HEVC学习（1）——Intra Prediction

在网上看到一篇学习HEVC帧内预测的文章http://blog.csdn.net/hevc_cjl/article/details/8175721

于是对应去看了一下文章中提到的相关文件的相关章节。

以前没有学习过视频编码的东西，也没有接触过H.264，就直接来HEVC了，看得云里雾里不知道从何下手。

 

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官方当前标准（JCTVC-J1003）draft 8.4.4.2.2（Reference sample substitution process for intra sample prediction）

8.4.4.2.2   Reference sample substitution process for intra sample prediction

Inputs to this process are:

–         reference samples p[ x ][ y ] with x = −1, y = −1..nT*2−1 and x = 0..nT*2−1, y = −1 for intra sample prediction,

–         a transform block size nT.

Outputs of this process are:

–         the modified reference samples p[ x ][ y ] with x = −1, y = −1..nT*2−1 and x = 0..nT*2−1, y = −1 for intra sample prediction.

The values of the samples p[ x ][ y ] with x = −1, y = −1..nT*2−1 and x = 0..nT*2−1, y = −1 are modified as follows:

–         If all samples p[ x ][ y ] with x = −1, y = −1..nT*2−1 and x = 0..nT*2−1, y = −1 are marked as "not available for intra prediction," the value ( 1 << ( BitDepth_Y − 1 ) ) is substituted for the values of all samples p[ x ][ y ].

–         Otherwise (at least one but not all samples p[ x ][ y ] are marked as "not available for intra prediction"), the following ordered steps are performed:

1. If p[ −1 ][ nT*2−1 ] is marked as "not available for intra prediction", searching sequentially starting from x = −1, y = nT*2−1 to x = −1, y = −1, then from x = 0, y = −1 to x = nT*2−1, y = −1. As soon as a sample p[ x ][ y ] marked as "available for intra prediction" is found, the search is terminated and the value of p[ x ][ y ] is assigned to p[ −1 ][ nT*2−1 ].
2. For x = −1, y = nT*2−2...−1, if p[ x ][ y ] is marked as "not available for intra prediction", the value of p[ x ][ y+1 ] is substituted for the value of p[ x ][ y].
3. For x = 0..nT*2−1, y = −1, if p[ x ][ y ] is marked as "not available for intra prediction", the value of p[ x−1 ][ y ] is substituted for the value of p[ x ][ y ].

All samples p[ x ][ y ] with x = −1, y = −1..nT*2−1 and x = 0..nT*2−1, y = −1 are marked as "available for intra prediction".

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1 << ( BitDepth_Y − 1 ) ，其中 BitDepth_Y指的是Y分量的bitdepth，通常都是8bit，所以 BitDepth_Y − 1 为7；<< 代表位运算左移，每左移一次相当于乘以2，所以最后的值为128.

 

1、如果黄色区域的sample全部都unavailable的话，就都填充为128.

2、如果黄色区域的sample不是全部都unavailable的话：

    a. 如果左下角的unavailable，那么按照从下往上，从左往右的顺序搜索，找到第一个available的，复制给左下角；

    b. 左下角的填充完了之后，按照从下往上，从左往右的顺序依次填充，如果某个sample是unavailable的，那么用它的前一个去填充它。