【VTM10.0】反量化之RDOQ、一般量化

RDOQ与一般量化的过程虽然不同，但是解码的步骤时在相同的，如下：

解码都调用的dequant函数：
该函数主要完成写下面的公式，进行反量化。

void Quant::dequant(const TransformUnit &tu,
                             CoeffBuf      &dstCoeff,
                       const ComponentID   &compID,
                       const QpParam       &cQP)
{
  const SPS            *sps                = tu.cs->sps;
  const CompArea       &area               = tu.blocks[compID];
  const uint32_t            uiWidth            = area.width;
  const uint32_t            uiHeight           = area.height;
        TCoeff   *const piCoef             = dstCoeff.buf;
  const uint32_t            numSamplesInBlock  = uiWidth * uiHeight;
  const int             maxLog2TrDynamicRange = sps->getMaxLog2TrDynamicRange(toChannelType(compID));
  const TCoeff          transformMinimum   = -(1 << maxLog2TrDynamicRange);
  const TCoeff          transformMaximum   =  (1 << maxLog2TrDynamicRange) - 1;
  const bool            isTransformSkip = (tu.mtsIdx[compID] == MTS_SKIP);

  const bool            disableSMForLFNST = tu.cs->slice->getExplicitScalingListUsed() ? tu.cs->slice->getSPS()->getDisableScalingMatrixForLfnstBlks() : false;
  const bool            isLfnstApplied = tu.cu->lfnstIdx > 0 && (tu.cu->isSepTree() ? true : isLuma(compID));
  const bool            disableSMForACT = tu.cs->slice->getSPS()->getScalingMatrixForAlternativeColourSpaceDisabledFlag() && (tu.cs->slice->getSPS()->getScalingMatrixDesignatedColourSpaceFlag() == tu.cu->colorTransform);
  const bool            enableScalingLists = getUseScalingList(uiWidth, uiHeight, isTransformSkip, isLfnstApplied, disableSMForLFNST, disableSMForACT);
  const int             scalingListType    = getScalingListType(tu.cu->predMode, compID);
  const int             channelBitDepth    = sps->getBitDepth(toChannelType(compID));

  const TCoeff          *coef;
  if ((tu.cu->bdpcmMode && isLuma(compID)) || ( tu.cu->bdpcmModeChroma && isChroma(compID) ))
  {
    invResDPCM( tu, compID, dstCoeff );
    coef = piCoef;
  }
  else
  {
    coef = tu.getCoeffs(compID).buf;
  }
  const TCoeff          *const piQCoef = coef;
  CHECK(scalingListType >= SCALING_LIST_NUM, "Invalid scaling list");
  CHECK(uiWidth > m_uiMaxTrSize, "Unsupported transformation size");

  // Represents scaling through forward transform
  const bool bClipTransformShiftTo0 = tu.mtsIdx[compID] != MTS_SKIP && sps->getSpsRangeExtension().getExtendedPrecisionProcessingFlag();
  const int  originalTransformShift = getTransformShift(channelBitDepth, area.size(), maxLog2TrDynamicRange);
  const bool needSqrtAdjustment     = TU::needsBlockSizeTrafoScale( tu, compID );
  const int  iTransformShift        = (bClipTransformShiftTo0 ? std::max<int>(0, originalTransformShift) : originalTransformShift) + (needSqrtAdjustment?-1:0);

  const int QP_per = cQP.per(isTransformSkip);//  QP/6
  const int QP_rem = cQP.rem(isTransformSkip);//  QP%6

  const int  rightShift = (IQUANT_SHIFT - ((isTransformSkip ? 0 : iTransformShift) + QP_per)) + (enableScalingLists ? LOG2_SCALING_LIST_NEUTRAL_VALUE : 0);

  if(enableScalingLists)//是否使用量化矩阵
  {
    //from the dequantization equation:
    //iCoeffQ                         = ((Intermediate_Int(clipQCoef) * piDequantCoef[deQuantIdx]) + iAdd ) >> rightShift
    //(sizeof(Intermediate_Int) * 8)  =              inputBitDepth    +    dequantCoefBits                   - rightShift
    const uint32_t             dequantCoefBits     = 1 + IQUANT_SHIFT + SCALING_LIST_BITS;
    const uint32_t             targetInputBitDepth = std::min<uint32_t>((maxLog2TrDynamicRange + 1), (((sizeof(Intermediate_Int) * 8) + rightShift) - dequantCoefBits));

    const Intermediate_Int inputMinimum        = -(1 << (targetInputBitDepth - 1));
    const Intermediate_Int inputMaximum        =  (1 << (targetInputBitDepth - 1)) - 1;

    const uint32_t uiLog2TrWidth  = floorLog2(uiWidth);
    const uint32_t uiLog2TrHeight = floorLog2(uiHeight);
    int *piDequantCoef        = getDequantCoeff(scalingListType, QP_rem, uiLog2TrWidth, uiLog2TrHeight);

    if(rightShift > 0)
    {
      const Intermediate_Int iAdd = (Intermediate_Int) 1 << (rightShift - 1);

      for( int n = 0; n < numSamplesInBlock; n++ )
      {
        const TCoeff           clipQCoef = TCoeff(Clip3<Intermediate_Int>(inputMinimum, inputMaximum, piQCoef[n]));
        const Intermediate_Int iCoeffQ   = ((Intermediate_Int(clipQCoef) * piDequantCoef[n]) + iAdd ) >> rightShift;

        piCoef[n] = TCoeff(Clip3<Intermediate_Int>(transformMinimum,transformMaximum,iCoeffQ));
      }
    }
    else
    {
      const int leftShift = -rightShift;

      for( int n = 0; n < numSamplesInBlock; n++ )
      {
        const TCoeff           clipQCoef = TCoeff(Clip3<Intermediate_Int>(inputMinimum, inputMaximum, piQCoef[n]));
        const Intermediate_Int iCoeffQ   = (Intermediate_Int(clipQCoef) * piDequantCoef[n]) << leftShift;

        piCoef[n] = TCoeff(Clip3<Intermediate_Int>(transformMinimum,transformMaximum,iCoeffQ));
      }
    }
  }
  else//不使用量化矩阵
  {
    const int scale     = g_invQuantScales[needSqrtAdjustment?1:0][QP_rem];
    const int scaleBits = ( IQUANT_SHIFT + 1 );

    //from the dequantisation equation:
    //iCoeffQ                         = Intermediate_Int((int64_t(clipQCoef) * scale + iAdd) >> rightShift);
    //(sizeof(Intermediate_Int) * 8)  =                    inputBitDepth   + scaleBits      - rightShift
    const uint32_t             targetInputBitDepth = std::min<uint32_t>((maxLog2TrDynamicRange + 1), (((sizeof(Intermediate_Int) * 8) + rightShift) - scaleBits));
    const Intermediate_Int inputMinimum        = -(1 << (targetInputBitDepth - 1));
    const Intermediate_Int inputMaximum        =  (1 << (targetInputBitDepth - 1)) - 1;

    if (rightShift > 0)//如果右移位数大于0
    {
      const Intermediate_Int iAdd = (Intermediate_Int) 1 << (rightShift - 1);

      for( int n = 0; n < numSamplesInBlock; n++ )
      {
        const TCoeff           clipQCoef = TCoeff(Clip3<Intermediate_Int>(inputMinimum, inputMaximum, piQCoef[n]));
        const Intermediate_Int iCoeffQ   = (Intermediate_Int(clipQCoef) * scale + iAdd) >> rightShift;

        piCoef[n] = TCoeff(Clip3<Intermediate_Int>(transformMinimum,transformMaximum,iCoeffQ));
      }
    }
    else//如果是不移或者左移（其实与右移相似，只是左移不用再进行四舍五入了）
    {
      const int leftShift = -rightShift;

      for( int n = 0; n < numSamplesInBlock; n++ )
      {
        const TCoeff           clipQCoef = TCoeff(Clip3<Intermediate_Int>(inputMinimum, inputMaximum, piQCoef[n]));
        const Intermediate_Int iCoeffQ   = (Intermediate_Int(clipQCoef) * scale) << leftShift;

        piCoef[n] = TCoeff(Clip3<Intermediate_Int>(transformMinimum,transformMaximum,iCoeffQ));
      }
    }
  }
}