KR101246119B1 - Intra prediction mode decision method and apparatus - Google Patents

Abstract

The present invention relates to a video data compression technique, and more particularly, to a method and apparatus for determining an intra prediction mode for reducing the amount of computation and the computation time required for an intra prediction process. An intra prediction mode determination method according to the present invention comprises the steps of: calculating a variance of pixel values of a block of a predetermined size in a macro block; Comparing the calculated variance with a predetermined threshold, and performing intra prediction in 16 × 16 prediction mode and 4 × 4 intra prediction mode or performing intra prediction only in 4 × 4 intra prediction mode according to the result; And determining an intra prediction mode based on the result of performing the intra prediction.

Description

Intra prediction mode decision method and apparatus

The present invention relates to a video data compression technique, and more particularly, to a method and apparatus for determining an intra prediction mode for reducing the amount of computation and the computation time required for an intra prediction process.

According to H.264 / Advanced Video Coding (AVC) on video compression, one picture is divided into macroblocks to encode a video, and all the encoding available in inter prediction and intra prediction. After each macroblock is encoded in the mode, the macroblock is encoded by setting one encoding mode according to the bit rate required for encoding the macroblock and the degree of distortion between the original macroblock and the decoded macroblock.

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 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, there are four modes in the 16 × 16 intra prediction mode, that is, a vertical mode, a horizontal mode, a direct current (DC) mode, and a plane mode. Also, referring to FIG. 2, the 4X4 intra prediction mode includes a vertical mode, a horizontal mode, a direct current mode, a diagonal down-left mode, and a diagonal down-right mode. There are a total of nine modes: mode, vertical right mode, vertical left mode, horizontal-up mode, and horizontal-down mode.

For example, an operation of predictively encoding a current block having a size of 4 × 4 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 4 × 4 current block are predicted as the pixel values of the 4 × 4 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 the 4X4 current block. The four pixel values included in the third column of C are predicted to be the 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 then, the mode is the least cost among them. Perform intra coding. 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 4X4 intra prediction modes are sequentially performed on the 4X4 sub-blocks, respectively. Select the mode with the lowest cost per block. 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.

In H.264 / AVC, intra prediction is performed in a total of 13 modes of 9 4X4 intra prediction modes and 4 16X16 intra prediction modes for macro blocks that are intra coded when determining a mode for intra prediction. Inefficient in terms of computation time.

An object of the present invention is to provide an intra prediction mode determination method and apparatus for reducing the amount of computation and the computation time required in the intra prediction process.

In order to solve the above technical problem, the intra prediction mode determination method according to the present invention comprises the steps of: (a) calculating the variance of the pixel value of a block of a predetermined size in a macro block; (b) comparing the calculated variance with a predetermined threshold, and performing intra prediction in 16x16 prediction mode and 4x4 intra prediction mode or performing intra prediction only in 4x4 intra prediction mode according to the result; And (c) determining an intra prediction mode based on the result of performing the intra prediction.

In one embodiment, the predetermined size block may be an 8 × 8 block in the macro block.

In one embodiment, step (b) may perform intra prediction only in 4 × 4 intra prediction mode when the calculated variance is greater than the predetermined threshold.

In one embodiment, in performing intra prediction in the 4X4 intra prediction mode in step (b), 4X4 intra prediction is performed according to the variance of pixel values around the 4X4 subblock and the variance of pixel values inside the 4X4 subblock. Intra prediction may be performed only in some prediction modes of the modes.

In one embodiment, in performing intra prediction in the 4X4 intra prediction mode in the step (b), if the variance of pixel values around the 4X4 subblock is smaller than a predetermined threshold, the MPM predicts the prediction mode of the 4X4 subblock. (most probable mode).

In one embodiment, in performing intra prediction in the 4X4 intra prediction mode in the step (b), when the variance of pixel values in the 4X4 subblock is smaller than a predetermined threshold, the prediction mode of the 4X4 subblock is DC. Can be set to (Direct Current) mode.

In one embodiment, in performing the intra prediction in the 4X4 intra prediction mode in the step (b), if the variance of the pixel value on the upper side of the 4X4 subblock is smaller than a predetermined threshold value, VERTICAL (mode) Intra prediction can be performed only for HORIZONTAL (mode 1), HORIZONTAL-DOWN (mode 6), and HORIZONTAL-UP (mode 8) modes.

In one embodiment, in performing intra prediction in the 4X4 intra prediction mode in the step (b), if the variance of the pixel value on the left side of the 4X4 subblock is smaller than a predetermined threshold value, VERTICAL (mode) is used for the 4X4 subblock. Intra prediction can only be performed for 0), HORIZONTAL (mode 1), VERTICAL-RIGHT (mode 5), and VERTICAL-LEFT (mode 7) modes.

In order to solve the above technical problem, the intra prediction mode determination device according to the present invention, the dispersion calculation unit for calculating the variance of the pixel value of a block of a predetermined size in a macro block; An intra prediction performing unit comparing the calculated variance with a predetermined threshold value and performing intra prediction in the 16X16 prediction mode and the 4X4 intra prediction mode or performing the intra prediction only in the 4X4 intra prediction mode according to the result; And a prediction mode determiner configured to determine an intra prediction mode based on the intra prediction performance result.

In one embodiment, the intra prediction performing unit may perform intra prediction only in the 4 × 4 intra prediction mode when the calculated variance is greater than the predetermined threshold.

In one embodiment, the intra prediction execution unit, in performing the intra prediction in the 4X4 intra prediction mode, 4X4 intra prediction according to the variance of pixel values around the 4X4 sub-blocks and the variance of pixel values inside the 4X4 sub-blocks Intra prediction may be performed only in some prediction modes of the modes.

In one embodiment, the intra prediction execution unit, when performing intra prediction in the 4X4 intra prediction mode, MPM to predict the prediction mode of the 4X4 sub-block when the variance of pixel values around the 4X4 sub-block is less than a predetermined threshold value (most probable mode).

In one embodiment, the intra prediction execution unit, when performing the intra prediction in the 4X4 intra prediction mode, DC in the prediction mode of the 4X4 sub-block when the variance of the pixel value in the 4X4 sub-block is less than a predetermined threshold value Can be set to (Direct Current) mode.

In one embodiment, the intra prediction execution unit, when performing intra prediction in the 4X4 intra prediction mode, the VERTICAL (mode) for the 4X4 subblock when the variance of the pixel value of the upper side of the 4X4 subblock is less than a predetermined threshold value Intra prediction can be performed only for HORIZONTAL (mode 1), HORIZONTAL-DOWN (mode 6), and HORIZONTAL-UP (mode 8) modes.

In one embodiment, the intra prediction execution unit, when performing intra prediction in the 4X4 intra prediction mode, the VERTICAL (mode) for the 4X4 subblock when the variance of the pixel value of the left side of the 4X4 subblock is less than a predetermined threshold value Intra prediction can only be performed for 0), HORIZONTAL (mode 1), VERTICAL-RIGHT (mode 5), and VERTICAL-LEFT (mode 7) modes.

In order to solve the above technical problem, there is provided a computer-readable recording medium having recorded thereon a program for executing the above-described intra prediction mode determination method according to the present invention.

According to the present invention described above, it is possible to reduce the amount of computation and computation time required in the intra prediction process without degrading performance.

1 illustrates a 16 × 16 intra prediction mode according to the H.264 standard.
2 is a diagram illustrating a 4 × 4 intra prediction mode according to the H.264 standard.
3 is a block diagram illustrating a configuration of an intra prediction mode determining apparatus according to an embodiment of the present invention.
4 is a flowchart of a method of determining an intra prediction mode according to an embodiment of the present invention.
5 shows a middle 8X8 block in a 16X16 macroblock.
6 is a flowchart specifically illustrating a 4 × 4 intra prediction process according to an embodiment of the present invention.
7A shows pixels around a 4 × 4 subblock.
7B shows a pixel inside the 4 × 4 subblock.
7C shows a pixel above the 4X4 subblock.
7D shows pixels on the left side of the 4X4 subblock.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the following description and the accompanying drawings, substantially the same components are denoted by the same reference numerals, and redundant description will be omitted. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

3 is a block diagram illustrating a configuration of an intra prediction mode determining apparatus according to an embodiment of the present invention. The intra prediction mode determining apparatus includes a variance calculator 310 that calculates a variance of pixel values of a block of a predetermined size in the current macroblock, and compares the calculated variance with a predetermined threshold value, and according to the result, the 16X16 prediction mode and the 4X4. An intra prediction mode for the current macro block is performed based on the intra prediction performance of the intra prediction execution unit 320 and the intra prediction execution unit 320 that performs intra prediction in the intra prediction mode or performs the intra prediction only in the 4X4 intra prediction mode. It includes a prediction mode determiner 330 to determine.

Hereinafter, a detailed operation of the intra prediction mode determination apparatus according to the present embodiment will be described with reference to FIG. 4, which shows a flowchart of the intra prediction mode determination method according to an embodiment of the present invention.

First, the variance calculator 310 calculates a variance V of pixel values of a block of a predetermined size in a macro block (step 410). For example, as shown in FIG. 5, the variance of pixel values of the center 8X8 block 510 in the 16X16 macroblock is calculated. Here, of course, the variance of pixel values of blocks larger or smaller than an 8X8 block may be calculated, and the variance of pixel values of the entire macroblock may be calculated. Small dispersion of pixel values in a block means that the pixel values are similar in general, and large distribution of pixel values in the block means that the distribution of pixel values is wide. Therefore, if the variance of pixel values is large, it may be said that the intra prediction mode of the macroblock is more likely to be determined as the optimal intra prediction mode than the 4 × 4 intra prediction mode rather than the 16 × 16 intra prediction mode.

The intra prediction execution unit 320 determines whether the variance V of the pixel values of the 8 × 8 block is greater than a predetermined threshold value TH (step 420). The threshold TH may be set to an appropriate value by one skilled in the art through experiments.

If the variance V is greater than the threshold TH, the intra prediction performing unit 320 does not perform intra prediction with respect to the 16 × 16 intra prediction mode, but performs intra prediction with only the 4 × 4 intra prediction mode (step 440). If the variance V is not greater than the threshold TH, the intra prediction performing unit 320 performs intra prediction in both the 16 × 16 intra prediction mode and the 4 × 4 intra prediction mode (step 430). In operation 450, the prediction mode determiner 330 determines an intra prediction mode for the current macroblock based on the intra prediction performed by the intra prediction performer 320.

Specifically, if the variance V is not greater than the threshold value TH, the intra prediction execution unit 320 encodes the current macro block in four 16 × 16 intra prediction modes to calculate the cost, and configures the current macro block 16. 4x4 subblocks are encoded in 4X4 intra prediction mode to select a prediction mode having the smallest cost for each subblock, and the prediction mode determiner 330 calculates the cost of the 16X16 intra prediction mode and the cost of each subblock. The cost of the combined 4 × 4 intra prediction mode is compared to finally select the intra prediction mode with the lowest cost.

If the variance V is greater than the threshold value TH, the intra prediction execution unit 320 encodes the 16 4X4 subblocks constituting the current macroblock in 4X4 intra prediction mode to increase the cost for each subblock. The smallest prediction mode is selected, and the prediction mode determiner 330 determines the prediction mode of each selected sub block as the final intra prediction mode.

According to the present exemplary embodiment, when the variance V is greater than the threshold TH, the intra prediction operation for the 16X16 intra prediction mode is removed, thereby greatly reducing the amount of calculation and the calculation time.

In an embodiment of the present invention, when the intra prediction execution unit 320 performs the intra prediction in the 4X4 intra prediction mode in steps 430 and 440, for each 4X4 subblock, the periphery of the corresponding 4X4 subblock is performed. Intra prediction is performed in only some prediction modes of the 4X4 intra prediction mode according to the variance of the pixel value of and the variance of the pixel value inside the corresponding 4X4 subblock. In other words, instead of performing intra coding on all nine 4X4 intra prediction modes for the 4X4 subblock and calculating the cost, the dispersion of pixel values around the 4X4 subblock and the distribution of internal pixel values are calculated. Depending on whether the value satisfies a predetermined specific condition, intra coding is performed only in some prediction modes of the nine 4x4 intra prediction modes and the cost is calculated.

6 is a flowchart illustrating a process of performing 4 × 4 intra prediction in detail.

Referring to FIG. 6, first, a variance V1 of pixel values around a 4 × 4 subblock is calculated (step 610). For example, as illustrated in FIG. 7A, the variance of pixel values around the 4 × 4 subblock is calculated. The small variance of the pixel values around the sub-blocks means that the neighboring pixel values are generally similar, and thus the prediction mode is almost unchanged according to the prediction mode. Can be used as anything. Accordingly, it is determined whether the variance V1 of the pixel values surrounding the 4X4 subblock is smaller than the predetermined first threshold value TH1 (step 615). If so, the prediction mode of the 4X4 subblock is set to Most Probable Mode (MPM). Determine (step 618). Here, Most Probable Mode (MPM) indicates a mode having a smaller cost value among upper and left blocks of the current 4 × 4 subblock, as described in the H.264 standard. Determining with MPM has the effect of saving 3 bits compared to determining with other prediction modes.

If the variance V1 of the pixel values surrounding the 4X4 subblock is not smaller than the first threshold value TH1, the variance V2 of the pixel values inside the 4X4 subblock is calculated (step 620). For example, as illustrated in FIG. 7B, the variance of pixel values inside the 4 × 4 subblock is calculated. The small dispersion of pixel values in the block means that the pixel values in the whole are similar in general, so that the DC mode is more likely to be adopted. Therefore, it is determined whether the variance V2 of the pixel value inside the 4X4 subblock is smaller than the predetermined second threshold value TH2 (step 625), and if so, the prediction mode of the corresponding 4X4 subblock is determined as the DC mode. (628 steps).

If the variance V2 of the pixel values inside the 4X4 subblock is not smaller than the second threshold value TH2, the variance V3 of the pixel values above the 4X4 subblock is calculated (step 630). For example, as illustrated in FIG. 7C, the variance of pixel values above the 4 × 4 subblock is calculated. The small variance of pixel values on the upper side of the block means that the pixel values on the upper side of the block are similar in general, and thus, VERTICAL (mode 0) and DIAGONAL DOWN-LEFT ( Mode 3), DIAGONAL DOWN-RIGHT (Mode 4), VERTICAL-RIGHT (Mode 5), and VERTICAL-LEFT (Mode 7) have little difference in prediction blocks. Therefore, among these, VERTICAL (mode 0) mode can be used as a representative value. Therefore, it is determined whether the variance V3 of the pixel value on the upper side of the 4X4 subblock is smaller than the predetermined third threshold value TH3 (step 635), and if so, VERTICAL (mode 0), HORIZONTAL (mode 1), and HORIZONTAL. -DOWN (mode 6) and HORIZONTAL-UP (mode 8) are determined as prediction mode candidate groups (step 638). Intra-prediction is performed on the prediction mode included in the prediction mode candidate group (step 660). That is, intra coding is performed in mode 0, mode 1, mode 6, and mode 8, and the cost is calculated. The mode having the least cost among them is determined as the prediction mode of the corresponding 4X4 subblock (step 670).

If the variance V3 of the pixel value on the upper side of the 4X4 subblock is not smaller than the third threshold value TH3, the variance V4 of the pixel value on the left side of the 4X4 subblock is calculated (step 640). For example, as illustrated in FIG. 7D, the variance of pixel values on the left side of the 4 × 4 subblock is calculated. The small variance of the pixel values on the left side of the block means that the pixel values on the left side of the block are similar in general. Therefore, in FIG. 2, HORIZONTAL (mode 1) and DIAGONAL DOWN-LEFT ( Mode 4), HORIZONTAL-DOWN (mode 6), and HORIZONTAL-UP (mode 8) have little difference in prediction blocks. Therefore, among these, HORIZONTAL (mode 1) mode can be used as a representative value. Therefore, it is determined whether the variance V4 of the pixel value on the left side of the 4X4 subblock is smaller than the predetermined fourth threshold value TH4 (step 645), and if so, VERTICAL (mode 0), HORIZONTAL (mode 1), VERTICAL RIGHT (mode 5) and VERTICAL-LEFT (mode 7) are determined as prediction mode candidate groups (step 648). Intra-prediction is performed on the prediction mode included in the prediction mode candidate group (step 660). That is, intra coding is performed in mode 0, mode 1, mode 5, and mode 7, and the cost is calculated. The mode having the least cost among them is determined as the prediction mode of the corresponding 4X4 subblock (step 670).

If the variance V4 of the pixel value on the left side of the 4 × 4 subblock is not smaller than the fourth threshold value TH4, intra prediction is performed on all 4 × 4 intra prediction modes (step 650). That is, intra coding is performed in modes 0 to 8 and the cost is calculated. The mode having the least cost among them is determined as the prediction mode of the corresponding 4X4 subblock (step 670).

In the above-described embodiment, the first threshold value TH1, the second threshold value TH2, the third threshold value TH3, and the fourth threshold value TH4 may be set to appropriate values by a person skilled in the art through experiments.

According to the embodiment of the present invention described above, if the variance V1 of the pixel values surrounding the 4X4 sub-block is smaller than the first threshold value TH1, the intra prediction operation for all 4X4 intra prediction modes is removed. In addition, when the variance V2 of the pixel value inside the 4 × 4 subblock is smaller than the second threshold value TH2, the intra prediction operation for the prediction mode other than the DC mode is removed. In addition, when the variance V3 of the pixel value above the 4X4 subblock is smaller than the third threshold value V3, the intra prediction operation for the prediction modes other than the mode 0, the mode 1, the mode 6, and the mode 8 is removed. In addition, when the variance V4 of the pixel value on the left side of the 4 × 4 subblock is smaller than the fourth threshold value V4, intra prediction operations for prediction modes other than modes 0, 1, 5, and 7 are removed. In a very limited case, intra prediction is performed on all 4 × 4 intra prediction modes as in step 650. Therefore, the amount of computation and the computation time can be significantly reduced during intra prediction in the 4X4 intra prediction mode.

The above-described embodiments of the present invention can be embodied in a general-purpose digital computer that can be embodied as a program that can be executed by a computer and operates the program using a computer-readable recording medium. The computer-readable recording medium includes a storage medium such as a magnetic storage medium (e.g., ROM, floppy disk, hard disk, etc.), optical reading medium (e.g., CD ROM,

So far I looked at the center of the preferred embodiment for the present invention. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the present invention is defined by the appended claims rather than by the foregoing description, and all differences within the scope of equivalents thereof should be construed as being included in the present invention.

Claims (17)

(a) calculating a variance of pixel values of blocks of a predetermined size in the macro block;
(b) comparing the calculated variance with a predetermined threshold, and performing intra prediction in 16x16 prediction mode and 4x4 intra prediction mode or performing intra prediction only in 4x4 intra prediction mode according to the result; And
(c) determining an intra prediction mode based on the result of performing the intra prediction,
In performing the intra prediction in the 4x4 intra prediction mode in the step (b),
As a result of comparing the dispersion of pixel values in the periphery of the 4X4 sub-block with a predetermined first threshold, as a result of comparing the dispersion of pixel values in the 4X4 sub-block with a predetermined second threshold, Intra only in the prediction mode of some of the 4X4 intra prediction modes according to a result of comparing the variance of the pixel value with a predetermined third threshold and comparing the variance of the pixel value on the left side of the 4X4 sub-block with a predetermined fourth threshold. A method of determining an intra prediction mode comprising performing prediction. The method of claim 1,
And the block having the predetermined size is an 8 × 8 block in the macro block. The method of claim 1,
In the step (b), if the calculated variance is greater than the predetermined threshold, intra prediction mode determination method, characterized in that to perform the intra prediction only in 4x4 intra prediction mode. delete The method of claim 1,
In performing the intra prediction in the 4x4 intra prediction mode in the step (b),
And determining the prediction mode of the 4X4 subblock as the most probable mode (MPM) when the variance of pixel values in the periphery of the 4X4 subblock is smaller than the predetermined first threshold value. The method of claim 1,
In performing the intra prediction in the 4x4 intra prediction mode in the step (b),
And determining a prediction mode of the 4x4 subblock as a direct current (DC) mode when the variance of pixel values in the 4x4 subblock is smaller than the predetermined second threshold. The method of claim 1,
In performing the intra prediction in the 4x4 intra prediction mode in the step (b),
VERTICAL (mode 0), HORIZONTAL (mode 1), HORIZONTAL-DOWN (mode 6), and HORIZONTAL-UP for the 4X4 subblock when the variance of pixel values on the upper side of the 4X4 subblock is smaller than the predetermined third threshold value. (Mode 8) An intra prediction mode determination method characterized in that intra prediction is performed only for a mode. The method of claim 1,
In performing the intra prediction in the 4x4 intra prediction mode in the step (b),
VERTICAL (mode 0), HORIZONTAL (mode 1), VERTICAL-RIGHT (mode 5), VERTICAL-LEFT for the 4X4 subblock when the variance of pixel values on the left side of the 4X4 subblock is smaller than the predetermined fourth threshold value. (Mode 7) An intra prediction mode determination method characterized in that intra prediction is performed only for a mode. A dispersion calculator for calculating a variance of pixel values of blocks of a predetermined size in the macro block;
An intra prediction performing unit comparing the calculated variance with a predetermined threshold value and performing intra prediction in the 16X16 prediction mode and the 4X4 intra prediction mode or performing the intra prediction only in the 4X4 intra prediction mode according to the result; And
A prediction mode determiner configured to determine an intra prediction mode based on a result of the intra prediction;
In performing the intra prediction in the 4X4 intra prediction mode, the intra prediction execution unit compares the variance of pixel values around the 4X4 subblock with a predetermined first threshold, and thus, the variance of the pixel value inside the 4X4 subblock. Is compared with a predetermined second threshold, and as a result of comparing the variance of the pixel value on the upper side of the 4X4 sub-block with the predetermined third threshold, and the variance of the pixel value on the left side of the 4X4 sub-block with the predetermined fourth threshold. Intra prediction mode determination device, characterized in that for performing the intra prediction only in the prediction mode of some of the 4X4 intra prediction mode according to the result compared with the value. 10. The method of claim 9,
And the predetermined size block is an 8 × 8 block in the macro block. 10. The method of claim 9,
And wherein the intra prediction execution unit performs intra prediction only in 4 × 4 intra prediction mode when the calculated variance is greater than the predetermined threshold. delete 10. The method of claim 9,
The intra prediction execution unit, when performing intra prediction in the 4X4 intra prediction mode, when the variance of pixel values around the 4X4 subblock is smaller than the predetermined first threshold, the prediction mode of the 4X4 subblock is MPM (most and an intra prediction mode determination device. 10. The method of claim 9,
The intra prediction execution unit, when performing intra prediction in the 4X4 intra prediction mode, directs the prediction mode of the 4X4 subblock to DC when the variance of pixel values in the 4X4 subblock is smaller than the predetermined second threshold. And current mode). 10. The method of claim 9,
The intra prediction execution unit, when performing intra prediction in the 4X4 intra prediction mode, VERTICAL (mode 0) for the 4X4 subblock when the variance of the pixel value of the upper side of the 4X4 subblock is smaller than the predetermined fourth threshold value. Intra prediction mode determination device characterized in that the intra prediction is performed only for the HORIZONTAL (mode 1), HORIZONTAL-DOWN (mode 6), HORIZONTAL-UP (mode 8) mode. 10. The method of claim 9,
The intra prediction execution unit, when performing intra prediction in a 4X4 intra prediction mode, VERTICAL (mode 0) for the 4X4 subblock when the variance of pixel values on the left side of the 4X4 subblock is smaller than the predetermined fourth threshold value. Intra prediction mode determination device, characterized in that the intra prediction is performed only for the HORIZONTAL (mode 1), VERTICAL-RIGHT (mode 5), VERTICAL-LEFT (mode 7) mode. A computer-readable recording medium having recorded thereon a program for executing the intra prediction mode determination method according to any one of claims 1 to 3 and 5 to 8.

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