unit to determine an intra prediction mode of the current block; A storage unit for storing a plurality of mode ranking tables ranked according to a probability of occurrence of an intra prediction mode; And an encoder for encoding an intra prediction mode of the current block by referring to a mode ranking table corresponding to the type of the current block determined according to the difference.

The intra prediction method according to an embodiment of the present invention may be implemented in a computer-executable program and recorded on a computer-readable recording medium.

According to the present invention, the probability that the intra prediction mode of the current block is located at a higher ranking in the mode ranking table used for variable length encoding is increased, so that the number of bits of the encoded data can be reduced.

Furthermore, according to the present invention, by reducing the number of code bits encoding the intra prediction mode of the current block, the overall compression efficiency of the image can be obtained.

1 is a block diagram illustrating an intra prediction apparatus according to an embodiment of the present invention.
2 is a diagram illustrating an image to be encoded or decoded according to an embodiment of the present invention.
3 is a diagram illustrating a current block to be intra predicted and its neighboring pixels according to an embodiment of the present invention.
4 is a diagram illustrating neighboring pixels used for intra prediction and pixel values of the neighboring pixels according to an embodiment of the present invention.
5 is a diagram illustrating an intra prediction mode having a high probability of occurrence according to each type of a current block.
6 is a diagram illustrating an intra prediction mode used for intra prediction according to an embodiment of the present invention.
7 is a graph illustrating the frequency of intra prediction modes occurring in the entire block of an image according to an embodiment of the present invention.
FIG. 8 is a graph showing the frequency of intra prediction modes occurring in both sides of a high differential block type in an image according to an embodiment of the present invention. FIG.
FIG. 9 is a graph showing the frequency of intra prediction modes occurring in both sides of a low difference block type in an image according to an embodiment of the present invention.
FIG. 10 is a graph illustrating the frequency of intra prediction modes occurring in an upper high-order block type among images according to an embodiment of the present invention. FIG.
FIG. 11 is a graph illustrating the frequency of intra prediction modes occurring in a left high-order block type in an image according to an embodiment of the present invention. FIG.
12 is a flowchart illustrating an intra prediction method according to an embodiment of the present invention.
FIG. 13 is a flowchart illustrating an operation of calculating a difference between pixel values of neighboring pixels, according to an exemplary embodiment.
14 is a flowchart for describing a step of determining a type of a current block based on a difference according to an embodiment of the present invention.
15 is a flowchart illustrating an intra prediction method performed when decoding an image according to an embodiment of the present invention.
16 is a block diagram illustrating a video encoding apparatus according to an embodiment of the present invention.
17 is a block diagram illustrating an image decoding apparatus according to an embodiment of the present invention.

Other advantages and features of the present invention and methods of achieving them will become apparent with reference to the embodiments described below in detail with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. Is provided to fully convey the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims.

Unless defined otherwise, all terms (including technical or scientific terms) used herein have the same meaning as commonly accepted by the generic art in the prior art to which this invention belongs. Terms defined by generic dictionaries may be interpreted to have the same meaning as in the related art and / or in the text of this application, and may be conceptualized or overly formalized, even if not expressly defined herein I will not.

The terminology used herein is for the purpose of illustrating embodiments and is not intended to be limiting of the present invention. In the present specification, the singular form includes plural forms unless otherwise specified in the specification. As used herein, the terms' comprise 'and / or various forms of use of the verb include, for example,' including, '' including, '' including, '' including, Steps, operations, and / or elements do not preclude the presence or addition of one or more other compositions, components, components, steps, operations, and / or components. The term 'and / or' as used herein refers to each of the listed configurations or various combinations thereof.

It should be noted that the terms such as '~', '~ period', '~ block', 'module', etc. used in the entire specification may mean a unit for processing at least one function or operation. For example, a hardware component, such as a software, FPGA, or ASIC. However, '~ part', '~ period', '~ block', '~ module' are not meant to be limited to software or hardware. Modules may be configured to be addressable storage media and may be configured to play one or more processors. ≪ RTI ID = 0.0 >

Thus, by way of example, the terms 'to', 'to', 'to block', 'to module' refer to components such as software components, object oriented software components, class components and task components Microcode, circuitry, data, databases, data structures, tables, arrays, and the like, as well as components, Variables. The functions provided in the components and in the sections ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ' , '~', '~', '~', '~', And '~' modules with additional components.

The present invention proposes an intra prediction method and apparatus for encoding or decoding an intra prediction mode of a current block by referring to a different mode ranking table according to a difference between pixel values of neighboring pixels adjacent to a current block to be encoded or decoded.

1 is a block diagram illustrating an intra prediction apparatus according to an embodiment of the present invention. As shown in FIG. 1, the intra prediction apparatus 100 according to an exemplary embodiment of the present invention includes a difference calculator 101, a mode determiner 102, a storage 103, and an encoder 104. can do. According to another embodiment of the present invention, the intra prediction apparatus 100 may further include an updater 105.

The difference calculator 101 calculates a difference between pixel values of neighboring pixels adjacent to a current block to be encoded or decoded. The mode determiner 102 determines an intra prediction mode of the current block. The storage unit 103 stores a plurality of mode ranking tables that are ranked according to the probability of occurrence of the intra prediction mode. The encoder 104 encodes the intra prediction mode of the current block by referring to a mode ranking table corresponding to the type of the current block determined according to the difference. When the ranking corresponding to the intra prediction mode of the current block is not the highest in the referenced mode ranking table, the updater 105 updates the mode ranking table by raising the ranking of the intra prediction mode of the current block.

2 illustrates an image to be encoded or decoded and blocks included in the image according to an embodiment of the present invention. The image 20 is coded in an intra mode or an inter mode, and an intra prediction method or an inter prediction method may be selectively applied to each block to determine an optimal prediction method for blocks constituting the image. The present invention relates to a method and apparatus for intra prediction of a block 201 included in an image 20.

3 illustrates a current block 201 and neighboring pixels 202 and 203 adjacent to the current block in accordance with one embodiment of the present invention. As shown in FIG. 3, the peripheral pixels 202 and 203 according to an embodiment of the present invention are the upper peripheral pixel group 202 and the current block 201 located adjacent to the upper side of the current block 201. ) May include a left peripheral pixel group 203 positioned adjacent to a left side of the. However, the peripheral pixels 202 and 203 are not limited to pixels located above and left as described above, and according to an embodiment, pixels located above and right, below and left, or below and right of the current block. It may also include.

The difference calculator 101 calculates a difference between pixel values of neighboring pixels 202 and 203 adjacent to the current block 201. According to an embodiment of the present disclosure, the difference calculator 101 may calculate an upper peripheral pixel group difference value by summing an absolute value of a difference between pixel values among adjacent pixels among the upper peripheral pixel group. According to an embodiment of the present invention, the difference calculator 101 may calculate a left peripheral pixel group difference value by summing an absolute value of a difference between pixel values among adjacent pixels in the left peripheral pixel group.

4 is a diagram illustrating peripheral pixels 202 and 203 and pixel values of the peripheral pixels used for intra prediction according to an embodiment of the present invention. Referring to FIG. 4, the difference calculator 101 calculates a difference between pixel values between adjacent pixels (eg, 2021 and 2022, 2022 and 2023,..., 2024 and 2025) among the upper peripheral pixel group 202. Can be calculated Here, the pixel value means a luminance value, but is not limited thereto and may mean a color difference value, an R, G, or B value according to an embodiment. Therefore, referring to FIG. 4A, the difference calculating unit 101 determines a difference between pixel values among adjacent pixels among pixels belonging to the upper peripheral pixel group 202, for example, Y ₁₁ -Y ₂₁ , Y _21. -Y ₃₁ , ..., Y _{n -1 1} -Y _{n 1} can be calculated and their absolute values summed to obtain an upper peripheral pixel group difference value. In addition, the difference calculator 102 may calculate a difference of pixel values between adjacent pixels (eg, 2031 and 2032, 2032 and 2033,..., 2034 and 2035) of the left peripheral pixel group 203. . For example, referring to FIG. 4B, the difference calculator 102 calculates Y ₁₁ -Y ₁₂ , Y ₁₂ -Y ₁₃ , ..., Y _{1 n-1} -Y _{1 n} . By summing these absolute values, the left peripheral pixel group difference value can be obtained.

The encoder 104 determines the type of the current block 201 according to the difference, and among the plurality of mode ranking tables stored in the storage 103, a mode ranking table corresponding to the type of the current block 201. The intra prediction mode of the current block 201 may be encoded with reference to FIG.

According to an embodiment of the present invention, the encoder 104, when the upper peripheral pixel group difference value is greater than a predetermined threshold value, and the left peripheral pixel group difference value is less than or equal to the threshold value, The type of the current block 201 may be determined as an upper high difference block (Above_high Block).

According to an embodiment of the present invention, the encoder 104, when the upper peripheral pixel group difference value is less than or equal to a predetermined threshold value, and the left peripheral pixel group difference value is larger than the threshold value, the The type of the current block 201 may be determined as a left high difference block (Left_high Block).

According to an embodiment of the present invention, the encoder 104 determines the type of the current block 201 when the upper peripheral pixel group difference value and the left peripheral pixel group difference value are larger than a predetermined threshold value. It can be determined as a bilateral high-order block (All_high Block).

According to an embodiment of the present invention, the encoder 104 may determine that the upper peripheral pixel group difference value and the left peripheral pixel group difference value are smaller than or equal to a predetermined threshold value. The type may be determined as a bilateral low difference block (All_low Block).

 5 is a diagram illustrating a most probable mode according to each type of the current block 201. As shown in FIG. 5A, when the difference value of the upper peripheral pixel group 202 is larger than a predetermined threshold and the difference value of the left peripheral pixel group 203 is smaller than or equal to the threshold, the current The pixels constituting the block 201 are also likely to have a large difference in pixel values in the horizontal direction but a small difference in pixel values in the vertical direction. Therefore, in this case, it can be expected that the intra prediction mode of the current block 201 has a high probability of being a vertical mode.

On the other hand, as shown in (b) of FIG. 5, when the difference value of the upper peripheral pixel group 202 is smaller than or equal to the threshold value and the difference value of the left peripheral pixel group 203 is larger than the threshold value, the current The pixels constituting the block 201 are also likely to have a large difference in pixel values in the vertical direction but a small difference in pixel values in the horizontal direction. Therefore, in this case, it can be expected that the intra prediction mode of the current block 201 has a high probability of being in a horizontal mode.

The mode determiner 102 determines an intra prediction mode of the current block 201. For example, when a total of 35 intra prediction modes are used for intra prediction, as shown in FIG. 7, the intra prediction mode of the current block 201 may be determined as one of 35 modes.

The storage unit 103 stores a plurality of mode ranking tables that are ranked according to the probability of occurrence of the intra prediction mode. According to one embodiment of the invention, the storage unit 103, the intra prediction mode toward the upper side of the block (for example, modes 4, 19, ..., 26, 7 shown in Figure 6 shown in the upward direction) Occurrence probability ranking of the forward facing mode is more than the occurrence probability ranking of the intra prediction mode facing the left side of the block (e.g., facing left as shown in Figures 27, 15, ..., 34, 10). A high first mode ranking table, a second mode ranking table in which the occurrence probability ranking of the intra prediction mode towards the left side of the block is higher than the occurrence probability ranking of the intra prediction mode towards the upper side of the block, and the intra prediction mode towards the upper side of the block And a third mode ranking table which is ranked in advance of the probability of occurrence of the intra prediction mode toward the left side of the block according to the statistics regarding the mode occurrence.

In general, when analyzing the intra prediction modes of the blocks included in the image, among the 35 modes, planar mode, DC mode, vertical mode, and horizontal mode frequently occur, and the other modes occur statistically regardless of the direction. You can check with 7 is a graph illustrating the frequency of intra prediction modes occurring in the entire block of an image according to an embodiment of the present invention. In the entire block included in the image, the frequency of occurrence of the planar, DC, vertical, and horizontal modes is high, and the remaining modes are uniformly generated.

FIG. 8 is a graph showing the frequency of intra prediction modes occurring in both types of all_high block types in an image according to an embodiment of the present invention, and FIG. 9 is a graph showing both low and low frequencies in an image according to an embodiment of the present invention. A graph showing the frequency of intra prediction modes occurring in the differential block type (All_low Block). As shown in FIGS. 8 and 9, when both the difference value of the upper peripheral pixel group 202 and the difference value of the left peripheral pixel group 203 are greater than or less than or equal to the threshold value, Similar to the mode occurrence frequency of the entire block shown in FIG. 7, it can be seen that the occurrence frequency of the planar, DC, vertical and horizontal modes is high, and the remaining modes are generated evenly regardless of the direction.

However, when only the difference value of any one of the upper peripheral pixel group 202 and the left peripheral pixel group 203 is larger than the threshold value, either one of the upward facing intra prediction mode and the left facing intra prediction mode is the other. It may be more frequent. FIG. 10 is a graph illustrating the frequency of intra prediction modes occurring in an upper high-order block type of an image according to an embodiment of the present invention, and FIG. 11 is a diagram of an upper high-order block type in an image according to an embodiment of the present invention. It is a graph showing the frequency of intra prediction modes generated.

As shown in FIG. 10, when the difference value of the upper peripheral pixel group 202 is larger than the threshold value, and the difference value of the left peripheral pixel group 203 is smaller than or equal to the threshold value (that is, the upper high difference block ( Above_high Block) type), and the frequency of occurrence of the intra prediction mode toward the upper side of the block is higher than the frequency of occurrence of the intra prediction mode toward the left side of the block.

In addition, as shown in FIG. 11, when the difference value of the upper peripheral pixel group 202 is less than or equal to the threshold value, and the difference value of the left peripheral pixel group 203 is larger than the threshold value (that is, the left high difference value). It can be seen that the frequency of occurrence of the intra prediction mode toward the left side of the block (block type) is higher than that of the intra prediction mode toward the upper side of the block.

The present invention focuses on the fact that the frequency of occurrence of the intra prediction mode toward the upper or left direction is distributed differently according to the type of the block as described above, and corresponds to the type of the current block 201 among the plurality of mode ranking tables. The intra prediction mode of the current block 201 is encoded by referring to the mode ranking table.

The first mode ranking table stored in the storage unit 103 is a mode ranking table corresponding to the type of the high high block (Above_high Block), and the probability of occurrence of the intra prediction mode toward the upper side of the block is intra to the left side of the block. It is set higher than the occurrence probability ranking of the prediction mode.

The second mode ranking table stored in the storage unit 103 is a mode ranking table corresponding to a left high-order block type (Left_high Block) type. It is set higher than the occurrence probability ranking of the prediction mode.

The third mode ranking table stored in the storage unit 103 is a mode ranking table corresponding to both high differential block types and both low differential block types, and the intra prediction mode toward the upper side of the block and the intra prediction mode toward the left side of the block. The occurrence probability ranking of is determined according to the occurrence frequency statistics for each pre-analyzed mode as shown in FIG. 7. The table below shows the first to third mode ranking tables according to an embodiment of the present invention, wherein the number of modes used in the table corresponds to the number of modes used in FIG.

ranking One 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1st mode ranking table 0 One 3 22 23 12 21 13 5 24 20 11 4 6 19 2 2nd mode ranking table 0 2 3 31 30 17 16 9 32 One 29 4 8 5 27 11 3rd mode ranking table 0 2 3 29 One 8 30 21 28 16 7 15 20 31 9 11

ranking 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 1st mode ranking table 8 10 15 28 9 27 29 18 16 17 25 14 31 34 32 2nd mode ranking table 20 33 15 19 12 28 18 21 7 22 6 13 23 26 10 3rd mode ranking table 6 4 5 12 10 14 22 19 17 27 13 18 23 26 32

ranking 32 33 34 35 1st mode ranking table 7 30 26 33 2nd mode ranking table 24 14 34 35 3rd mode ranking table 24 25 33 34

The intra prediction mode of the current block 201 is encoded by referring to a mode ranking table corresponding to a high order block, a left high order block, both high order blocks, or both low order blocks.

According to an embodiment of the present invention, the encoder 104 may determine that the upper peripheral pixel group difference value is greater than a threshold value and the left peripheral pixel group difference value is smaller than a threshold value (ie, the upper high difference block). The intra prediction mode of the current block 201 may be encoded by referring to the one mode ranking table.

According to an embodiment of the present invention, the encoder 104 may determine that the upper peripheral pixel group difference value is less than or equal to a threshold value and the left peripheral pixel group difference value is larger than a threshold value (that is, the left high difference block). Intra prediction mode of the current block 201 may be encoded by referring to the second mode ranking table.

According to an embodiment of the present invention, the encoder 104 determines that both the upper peripheral pixel group difference value and the left peripheral pixel group difference value are both (i) greater than the threshold or (ii) less than the threshold. In this case, the intra prediction mode of the current block 201 may be encoded by referring to the third mode ranking table.

According to an embodiment of the present invention, the probability ranking of the first mode ranking table corresponding to the upper high-order block may increase as the intra prediction mode is directed toward the vertical direction. For example, referring to FIG. 6 and Tables 1 to 3, it can be seen that in the first mode ranking table, mode_22 and mode_23 which are close to vertical are ranked higher than other modes such as mode 19 and mode_26.

According to an embodiment of the present invention, the probability ranking of the mode ranking table corresponding to the left high-order block may increase as the intra prediction mode is toward the horizontal direction. For example, referring to FIG. 6 and Tables 1 to 3, it can be seen that in the second mode ranking table, mode_30 and mode_31 which are close to horizontal are ranked higher than other modes such as mode_27 and mode_34.

When the ranking corresponding to the intra prediction mode of the current block 201 in the mode ranking table referred to the encoding is not the highest rank (that is, not the rank 1), the updater 105 determines the current block in the mode ranking table. The mode ranking table may be updated by increasing the ranking of the intra prediction mode of 201). According to an embodiment of the present invention, the updater 105 may raise the ranking of the intra prediction mode of the current block 201 by one step. However, the present invention is not limited thereto and two or more steps may be performed. It may be raised, or one step may be raised in multiple times (eg, one step in two or three times).

12 is a flowchart illustrating an intra prediction method according to an embodiment of the present invention. As shown in FIG. 12, the intra prediction method according to an exemplary embodiment of the present disclosure may include calculating a difference between pixel values of neighboring pixels adjacent to the current block 201 (S11), and based on the difference. Determining the type of 201 (S12), Determining the intra prediction mode of the current block 201 (S13), and the intra prediction mode of the current block 201 corresponding to the type of the current block 201 The method may include encoding by referring to a mode ranking table (S14).

The peripheral pixels may include an upper peripheral pixel group 202 adjacent to an upper side of the current block 201 and a left peripheral pixel group 203 adjacent to a left side of the current block 201.

FIG. 13 is a flowchart illustrating a step S11 of calculating a difference between pixel values of neighboring pixels according to an exemplary embodiment of the present invention. According to an embodiment of the present disclosure, calculating the difference of pixel values of neighboring pixels adjacent to the current block 201 (S11) may include determining a difference between pixel values between adjacent pixels in the upper peripheral pixel group 202. Computing the difference value of the upper peripheral pixel group by summing the absolute values (S111), and calculating the left peripheral pixel group difference value by summing the absolute value of the difference of pixel values between adjacent pixels among the left peripheral pixel group 203. It may include the step (S112).

14 is a flowchart illustrating a step S12 of determining a type of a current block based on a difference according to an embodiment of the present invention. According to an embodiment of the present invention, in the step S12 of determining the type of the current block 201 based on the difference, the upper peripheral pixel group difference value is larger than a predetermined threshold value (YES in S121), and the left peripheral point. If the pixel group difference value is less than or equal to the threshold value (NO in S122), determining the type of the current block 201 as an upper high difference block (Above_high Block) may be included (S124).

According to one embodiment of the present invention, in the step S12 of determining the type of the current block 201 based on the difference, the upper peripheral pixel group difference value is less than or equal to a predetermined threshold value (NO in S121). If the left peripheral pixel group difference value is larger than the threshold value (YES in S123), determining the type of the current block 201 as the left high difference block (Left_high Block) may be included (S126).

According to an embodiment of the present disclosure, the determining of the type of the current block 201 based on the difference (S12) may be performed when the upper peripheral pixel group difference value and the left peripheral pixel group difference value are larger than a predetermined threshold. (YES in S121 and S122), the method may include determining the type of the current block 201 as the two-sided high difference block (All_high Block) (S125).

According to an embodiment of the present invention, in the determining of the type of the current block 201 based on the difference (S12), the upper peripheral pixel group difference value and the left peripheral pixel group difference value are smaller than or equal to a predetermined threshold value. In the same case (NO in S121 and S123), the method may include determining a type of the current block 201 as two-sided low difference blocks (All_low Block) (S127).

According to one embodiment of the invention, the threshold may be set in inverse proportion to the size of the current block 201. For example, the threshold used to calculate the difference value of the upper peripheral pixel group 202 is inversely proportional to the size of the current block 201 to the sum of the pixel values of the pixels constituting the upper peripheral pixel group 202. It can be calculated by multiplying the coefficients. Further, the threshold value used to calculate the difference value of the left peripheral pixel group 203 may have a coefficient that is inversely proportional to the size of the current block 201 to the sum of the pixel values of the pixels constituting the left peripheral pixel group 203. Can be calculated by multiplication. According to an embodiment of the present invention, the coefficient may be 1/16 for 4 X 4 blocks, 1/32 for 8 X 8 blocks, or 1/64 for 16 X 16 or larger blocks.

15 is a flowchart illustrating an intra prediction method performed when decoding an image according to an embodiment of the present invention. As illustrated in FIG. 15, in the intra prediction method performed when decoding an image according to an embodiment of the present disclosure, calculating a difference between pixel values of neighboring pixels adjacent to a current block 201 to be decoded (S31). Determining a type of the current block 201 based on the difference (S32), and obtaining an intra prediction mode of the current block 201 by referring to a mode ranking table corresponding to the type of the current block 201. (S33) and decoding the current block 201 using the intra prediction mode of the current block 201 and the reference block decoded before the current block (S34).

Similarly as described in the encoding process described above, in the decoding process, the neighboring pixels include the upper peripheral pixel group 202 adjacent to the upper side of the current block 201 and the left peripheral pixel group 203 adjacent to the left side of the current block 201. It may include.

In operation S31, the difference between pixel values of neighboring pixels may be calculated by adding the absolute values of the difference between pixel values among adjacent pixels in the upper peripheral pixel group 202 to calculate the upper peripheral pixel group difference. And calculating the left peripheral pixel group difference value by summing an absolute value of a difference of pixel values between adjacent pixels among the left peripheral pixel group 203.

Similar to the above-described encoding process, the type of the current block 201 includes (i) the upper high difference block (Above_high Block), (ii) the left high difference block (Left_high Block), and (iii) both high order differences. Blocks (All_high Block), and (iv) both low-order blocks (All_low Block).

Further, the mode ranking table may include a first mode ranking table in which an occurrence probability ranking of an intra prediction mode toward the upper side of the block is higher than a ranking of an intra prediction mode toward the left side of the block, and generation of an intra prediction mode toward the left side of the block. The second mode ranking table in which the probability ranking is higher than the ranking of the intra prediction mode toward the upper side of the block, and the probability prediction of the intra prediction mode towards the upper layer of the block and the intra prediction mode toward the left side of the block are generated. And a third mode ranking table rated according to the statistics for. The first mode ranking table may correspond to an upper high difference block, the second mode ranking table may correspond to a left high difference block, and the third mode ranking table may correspond to both high difference blocks and both low difference blocks.

According to an embodiment of the present invention, if the ranking corresponding to the intra prediction mode of the current block 201 in the referenced mode ranking table is not the highest, the mode of the intra prediction mode of the current block 201 is increased. The method may further include updating the ranking table. As described above, according to the present invention, the intra prediction mode of the current block may be decoded by referring to different mode ranking tables according to the type of the current block to be decoded.

16 is a block diagram illustrating a video encoding apparatus according to an embodiment of the present invention. Referring to FIG. 16, the image encoding apparatus 200 may include a motion predictor 211, a motion compensator 212, an intra predictor 220, a switch 215, a subtractor 225, a converter 230, A quantizer 240, an entropy encoder 250, an inverse quantizer 260, an inverse transformer 270, an adder 275, a filter 280, and a reference image buffer 290 are included.

The image encoding apparatus 200 performs encoding in an intra prediction mode or an inter prediction mode on an input image and outputs a bit stream. In order to determine an optimal prediction method for the prediction unit, an intra prediction method and an inter prediction method may be selectively used for the prediction unit. The image encoding apparatus 200 generates a prediction block for the original block of the input image, and then encodes the difference between the original block and the prediction block.

In the intra-prediction mode, the intra-prediction unit 220 performs spatial prediction using the pixel values of the already-coded blocks around the current block to generate a prediction block.

The intraprediction unit 220 calculates a SATD for the intra prediction mode for a predetermined prediction unit, calculates a first intra-picture prediction mode corresponding to the calculated first and second SATD values, and a first SATD value The predicted block of the predetermined prediction unit can be generated by storing the predicted block in the candidate intra prediction mode list and determining whether the difference between the first SATD value and the second SATD value is less than a predetermined threshold value. If the difference between the first SATD value and the second SATD value is greater than the predetermined threshold value, the intra prediction mode corresponding to the first SATD value is determined as the final intra prediction mode of the current prediction unit, And the second SATD value is less than or equal to a predetermined threshold value, the additional intra prediction mode is included in the intra prediction mode list to calculate the RD cost calculated based on the intra prediction mode stored in the intra prediction mode list To determine the final in-picture prediction mode.

In addition, the intra-prediction unit 220 determines whether or not the SATD value for a predetermined encoding unit exceeds the threshold SATD value, and when the SATD value for a predetermined encoding unit is smaller than the threshold SATD value, the encoding unit is not further divided And if the SATD value for a predetermined encoding unit is equal to or larger than the threshold SATD value, the encoding unit can be further divided.

Here, the intraprediction unit 220 may include an intraprediction apparatus according to an embodiment of the present invention.

In the case of the inter-view prediction mode, the motion prediction unit 211 finds a motion vector by searching an area where the best match with the input block is obtained from the reference image stored in the reference image buffer 290 in the motion prediction process. The motion compensation unit 212 generates a prediction block by performing motion compensation using a motion vector.

The subtractor 225 generates a residual block by a difference between the input block and the generated prediction block. The transform unit 230 performs a transform on the residual block to output a transform coefficient. The quantization unit 240 quantizes the input transform coefficients according to the quantization parameters and outputs a quantized coefficient. The entropy encoding unit 250 entropy-codes the input quantized coefficients according to a probability distribution to output a bit stream.

Since HEVC performs inter prediction encoding, the currently encoded picture needs to be decoded and stored to be used as a reference picture. Accordingly, the quantized coefficients are inversely quantized in the inverse quantization unit 260 and inversely transformed in the inverse transformation unit 270. The inverse quantized and inverse transformed coefficients are added to the prediction block through an adder 275, and a reconstruction block is generated.

The restoration block passes through the filter unit 280 and the filter unit 280 applies at least one of a deblocking filter, a sample adaptive offset (SAO), and an adaptive loop filter (ALF) can do. The filter unit 280 may be referred to as an adaptive in-loop filter. The deblocking filter can remove block distortion occurring at the boundary between the blocks. The SAO may add a proper offset value to the pixel value to compensate for coding errors. The ALF may perform filtering based on a comparison between the reconstructed image and the original image, and may be performed only when high efficiency is applied. The reconstruction block having passed through the filter unit 280 is stored in the reference image buffer 290.

17 is a block diagram illustrating an image decoding apparatus according to an embodiment of the present invention.

Referring to FIG. 17, the image decoding apparatus 300 may include an entropy decoder 310, an inverse quantizer 320, an inverse transformer 330, an intra predictor 340, a motion compensator 350, and a filter. 360 and a reference image buffer 370.

The video decoding apparatus 300 receives the bit stream output from the encoder and decodes the video stream into an intra mode or an inter mode, and outputs a reconstructed video, that is, a reconstructed video. In the intra mode, a prediction block is generated using an intra prediction mode, and a prediction block is generated using an inter prediction method in an inter mode. The video decoding apparatus 300 obtains a residual block from the input bitstream, generates a prediction block, and then adds the residual block and the prediction block to generate a reconstructed block, that is, a reconstruction block.

The entropy decoding unit 310 entropy-decodes the input bitstream according to a probability distribution and outputs a quantized coefficient. The quantized coefficients are inversely quantized in the inverse quantization unit 320 and inversely transformed in the inverse transformation unit 330. As a result of inverse quantization / inverse transformation of the quantized coefficients, a residual block is generated.

In the intra-prediction mode, the intra-prediction unit 340 performs spatial prediction using the pixel values of the already-coded blocks around the current block to generate a prediction block.

In the inter prediction mode, the motion compensation unit 350 generates a prediction block by performing motion compensation using a motion vector and a reference image stored in the reference image buffer 370.

The residual block and the prediction block are added through the adder 355, and the added block is passed through the filter unit 360. [ The filter unit 360 may apply at least one of a deblocking filter, SAO, and ALF to a restoration block or a restored picture. The filter unit 360 outputs a reconstructed image, that is, a reconstructed image. The restored image is stored in the reference image buffer 370 and can be used for inter prediction.

Methods for improving the prediction performance of the encoding / decoding apparatus include a method of increasing the accuracy of the interpolation image and a method of predicting the difference signal. Here, the difference signal is a signal indicating the difference between the original image and the predicted image. In the present invention, the term " difference signal " may be replaced by a " difference signal ", " residual block ", or " difference block " depending on the context. Those skilled in the art may influence the idea You will be able to distinguish this within the scope of not giving.

In the present specification, a coding unit (coding unit) is used as a coding unit for convenience of explanation, but it may be a unit for performing not only coding but also decoding. The above-described intra prediction method according to an embodiment of the present invention may be implemented according to the functions of the modules described with reference to FIGS. 11 and 12, and such an encoder and a decoder are included in the scope of the present invention. That is, the intra prediction method according to an embodiment of the present invention may be performed by each component included in the image encoder and the image decoder described with reference to FIGS. 11 and 12. The meaning of the component may include not only the hardware meaning but also a software processing unit that may be performed through an algorithm.

In addition, the intraprediction method according to an embodiment of the present invention described above can be stored in a computer-readable recording medium made of a program to be executed in a computer. The computer-readable recording medium includes all kinds of storage devices in which data that can be read by a computer system is stored. Examples of the computer-readable recording medium include ROM, RAM, CD-ROM, magnetic tape, floppy disk, optical data storage, and the like.

In the above, the difference of pixel values between neighboring pixels adjacent to the current block to be encoded or decoded is calculated, and the intra prediction mode of the current block is referred to by referring to a different mode ranking table according to the type of the current block determined according to the calculated difference. An intra prediction method and apparatus for encoding or decoding have been described. According to the intra prediction method and the apparatus according to the embodiment of the present invention, the number of bits of data representing the intra prediction mode of the current block is reduced as compared with the conventional method, thereby increasing the compression ratio of the image.

100: intra prediction device 101: difference calculation unit
102: mode determination unit 103: storage unit
104: encoder 105: update unit
200: video encoding apparatus 300: video decoding apparatus

Claims (22)

Calculating a difference between pixel values of neighboring pixels adjacent to the current block to be encoded;
Determining a type of the current block based on the difference;
Determining an intra prediction mode of the current block;
Encoding an intra prediction mode of the current block with reference to a mode ranking table corresponding to the type of the current block; And
Updating the mode ranking table by raising the ranking of the intra prediction mode of the current block when the ranking corresponding to the intra prediction mode of the current block is not the highest in the mode ranking table;
/ RTI > The method of claim 1,
The peripheral pixels include an upper peripheral pixel group adjacent to an upper side of the current block and a left peripheral pixel group adjacent to a left side of the current block. 3. The method of claim 2,
The step of calculating the difference of pixel values of the neighboring pixels is:
Calculating an upper peripheral pixel group difference value by summing an absolute value of a difference of pixel values between adjacent pixels in the upper peripheral pixel group; And
Calculating a left peripheral pixel group difference value by summing an absolute value of a difference of pixel values between adjacent pixels in the left peripheral pixel group;
/ RTI > The method of claim 3, wherein
Determining the type of the current block based on the difference:
If the upper peripheral pixel group difference is greater than a predetermined threshold and the left peripheral pixel group difference is less than or equal to the threshold, determining the type of the current block as an upper high difference block; Forecast method. The method of claim 3, wherein
Determining the type of the current block based on the difference:
If the upper peripheral pixel group difference is less than or equal to a predetermined threshold and the left peripheral pixel group difference is greater than the threshold, determining the type of the current block as a left high difference block; Forecast method. The method of claim 3, wherein
Determining the type of the current block based on the difference:
And determining the type of the current block as a bilateral high difference block when the upper peripheral pixel group difference value and the left peripheral pixel group difference value are larger than a predetermined threshold value. The method of claim 3, wherein
Determining the type of the current block based on the difference:
And determining the type of the current block as both low-order blocks when the upper peripheral pixel group difference value and the left peripheral pixel group difference value are less than or equal to a predetermined threshold value. 5. The method of claim 4,
And a mode ranking table corresponding to the upper higher difference block has a higher probability of occurrence of an intra prediction mode toward an upper side of the block than a ranking of an intra prediction mode toward the left side of the block. The method of claim 8,
And a mode ranking table corresponding to the upper high-order block has a higher probability of occurrence ranking as the intra prediction mode is directed toward the vertical direction. The method of claim 5, wherein
And a mode ranking table corresponding to the left high-order block has a higher probability of occurrence of the intra prediction mode toward the left side of the block than an occurrence probability ranking of the intra prediction mode toward the upper side of the block. 11. The method of claim 10,
And a mode ranking table corresponding to the left high-order block has a higher probability of occurrence ranking as the intra prediction mode is directed toward a horizontal direction. Calculating a difference between pixel values of neighboring pixels adjacent to the current block to be encoded;
Determining a type of the current block based on the difference;
Determining an intra prediction mode of the current block; And
Encoding the intra prediction mode of the current block with reference to a mode ranking table corresponding to the type of the current block,
The peripheral pixels include an upper peripheral pixel group adjacent to an upper side of the current block and a left peripheral pixel group adjacent to a left side of the current block;
The step of calculating the difference of pixel values of the neighboring pixels is:
Calculating an upper peripheral pixel group difference value by summing an absolute value of a difference of pixel values between adjacent pixels in the upper peripheral pixel group; And
Calculating a left peripheral pixel group difference value by summing an absolute value of a difference of pixel values between adjacent pixels in the left peripheral pixel group;
Determining the type of the current block based on the difference:
Determining the type of the current block as an upper higher difference block when the upper peripheral pixel group difference value is greater than a predetermined threshold and the left peripheral pixel group difference value is less than or equal to the threshold value;
If the upper peripheral pixel group difference value is less than or equal to a predetermined threshold value and the left peripheral pixel group difference value is greater than the threshold value, determining a type of the current block as a left high difference block;
If the upper peripheral pixel group difference value and the left peripheral pixel group difference value are larger than a predetermined threshold value, determining the type of the current block as both high differential blocks; And
If the upper peripheral pixel group difference value and the left peripheral pixel group difference value are less than or equal to a predetermined threshold value, determining the type of the current block as both lower difference blocks;
, ≪ / RTI >
And the threshold is inversely proportional to the size of the current block. delete A difference calculator which calculates a difference between pixel values of neighboring pixels adjacent to the current block to be encoded;
A mode determination unit to determine an intra prediction mode of the current block;
A storage unit for storing a plurality of mode ranking tables ranked according to a probability of occurrence of an intra prediction mode;
An encoder which encodes an intra prediction mode of the current block by referring to a mode ranking table corresponding to the type of the current block determined according to the difference; And
An updater configured to update the mode ranking table by raising the ranking of the intra prediction mode of the current block when the ranking corresponding to the intra prediction mode of the current block is not the highest in the mode ranking table;
And an intra prediction unit. 15. The method of claim 14,
The peripheral pixels include an upper peripheral pixel group adjacent to an upper side of the current block and a left peripheral pixel group adjacent to a left side of the current block. The method of claim 15,
The difference calculator calculates an upper peripheral pixel group difference value by summing an absolute value of a difference of pixel values between adjacent pixels in the upper peripheral pixel group, and calculates a difference of pixel values between adjacent pixels in the left peripheral pixel group. An intra prediction device that calculates a difference of left peripheral pixel groups by summing absolute values. 17. The method of claim 16,
Wherein the storage unit comprises:
A first mode ranking table in which an occurrence probability ranking of the intra prediction mode facing upwards of the block is higher than an occurrence probability ranking of the intra prediction mode facing leftward of the block;
A second mode ranking table in which an occurrence probability ranking of the intra prediction mode toward the left side of the block is higher than an occurrence probability ranking of the intra prediction mode toward the upper side of the block; And
A third mode ranking table in which an occurrence probability ranking of the intra prediction mode toward the upper side of the block and the intra prediction mode toward the left side of the block is ranked according to the statistics on the mode occurrence;
Intra prediction device for storing the. The method of claim 17,
If the upper peripheral pixel group difference value is greater than a predetermined threshold and the left peripheral pixel group difference value is less than or equal to the threshold value, the encoder may refer to the first mode ranking table to predict an intra of the current block. Intra prediction device for encoding the mode. The method of claim 17,
The encoder, when the upper peripheral pixel group difference value is less than or equal to a predetermined threshold value and the left peripheral pixel group difference value is larger than the threshold value, refers to an intra prediction of the current block by referring to the second mode ranking table. Intra prediction device for encoding the mode. The method of claim 17,
The encoder may determine the current mode by referring to the third mode ranking table when both the upper peripheral pixel group difference value and the left peripheral pixel group difference value are greater than or equal to or less than a predetermined threshold. An intra prediction apparatus for encoding an intra prediction mode of a block. delete In a computer-readable recording medium, the recording medium may be:
Calculating a difference between pixel values of neighboring pixels adjacent to the current block to be encoded;
Determining a type of the current block based on the difference;
Determining an intra prediction mode of the current block;
Encoding an intra prediction mode of the current block with reference to a mode ranking table corresponding to the type of the current block; And
Updating the mode ranking table by raising the ranking of the intra prediction mode of the current block when the ranking corresponding to the intra prediction mode of the current block is not the highest in the mode ranking table;
The recording medium on which a program for executing the intra prediction process is recorded.

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