【HEVC帧间预测论文】P1.5 Fast Coding Unit Size Selection for HEVC based on Bayesian Decision Rule

Fast Coding Unit Size Selection for HEVC based on Bayesian Decision Rule

《HEVC标准介绍、HEVC帧间预测论文笔记》系列博客,目录见:http://www.cnblogs.com/DwyaneTalk/p/5711333.htmlMotion Vectors Merging Low Complexity Prediction Unit Decision Heuristic for the InterPrediction of HEVC Encoders.pdf

Fast Coding Unit Size Selection for HEVC based on Bayesian Decision Rule .pdf

2012 Picture Coding Symposium May 7-9, 2012

以最小决策代价来进行贝叶斯决策,判断对于当前CU是否进行四叉树划分。代价是RD值,每个块选取3个值作为特征。

 

核心公式:

   W是决策分类,  分别表示划分和不划分。

         1

1)式为naïve bayes的公式,依次是类条件、先验和后验(似然)概率。

 2

2)表示决策代价,表示应该决策为Ws而实际是W的代价,其他类似。

3)、(4)式为最终的决策表达式。决策如下:

 

对于特征F,可以表示图像的特征很多,算法中从下面6个中间选择3个:

A、fvar :The variance of mode Inter_2Nx2N prediction errors in current CU

B、fsatd:The sum of absolute transformed difference (SATD) between original and prediction of mode Inter_2Nx2N

C、fvsatd :The variance of 4 SATDs (The prediction errors of mode Inter_2Nx2N is split into 4 sub-squares and calculate SATD on each sub-square)

D、fmvg:MV magnitude(就是MV的模)

E、fp:Percentage of coefficients cost in RD cost。就是中拉格朗日系数lamda

F、frdc:RD cost of mode Inter_2Nx2N

         从A~F的6个特征中选择3个,是通过贪心的sequential forward selection (SFS) algorithm 来选择使互信息量MI最大的3个特征f。

         I(F:W)就是互信息量MI。在5个1080p的测试序列上,计算不同f的MI如下表:

根据表格可以看出,最优的三个特征是fvar、fp和fvsatd。所以最终选择这三个组成决策表达式中的F。

fvar、fp和fvsatd都量化成10个取值,所以F有1000个取值,相应有2000个取值,所以是通过特定的方法进行off-line估计,然后存在查找表(LUT)中。

则是一个和QP、图像分辨率、CU划分深度等有关的判断阈值。通过测试2个1080p和2个WVGA的视频序列,计算其中的值,然后保存在另一个LUT里。

算法流程:

         算法简述:

1、Initialize Bayesian threshold in (6) with the QP and resolution settings.

2、RDO process starts from one LCU with CU_depth=0;

3、For the current CU_depth, try mode Inter_2Nx2N, and calculate the feature vector F=[f

var, fp, fvsatd] online;

4、For a feature F, find the class-conditional probability according to pdf p(F|wi) i∈{N, S} in the LUT. Make a decision according to (6). If the Non-SPLIT decision is made, proceed to step 5); otherwise, set CU_depth as CU_depth+1, and then return back to step 3) to perform the RDO process of the four sub-CU;

5、Perform RDO on mode Inter_2NxN, Inter_Nx2N and Intra_2Nx2N (Inter_NxN and Intra_NxN) to decide the optimal mode of the current CU.

6、Exit the RDO process and encode the LCU.

实验结果:(HM4.0rc1,4个测试序列,Rand Access和Low Delay两种HM的configuration)

 

 

 

posted @ 2016-07-28 17:02  DwyaneTalk  阅读(...)  评论(... 编辑 收藏