HM模型学习（三）

原文出处：http://blog.csdn.net/hevc_cjl/article/details/8184276

今天主要介绍帧内预测一个很重要的函数initAdiPattern，它的主要功能有三个，（1）检测当前PU的相邻样点包括左上、上、右上、左、左下邻域样点值的可用性，或者说检查这些点是否存在；（2）参考样点的替换过程，主要实现的是JCTVC-J1003即draft 8.4.4.2.2的内容，主要由函数fillReferenceSamples来完成，这个在之前的文章已经讨论过了；（3）相邻样点即参考样点的平滑滤波，主要实现draft 8.4.4.2.3的内容。话不多说，下面给出initAdiPattern的实现和我个人的一些注释，供大家参考。

在HM16.9中，该部分函数被拆分成两个函数对应于工程中的：

其中主要是最下面的函数，上面的函数作用是给出是否滤波的布尔值，然后该值作为参数传入下面的函数中。

对应的HM16.9的解释如下，有些地方不能很好地理解。9.0可参考原文出处。

Void TComPrediction::initIntraPatternChType( TComTU &rTu, const ComponentID compID, const Bool bFilterRefSamples DEBUG_STRING_FN_DECLARE(sDebug))
{
  const ChannelType chType    = toChannelType(compID);

  TComDataCU *pcCU=rTu.getCU();
  const TComSPS &sps = *(pcCU->getSlice()->getSPS());
  const UInt uiZorderIdxInPart=rTu.GetAbsPartIdxTU();
  const UInt uiTuWidth        = rTu.getRect(compID).width;//!< CU的宽度
  const UInt uiTuHeight       = rTu.getRect(compID).height;//!< CU的高度
  const UInt uiTuWidth2       = uiTuWidth  << 1;
  const UInt uiTuHeight2      = uiTuHeight << 1;

  const Int  iBaseUnitSize    = sps.getMaxCUWidth() >> sps.getMaxTotalCUDepth();
  const Int  iUnitWidth       = iBaseUnitSize  >> pcCU->getPic()->getPicYuvRec()->getComponentScaleX(compID);
  const Int  iUnitHeight      = iBaseUnitSize  >> pcCU->getPic()->getPicYuvRec()->getComponentScaleY(compID);
  const Int  iTUWidthInUnits  = uiTuWidth  / iUnitWidth;
  const Int  iTUHeightInUnits = uiTuHeight / iUnitHeight;
  const Int  iAboveUnits      = iTUWidthInUnits  << 1;//上方相邻unit个数
  const Int  iLeftUnits       = iTUHeightInUnits << 1;//左方相邻unit个数
  const Int  bitDepthForChannel = sps.getBitDepth(chType);

  assert(iTUHeightInUnits > 0 && iTUWidthInUnits > 0);

  //! 获取当前PU左上角LT，右上角RT以及左下角LB 以4x4块为单位的Zorder
  const Int  iPartIdxStride   = pcCU->getPic()->getNumPartInCtuWidth();
  const UInt uiPartIdxLT      = pcCU->getZorderIdxInCtu() + uiZorderIdxInPart;
  const UInt uiPartIdxRT      = g_auiRasterToZscan[ g_auiZscanToRaster[ uiPartIdxLT ] +   iTUWidthInUnits  - 1                   ];
  const UInt uiPartIdxLB      = g_auiRasterToZscan[ g_auiZscanToRaster[ uiPartIdxLT ] + ((iTUHeightInUnits - 1) * iPartIdxStride)];

  Int   iPicStride = pcCU->getPic()->getStride(compID);
  Bool  bNeighborFlags[4 * MAX_NUM_PART_IDXS_IN_CTU_WIDTH + 1]; //!< 用于存放4个方向上的相邻样点值的可用性, 4 x 32 + 1
  Int   iNumIntraNeighbor = 0; //!< 给可用邻块进行计数


  //! 扫描顺序是从左下到左上，再从左上到右上
  bNeighborFlags[iLeftUnits] = isAboveLeftAvailable( pcCU, uiPartIdxLT );//为每个邻块的可用性进行
  iNumIntraNeighbor += bNeighborFlags[iLeftUnits] ? 1 : 0;//邻块可用则+1计数
  iNumIntraNeighbor  += isAboveAvailable     ( pcCU, uiPartIdxLT, uiPartIdxRT, (bNeighborFlags + iLeftUnits + 1)                    );
  iNumIntraNeighbor  += isAboveRightAvailable( pcCU, uiPartIdxLT, uiPartIdxRT, (bNeighborFlags + iLeftUnits + 1 + iTUWidthInUnits ) );
  iNumIntraNeighbor  += isLeftAvailable      ( pcCU, uiPartIdxLT, uiPartIdxLB, (bNeighborFlags + iLeftUnits - 1)                    );
  iNumIntraNeighbor  += isBelowLeftAvailable ( pcCU, uiPartIdxLT, uiPartIdxLB, (bNeighborFlags + iLeftUnits - 1 - iTUHeightInUnits) );

  const UInt         uiROIWidth  = uiTuWidth2+1;
  const UInt         uiROIHeight = uiTuHeight2+1;

  // number of elements in one buffer
  assert(uiROIWidth*uiROIHeight <= m_iYuvExtSize);//assert作用是如果它的条件返回错误，则终止程序执行

#if DEBUG_STRING
  std::stringstream ss(stringstream::out);
#endif

  {
    Pel *piIntraTemp   = m_piYuvExt[compID][PRED_BUF_UNFILTERED];
    Pel *piRoiOrigin = pcCU->getPic()->getPicYuvRec()->getAddr(compID, pcCU->getCtuRsAddr(), pcCU->getZorderIdxInCtu()+uiZorderIdxInPart); //! piRoiOrigin指向当前PU左上角 
#if O0043_BEST_EFFORT_DECODING
    const Int  bitDepthForChannelInStream = sps.getStreamBitDepth(chType);
    fillReferenceSamples (bitDepthForChannelInStream, bitDepthForChannelInStream - bitDepthForChannel,
#else
    fillReferenceSamples (bitDepthForChannel,
#endif
                          piRoiOrigin, piIntraTemp, bNeighborFlags, iNumIntraNeighbor,  iUnitWidth, iUnitHeight, iAboveUnits, iLeftUnits,
                          uiROIWidth, uiROIHeight, iPicStride);//填充参考样点


#if DEBUG_STRING
    if (DebugOptionList::DebugString_Pred.getInt()&DebugStringGetPredModeMask(MODE_INTRA))
    {
      ss << "###: generating Ref Samples for channel " << compID << " and " << rTu.getRect(compID).width << " x " << rTu.getRect(compID).height << "\n";
      for (UInt y=0; y> shift;
        }

        piSrcPtr -= stride * (uiTuHeight2 - 1);
      }
      else
      {
        for(UInt i=1; i> 2;//!< 对中间样点值进行3抽头[1 2 1] / 4 的平滑滤波
        }
      }

      //------------------------------------------------

      //top-left

      if (useStrongIntraSmoothing)
      {
        *piDestPtr = piSrcPtr[0];
      }
      else
      {
        *piDestPtr = ( piSrcPtr[stride] + 2*piSrcPtr[0] + piSrcPtr[1] + 2 ) >> 2;
      }
      piDestPtr += 1;
      piSrcPtr  += 1;

      //------------------------------------------------

      //top row (left-to-right)

      if (useStrongIntraSmoothing)
      {
        const Int shift = g_aucConvertToBit[uiTuWidth] + 3; //log2(uiTuWidth2)

        for(UInt i=1; i> shift;
        }

        piSrcPtr += uiTuWidth2 - 1;
      }
      else
      {
        for(UInt i=1; i> 2;
        }
      }

      //------------------------------------------------

      *piDestPtr=*piSrcPtr; // far right is not filtered

最后附上图，以帮助大家更好地理解代码，我就不对图多作解释了，相信大家对着代码能比较容易看明白的。

 （注，上图中，uiWidth和uiHeight实际上对应的是代码中的uiCUWidth和uiCUHeight，因画图的时候发生了遗漏，特此说明）