H.266/VVC code learning: MIP technology related code

Introduction to MIP technology principle: https://blog.csdn.net/BigDream123/article/details/104939645

The related function code of MIP is called for the first time in the estIntraPredLumaQT function, as shown in the following code, where

The initIntraMip function is used to downsample the reference pixels and prepare input data for MIP matrix multiplication
The getNumModesMip function obtains the number of different MIP modes according to the size of the current block
The predIntraMip function performs matrix operations and up-sampling interpolation to obtain the predicted value of the entire block

Note: There is a block size limitation for MIP use: the aspect ratio cannot exceed 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 can be divided into the following three cases according to the block size:

	Block size	MIP mode
mipSizeId = 0	4x4	32
mipSizeId = 1	4xN, Nx4, 8x8	16
mipSizeId = 2	Rest block	12

Among them, the transposition mark of MIP is related to the mode number of MIP:

When mipSizdId = 0, the mipTransposedFlag of the first 16 modes is 0, and the mipTransposedFlag of the last 16 modes is 1
When mipSizeId = 1, the mipTransposedFlag of the first 8 modes is 0, and the mipTransposedFlag of the last 8 modes is 1
When mipSizeId = 2, mipTransposedFlag = 0 for the first 6 modes and mipTransposedFlag = 1 for the last 6 modes

The getNumModesMip function code is as follows:

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 function related code reference: https://blog.csdn.net/BigDream123/article/details/107018446

PredIntraMip function related code reference: https://blog.csdn.net/BigDream123/article/details/107019458

H.266/VVC code learning: MIP technology related code

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