【HEVC学习与研究】32、编码一个CU（帧内部分）1
在一个compressSlice()中，在compressCU函数中实现对一个CU的编码，其中主要进行了CU的初始化，以及实际的编码操作。
Void TEncCu::compressCU( TComDataCU*& rpcCU )
{
// initialize CU data
m_ppcBestCU[0]->initCU( rpcCU->getPic(), rpcCU->getAddr() );
m_ppcTempCU[0]->initCU( rpcCU->getPic(), rpcCU->getAddr() );
#if RATE_CONTROL_LAMBDA_DOMAIN
m_addSADDepth = 0;
m_LCUPredictionSAD = 0;
m_temporalSAD = 0;
#endif
// analysis of CU
xCompressCU( m_ppcBestCU[0], m_ppcTempCU[0], 0 );
#if ADAPTIVE_QP_SELECTION
if( m_pcEncCfg->getUseAdaptQpSelect() )
{
if(rpcCU->getSlice()->getSliceType()!=I_SLICE) //IIII
{
xLcuCollectARLStats( rpcCU);
}
}
#endif
}其中完成实际编码一个CU操作的是xCompressCU方法。前面的综述中已经描述过，每一个CTU按照四叉树结构进行划分，CompressCU中调用的
xCompressCU则相当于四叉树的根节点。另外，在每一个xCompressCU方法中间，会对每一个CU进行分析判断是否进行下一级划分。
xCompressCU函数由于包含了Intra和InterFrame编码的代码，因此同样非常长，共有600余行。下面着重对帧内编码的部分做一下梳理。
实现帧内编码的部分代码如下：
Void TEncCu::xCompressCU( TComDataCU*& rpcBestCU, TComDataCU*& rpcTempCU, UInt uiDepth, PartSize eParentPartSize )
{
//......
// do normal intra modes
if ( !bEarlySkip )
{
// speedup for inter frames
if( rpcBestCU->getSlice()->getSliceType() == I_SLICE ||
rpcBestCU->getCbf( 0, TEXT_LUMA ) != 0 ||
rpcBestCU->getCbf( 0, TEXT_CHROMA_U ) != 0 ||
rpcBestCU->getCbf( 0, TEXT_CHROMA_V ) != 0 ) // avoid very complex intra if it is unlikely
{
xCheckRDCostIntra( rpcBestCU, rpcTempCU, SIZE_2Nx2N );
rpcTempCU->initEstData( uiDepth, iQP );
if( uiDepth == g_uiMaxCUDepth - g_uiAddCUDepth )
{
if( rpcTempCU->getWidth(0) > ( 1 << rpcTempCU->getSlice()->getSPS()->getQuadtreeTULog2MinSize() ) )
{
xCheckRDCostIntra( rpcBestCU, rpcTempCU, SIZE_NxN );
rpcTempCU->initEstData( uiDepth, iQP );
}
}
}
}
//......
}在这部分代码中xCheckRDCostIntra( rpcBestCU, rpcTempCU, SIZE_2Nx2N )查看了各种intra预测模式下的代价：
Void TEncCu::xCheckRDCostIntra( TComDataCU*& rpcBestCU, TComDataCU*& rpcTempCU, PartSize eSize )
{
UInt uiDepth = rpcTempCU->getDepth( 0 );
rpcTempCU->setSkipFlagSubParts( false, 0, uiDepth );
rpcTempCU->setPartSizeSubParts( eSize, 0, uiDepth );
rpcTempCU->setPredModeSubParts( MODE_INTRA, 0, uiDepth );
rpcTempCU->setCUTransquantBypassSubParts( m_pcEncCfg->getCUTransquantBypassFlagValue(), 0, uiDepth );
Bool bSeparateLumaChroma = true; // choose estimation mode
UInt uiPreCalcDistC = 0;
if( !bSeparateLumaChroma )
{
m_pcPredSearch->preestChromaPredMode( rpcTempCU, m_ppcOrigYuv[uiDepth], m_ppcPredYuvTemp[uiDepth] );
}
m_pcPredSearch ->estIntraPredQT ( rpcTempCU, m_ppcOrigYuv[uiDepth], m_ppcPredYuvTemp[uiDepth], m_ppcResiYuvTemp[uiDepth], m_ppcRecoYuvTemp[uiDepth], uiPreCalcDistC, bSeparateLumaChroma );
m_ppcRecoYuvTemp[uiDepth]->copyToPicLuma(rpcTempCU->getPic()->getPicYuvRec(), rpcTempCU->getAddr(), rpcTempCU->getZorderIdxInCU() );
m_pcPredSearch ->estIntraPredChromaQT( rpcTempCU, m_ppcOrigYuv[uiDepth], m_ppcPredYuvTemp[uiDepth], m_ppcResiYuvTemp[uiDepth], m_ppcRecoYuvTemp[uiDepth], uiPreCalcDistC );
m_pcEntropyCoder->resetBits();
if ( rpcTempCU->getSlice()->getPPS()->getTransquantBypassEnableFlag())
{
m_pcEntropyCoder->encodeCUTransquantBypassFlag( rpcTempCU, 0, true );
}
m_pcEntropyCoder->encodeSkipFlag ( rpcTempCU, 0, true );
m_pcEntropyCoder->encodePredMode( rpcTempCU, 0, true );
m_pcEntropyCoder->encodePartSize( rpcTempCU, 0, uiDepth, true );
m_pcEntropyCoder->encodePredInfo( rpcTempCU, 0, true );
m_pcEntropyCoder->encodeIPCMInfo(rpcTempCU, 0, true );
// Encode Coefficients
Bool bCodeDQP = getdQPFlag();
m_pcEntropyCoder->encodeCoeff( rpcTempCU, 0, uiDepth, rpcTempCU->getWidth (0), rpcTempCU->getHeight(0), bCodeDQP );
setdQPFlag( bCodeDQP );
if( m_bUseSBACRD ) m_pcRDGoOnSbacCoder->store(m_pppcRDSbacCoder[uiDepth][CI_TEMP_BEST]);
rpcTempCU->getTotalBits() = m_pcEntropyCoder->getNumberOfWrittenBits();
if(m_pcEncCfg->getUseSBACRD())
{
rpcTempCU->getTotalBins() = ((TEncBinCABAC *)((TEncSbac*)m_pcEntropyCoder->m_pcEntropyCoderIf)->getEncBinIf())->getBinsCoded();
}
rpcTempCU->getTotalCost() = m_pcRdCost->calcRdCost( rpcTempCU->getTotalBits(), rpcTempCU->getTotalDistortion() );
xCheckDQP( rpcTempCU );
xCheckBestMode(rpcBestCU, rpcTempCU, uiDepth);
}
在这个函数中，调用了estIntraPredQT和estIntraPredChromaQT方法，这两个函数的作用是类似的，区别只在于前者针对亮度分量后者针对色度分量。我们重点关注对亮度分量的操作，即estIntraPredQT函数。
下面是estIntraPredQT的一段代码：
Void
TEncSearch::estIntraPredQT( TComDataCU* pcCU,
TComYuv* pcOrgYuv,
TComYuv* pcPredYuv,
TComYuv* pcResiYuv,
TComYuv* pcRecoYuv,
UInt& ruiDistC,
Bool bLumaOnly )
{
//......
for( Int modeIdx = 0; modeIdx < numModesAvailable; modeIdx++ )
{
UInt uiMode = modeIdx;
predIntraLumaAng( pcCU->getPattern(), uiMode, piPred, uiStride, uiWidth, uiHeight, bAboveAvail, bLeftAvail );
// use hadamard transform here
UInt uiSad = m_pcRdCost->calcHAD(g_bitDepthY, piOrg, uiStride, piPred, uiStride, uiWidth, uiHeight );
UInt iModeBits = xModeBitsIntra( pcCU, uiMode, uiPU, uiPartOffset, uiDepth, uiInitTrDepth );
Double cost = (Double)uiSad + (Double)iModeBits * m_pcRdCost->getSqrtLambda();
CandNum += xUpdateCandList( uiMode, cost, numModesForFullRD, uiRdModeList, CandCostList );
}
//......
}
这个for循环的意义就是遍历多种帧内预测模式，其中numModesAvailable==35，对应整个intra的35个模式。
在predIntraLumaAng函数中，编码器完成计算出当前PU的预测值：
Void TComPrediction::predIntraLumaAng(TComPattern* pcTComPattern, UInt uiDirMode, Pel* piPred, UInt uiStride, Int iWidth, Int iHeight, Bool bAbove, Bool bLeft )
{
Pel *pDst = piPred;
Int *ptrSrc;
assert( g_aucConvertToBit[ iWidth ] >= 0 ); // 4x 4
assert( g_aucConvertToBit[ iWidth ] <= 5 ); // 128x128
assert( iWidth == iHeight );
ptrSrc = pcTComPattern->getPredictorPtr( uiDirMode, g_aucConvertToBit[ iWidth ] + 2, m_piYuvExt );
// get starting pixel in block
Int sw = 2 * iWidth + 1;
// Create the prediction
if ( uiDirMode == PLANAR_IDX )
{
xPredIntraPlanar( ptrSrc+sw+1, sw, pDst, uiStride, iWidth, iHeight );
}
else
{
if ( (iWidth > 16) || (iHeight > 16) )
{
xPredIntraAng(g_bitDepthY, ptrSrc+sw+1, sw, pDst, uiStride, iWidth, iHeight, uiDirMode, bAbove, bLeft, false );
}
else
{
xPredIntraAng(g_bitDepthY, ptrSrc+sw+1, sw, pDst, uiStride, iWidth, iHeight, uiDirMode, bAbove, bLeft, true );
if( (uiDirMode == DC_IDX ) && bAbove && bLeft )
{
xDCPredFiltering( ptrSrc+sw+1, sw, pDst, uiStride, iWidth, iHeight);
}
}
}
}在这个函数中主要起作用的是xPredIntraPlanar和xPredIntraAng两个函数，另外在PU大小小于16×16，且模式为DC模式时还会调用xDCPredFiltering函数。在这里我们主要关心前面两个。
xPredIntraPlanar的作用是以平面模式构建当前PU的帧内预测块：
Void TComPrediction::xPredIntraPlanar( Int* pSrc, Int srcStride, Pel* rpDst, Int dstStride, UInt width, UInt height )
{
assert(width == height);
Int k, l, bottomLeft, topRight;
Int horPred;
Int leftColumn[MAX_CU_SIZE], topRow[MAX_CU_SIZE], bottomRow[MAX_CU_SIZE], rightColumn[MAX_CU_SIZE];
UInt blkSize = width;
UInt offset2D = width;
UInt shift1D = g_aucConvertToBit[ width ] + 2;
UInt shift2D = shift1D + 1;
// Get left and above reference column and row
for(k=0;k<blkSize+1;k++)
{
topRow[k] = pSrc[k-srcStride];
leftColumn[k] = pSrc[k*srcStride-1];
}
// Prepare intermediate variables used in interpolation
bottomLeft = leftColumn[blkSize];
topRight = topRow[blkSize];
for (k=0;k<blkSize;k++)
{
bottomRow[k] = bottomLeft - topRow[k];
rightColumn[k] = topRight - leftColumn[k];
topRow[k] <<= shift1D;
leftColumn[k] <<= shift1D;
}
// Generate prediction signal
for (k=0;k<blkSize;k++)
{
horPred = leftColumn[k] + offset2D;
for (l=0;l<blkSize;l++)
{
horPred += rightColumn[k];
topRow[l] += bottomRow[l];
rpDst[k*dstStride+l] = ( (horPred + topRow[l]) >> shift2D );
}
}
}而
xPredIntraAng函数则承担了其他模式的预测块构建，也即，不同的模式索引值代表N多中不同的预测角度，从这些角度上以参考数据构建预测块。
Void TComPrediction::xPredIntraAng(Int bitDepth, Int* pSrc, Int srcStride, Pel*& rpDst, Int dstStride, UInt width, UInt height, UInt dirMode, Bool blkAboveAvailable, Bool blkLeftAvailable, Bool bFilter )
{
Int k,l;
Int blkSize = width;
Pel* pDst = rpDst;
// Map the mode index to main prediction direction and angle
assert( dirMode > 0 ); //no planar
Bool modeDC = dirMode < 2;
Bool modeHor = !modeDC && (dirMode < 18);
Bool modeVer = !modeDC && !modeHor;
Int intraPredAngle = modeVer ? (Int)dirMode - VER_IDX : modeHor ? -((Int)dirMode - HOR_IDX) : 0;
Int absAng = abs(intraPredAngle);
Int signAng = intraPredAngle < 0 ? -1 : 1;
// Set bitshifts and scale the angle parameter to block size
Int angTable[9] = {0, 2, 5, 9, 13, 17, 21, 26, 32};
Int invAngTable[9] = {0, 4096, 1638, 910, 630, 482, 390, 315, 256}; // (256 * 32) / Angle
Int invAngle = invAngTable[absAng];
absAng = angTable[absAng];
intraPredAngle = signAng * absAng;
// Do the DC prediction
if (modeDC)
{
Pel dcval = predIntraGetPredValDC(pSrc, srcStride, width, height, blkAboveAvailable, blkLeftAvailable);
for (k=0;k<blkSize;k++)
{
for (l=0;l<blkSize;l++)
{
pDst[k*dstStride+l] = dcval;
}
}
}
// Do angular predictions
else
{
Pel* refMain;
Pel* refSide;
Pel refAbove[2*MAX_CU_SIZE+1];
Pel refLeft[2*MAX_CU_SIZE+1];
// Initialise the Main and Left reference array.
if (intraPredAngle < 0)
{
for (k=0;k<blkSize+1;k++)
{
refAbove[k+blkSize-1] = pSrc[k-srcStride-1];
}
for (k=0;k<blkSize+1;k++)
{
refLeft[k+blkSize-1] = pSrc[(k-1)*srcStride-1];
}
refMain = (modeVer ? refAbove : refLeft) + (blkSize-1);
refSide = (modeVer ? refLeft : refAbove) + (blkSize-1);
// Extend the Main reference to the left.
Int invAngleSum = 128; // rounding for (shift by 8)
for (k=-1; k>blkSize*intraPredAngle>>5; k--)
{
invAngleSum += invAngle;
refMain[k] = refSide[invAngleSum>>8];
}
}
else
{
for (k=0;k<2*blkSize+1;k++)
{
refAbove[k] = pSrc[k-srcStride-1];
}
for (k=0;k<2*blkSize+1;k++)
{
refLeft[k] = pSrc[(k-1)*srcStride-1];
}
refMain = modeVer ? refAbove : refLeft;
refSide = modeVer ? refLeft : refAbove;
}
if (intraPredAngle == 0)
{
for (k=0;k<blkSize;k++)
{
for (l=0;l<blkSize;l++)
{
pDst[k*dstStride+l] = refMain[l+1];
}
}
if ( bFilter )
{
for (k=0;k<blkSize;k++)
{
pDst[k*dstStride] = Clip3(0, (1<<bitDepth)-1, pDst[k*dstStride] + (( refSide[k+1] - refSide[0] ) >> 1) );
}
}
}
else
{
Int deltaPos=0;
Int deltaInt;
Int deltaFract;
Int refMainIndex;
for (k=0;k<blkSize;k++)
{
deltaPos += intraPredAngle;
deltaInt = deltaPos >> 5;
deltaFract = deltaPos & (32 - 1);
if (deltaFract)
{
// Do linear filtering
for (l=0;l<blkSize;l++)
{
refMainIndex = l+deltaInt+1;
pDst[k*dstStride+l] = (Pel) ( ((32-deltaFract)*refMain[refMainIndex]+deltaFract*refMain[refMainIndex+1]+16) >> 5 );
}
}
else
{
// Just copy the integer samples
for (l=0;l<blkSize;l++)
{
pDst[k*dstStride+l] = refMain[l+deltaInt+1];
}
}
}
}
// Flip the block if this is the horizontal mode
if (modeHor)
{
Pel tmp;
for (k=0;k<blkSize-1;k++)
{
for (l=k+1;l<blkSize;l++)
{
tmp = pDst[k*dstStride+l];
pDst[k*dstStride+l] = pDst[l*dstStride+k];
pDst[l*dstStride+k] = tmp;
}
}
}
}
}具体的预测块构建的原理，将在下篇文章中详述。