HEVC學習（十） —— 與變換有關的幾個主要函數及重要變量

本文主要是列出幾個與變換有關的函數，以及涉及到的比較重要的變量，但不會去深入討論函數的實現，日後有機會的話會更詳細地討論這幾個函數，這裏僅是列舉出來，起到備忘的作用，也能供大家參考。

 

如何定位到這幾個函數的，方法與前面的一篇博客HEVC學習（八） —— 以SAO爲例淺析跟蹤代碼方法類似，有興趣的朋友可以去看看，這裏就不重複這個過程了。

 

在xCompressCU函數中，有這麼幾個函數值得我們注意的，xCheckRDCostInter、xCheckRDCostMerge2Nx2N、xCheckRDCostIntra。它們分別是實現幀間預測模式、Merge模式、幀內預測式的主函數。前兩個函數的子函數xEstimateResidualQT（實際上通過調用函數encodeResAndCalcRdInterCU）、第三個函數的子函數xRecurIntraCodingQT（實際上通過調用xIntraCodingLumaBlk、xIntraCodingChromaBlk）均會調用函數transformNxN，該函數如下定義：

Void TComTrQuant::transformNxN( TComDataCU* pcCU,
                               Pel*        pcResidual,
                               UInt        uiStride,
                               TCoeff*     rpcCoeff,
#if ADAPTIVE_QP_SELECTION
                               Int*&       rpcArlCoeff,
#endif
                               UInt        uiWidth,
                               UInt        uiHeight,
                               UInt&       uiAbsSum,
                               TextType    eTType,
                               UInt        uiAbsPartIdx,
                               Bool        useTransformSkip
                               )
{
  if (pcCU->getCUTransquantBypass(uiAbsPartIdx))
  {
    uiAbsSum=0;
    for (UInt k = 0; k<uiHeight; k++)
    {
      for (UInt j = 0; j<uiWidth; j++)
      {
        rpcCoeff[k*uiWidth+j]= pcResidual[k*uiStride+j];
        uiAbsSum += abs(pcResidual[k*uiStride+j]);
      }
    }
    return;
  }
  UInt uiMode;  //luma intra pred
  if(eTType == TEXT_LUMA && pcCU->getPredictionMode(uiAbsPartIdx) == MODE_INTRA )
  {
    uiMode = pcCU->getLumaIntraDir( uiAbsPartIdx );
  }
  else
  {
    uiMode = REG_DCT;
  }

  uiAbsSum = 0;
  assert( (pcCU->getSlice()->getSPS()->getMaxTrSize() >= uiWidth) );
  if(useTransformSkip)
  {
    xTransformSkip( pcResidual, uiStride, m_plTempCoeff, uiWidth, uiHeight );
  }
  else
  {
    xT( uiMode, pcResidual, uiStride, m_plTempCoeff, uiWidth, uiHeight );
  }
  xQuant( pcCU, m_plTempCoeff, rpcCoeff,
#if ADAPTIVE_QP_SELECTION
       rpcArlCoeff,
#endif
       uiWidth, uiHeight, uiAbsSum, eTType, uiAbsPartIdx );
}

這個函數主要調用了xTransformSkip、xT、xQuant三個函數，分別實現對殘差進行TS(Transform Skip)模式、普通變換模式以及量化的功能。對於第二個函數xT來說，它調用了xTrNxN，該函數的實現如下所示：

/** MxN forward transform (2D)
*  \param block input data (residual)
*  \param coeff output data (transform coefficients)
*  \param iWidth input data (width of transform)
*  \param iHeight input data (height of transform)
*/
void xTrMxN(short *block,short *coeff, int iWidth, int iHeight, UInt uiMode)
{
#if FULL_NBIT
  int shift_1st = g_aucConvertToBit[iWidth]  + 1 + g_uiBitDepth - 8; // log2(iWidth) - 1 + g_uiBitDepth - 8
#else
  int shift_1st = g_aucConvertToBit[iWidth]  + 1 + g_uiBitIncrement; // log2(iWidth) - 1 + g_uiBitIncrement
#endif
  int shift_2nd = g_aucConvertToBit[iHeight]  + 8;                   // log2(iHeight) + 6

  short tmp[ 64 * 64 ];

#if !REMOVE_NSQT
  if( iWidth == 16 && iHeight == 4)
  {
    partialButterfly16( block, tmp, shift_1st, iHeight );
    partialButterfly4( tmp, coeff, shift_2nd, iWidth );
  }
  else if( iWidth == 32 && iHeight == 8 )
  {
    partialButterfly32( block, tmp, shift_1st, iHeight );
    partialButterfly8( tmp, coeff, shift_2nd, iWidth );
  }
  else if( iWidth == 4 && iHeight == 16)
  {
    partialButterfly4( block, tmp, shift_1st, iHeight );
    partialButterfly16( tmp, coeff, shift_2nd, iWidth );
  }
  else if( iWidth == 8 && iHeight == 32 )
  {
    partialButterfly8( block, tmp, shift_1st, iHeight );
    partialButterfly32( tmp, coeff, shift_2nd, iWidth );
  }
  else
#endif
  if( iWidth == 4 && iHeight == 4)
  {
#if INTRA_TRANS_SIMP
    if (uiMode != REG_DCT)
    {
      fastForwardDst(block,tmp,shift_1st); // Forward DST BY FAST ALGORITHM, block input, tmp output
      fastForwardDst(tmp,coeff,shift_2nd); // Forward DST BY FAST ALGORITHM, tmp input, coeff output
    }
    else
    {
      partialButterfly4(block, tmp, shift_1st, iHeight);
      partialButterfly4(tmp, coeff, shift_2nd, iWidth);
    }

#else
    if (uiMode != REG_DCT && (!uiMode || (uiMode>=2 && uiMode <= 25)))    // Check for DCT or DST
    {
      fastForwardDst(block,tmp,shift_1st); // Forward DST BY FAST ALGORITHM, block input, tmp output
    }
    else
    {
      partialButterfly4(block, tmp, shift_1st, iHeight);
    }
    if (uiMode != REG_DCT && (!uiMode || (uiMode>=11 && uiMode <= 34)))    // Check for DCT or DST
    {
      fastForwardDst(tmp,coeff,shift_2nd); // Forward DST BY FAST ALGORITHM, tmp input, coeff output
    }
    else
    {
      partialButterfly4(tmp, coeff, shift_2nd, iWidth);
    }
#endif
  }
  else if( iWidth == 8 && iHeight == 8)
  {
    partialButterfly8( block, tmp, shift_1st, iHeight );
    partialButterfly8( tmp, coeff, shift_2nd, iWidth );
  }
  else if( iWidth == 16 && iHeight == 16)
  {
    partialButterfly16( block, tmp, shift_1st, iHeight );
    partialButterfly16( tmp, coeff, shift_2nd, iWidth );
  }
  else if( iWidth == 32 && iHeight == 32)
  {
    partialButterfly32( block, tmp, shift_1st, iHeight );
    partialButterfly32( tmp, coeff, shift_2nd, iWidth );
  }
}

到了這裏，相信大家光看名字也能看出這些代碼是做什麼事情的了，對幀內預測模式的4x4塊進行DST變換，其餘的根據塊大小分別做蝶形快速變換（4x4，8x8，16x16，32x32），不同尺寸的變換矩陣在代碼中如下表示：

const short g_aiT4[4][4] =
{
  { 64, 64, 64, 64},
  { 83, 36,-36,-83},
  { 64,-64,-64, 64},
  { 36,-83, 83,-36}
};

const short g_aiT8[8][8] =
{
  { 64, 64, 64, 64, 64, 64, 64, 64},
  { 89, 75, 50, 18,-18,-50,-75,-89},
  { 83, 36,-36,-83,-83,-36, 36, 83},
  { 75,-18,-89,-50, 50, 89, 18,-75},
  { 64,-64,-64, 64, 64,-64,-64, 64},
  { 50,-89, 18, 75,-75,-18, 89,-50},
  { 36,-83, 83,-36,-36, 83,-83, 36},
  { 18,-50, 75,-89, 89,-75, 50,-18}
};

const short g_aiT16[16][16] =
{
  { 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64},
  { 90, 87, 80, 70, 57, 43, 25,  9, -9,-25,-43,-57,-70,-80,-87,-90},
  { 89, 75, 50, 18,-18,-50,-75,-89,-89,-75,-50,-18, 18, 50, 75, 89},
  { 87, 57,  9,-43,-80,-90,-70,-25, 25, 70, 90, 80, 43, -9,-57,-87},
  { 83, 36,-36,-83,-83,-36, 36, 83, 83, 36,-36,-83,-83,-36, 36, 83},
  { 80,  9,-70,-87,-25, 57, 90, 43,-43,-90,-57, 25, 87, 70, -9,-80},
  { 75,-18,-89,-50, 50, 89, 18,-75,-75, 18, 89, 50,-50,-89,-18, 75},
  { 70,-43,-87,  9, 90, 25,-80,-57, 57, 80,-25,-90, -9, 87, 43,-70},
  { 64,-64,-64, 64, 64,-64,-64, 64, 64,-64,-64, 64, 64,-64,-64, 64},
  { 57,-80,-25, 90, -9,-87, 43, 70,-70,-43, 87,  9,-90, 25, 80,-57},
  { 50,-89, 18, 75,-75,-18, 89,-50,-50, 89,-18,-75, 75, 18,-89, 50},
  { 43,-90, 57, 25,-87, 70,  9,-80, 80, -9,-70, 87,-25,-57, 90,-43},
  { 36,-83, 83,-36,-36, 83,-83, 36, 36,-83, 83,-36,-36, 83,-83, 36},
  { 25,-70, 90,-80, 43,  9,-57, 87,-87, 57, -9,-43, 80,-90, 70,-25},
  { 18,-50, 75,-89, 89,-75, 50,-18,-18, 50,-75, 89,-89, 75,-50, 18},
  {  9,-25, 43,-57, 70,-80, 87,-90, 90,-87, 80,-70, 57,-43, 25, -9}
};

const short g_aiT32[32][32] =
{
  { 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64},
  { 90, 90, 88, 85, 82, 78, 73, 67, 61, 54, 46, 38, 31, 22, 13,  4, -4,-13,-22,-31,-38,-46,-54,-61,-67,-73,-78,-82,-85,-88,-90,-90},
  { 90, 87, 80, 70, 57, 43, 25,  9, -9,-25,-43,-57,-70,-80,-87,-90,-90,-87,-80,-70,-57,-43,-25, -9,  9, 25, 43, 57, 70, 80, 87, 90},
  { 90, 82, 67, 46, 22, -4,-31,-54,-73,-85,-90,-88,-78,-61,-38,-13, 13, 38, 61, 78, 88, 90, 85, 73, 54, 31,  4,-22,-46,-67,-82,-90},
  { 89, 75, 50, 18,-18,-50,-75,-89,-89,-75,-50,-18, 18, 50, 75, 89, 89, 75, 50, 18,-18,-50,-75,-89,-89,-75,-50,-18, 18, 50, 75, 89},
  { 88, 67, 31,-13,-54,-82,-90,-78,-46, -4, 38, 73, 90, 85, 61, 22,-22,-61,-85,-90,-73,-38,  4, 46, 78, 90, 82, 54, 13,-31,-67,-88},
  { 87, 57,  9,-43,-80,-90,-70,-25, 25, 70, 90, 80, 43, -9,-57,-87,-87,-57, -9, 43, 80, 90, 70, 25,-25,-70,-90,-80,-43,  9, 57, 87},
  { 85, 46,-13,-67,-90,-73,-22, 38, 82, 88, 54, -4,-61,-90,-78,-31, 31, 78, 90, 61,  4,-54,-88,-82,-38, 22, 73, 90, 67, 13,-46,-85},
  { 83, 36,-36,-83,-83,-36, 36, 83, 83, 36,-36,-83,-83,-36, 36, 83, 83, 36,-36,-83,-83,-36, 36, 83, 83, 36,-36,-83,-83,-36, 36, 83},
  { 82, 22,-54,-90,-61, 13, 78, 85, 31,-46,-90,-67,  4, 73, 88, 38,-38,-88,-73, -4, 67, 90, 46,-31,-85,-78,-13, 61, 90, 54,-22,-82},
  { 80,  9,-70,-87,-25, 57, 90, 43,-43,-90,-57, 25, 87, 70, -9,-80,-80, -9, 70, 87, 25,-57,-90,-43, 43, 90, 57,-25,-87,-70,  9, 80},
  { 78, -4,-82,-73, 13, 85, 67,-22,-88,-61, 31, 90, 54,-38,-90,-46, 46, 90, 38,-54,-90,-31, 61, 88, 22,-67,-85,-13, 73, 82,  4,-78},
  { 75,-18,-89,-50, 50, 89, 18,-75,-75, 18, 89, 50,-50,-89,-18, 75, 75,-18,-89,-50, 50, 89, 18,-75,-75, 18, 89, 50,-50,-89,-18, 75},
  { 73,-31,-90,-22, 78, 67,-38,-90,-13, 82, 61,-46,-88, -4, 85, 54,-54,-85,  4, 88, 46,-61,-82, 13, 90, 38,-67,-78, 22, 90, 31,-73},
  { 70,-43,-87,  9, 90, 25,-80,-57, 57, 80,-25,-90, -9, 87, 43,-70,-70, 43, 87, -9,-90,-25, 80, 57,-57,-80, 25, 90,  9,-87,-43, 70},
  { 67,-54,-78, 38, 85,-22,-90,  4, 90, 13,-88,-31, 82, 46,-73,-61, 61, 73,-46,-82, 31, 88,-13,-90, -4, 90, 22,-85,-38, 78, 54,-67},
  { 64,-64,-64, 64, 64,-64,-64, 64, 64,-64,-64, 64, 64,-64,-64, 64, 64,-64,-64, 64, 64,-64,-64, 64, 64,-64,-64, 64, 64,-64,-64, 64},
  { 61,-73,-46, 82, 31,-88,-13, 90, -4,-90, 22, 85,-38,-78, 54, 67,-67,-54, 78, 38,-85,-22, 90,  4,-90, 13, 88,-31,-82, 46, 73,-61},
  { 57,-80,-25, 90, -9,-87, 43, 70,-70,-43, 87,  9,-90, 25, 80,-57,-57, 80, 25,-90,  9, 87,-43,-70, 70, 43,-87, -9, 90,-25,-80, 57},
  { 54,-85, -4, 88,-46,-61, 82, 13,-90, 38, 67,-78,-22, 90,-31,-73, 73, 31,-90, 22, 78,-67,-38, 90,-13,-82, 61, 46,-88,  4, 85,-54},
  { 50,-89, 18, 75,-75,-18, 89,-50,-50, 89,-18,-75, 75, 18,-89, 50, 50,-89, 18, 75,-75,-18, 89,-50,-50, 89,-18,-75, 75, 18,-89, 50},
  { 46,-90, 38, 54,-90, 31, 61,-88, 22, 67,-85, 13, 73,-82,  4, 78,-78, -4, 82,-73,-13, 85,-67,-22, 88,-61,-31, 90,-54,-38, 90,-46},
  { 43,-90, 57, 25,-87, 70,  9,-80, 80, -9,-70, 87,-25,-57, 90,-43,-43, 90,-57,-25, 87,-70, -9, 80,-80,  9, 70,-87, 25, 57,-90, 43},
  { 38,-88, 73, -4,-67, 90,-46,-31, 85,-78, 13, 61,-90, 54, 22,-82, 82,-22,-54, 90,-61,-13, 78,-85, 31, 46,-90, 67,  4,-73, 88,-38},
  { 36,-83, 83,-36,-36, 83,-83, 36, 36,-83, 83,-36,-36, 83,-83, 36, 36,-83, 83,-36,-36, 83,-83, 36, 36,-83, 83,-36,-36, 83,-83, 36},
  { 31,-78, 90,-61,  4, 54,-88, 82,-38,-22, 73,-90, 67,-13,-46, 85,-85, 46, 13,-67, 90,-73, 22, 38,-82, 88,-54, -4, 61,-90, 78,-31},
  { 25,-70, 90,-80, 43,  9,-57, 87,-87, 57, -9,-43, 80,-90, 70,-25,-25, 70,-90, 80,-43, -9, 57,-87, 87,-57,  9, 43,-80, 90,-70, 25},
  { 22,-61, 85,-90, 73,-38, -4, 46,-78, 90,-82, 54,-13,-31, 67,-88, 88,-67, 31, 13,-54, 82,-90, 78,-46,  4, 38,-73, 90,-85, 61,-22},
  { 18,-50, 75,-89, 89,-75, 50,-18,-18, 50,-75, 89,-89, 75,-50, 18, 18,-50, 75,-89, 89,-75, 50,-18,-18, 50,-75, 89,-89, 75,-50, 18},
  { 13,-38, 61,-78, 88,-90, 85,-73, 54,-31,  4, 22,-46, 67,-82, 90,-90, 82,-67, 46,-22, -4, 31,-54, 73,-85, 90,-88, 78,-61, 38,-13},
  {  9,-25, 43,-57, 70,-80, 87,-90, 90,-87, 80,-70, 57,-43, 25, -9, -9, 25,-43, 57,-70, 80,-87, 90,-90, 87,-80, 70,-57, 43,-25,  9},
  {  4,-13, 22,-31, 38,-46, 54,-61, 67,-73, 78,-82, 85,-88, 90,-90, 90,-90, 88,-85, 82,-78, 73,-67, 61,-54, 46,-38, 31,-22, 13, -4}
};