KR20070005848A - Method and apparatus for intra prediction mode decision - Google Patents

Abstract

A method and an apparatus for determining an intra prediction mode are provided to more quickly determine the intra prediction mode for the intra prediction coding of images. An intra prediction performing unit(210) selects a candidate group having directionality similar to an intra prediction mode of the first block unit among intra prediction modes of the second block unit of a certain size by using the determination result of the intra prediction mode of the first block unit with a certain size. The intra prediction performing unit(210) performs the second block unit intra prediction for only the second block unit intra prediction modes which belong to the candidate group, and determines the second block unit intra prediction mode. A prediction mode determining unit(220) compares the cost of the first block unit intra prediction mode determined in the intra prediction performing unit(210) with the cost of the determined second block unit intra prediction mode, and determines the last prediction mode for predicting the intra prediction of an input block.

Description

Method and apparatus for determining intra prediction mode

1 shows a 16x16 intra prediction mode according to the H.264 standard.

2 shows a 4x4 intra prediction mode according to the H.264 standard.

3 is a block diagram illustrating a configuration of an image encoding apparatus to which an intra prediction apparatus according to the present invention is applied.

4 is a block diagram showing the configuration of an intra prediction apparatus according to the present invention;

FIG. 5 is a detailed block diagram of the intra prediction performing unit of FIG. 4. FIG.

6 is a diagram illustrating a 4x4 intra prediction mode used in an intra prediction apparatus according to the present invention.

7 illustrates a neighboring block used for intra prediction mode determination of a current block according to the present invention;

8 is a block diagram of an image decoding apparatus for decoding a bitstream encoded according to the present invention.

9 is a flowchart illustrating a method of determining an intra prediction mode according to the present invention.

The present invention relates to encoding of image data, and more particularly, to an intra prediction mode determination method and apparatus for reducing the time required for intra prediction when encoding image data.

According to H.264 / MPEG-4 Advanced Video Coding (AVC) regarding video compression, one picture is divided into macro blocks to encode a video. Then, after encoding each macroblock in all encoding modes available for inter prediction and intra prediction, the bit rate required for encoding the macroblock and the original macroblock and the decoded macroblock are encoded. The macroblock is encoded by setting one encoding mode according to the degree of distortion.

Intra prediction does not refer to a reference picture in order to encode a macroblock of a current picture, but calculates a prediction value for a macroblock to be encoded using a pixel value spatially adjacent to the macroblock to be encoded, and then calculates the prediction value. Encode the difference of pixel values. Here, the modes used for intra prediction are largely divided into 4x4 intra prediction mode, 8x8 intra prediction mode (for high profile), and 16x16 intra prediction mode.

1 is a diagram illustrating a 16 × 16 intra prediction mode according to the H.264 standard, and FIG. 2 is a diagram showing a 4 × 4 intra prediction mode according to the H.264 standard.

Referring to FIG. 1, a total of four modes exist in a 16 × 16 intra prediction mode, that is, a vertical mode, a horizontal mode, a direct current mode, and a plane mode. In addition, referring to FIG. 2, the 4 × 4 intra prediction mode includes a vertical mode, a horizontal mode, a direct current mode, a diagonal down-left mode, and a diagonal down- mode. There are a total of nine modes: right mode, vertical right mode, vertical left mode, horizontal-up mode, and horizontal-down mode.

For example, an operation of predictively encoding a 4 × 4 current block according to mode 0 of FIG. 2, that is, a vertical mode will be described. First, the pixel values of the pixels A to D adjacent to the top of the 4x4 current block are predicted as the pixel values of the 4x4 current block. That is, the value of pixel A is the four pixel values contained in the first column of the 4x4 current block, the value of pixel B is the four pixel values contained in the second column of the 4x4 current block, and the value of the pixel C is Is predicted as four pixel values included in the third column of the 4x4 current block, and the value of pixel D is predicted as four pixel values included in the fourth column of the 4x4 current block. Next, the difference value is obtained by subtracting the actual values of the predicted 4x4 current block and the pixels included in the original 4x4 current block using the pixels A to D, and then encoding the difference value.

When encoding an image according to the H.264 standard, the current macroblock is encoded in a total of 13 modes of the 4x4 intra prediction mode and the 16x16 intra prediction mode, and the lowest cost among them is then encoded. Perform intra coding in mode. Specifically, four 16x16 intra prediction modes are performed on the current macroblock to select the 16x16 intra prediction mode having the lowest cost, and nine 4x in sequence for the 4x4 subblock. Four intra prediction modes are performed to select a mode with the lowest cost for each subblock. Then, the cost of the selected 16 × 16 intra prediction mode is compared with the cost of the 4 × 4 intra prediction mode, which is the sum of the costs of the respective subblocks, and finally the mode having the smallest cost is selected.

H.264 has 20-50% higher compression efficiency than MPEG-4 part2 and up to 18 times higher compression efficiency than MPEG-2 applied to digital terrestrial broadcasting. However, in H.264, due to the introduction of 4x4 subblocks and the increase in the number of intra prediction modes, the amount of computation required for encoding is greatly increased. In addition, there is a problem that it is difficult to implement a real-time video encoder according to H.264 in a mobile device of limited resources due to the increase in the amount of computation. In addition, according to the related art, the information of the neighboring blocks cannot be used when determining the mode for intra prediction, and 9 4 × 4 intra prediction modes and 4 16 × 16 intra prediction modes for all macro blocks to be intra coded. Since coding is performed in 13 modes, the inefficiency in terms of calculation amount is achieved.

Accordingly, an object of the present invention is to provide an intra prediction mode determination method and apparatus for quickly determining an intra prediction mode for intra prediction encoding of an image.

Another object of the present invention is to provide an intra prediction mode determination method and apparatus capable of reducing the complexity of computation during intra prediction, so that the present invention can be applied to a real time encoder.

Another object of the present invention is to provide an intra prediction mode determination method and apparatus capable of shortening the time required for encoding without significant deterioration of image quality.

In order to solve the above technical problem, an intra prediction mode determining method according to the present invention performs the first prediction by performing intra prediction on a plurality of first block unit intra prediction modes of an input block in units of first blocks having a predetermined size. Determining a prediction mode; An intra prediction mode including a predetermined number of second block unit intra prediction modes among a plurality of second block unit intra prediction modes having a smaller size than the first block unit based on the determined direction of the first intra prediction mode. Determining a candidate group; Determining a second intra prediction mode by performing intra prediction on the input block in a second block unit according to second block unit intra prediction modes belonging to the determined intra prediction mode candidate group; And comparing the cost of the first intra prediction mode with the cost of the second intra prediction mode and determining an intra mode of the input block based on the result.

The intra prediction apparatus of an image according to the present invention uses an intra prediction mode of a first block unit of a predetermined size to determine an intra prediction mode of the determined first block unit among intra prediction modes of a second block unit of a predetermined size. An intra prediction performing unit selecting a candidate group having a similar directionality to and performing a second block unit intra prediction on only second block unit intra prediction modes belonging to the candidate group to determine a second block unit intra prediction mode; And determining a prediction mode for determining a final prediction mode for intra prediction of the input block by comparing the cost of the first block unit intra prediction mode determined by the intra prediction execution unit with the cost of the determined second block unit intra prediction mode. It is characterized by including a wealth.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3 is a block diagram illustrating a configuration of an image encoding apparatus to which an intra prediction apparatus according to the present invention is applied.

Referring to FIG. 3, the image encoding apparatus 100 may include a motion estimator 102, a motion compensator 104, an intra predictor 106, a transformer 108, a quantization unit 110, and a reordering unit 112. ), An entropy coding unit 114, an inverse quantization unit 116, an inverse transform unit 118, a filter 120, and a frame memory 122.

The motion estimation unit 102 performs the search for the predicted value of the macro block of the current picture in the reference picture for inter prediction. When the reference block is found in units of 1/2 or 1/4 pixels, the motion compensator 104 calculates these intermediate pixel values to determine the reference block data value. As such, inter prediction is performed by the motion estimator 102 and the motion compensator 104.

The intra predictor 106 performs intra prediction to find the predicted value of the macro block of the current picture in the current picture. In particular, the intra prediction unit 106 performs intra prediction by determining a mode suitable for intra prediction of the current macroblock among a plurality of intra prediction modes according to the intra prediction mode determination method according to the present invention.

If inter prediction or intra prediction is performed to find prediction data to be referred to by the macro block of the current frame, the quantization unit 110 performs quantization after subtracting it from the macro block of the current picture and performing transformation on the transform unit 108. do. Subtraction of the motion estimation reference block from the macroblock of the current frame is called residual. The residual value is encoded to reduce the amount of data during encoding. The quantized residual value passes through the reordering unit 112 for encoding in the entropy coding unit 114.

Meanwhile, in order to obtain a reference picture to be used for inter prediction, the current picture is reconstructed through the inverse quantizer 116 and the inverse transform unit 118. The reconstructed current picture is stored in the frame memory and used to perform inter prediction on the next picture.

4 is a block diagram illustrating a configuration of an intra prediction apparatus according to the present invention, and FIG. 5 is a detailed block diagram of the intra prediction execution unit 210 of FIG. 4. Here, the intra prediction apparatus 200 according to the present invention corresponds to the intra prediction unit 106 illustrated in FIG. 3.

Referring to FIG. 4, the intra prediction apparatus 200 according to the present invention includes an intra prediction performing unit 210 and a prediction mode determiner 220.

The intra prediction performing unit 210 uses the first block unit intra prediction mode determination result of a predetermined size, and the intra unit of the first block unit determined from among the intra prediction modes of the second block unit smaller than the first block unit. A candidate group having a similar direction as that of the prediction mode is selected, and second block-by-block intra prediction is performed only on second block-by-block intra prediction modes belonging to the candidate group. This uses the fact that there is a similarity between modes when there is a specific pattern in an image. First, intra prediction is performed in a first block unit having a smaller number of modes, and then the directionality similar to the determined first block unit intra prediction mode is obtained. The second block unit intra prediction is performed only for the second block unit intra prediction mode to shorten the time required for the second block unit intra prediction having a larger number of modes.

In particular, in order to reduce complex Rate Distortion Optimize (RDO) operations for nine intra prediction modes of 4 × 4 blocks, the present invention first uses the intra prediction mode decision result of 16 × 16 blocks to determine nine types of 4 × 4 blocks. It is possible to shorten the time required for the intra prediction process by selecting a candidate group having a high probability from the intra prediction modes and performing the 4 × 4 intra prediction mode only on the intra prediction modes of the 4 × 4 block included in the candidate group. have. In fact, the intra prediction process takes about 10% of the total image encoding process time, and the time required for intra prediction for 4 × 4 blocks is about 90% of the total intra prediction process, which takes up most of the entire intra prediction process. Therefore, if the intra prediction mode for the 4x4 block can be determined more quickly, the time required for the entire intra prediction process can be greatly shortened.

Referring to FIG. 5, the intra prediction execution unit 210 performs an intra prediction on an input block in a unit of a first block having a predetermined size to determine a first block unit intra prediction mode. 211) a second block unit intra prediction mode candidate group having a direction similar to the determined first block unit intra prediction mode among a plurality of second block unit intra prediction modes having a smaller size than the first block unit. According to the candidate group determiner 212 to determine and the second block unit intra prediction modes belonging to the determined second block unit intra prediction mode candidate group, the input block is subjected to intra prediction on a second block basis to perform the intra prediction. And a second block unit intra prediction execution unit 213 for determining a second block unit intra prediction mode corresponding to the second block unit intra prediction mode.

The prediction mode determiner 220 compares the cost of the first block unit intra prediction mode determined by the intra prediction execution unit 210 with the cost of the determined second block unit intra prediction mode to perform intra prediction of the input block. Determine the final prediction mode for

An operation of the intra prediction apparatus 200 according to the present invention having the above configuration will be described. Hereinafter, a case of using a 16 × 16 block in the first block unit and a 4 × 4 block in the second block unit will be described as an example.

6 is a diagram illustrating a 4x4 intra prediction mode used in the intra prediction apparatus 200 according to the present invention. Not shown DC mode (mode 2) is a mode for forming a prediction value of the current input block using the average value of the upper and left blocks. In addition, as described above with reference to FIG. 1, in the 16 × 16 intra prediction mode, a vertical mode (mode 0), a horizontal mode (mode 1), a DC mode (mode 2), and a planar mode (mode 3) are used.

The first block unit intra prediction execution unit 211 receives a current macro block to be predictively coded, performs intra prediction in the four 16 × 16 intra prediction modes of FIG. 1, and has the lowest cost 16 × 16 intra prediction. The mode is determined as the 16x16 intra prediction mode to be used for encoding the current macroblock.

The candidate group determiner 212 may have a spatial orientation similar to the 16 × 16 intra prediction mode determined by the first block unit intra prediction performer 211 among the nine 4 × 4 intra prediction modes of FIG. 6. Determine a 4x4 intra prediction mode candidate group having. The 4x4 intra prediction mode candidate group is determined according to which mode is determined as the 16x16 intra prediction mode, as shown in Table 1 below.

16 × 16 intra prediction mode 4 × 4 intra prediction mode candidate group Mode 0 (Vertical) Mode 7,0,5,2 (Mode A, B) Mode 1 (Horizontal) Mode 8,1,6,2 (Mode A, B) Mode 2 (DC) Mode 0,1,3,4,2 (Mode A, B) Mode 3 (Plane) Mode 0,1,3,2 (Mode A, B)

For example, when the vertical mode (mode 0) is determined to be a 16x16 intra prediction mode, the candidate group determiner 212 may have a vertical left mode (mode 7) and a vertical mode (mode) having a similar direction to the vertical mode. 0), the vertical right mode (mode 5) and the DC mode (mode 2) that are generally more likely to be selected are determined as the 4x4 intra prediction mode candidate group.

Similarly, when a horizontal mode (mode 1) is determined as the 16x16 intra prediction mode, the candidate group determiner 212 may have a horizontal upper mode (mode 8) and a horizontal mode (mode 1) having a similar direction to the horizontal mode. ), The horizontal down mode (mode 6) and the DC mode (mode 2) are determined as 4x4 intra prediction mode candidate groups.

In addition, when the DC mode (mode 2) is determined as the 16 × 16 intra prediction mode, the candidate group determiner 212 may include a vertical mode (mode 0), a horizontal mode (mode 1), and a diagonal indicating a basic direction of an image. The left mode (mode 3), diagonal right mode (mode 4) and DC mode (mode 2) are determined as 4x4 intra prediction mode candidate groups.

In addition, when the planar mode (mode 3) is determined as the 16x16 intra prediction mode, the candidate group determiner 212 may include a vertical mode (mode 0), a horizontal mode (mode 1), and a diagonal left mode (mode 3). And determine the DC mode (mode 2) as a 4x4 intra prediction mode candidate group.

7 is a diagram illustrating neighboring blocks used to determine an intra prediction mode of a current block according to the present invention.

The candidate group determiner 212 may include intra prediction modes A and B of the upper and left blocks of the input block C to be currently encoded in the candidate group in order to consider correlation with neighboring blocks. . For example, if mode 0 is selected as the second block unit intra prediction mode of the upper block in FIG. 7 and mode 1 is selected as the second block unit intra prediction mode of the left block, the candidate group determiner 212 may encode the current encoding. The mode 0 and the mode 1 are included in the intra prediction mode candidate group of the second block unit of the input block C.

As described above, when the 4x4 intra prediction mode candidate group is determined, the second block unit intra prediction execution unit 213 performs 4x4 intra prediction according to 4x4 intra prediction modes belonging to the candidate group. do. Here, since only an error rate of an image may increase when only a partial prediction mode is used among all 4 × 4 intra prediction modes, the second block unit intra prediction execution unit 213 may determine the most likely mode (Most Probable Mode). Only when belonging to the 4x4 intra prediction mode candidate group, intra prediction is performed on a part of the candidate group. Here, the most probable mode indicates a mode having a smaller mode value among upper and left blocks of an input block to be currently encoded, as described in the H.264 standard.

If the most probable mode is not included in the candidate group, the second block unit intra prediction execution unit 213 performs intra prediction on all available intra prediction modes.

The most probable mode is not a mode decision but a flag bit that refers to a mode value of a neighboring block in order to improve compression efficiency. Since the information of the encoded neighboring block is used as it is, an additional operation is performed. It is not necessary.

Referring back to FIG. 4, the prediction mode determiner 220 determines the cost of the 16 × 16 intra prediction mode determined by the first block unit intra prediction execution unit 211 and the second block unit intra prediction execution unit 213. The final prediction mode for intra prediction of the current input block is determined by comparing the costs of the 4 × 4 intra prediction mode determined in the " In this case, the cost calculation may be performed by various methods. The cost functions used include sum of absolute difference (SAD), sum of absolute transformed difference (SATD), sum of squared difference (SSD), mean of absolute difference (MAD), and lagrange function (Lagrange function). SAD is a value obtained by taking the absolute value of each 4x4 block prediction error value and adding the values together. The SATD is obtained by adding an absolute value of coefficients generated by applying a Hadamard transform to a prediction error value of each 4 × 4 block. The SSD is a value obtained by squaring the prediction error values of each 4x4 block prediction sample, and the MAD is a value obtained by taking an absolute value of the prediction error value of each 4x4 block prediction sample and calculating the average. The Lagrange function is a new function created by including the bitstream length information in the cost function.

8 is a block diagram of an image decoding apparatus for decoding a bitstream encoded according to the present invention.

Referring to FIG. 8, the decoding apparatus includes an entropy decoder 302, a reordering unit 304, an inverse quantization unit 306, an inverse transform unit 308, a motion compensator 310, an intra predictor 312, and a filter 314. ).

The entropy decoder 302 and the reordering unit 304 receive the compressed bitstream to perform entropy decoding to generate quantized coefficients X. The inverse quantizer 306 and the inverse transformer 308 perform inverse quantization and inverse transformation on the quantized coefficient X to extract transform coded coefficients, motion vector information, header information, and the like. The motion compensator 310 and the intra predictor 312 generate a prediction block according to the encoded picture type by using the decoded header information, and the prediction block is added to D ' _n representing an error value and thus uF'. _n is generated. UF ' _n generates a reconstructed picture F'n through the filter 314.

9 is a flowchart illustrating a method of determining an intra prediction mode according to the present invention.

Referring to FIG. 9, in operation 301, a first block intra prediction mode is determined. As described above, a block having a size of 16 × 16 may be used as the first block unit, and in this case, the least cost mode is performed by performing intra prediction according to four prediction modes. Decide on

In step 303, a second block unit intra prediction mode candidate group having a similar direction to the first block unit intra prediction mode is determined. When the first block unit is a block of size 16 × 16 and the second block unit is a block of size 4 × 4, the candidate group may be determined using Table 1 described above.

In step 305, it is determined whether the most likely mode determined from the neighboring blocks of the current input block is included in the determined second block unit intra prediction mode candidate group. As described above, the most probable mode indicates a mode having a smaller mode value among second block unit intra prediction modes of already encoded blocks on the upper and left sides of the current input block.

In step 307, if the most probable mode is included in the candidate group, second block intra prediction is performed on second block intra prediction modes belonging to the candidate group. In step 311, if the most probable mode is not included in the candidate group, second block intra prediction is performed according to all available second block intra prediction modes.

In operation 309, the mode having the smallest cost among the second block intra prediction modes is determined as the second block intra prediction mode.

In step 313, the prediction mode having the smaller cost is compared to the cost of the first block-by-block intra prediction mode determined in the step 301 and the second block-by-block intra prediction mode determined in the step 309. Determine the final intra prediction mode.

According to the present invention as described above, rather than performing all nine intra prediction modes for a 4 × 4 block according to the H.264 standard, the computational complexity is improved by performing only some intra prediction modes belonging to the candidate group. Can be reduced.

In the following description of the present invention, a case in which a 16 × 16 block is used as the first block unit and a 4 × 4 block is used as the second block unit has been described. Intra prediction is performed using a block of size 16 × 16 in units of the first block, and a block of size 8 × 8 in units of the second block, or a block of size 8 × 8 in the unit of the first block. The same applies to the case of performing intra prediction using blocks having a size of 4x4 in block units.

The invention can also be embodied as computer readable code on a computer readable recording medium. The computer-readable recording medium includes all kinds of recording devices in which data that can be read by a computer system is stored. Examples of computer-readable recording media include ROM, RAM, CD-ROM, magnetic tape, floppy disk, optical data storage, and the like, and may also be implemented in the form of a carrier wave (for example, transmission over the Internet). Include. The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion.

So far I looked at the center of the preferred embodiment for the present invention. Those skilled in the art will understand that the present invention may be implemented in a modified form without departing from the essential characteristics of the present invention. Therefore, the disclosed embodiments should be considered in descriptive sense only and not for purposes of limitation. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the scope will be construed as being included in the present invention.

According to the present invention as described above, it is possible to determine the intra prediction mode for the intra prediction encoding of the image faster, and to apply to the real-time image encoder by reducing the complexity of the operation during intra prediction.

In addition, the present invention can shorten the time required for coding without significant deterioration in image quality.

Claims (30)

In the intra prediction mode determination method of the image, Determining the first intra prediction mode by performing intra prediction on the plurality of first block unit intra prediction modes in a unit of a first block having a predetermined size; An intra prediction mode including a predetermined number of second block unit intra prediction modes among a plurality of second block unit intra prediction modes having a smaller size than the first block unit based on the determined direction of the first intra prediction mode. Determining a candidate group; Determining a second intra prediction mode by performing intra prediction on the input block in a second block unit according to second block unit intra prediction modes belonging to the determined intra prediction mode candidate group; And Comparing the cost of the first intra prediction mode with the cost of the second intra prediction mode and determining an intra mode of the input block based on the result. The method of claim 1, Performing intra prediction on the input block in units of second blocks according to second prediction units in intra prediction modes belonging to the determined intra prediction mode candidate group. And wherein the most probable mode determined in association with the prediction mode of the neighboring block of the current input block belongs to the determined intra prediction mode candidate group. The method of claim 2, The neighboring block is a block located above and to the left of the current input block. The method of claim 2, The most probable mode is determined as a mode having a smaller mode value among intra prediction modes of the upper and left blocks. The method of claim 1, If the most probable mode determined from the neighboring blocks of the current input block does not belong to the intra prediction mode candidate group, the second block-by-block intra prediction mode is performed for all the available second block-by-block intra prediction modes. And determining a second intra prediction mode corresponding to the input block. The method of claim 1, When the determined first intra prediction mode is a vertical mode (mode 0), the intra prediction mode candidate group includes a vertical mode (mode 0), a vertical right mode (mode 5), a vertical left mode (mode 7), and a DC mode ( Mode 2). The method of claim 1, When the determined first intra prediction mode is a horizontal mode (mode 1), the intra prediction mode candidate group includes a horizontal mode (mode 1), a horizontal down mode (mode 6), a horizontal up mode (mode 8), and a DC mode ( Mode 2). The method of claim 1, When the determined first intra prediction mode is a DC mode (mode 2), the intra prediction mode candidate group includes a vertical mode (mode 0), a horizontal mode (mode 1), a diagonal left mode (mode 3), and a diagonal right mode ( Mode 4) and a DC mode (mode 2). The method of claim 1, When the determined first intra prediction mode is a planar mode (mode 3), the intra prediction mode candidate group includes a vertical mode (mode 0), a horizontal mode (mode 1), a diagonal left mode (mode 3), and a DC mode (mode And 2) an intra prediction mode determination method. The method according to any one of claims 6 to 9, The intra prediction mode candidate group further includes intra prediction modes of blocks located above and to the left of the current input block. The method of claim 1, And wherein the first block unit is a block having a size of 16 × 16, and the second block unit is a block having a size of 4 × 4. The method of claim 1, And wherein the first block unit is a block having a size of 16 × 16, and the second block unit is a block having a size of 8 × 8. The method of claim 1, And wherein the first block unit is a block having a size of 8 × 8, and the second block unit is a block having a size of 4 × 4. The method of claim 1, The determined cost of the first intra prediction mode and the determined cost of the second intra prediction mode are sum of absolute difference (SAD), sum of absolute transformed difference (SATD), sum of squared difference (SSD), mean of absolute (MAD). Method for determining the intra prediction mode, characterized in that it is calculated using any one of Difference and Lagrange function. In the intra prediction device of the image, Using a result of determining a first block unit intra prediction mode having a predetermined size, selecting a candidate group having similar directionality to that of the determined first block unit among intra prediction modes of a second block unit having a predetermined size, An intra prediction performing unit configured to determine a second block unit intra prediction mode by performing second block unit intra prediction only on second block unit intra prediction modes belonging to the candidate group; And A prediction mode determiner configured to determine a final prediction mode for intra prediction of the input block by comparing the cost of the first block unit intra prediction mode determined by the intra prediction execution unit with the cost of the determined second block unit intra prediction mode Intra prediction device comprising a. The method of claim 15, The intra prediction performing unit, A first block unit intra prediction performer configured to determine the first block unit intra prediction mode by performing intra prediction on the input block in units of first blocks having a predetermined size; A candidate group for determining a second block unit intra prediction mode candidate group having a similar direction to the first block unit intra prediction mode among the plurality of second block unit intra prediction modes having a smaller size than the first block unit Decision unit; And The second block unit intra prediction mode corresponding to the input block is performed by performing intra prediction on the input block in a second block unit according to the second block unit intra prediction modes belonging to the determined second block unit intra prediction mode candidate group. And an intra prediction performing unit for determining a second block unit. The method of claim 16, The second block unit intra prediction execution unit, The determined second block unit intra prediction mode candidate group when the most probable mode determined from the neighboring blocks of the current input block belongs to the second block unit intra prediction mode candidate group determined by the candidate group determiner. And performing intra prediction on the input block in units of second blocks according to second block unit intra prediction modes belonging to. The method of claim 17, The neighboring block is a block located above and to the left of the current input block. The method of claim 17, And wherein the most probable mode is determined as a mode having a smaller mode value among intra prediction modes of the upper and left blocks. The method of claim 16, The second block unit intra prediction execution unit, If the most probable mode determined from the neighboring block of the current input block does not belong to the determined second block unit intra prediction mode candidate group, the second block for all available second block unit intra prediction modes. And performing a unit intra prediction to determine a second block unit intra prediction mode corresponding to the input block. The method of claim 16, The candidate group determination unit, When the determined first block unit intra prediction mode is a vertical mode (mode 0), the second block unit intra prediction mode candidate group is selected as a vertical mode (mode 0), a vertical right mode (mode 5), and a vertical left mode (mode 7) and a DC mode (mode 2). The method of claim 16, The candidate group determination unit, When the determined first block unit intra prediction mode is a horizontal mode (mode 1), the second block unit intra prediction mode candidate group may be selected from a horizontal mode (mode 1), a horizontal down mode (mode 6), and a horizontal up mode (mode). 8) and a DC mode (mode 2). The method of claim 16, The candidate group determination unit, When the determined first block unit intra prediction mode is a DC mode (mode 2), the second block unit intra prediction mode candidate group is selected as a vertical mode (mode 0), a horizontal mode (mode 1), and a diagonal left mode (mode 3). ), Diagonal right mode (mode 4) and DC mode (mode 2). The method of claim 16, The candidate group determination unit, When the determined first block unit intra prediction mode is a planar mode (mode 3), the second block unit intra prediction mode candidate group is selected as a vertical mode (mode 0), a horizontal mode (mode 1), and a diagonal left mode (mode 3). And DC mode (mode 2). The method according to any one of claims 21 to 24, The candidate group determination unit, And an intra prediction mode of blocks located above and to the left of the current input block as the second block unit intra prediction mode candidate group. The method of claim 15, Wherein the first block unit is a block having a size of 16 × 16, and the second block unit is a block having a size of 4 × 4. The method of claim 15, Wherein the first block unit is a block having a size of 16 × 16, and the second block unit is a block having a size of 8 × 8. The method of claim 15, The first block unit is a block having an 8 × 8 size, and the second block unit is a block having a 4 × 4 size. The method of claim 15, The prediction mode determiner, The first determined by using any one of Sum of Absolute Difference (SAD), Sum of Absolute Transformed Difference (SATD), Sum of Squared Difference (SSD), Mean of Absolute Difference (MAD), and Lagrange function (Lagrange function) And calculating the cost of the block unit intra prediction mode and the determined cost of the second block unit intra prediction mode. A computer-readable recording medium having recorded thereon a program for executing the invention according to any one of claims 1 to 14 on a computer.

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