H.266/VVC代码学习:MIP技术相关代码

MIP技术原理介绍：https://blog.csdn.net/BigDream123/article/details/104939645

MIP的相关函数代码在estIntraPredLumaQT函数中首次被调用，如下代码所示，其中

• initIntraMip函数用于对参考像素进行下采样，为MIP矩阵乘法准备输入数据
• getNumModesMip函数根据当前块的尺寸获取不同的MIP模式数目
• predIntraMip函数进行矩阵运算，并进行上采样插值，获得整个块的预测值

注意：MIP使用存在块尺寸限制：宽高比不能超过1:8/8:1

    //MIP允许使用标志
    const bool mipAllowed = sps.getUseMIP() && isLuma(partitioner.chType) && ((cu.lfnstIdx == 0) || allowLfnstWithMip(cu.firstPU->lumaSize()));
    //MIP模式测试标志：宽高比不能超过1:8/8:1
    const bool testMip = mipAllowed && !(cu.lwidth() > (8 * cu.lheight()) || cu.lheight() > (8 * cu.lwidth()));
    //MIP支持的最大块尺寸为64
    const bool supportedMipBlkSize = pu.lwidth() <= MIP_MAX_WIDTH && pu.lheight() <= MIP_MAX_HEIGHT;
...
...
...
// 初始化Mip模式
              initIntraPatternChType(cu, pu.Y());//获取参考像素并滤波
              initIntraMip(pu, pu.Y());
              // getNumModesMip函数根据当前CU的块尺寸获取不同的Mip模式数量16 8 6
              const int transpOff    = getNumModesMip(pu.Y());
              const int numModesFull = (transpOff << 1);//MIP模式总数分别是32 16 12
              
              for (uint32_t uiModeFull = 0; uiModeFull < numModesFull; uiModeFull++)
              {
                //对于另一半MIP模式，其需要进行转置
                const bool     isTransposed = (uiModeFull >= transpOff ? true : false);
                const uint32_t uiMode       = (isTransposed ? uiModeFull - transpOff : uiModeFull);

                pu.mipTransposedFlag           = isTransposed;
                pu.intraDir[CHANNEL_TYPE_LUMA] = uiMode;
                // Mip预测模式的函数入口，进行MIP预测
                predIntraMip(COMPONENT_Y, piPred, pu);

                // Use the min between SAD and HAD as the cost criterion
                // SAD is scaled by 2 to align with the scaling of HAD
                Distortion minSadHad =
                  std::min(distParamSad.distFunc(distParamSad) * 2, distParamHad.distFunc(distParamHad));

                m_CABACEstimator->getCtx() = SubCtx(Ctx::MipFlag, ctxStartMipFlag);

                uint64_t fracModeBits = xFracModeBitsIntra(pu, uiMode, CHANNEL_TYPE_LUMA);

                double cost            = double(minSadHad) + double(fracModeBits) * sqrtLambdaForFirstPass;
                mipHadCost[uiModeFull] = cost;
                DTRACE(g_trace_ctx, D_INTRA_COST, "IntraMIP: %u, %llu, %f (%d)\n", minSadHad, fracModeBits, cost,
                       uiModeFull);
                // 更新候选列表，将最优的Mip模式加入到RDCost的候选列表中
                updateCandList(ModeInfo(true, isTransposed, 0, NOT_INTRA_SUBPARTITIONS, uiMode), cost, uiRdModeList,
                               CandCostList, numModesForFullRD + 1);
                updateCandList(ModeInfo(true, isTransposed, 0, NOT_INTRA_SUBPARTITIONS, uiMode),
                               0.8 * double(minSadHad), uiHadModeList, CandHadList, numHadCand);
              }

MIP根据块尺寸可以分为以下三种情况：

	块尺寸	MIP模式
mipSizeId = 0	4x4	32
mipSizeId = 1	4xN、Nx4、8x8	16
mipSizeId = 2	其余块	12

其中，MIP的转置标志和MIP的模式号有关：

• mipSizdId = 0时，前16种模式的mipTransposedFlag= 0，后16种模式的mipTransposedFlag = 1
• mipSizeId = 1时，前8种模式的mipTransposedFlag= 0，后8种模式的mipTransposedFlag = 1
• mipSizeId = 2时，前6种模式的mipTransposedFlag= 0，后6种模式的mipTransposedFlag = 1

getNumModesMip函数代码如下：

int getNumModesMip(const Size& block)
{
  switch( getMipSizeId(block) )
  {
  case 0: return 16;
  case 1: return  8;
  case 2: return  6;
  default: THROW( "Invalid mipSizeId" );
  }
}

initIntraMip函数相关代码参考：https://blog.csdn.net/BigDream123/article/details/107018446

predIntraMip函数相关代码参考：https://blog.csdn.net/BigDream123/article/details/107019458