HEVC帧内预测：xPredIntraAng

 

 

Void TComPrediction::xPredIntraAng(       Int bitDepth,
                                    const Pel* pSrc,     Int srcStride,
                                          Pel* pTrueDst, Int dstStrideTrue,
                                          UInt uiWidth, UInt uiHeight, ChannelType channelType,
                                          UInt dirMode, const Bool bEnableEdgeFilters
                                  )
{
  Int width=Int(uiWidth);
  Int height=Int(uiHeight);

  // Map the mode index to main prediction direction and angle
  assert( dirMode != PLANAR_IDX ); //no planar
  const Bool modeDC        = dirMode==DC_IDX;

  // Do the DC prediction
  if (modeDC)
  {
    const Pel dcval = predIntraGetPredValDC(pSrc, srcStride, width, height);

    for (Int y=height;y>0;y--, pTrueDst+=dstStrideTrue)
    {
      for (Int x=0; x<width;) // width is always a multiple of 4.
      {
        pTrueDst[x++] = dcval;
      }
    }
  }
  else // Do angular predictions
  {
    //判断是否为垂直类模式
    const Bool       bIsModeVer         = (dirMode >= 18);
    const Int        intraPredAngleMode = (bIsModeVer) ? (Int)dirMode - VER_IDX :  -((Int)dirMode - HOR_IDX);
    const Int        absAngMode         = abs(intraPredAngleMode);
    const Int        signAng            = intraPredAngleMode < 0 ? -1 : 1;
    const Bool       edgeFilter         = bEnableEdgeFilters && isLuma(channelType) && (width <= MAXIMUM_INTRA_FILTERED_WIDTH) && (height <= MAXIMUM_INTRA_FILTERED_HEIGHT);

    // Set bitshifts and scale the angle parameter to block size
    //注意偏移值的对称性
    static const Int angTable[9]    = {0,    2,    5,   9,  13,  17,  21,  26,  32};
    //invAngTable[i] = 256*32/angTable[i]
    static const Int invAngTable[9] = {0, 4096, 1638, 910, 630, 482, 390, 315, 256}; // (256 * 32) / Angle
    Int invAngle                    = invAngTable[absAngMode];
    Int absAng                      = angTable[absAngMode];
    Int intraPredAngle              = signAng * absAng;

    Pel* refMain;
    Pel* refSide;

    Pel  refAbove[2*MAX_CU_SIZE+1];
    Pel  refLeft[2*MAX_CU_SIZE+1];

    // Initialize the Main and Left reference array.
    //偏移值<0,此时需要参考像素
    if (intraPredAngle < 0)
    {
      const Int refMainOffsetPreScale = (bIsModeVer ? height : width ) - 1;
      const Int refMainOffset         = height - 1;
      for (Int x=0;x<width+1;x++)
      {
        refAbove[x+refMainOffset] = pSrc[x-srcStride-1];
      }
      for (Int y=0;y<height+1;y++)
      {
        refLeft[y+refMainOffset] = pSrc[(y-1)*srcStride-1];
      }
      //HEVC中块width和height一致，不用像VVC中区分
      //VVC： refMain = bIsModeVer ? refAbove + height : refLeft + width;
      //      refSide = bIsModeVer ? refLeft + width : refAbove + height;
      refMain = (bIsModeVer ? refAbove : refLeft)  + refMainOffset;
      refSide = (bIsModeVer ? refLeft  : refAbove) + refMainOffset;

      // Extend the Main reference to the left.
      Int invAngleSum    = 128;       // rounding for (shift by 8)
      //像素映射：pos = y*offset[M]>>5
      for (Int k=-1; k>(refMainOffsetPreScale+1)*intraPredAngle>>5; k--)
      {
        invAngleSum += invAngle;
        refMain[k] = refSide[invAngleSum>>8];
      }
    }
    else
    {
      for (Int x=0;x<2*width+1;x++)
      {
        refAbove[x] = pSrc[x-srcStride-1];
      }
      for (Int y=0;y<2*height+1;y++)
      {
        refLeft[y] = pSrc[(y-1)*srcStride-1];
      }
      refMain = bIsModeVer ? refAbove : refLeft ;
      refSide = bIsModeVer ? refLeft  : refAbove;
    }

    // swap width/height if we are doing a horizontal mode:
    Pel tempArray[MAX_CU_SIZE*MAX_CU_SIZE];
    const Int dstStride = bIsModeVer ? dstStrideTrue : MAX_CU_SIZE;
    Pel *pDst = bIsModeVer ? pTrueDst : tempArray;
    if (!bIsModeVer)
    {
      std::swap(width, height);
    }

    if (intraPredAngle == 0)  // pure vertical or pure horizontal
    {
      for (Int y=0;y<height;y++)
      {
        for (Int x=0;x<width;x++)
        {
          pDst[y*dstStride+x] = refMain[x+1];
        }
      }

      if (edgeFilter)
      {
        for (Int y=0;y<height;y++)
        {
          pDst[y*dstStride] = Clip3 (0, ((1 << bitDepth) - 1), pDst[y*dstStride] + (( refSide[y+1] - refSide[0] ) >> 1) );
        }
      }
    }
    else
    {
      //非垂直、水平模式
      Pel *pDsty=pDst;

      for (Int y=0, deltaPos=intraPredAngle; y<height; y++, deltaPos+=intraPredAngle, pDsty+=dstStride)
      {
        const Int deltaInt   = deltaPos >> 5;
        const Int deltaFract = deltaPos & (32 - 1);

        if (deltaFract)
        {
          // Do linear filtering
          const Pel *pRM=refMain+deltaInt+1;
          Int lastRefMainPel=*pRM++;
          for (Int x=0;x<width;pRM++,x++)
          {
            Int thisRefMainPel=*pRM;
            //参考像素计算
            pDsty[x+0] = (Pel) ( ((32-deltaFract)*lastRefMainPel + deltaFract*thisRefMainPel +16) >> 5 );
            lastRefMainPel=thisRefMainPel;
          }
        }
        else
        {
          // Just copy the integer samples
          for (Int x=0;x<width; x++)
          {
            pDsty[x] = refMain[x+deltaInt+1];
          }
        }
      }
    }

    // Flip the block if this is the horizontal mode
    if (!bIsModeVer)
    {
      for (Int y=0; y<height; y++)
      {
        for (Int x=0; x<width; x++)
        {
          pTrueDst[x*dstStrideTrue] = pDst[x];
        }
        pTrueDst++;
        pDst+=dstStride;
      }
    }
  }
}