KR101724212B1 - Apparatus and method for Intra Mode Decision - Google Patents

Abstract

Disclosed are an apparatus and method for determining an intra mode. The method for determining an intra mode includes the steps of: checking the number of common modes which simultaneously belong to a plurality of first modes determined in rough mode decision (RMD) and a plurality of second modes determined by a most probable mode (MPM); and skipping an examination of at least one partial mode of the plurality of first modes and the plurality of second modes by considering the prediction unit (PU) size and the number of the common modes. Accordingly, the present invention can efficiently use a specific mode which belongs to an RMD mode and the MPM.

Description

[0001] Apparatus and method for Intra Mode Decision [

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high efficiency video coding, and more particularly, to a method and apparatus for intra mode determination for high efficiency video coding.

High Efficiency Video Coding (HEVC), the latest video coding standard, uses several new coding tools. This new coding tool includes coding units (CU) of a quad tree structure, prediction units (PU) of various types, and transform units (TUs) of various sizes. For intra-prediction, HEVC supports 35 modes, whereas H.264 / AVC supports only 9 (or 4) modes.

The intra prediction procedure in the HMV (HEVC test model), which is the HEVC reference software, includes a rough mode decision (RMD) step, a most probable mode selection step, a best mode selection step based on rate-distortion optimization (RDO) residual quad-tree transform).

In the RMD step, HM computes the H-cost (Hadamard cost) for each of the 35 intra-prediction modes. Then, HM selects several candidate modes with the lowest H-cost value. In the MPM step, some modes with spatial correlation are further added to the candidate mode list. In the RDO step, the RD cost for each RMD and MPM candidate mode is calculated, and the mode with the lowest RD cost is selected as the best intra prediction mode. Finally, the best TU size is determined in the RQT step.

Many fast algorithms have been proposed to reduce the coding complexity of HEVC intra prediction. Some fast algorithms reduce the number of modes being examined at the RMD stage so that only a few of the 35 modes are examined.

For example, the algorithm of Fini and Zargari ("A fast intra mode decision method based on reduction of the number of modes in HEVC standard," IEEE Int. Symp. Telecommunications, 2014, pp.839-843) Check 19 modes. Then, the H-cost value of the remaining mode is indirectly obtained from the H-cost value of the 17 angular modes that were previously checked. Yao, Li, and Lu ("Fast intra mode decision algorithm for HEVC based on dominant edge assent distribution," Multimedia Tools and Applications, pp. 1-19, Nov. 2014) DEA (dominant edge assent) is calculated and DEA is used to determine the mode required for RMD inspection. In addition, the algorithm of Liu, Liu and Shao ("Fast intra-mode decision algorithm for HEVC based on texture direction," IEEE Int. Conf. On Computational Science and Engineering, 2014, pp. 1047-1050) texture) analysis to limit dominant direction and the number of modes in RMD inspection. Zhang and Ma ("Fast intra mode decision for high efficiency video coding (HEVC), IEEE Trans. Circuits Syst. Video Tech., Vol. 24, no. 4, pp. 660-668, Apr. 2014) A progressive rough mode search method is proposed. This method initially identifies nine modes with equal spacing, and continues to add more neighboring modes. Although this fast RMD algorithm supports reducing coding complexity, the overall effect is negligible. Since the RMD step occupies only a small portion of the entire intra prediction procedure (according to the simulation results, the RMD step occupies only 12.4% of the total encoding complexity of the four intra prediction steps).

Thus, most fast intra prediction methods are focused on reducing the number of modes examined in the RDO stage.

For example, the algorithm of Shen, Zhang and An ("Fast CU size decision and mode decision algorithm for HEVC intra coding", IEEE Trans. Consumer Electronics, vol. 59, no. 1, pp. 207-213, Feb. 2013 ) Skips the mode where the RD cost exceeds the threshold value. This mode is determined by the RD cost of the parent CU and neighboring blocks. Kim, Jun, Jung, Choi, and Kim ("Fast fast intra-prediction method in HEVC using rate-distortion estimation based on Hadamard transform", ETRI Journal, vol. 35, no. , Apr. 2013) checks only the first RMD mode if the H-cost of the first RMD mode is much lower than other RMD modes. Zhang and Ma and Gan, Zhao and Zhang ("Fast intra-mode decision for high efficiency video coding (HEVC)," IEEE Trans. Circuits Syst. Video Tech., Vol. 24, No. 4, pp. 660-668 , Apr. 2014, "Fast Algorithm with Early Termination CU Split and Mode Decision," Int. Journal of Control and Automation, Vol.8, no.2, pp. 83-94, Feb. 2015) And skips the first two RMD modes and the nearest neighbor mode. Zhu, Zhao and Li ("Adaptive fast intra prediction for high efficiency video coding," Multimedia Tools and Applications, pp. 1-15, May 2015) difference value and SATD (sum of absolute Hadamard transformed difference) values.

The present invention is intended to provide an intra mode determination method and apparatus for an HEVC that efficiently uses the characteristics of a specific mode belonging to both the RMD mode and the MPM.

According to an aspect of the present invention, an intra mode determination method performed by an intra mode determination apparatus for luma components is disclosed.

A method for determining an intra mode according to an embodiment of the present invention includes determining a plurality of first modes determined in a rough mode decision (RMD) and a plurality of second modes determined in an MPM (most probable mode) Checking the number of common modes, and skipping the examination of at least one of the plurality of first modes and the plurality of second modes in consideration of the number of the common modes and the PU (prediction units) size .

If the prediction units (PU) size is large, the number of the plurality of first modes is 3, and the number of the plurality of second modes is at most 2.

If the PU (prediction units) size is large, the step of skipping the checking of the partial modes may include: if the number of the common modes is 2, the two common modes and the H-cost (Hadamard cost) Inspecting the first mode if the number of the common modes is 1, checking all of the plurality of first modes when the number of the common modes is 1, and if the number of the common modes is 0, Examining each first mode and examining a second mode with a smaller H-cost.

Checking the first mode having the smallest H-cost and the second common mode has a relatively high probability that the two common modes can be selected as the best mode and the first mode having the smallest H- The probability of being selected as the best mode is higher than that of the second mode.

The checking of all of the plurality of first modes may skip checking of the common second mode when only one of the two modes is the common mode.

Checking each first mode according to the H-cost of each first mode and checking a second mode having a smaller H-cost may include: determining a first mode having H-cost satisfying a condition of the following formula And the second mode having a larger H-cost among the two second modes is highly likely not to be selected as the best mode.

Here, H-cost _cur and H-cost _{RMD [0]} are H-cost of the first mode in which the H-cost and H-cost of the current mode to be examined are the smallest, respectively, and?

If the prediction units (PU) size is small, the number of the plurality of first modes is eight, and the number of the plurality of second modes is at most two.

Wherein the step of skipping the checking of the partial mode when the PU (prediction units) size is small is performed by sequentially checking all of the plurality of first modes when the number of the common modes is 2, Checking whether each of the common modes has been checked, terminating if both common modes are checked, checking each first mode according to the H-cost of each first mode when the number of the common modes is 1 Checking the common second mode when the common second mode is not checked and checking each first mode according to the H-cost of each first mode when the number of the common modes is zero And examining a second mode with a smaller H-cost.

The step of checking all of the plurality of first modes sequentially, and the step of verifying whether both common modes are checked, sequentially checks each first mode in ascending order of H-cost.

Checking each first mode according to the H-cost of each of the first modes, and when the common second mode is not inspected, checking the common second mode comprises the steps of: And examines a non-common first mode having H-cost.

Here, H-cost _cur and H-cost _{RMD [0]} are H-cost of the first mode having the smallest H-cost and H-cost of the current mode to be inspected, respectively.

Checking each first mode according to the H-cost of each first mode and checking a second mode having a smaller H-cost may include: determining a first mode having H-cost satisfying a condition of the following formula Checking only one second mode having a smaller H-cost, and skipping the other second mode.

Here, H-cost _cur and H-cost _{RMD [0]} are H-cost of the first mode having the smallest H-cost and H-cost of the current mode to be inspected, respectively.

According to another aspect of the present invention, an intra mode determination apparatus for determining an intra mode for luma components is disclosed.

An intra mode determination apparatus according to an embodiment of the present invention includes a memory for storing an instruction and a processor for executing the instruction, wherein the instruction includes a plurality of first modes determined in a rough mode decision (RMD) determining a number of common modes simultaneously belonging to a plurality of second modes determined by the number of common modes and a prediction unit size of the common mode, And skipping the examination of at least one of the plurality of second modes.

The intra mode determination method and apparatus for an HEVC according to the present invention can significantly improve performance compared to a conventional intra mode determination method by effectively using characteristics of specific modes belonging to both RMD mode and MPM.

1 is a diagram illustrating intra prediction modes in HEVC (High Efficiency Video Coding);
2 illustrates a method for determining an intra mode according to an embodiment of the present invention.
3 is a flowchart illustrating an intra mode determination method according to an embodiment of the present invention.
4 is a flowchart illustrating an intra mode determination method according to another embodiment of the present invention.
5 is a diagram schematically illustrating a configuration of an intra mode determination apparatus according to an embodiment of the present invention.

As used herein, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. In this specification, the terms "comprising ", or" comprising "and the like should not be construed as necessarily including the various elements or steps described in the specification, Or may be further comprised of additional components or steps. Also, the terms "part," " module, "and the like described in the specification mean units for processing at least one function or operation, which may be implemented in hardware or software or a combination of hardware and software .

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

FIG. 1 is a diagram illustrating intra prediction modes in High Efficiency Video Coding (HEVC), and FIG. 2 is a diagram illustrating an intra mode determination method according to an embodiment of the present invention.

The HEVC standard supports 35 intra prediction modes, as shown in FIG. For example, the 35 intra prediction modes may be a planar prediction mode, a DC prediction mode, and 33 angular prediction modes. Hereinafter, for the convenience of understanding and explanation of the present invention, 35 modes are m ₀ , m ₁ , ... , and m ₃₄ , respectively.

Referring to FIG. 2, an intra mode determination method according to an exemplary embodiment of the present invention includes a rough mode decision step S210, a most probable mode step S220, a rate-distortion optimization step S230, And a residual quad-tree transform (RQT) step S240.

In RMD step S210, the intra mode determination apparatus calculates H-cost (H-cost) for each of the 35 intra-prediction modes.

For example, H-cost can be defined by the following equation.

Here, SATD represents a sum of the absolute transformed difference, and Bit _pred represents an evaluation value for bit generation. And _{,? Pred} represents a Lagrangian coefficient and can be calculated by the following equation.

Here, QP represents a quantization parameter.

For example, the intra mode decision unit determines RMD [0], RMD [1], ..., RMD having the smallest H- , And RMD [N-1]. Here, RMD [n] represents the n-th mode having the smallest H-cost value. And N is 3 in large PU (prediction units) (e.g., 64 × 64, 32 × 32 or 16 × 16 PU), while a small PU (eg, 8 × 8 or 4 x 4 PU).

In the MPM step S220, the intra mode determination apparatus further adds the MPM to the candidate mode list. For example, the number of MPMs added to the candidate mode list may be 1 or 2, and may be determined by the mode information of neighboring blocks.

In the RDO step S230, the intra mode determination apparatus checks the RMD mode first and then the MPM.

For example, the N RMD modes can be checked in ascending order of H-cost. Here, some RMD modes may belong to both the RMD mode set and the MPM set. Hereinafter, for the convenience of understanding and explanation of the invention, when the MPM coincides with one of the N RMD modes, this mode will be referred to as a common mode. Since one or two MPMs can be identified in the RDO phase, the number of common modes can be from 0 to 2, and the total number of modes examined in the RDO phase can be N + 2.

For example, Table 1 below shows the simulation results showing the probability of the number of common modes for each PU size.

Number of common modes 64 x 64
PU 32 x 32
PU 16 × 16
PU Average for large PUs 8 x 8
PU 4 × 4
PU Average for small PUs 0 33.4% 46.2% 43.4% 41.0% 15.3% 11.2% 13.3% One 53.5% 45.1% 44.9% 47.8% 50.1% 51.7% 50.9% 2 13.0% 8.7% 11.7% 11.2% 34.6% 37.1% 35.8%

Since N in the large PU is significantly different from N in the small PU, it is effective to apply a different intra mode determination method to each case. That is, the intra mode determination method according to the embodiment of the present invention can be divided into two cases for the large PU and the small PU. The intra mode determination method for the large PU and the small PU according to the embodiment of the present invention is for luma components. This will be described later with reference to FIG. 3 and FIG.

3 is a flowchart illustrating an intra mode determination method according to an embodiment of the present invention. 3, a method of determining an intra mode for a large PU will be described.

In step S301, the intra mode determination apparatus determines whether the number of common modes is 0 or not.

In step S302, if the number of common modes is not 0, the intra mode determination apparatus determines whether the number of common modes is 1 or not.

In step S303, the intra mode determination apparatus checks two common modes when the number of common modes is not 1, that is, when the number of common modes is two.

In step S304, the intra mode determination apparatus checks RMD [0] if RMD [0] has not been already checked.

The common mode has a relatively high probability of being selected as the best mode. When there are two common modes, the probability that one of the common modes is selected as the best mode is much higher. For example, as shown in Table 2 below, for a large PU, the probability that one of the common modes is selected as the best mode is 87.4%.

64 x 64 PU 32 x 32 PU 16 x 16 PU Average Probability 88.5% 86.9% 86.9% 87.4%

Thus, when there are two common modes in a large PU, it is possible to check only two common modes, and skip the inspection of one RMD mode other than the common mode. However, if one RMD mode other than the common mode is RMD [0] (instead of RMD [1] or RMD [2]), the rate of missing the best mode is relatively high. For example, Table 3 below shows the probability that each RMD mode is selected as the best mode.

64 x 64
PU 32 x 32
PU 16 × 16
PU 8 x 8
PU 4 × 4
PU RMD [0] 46.7% 51.9% 57.1% 58.3% 65.5% RMD [1] 22.4% 19.1% 19.4% 15.7% 13.1% RMD [2] 7.7% 10.6% 10.6% 7.5% 5.9% RMD [3] 4.6% 3.3% RMD [4] 3.5% 2.6% RMD [5] 2.8% 2.2% RMD [6] 2.3% 1.8% RMD [7] 1.9% 1.6% total 76.8% 81.6% 87.6% 96.5% 96.0%

As shown in Table 3, RMD [0] has the highest probability of being selected as the best mode. Therefore, when there are two common modes in the large PU, the intra mode determination method according to the embodiment of the present invention checks only two common modes only when one RMD mode other than the common mode is not RMD [0] .

That is, the intra mode determination method in the large PU according to the embodiment of the present invention always checks not only the two common modes but also RMD [0] when there are two common modes. For example, Table 4 below shows the hit rate of the intra mode determination method when there are two common modes in a large PU according to the embodiment of the present invention. Here, the hit rate indicates the probability that the original HM (HEVC test model) and the intra mode determination method in the large PU according to the embodiment of the present invention generate the same best mode.

64 x 64 PU 32 x 32 PU 16 x 16 PU Average Hit rate 93.6% 92.9% 93.2% 93.2%

As shown in Table 4, the hit rate increases from 87.4% to 93.2%.

In step S305, when the number of common modes is 1, the intra mode determination apparatus sets n to 0.

In step S306, the intra mode determination apparatus checks RMD [n].

In step S307, the intra mode determination apparatus determines whether n = 2. If n = 2, the intra mode determination method ends.

In step S308, if n is not 2, the intra mode determination apparatus increments n by 1, and then returns to step S306.

The probability that the non-common mode is selected as the best mode is relatively low. Thus, the intra mode determination method in the large PU according to the embodiment of the present invention skips the non-common mode.

That is, when two MPMs are added to the candidate mode list and only one common mode exists, one of the two MPMs is in a common mode and the other MPM is in a non-common mode. For example, according to simulation results, the probability that a non-common mode MPM is selected as a best mode is 11.5% for a large PU and 5.6% for a small PU. Considering that there are four candidate modes in this case, this probability is considerably lower than the average probability (25%). Thus, in the intra mode determination method in the large PU according to the embodiment of the present invention, when only one of the two MPMs is in the common mode, the inspection of the MPM in the non-common mode is skipped.

In step S309, the intra mode determination apparatus sets n to 0 when the number of common modes is zero.

In step S310, the intra mode determination apparatus determines whether or not RMD [n] satisfies the following equation (3). If RMD [n] does not satisfy the following equation (3), the process proceeds to step S314.

Here, H-cost _cur and H-cost _{RMD [0]} are the H-cost of the current mode being examined and the H-cost of _{RMD [0]} , respectively. And,? Is a parameter larger than one.

In step S311, the intra mode determination apparatus checks RMD [n] when RMD [n] satisfies Equation (3).

In step S312, the intra mode determination apparatus determines whether n is 2 or not.

In step S313, if n is not 2, the intra mode determination apparatus increments n by 1 and enters S310 again.

In step S314, the intra mode determination apparatus examines one MPM having a lower H-cost when n = 2 or when RMD [n] does not satisfy Equation (3).

When there is no common mode, the intra mode determination method in the large PU according to the embodiment of the present invention skips some RMD modes and some MPMs.

That is, as shown in Table 3, there is a high correlation between the H-cost calculated in the RMD step and the RD cost calculated in the RDO step. That is, the RMD mode having a large H-cost has a very low probability of being selected as the best mode. Therefore, in the intra mode determination method in the large PU according to the embodiment of the present invention, the RMD mode having the H-cost satisfying the condition of Equation (3) is checked, and the remaining RMD mode is skipped.

Also, in the intra mode determination method in the large PU according to the embodiment of the present invention, when there is no common mode, some MPMs are skipped.

That is, first, in the RDO step, one or two MPMs are added to the candidate mode list, as described above. If two MPMs are added because there is no common mode, it is very likely that MPMs with larger H-cost will not be selected as the best mode. This is because MPMs with larger H-cost are in a non-common mode and have a large H-cost. Therefore, in the intra mode determination method in the large PU according to the embodiment of the present invention, only one MPM having a smaller H-cost is checked, and the other MPM is skipped.

If one MPM is added in the RDO step, the intra mode determination method in the large PU according to the embodiment of the present invention does not skip the MPM.

Table 5 shows hit rates by alpha value of the intra mode determination method when there is no common mode in a large PU according to an embodiment of the present invention.

alpha 64 x 64 PU 32 x 32 PU 16 x 16 PU Average 1.05 79.8% 84.1% 85.1% 83.0% 1.10 80.9% 87.5% 90.3% 86.2% 1.15 81.1% 88.6% 92.0% 87.2%

As shown in Table 5, as the value of α increases, the hit rate also increases. However, the encoding time (e.g., coding complexity) also increases.

Table 6 below shows the average number of modes examined in the HM, the average mode number and hit rate of the intra mode determination method (a = 1.1) in the large PU according to the embodiment of the present invention.

64 x 64 PU 32 x 32 PU 16 x 16 PU Average HM 3.92 4.14 4.09 4.05 Proposed method for large PUs 3.12
(79.5%) 3.21
(77.4%) 3.13
(76.6%) 3.15
(77.9%) Hit rate 85.1% 88.4% 91.6% 88.4%

As shown in Table 6, the intra mode determination method in the large PU according to the embodiment of the present invention only checks 77.9% of the average mode number checked in the HM.

4 is a flowchart illustrating an intra mode determination method according to another embodiment of the present invention. 4, a method for determining an intra mode for a small PU will be described.

In step S401, the intra mode determination apparatus determines whether the number of common modes is 0 or not.

In step S402, the intra mode determination apparatus determines whether the number of common modes is 1 when the number of common modes is not zero.

In step S403, when the number of common modes is not 1, that is, when the number of common modes is 2, the intra mode determination apparatus sets n to 0.

In step S404, the intra mode determination apparatus checks RMD [n].

In step S405, the intra mode determination apparatus determines whether both common modes have already been checked. If the two common modes have already been checked, the intra mode determination method ends.

In step S406, if both common modes are not already checked, the intra mode determination apparatus determines whether n is seven.

In step S407, if n = 7, the intra mode determination apparatus increments n by 1, and then returns to step S404.

While only three RMD candidate modes exist for a large PU (e.g., 64x64, 32x32 or 16x16 PU), a small PU (e.g., 8x8 or 4x4 PU ), There are eight RMD candidate modes. This difference makes a lot of difference in small PUs. First, as shown in Table 1, there are more common modes on average for the small PU. The other difference is that there are more non-common modes for small PUs. For example, if there are two common modes, there is only one non-common RMD mode in a large PU, whereas there are six non-common RMD modes in a small PU. So, in order to handle this difference, other algorithms have to be applied in the case of small PUs. For example, when there are two common modes, both common modes and RMD [0] are sufficient for large PUs, but not for small PUs. Thus, the intra mode determination method in the small PU according to another embodiment of the present invention checks more prediction modes.

That is, first, the intra mode determination apparatus sequentially checks each RMD mode in ascending order of H-cost (for example, RMD [0], RMD [1], ...). After each RMD mode is checked, the intra mode determination device checks whether both common modes have been checked. Then, the intra mode determination apparatus ends the inspection procedure when both common modes are checked. For example, if RMD [0], RMD [1], ... , The _{m 0, RMD [7] m} 26, m 15, m 14, m 1, m 34, m 33 and m _10, and, when two MPM is assumed that m _26, and m _1, the intra mode decision apparatus m ₀ , m ₂₆ , m ₁₅ , m ₁₄ and m ₁ , and skips m ₃₄ , m ₃₃ and m ₁₀ .

In step S408, when the number of common modes is 1, the intra mode determination apparatus sets n to zero.

In step S409, the intra mode determination apparatus determines whether RMD [n] satisfies the following equation (4). If RMD [n] does not satisfy the following equation (4), the process proceeds to step S413.

Here, H-cost _cur and H-cost _{RMD [0]} are the H-cost of the current mode being examined and the H-cost of _{RMD [0]} , respectively. And? Is a parameter larger than one.

The condition of Equation (4) is the same as that of Equation (3) except that other parameters are used. The parameter β affects both the hit rate and the encoding time, as the parameter α. Although? And? May be used with the same value, the use of different values may give more options in the tradeoff between performance and encoding time.

In step S410, the intra mode determination apparatus checks RMD [n] when RMD [n] satisfies Equation (4).

In step S411, the intra mode determination apparatus determines whether n is 7 or not.

In step S412, if n is not 7, the intra mode determination apparatus increments n by 1 and enters the step S409 again.

In step S413, the intra mode determination apparatus checks the MPM if n = 7 or when RMD [n] does not satisfy equation (4), if the common MPM has not been already checked.

When there is only one common mode in the small PU, the intra mode determination method in the small PU according to another embodiment of the present invention skips some RMD modes and some MPMs.

That is, when there is only one common mode in the small PU, there may be one or zero non-common MPMs, since there are two or one MPM in the candidate list. When there is one uncommon MPM, the intra mode determination apparatus skips the inspection of the uncommon MPM as in the case of the large PU. If there is no uncommon MPM, the intra mode determination apparatus does not skip the MPM check because there is only one MPM.

For the non-common RMD mode, a different algorithm is applied to handle the difference for N. That is, in the case of a large PU, when there is only one common mode, there are only two non-common RMD modes. Thus, the intra mode determination apparatus checks both of the two non-common RMD modes in order not to reduce the performance. On the other hand, in the case of a small PU, when there is only one common mode, there exist seven non-common RMD modes. Therefore, another algorithm is needed to increase the coding efficiency. Thus, instead of inspecting all of the seven non-common RMD modes, the intra mode determination apparatus examines only the non-common RMD mode satisfying the above-described condition of Equation (4).

In step S414, the intra mode determination apparatus sets n to 0 when the number of common modes is zero.

In step S415, the intra mode determination apparatus determines whether RMD [n] satisfies Equation (4) described above. If RMD [n] does not satisfy Equation (4), the process proceeds to step S419.

In step S416, the intra mode determination apparatus checks RMD [n] when RMD [n] satisfies Equation (4).

In step S417, the intra mode determination apparatus determines whether n is seven.

In step S418, if n is not 7, the intra mode determination apparatus increments n by 1 and enters the step S415 again.

In step S419, the intra mode determination apparatus examines one MPM having lower H-cost when n = 7 or when RMD [n] does not satisfy Equation (4).

That is, when the common mode does not exist in the small PU, the intra mode determination method used in the case of the large PU can be applied most similarly. That is, in the intra-mode determination method in the small PU according to another embodiment of the present invention, only one MPM having a lower H-cost is examined, the other MPMs are skipped, and in the RMD mode, Only the RMD mode satisfying the condition of Equation 4 is examined.

Table 7 below shows the average number of modes tested in the HM, the average mode number and hit rate of the intra mode determination method (β = 1.15) in the small PU according to another embodiment of the present invention.

8 x 8 PU 4 × 4 PU Average HM 8.54 8.39 8.47 Proposed method for small PUs 4.98
(58.3%) 3.80
(45.3%) 4.39
(51.8%) Hit rate 93.9% 93.5% 93.7%

As shown in Table 7, the intra mode determination method in the small PU according to another embodiment of the present invention only checks 51.8% of the average mode number checked in the HM.

As described above, in the intra mode determination method according to the embodiment of the present invention described above with reference to FIGS. 3 and 4, different techniques may be applied depending on the size of the PU and the number of common modes.

Simulation result

The intra mode determination method according to the embodiment of the present invention was executed with HM software, and various test sequences were simulated. The simulation parameters are summarized in Table 8 below.

Parameter Mode / Value Profile Main GOP AI (all intra) QP 22, 27, 32, 37 Number of frames 30

Table 9 below shows the performance and the encoding time reduction rate of the intra mode determination method according to the embodiment of the present invention. In Table 9, Technique 1 represents the intra mode determination method of FIG. 3, and Technique 2 represents the intra mode determination method of FIG.

Class Sequence Technique 1 Technique 2 BD-BR
(%) ΔTime
(%) BD-BR
(%) ΔTime
(%) A (2560 x 1600) NebutaFestival 0.07 2.1 0.04 19.1 Traffic 0.06 2.4 0.22 22.0 B (1920 x 1080) Cactus 0.05 2.7 0.22 20.0 Kimono 0.28 2.2 0.02 22.0 C (832 x 480) BasketballDrill 0.09 2.9 0.21 21.0 PartyScene 0.00 2.6 0.33 17.4 D (416 x 240) BasketballPass 0.03 2.6 0.26 21.9 RaceHorses 0.00 1.8 0.31 19.4 E (1280 x 720) FourPeople 0.07 2.8 0.26 23.8 KristenandSara 0.12 2.7 0.27 24.4 Average 0.08 2.5 0.21 21.1

3 and 4 were set to 1.10 and 1.15, respectively, in the simulation. To analyze the effects of each of the methods described in FIGS. 3 and 4, Table 9 shows the results of each method. Instead of using PSNR and BR separately, a Bjøntegaard delta (BD) method was used for performance evaluation. In Table 9,? Time represents the encoding time reduction rate, which can be defined by the following equation.

Here, T _HM and T _proposed represent the encoding time of the HM software and the encoding time of the intra mode determination method according to the embodiment of the present invention, respectively.

3 and 4, the method of FIG. 3 is for a luma component in a large PU, whereas the method of FIG. 4 is for a luma component in a small PU. Of the methods of Figures 3 and 4, the method of Figure 4 shows a higher ΔTime value. This is because there are more candidate modes in the small PU case. As described above, the total number of modes checked in the RDO step ranges from N to N + 2. Here, N is 3 in the large PU and 8 in the small PU. Thus, if the same number of modes are skipped in the large PU and the small PU, the performance reduction is worse in the large PU case. One method can be applied to both large PU and small PU. For example, the method of FIG. 3 can be applied to a small PU as well as a large PU. However, the method of FIG. 3 has been developed specifically for the case where the PU size is relatively large and N is relatively small, whereas the method of FIG. 4 is specifically developed for the case where the PU size is relatively small and N is relatively large. One of the main advantages of the intra mode determination method according to the embodiment of the present invention is that different algorithms are adaptively applied to different PU sizes. In addition, the intra mode determination method according to the embodiment of the present invention applies different algorithms according to the number of common modes. As a result, each case can be efficiently coded to obtain a good tradeoff between performance and reduced complexity.

Table 10 below compares the intra mode determination method and other intra mode determination methods according to the embodiment of the present invention.

Class Sequence Zhang Shen Kim Gan Proposed Method BD-BR
(%) ΔTime
(%) BD-BR
(%) ΔTime
(%) BD-BR
(%) ΔTime
(%) BD-BR
(%) ΔTime
(%) BD-BR
(%) ΔTime
(%) A NebutaFestival 0.15 28.9 0.38 16.5 0.22 30.3 0.27 29.0 0.11 23.3 Traffic 0.46 29.0 0.86 20.6 0.57 26.8 0.66 30.9 0.36 30.2 B Cactus 0.43 28.6 0.83 21.2 0.58 28.4 0.65 31.1 0.36 28.3 Kimono 0.16 30.8 0.59 20.1 0.11 29.5 0.44 32.2 0.36 28.6 C BasketballDrill 0.59 26.9 0.80 20.6 0.77 26.4 0.70 30.9 0.40 29.6 PartyScene 0.66 25.8 0.93 18.7 0.87 28.9 0.84 27.0 0.41 23.8 D BasketballPass 0.59 27.7 0.89 22.1 0.76 26.9 0.74 31.3 0.43 30.1 RaceHorses 0.62 27.2 0.87 17.8 0.97 28.2 0.81 27.8 0.46 25.0 E FourPeople 0.54 29.0 1.01 23.0 0.64 25.9 0.86 32.0 0.51 33.6 KristenandSara 0.59 29.5 0.89 24.0 0.73 25.6 0.84 32.8 0.54 34.4 Average 0.48 28.3 0.81 20.5 0.62 27.7 0.68 30.5 0.39 28.7

Other intra mode determination methods include other high speed algorithms such as a fast CU size determination algorithm as well as a fast intra coding algorithm. For fair comparison only high speed intra coding algorithms are executed and compared. As shown in Table 10, the average BD-BR of the proposed method is considerably smaller than the other methods. The reason for the large performance difference can be explained as follows. First, the proposed method applies different algorithms according to the PU size, while the other methods use the same method regardless of the PU size. As described above, the number of candidate modes to be processed in an efficient intra coding method varies considerably with PU size. The common mode has considerably different elements compared to the non-common mode, and the number of common modes greatly affects the statistics for the best mode. Depending on the number of common modes, the proposed method uses a different scheme developed specifically for each case. Thus, the proposed method can determine the best mode more efficiently than other methods.

Although the average ΔTime at Gan is slightly greater than the proposed method, the average BD-BR at Gan is considerably larger than the proposed method. the proposed method can obtain a larger ΔTime at the expense of a slightly smaller BD-BR by changing the values of α and β in equations (3) and (4). As described above in Figs. 3 and 4, if a and / or b decrease towards 1, the encoding time decreases with the sacrifice of the decreased hit rate (e.g., increased BD-BR). Thus, the parameters alpha and beta can be used to fine tune the overall performance and encoding time. This may be another advantage of the intra mode determination method according to the embodiment of the present invention.

5 is a diagram schematically illustrating a configuration of an intra mode determination apparatus according to an embodiment of the present invention.

Referring to FIG. 5, an intra mode determination apparatus according to an embodiment of the present invention includes a processor 510, a memory 520, an input unit 530, and a display unit 540.

Processor 510 may be a CPU or a semiconductor device that executes processing instructions stored in memory 520.

The memory 520 may include various types of volatile or non-volatile storage media. For example, memory 520 may include ROM, RAM, and the like.

For example, the memory 520 may store instructions for performing an intra mode determination method according to an embodiment of the present invention.

The input unit 530 is means for receiving various commands, information, and the like from the user to control the intra mode determination apparatus or to execute an application installed in the intra mode determination apparatus. The input unit 530 may include at least one key button, and may include a touch input module formed integrally with the display unit 540.

The display unit 540 is means for displaying various data input to the intra mode determination apparatus or stored in the intra mode determination apparatus in the form of time information. For example, the display unit 540 may be a liquid crystal display (LCD).

On the other hand, the components of the above-described embodiment can be easily grasped from a process viewpoint. That is, each component can be identified as a respective process. Further, the process of the above-described embodiment can be easily grasped from the viewpoint of the components of the apparatus.

In addition, the above-described technical features may be implemented in the form of program instructions that can be executed through various computer means and recorded in a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, and the like, alone or in combination. The program instructions recorded on the medium may be those specially designed and constructed for the embodiments or may be available to those skilled in the art of computer software. Examples of computer-readable media include magnetic media such as hard disks, floppy disks and magnetic tape; optical media such as CD-ROMs and DVDs; magnetic media such as floppy disks; Magneto-optical media, and hardware devices specifically configured to store and execute program instructions such as ROM, RAM, flash memory, and the like. Examples of program instructions include machine language code such as those produced by a compiler, as well as high-level language code that can be executed by a computer using an interpreter or the like. The hardware device may be configured to operate as one or more software modules to perform the operations of the embodiments, and vice versa.

It will be apparent to those skilled in the art that various modifications, additions and substitutions are possible, without departing from the spirit and scope of the invention as defined by the appended claims. Should be regarded as belonging to the following claims.

510: Processor
520: Memory
530:
540:

Claims (12)

1. An intra mode determination method performed by an intra mode determination apparatus with respect to luma components,
Determining a number of common modes belonging to a plurality of first modes determined in rough mode decision (RMD) and a plurality of second modes determined by MPM (most probable mode); And
Skipping the examination of at least one of the plurality of first modes and the plurality of second modes in consideration of the number of common modes and prediction units (PU) sizes,
When the PU (prediction units) size is large, which is any one of 64x64, 32x32, or 16x16, the number of the first modes is 3, and the number of the plurality of second modes Is a maximum of 2,
If the prediction units (PU) size is large, skipping the examination of the partial mode may include:
Checking a first mode in which two common modes and H-cost (Hadamard cost) are the smallest when the number of common modes is 2;
Checking all of the plurality of first modes when the number of the common modes is 1; And
Checking each first mode according to the H-cost of each first mode when the number of the common modes is 0 and examining a second mode having a smaller H-cost, Determination method.
delete delete The method according to claim 1,
Checking the first mode having the smallest H-cost and the two common modes,
Wherein the two common modes have a relatively high probability of being selected as the best mode, and the first mode with the smallest H-cost has the highest probability of being selected as the best mode, Determination method.
The method according to claim 1,
Wherein the step of inspecting the plurality of first modes includes:
And skipping the examination of the common second mode when only one of the two modes is the common mode.
The method according to claim 1,
Checking each first mode according to the H-cost of each first mode and checking a second mode having a smaller H-
The first mode having the H-cost satisfying the condition of the following equation is inspected, the inspection of the remaining first mode is skipped,
And the second mode having a larger H-cost among the two modes is more likely not to be selected as the best mode.

Here, H-cost _cur and H-cost _{RMD [0]} are H-cost of the first mode in which the H-cost and H-cost of the current mode to be examined are the smallest, respectively, and?
The method according to claim 1,
If the PU (prediction units) size is small, which is either 8 x 8 or 4 x 4, the number of the first modes is 8, and the number of the plurality of second modes is 2 Wherein the intra mode determination method comprises the steps of:
8. The method of claim 7,
If the prediction units (PU) size is smaller than the smallest prediction unit size,
Sequentially checking all of the plurality of first modes when the number of common modes is 2, checking whether both common modes are checked;
Terminating if both common modes are checked;
Checking each first mode according to the H-cost of each first mode when the number of the common modes is 1 and checking the common second mode when the common second mode is not checked; And
Checking each first mode according to the H-cost of each first mode when the number of the common modes is 0 and examining a second mode having a smaller H-cost, Determination method.
9. The method of claim 8,
Sequentially checking all of the plurality of first modes, and verifying whether both common modes have been checked,
And sequentially examining each first mode in ascending order of H-cost.
9. The method of claim 8,
Checking each first mode according to the H-cost of each first mode and checking the common second mode when the common second mode is not checked,
And a non-common first mode having H-cost satisfying the condition of the following equation is inspected.

Here, H-cost _cur and H-cost _{RMD [0]} are H-cost of the first mode having the smallest H-cost and H-cost of the current mode to be inspected, respectively.
9. The method of claim 8,
Checking each first mode according to the H-cost of each first mode and checking a second mode having a smaller H-
Checking a first mode having an H-cost satisfying a condition of the following equation; And
Checking only one second mode having a smaller H-cost, and skipping the other second mode.

Here, H-cost _cur and H-cost _{RMD [0]} are H-cost of the first mode having the smallest H-cost and H-cost of the current mode to be inspected, respectively.
An intra mode determination apparatus for determining an intra mode for luma components, comprising:
A memory for storing instructions; And
And a processor for executing the instruction,
Wherein the command comprises:
Determining a number of common modes belonging to a plurality of first modes determined in rough mode decision (RMD) and a plurality of second modes determined by MPM (most probable mode); And
And skipping the examination of at least one of the plurality of first modes and the plurality of second modes in consideration of the number of common modes and prediction units (PU) size In addition,
When the PU (prediction units) size is large, which is any one of 64x64, 32x32, or 16x16, the number of the first modes is 3, and the number of the plurality of second modes Is a maximum of 2,
If the prediction units (PU) size is large, skipping the examination of the partial mode may include:
Checking a first mode in which two common modes and H-cost (Hadamard cost) are the smallest when the number of common modes is 2;
Checking all of the plurality of first modes when the number of the common modes is 1; And
Checking each first mode according to the H-cost of each first mode when the number of the common modes is 0 and examining a second mode having a smaller H-cost, Crystal device.

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