之前VTM3.0色度幀內預測跟進中學習了VTM3.0的色度幀內預測過程，今天來看下具體函數estIntraPredChromaQT。
VTM3.0色度幀內預測分成兩個階段：
1.粗選：按DC、Ver、Hor、LM_L、LM_T進行預測，按SATD排序，去掉兩個SATD最大的模式。
2.細選：粗選剩下三個模式和Planar、LM、DM（共六種）進行RD檢測選最優。其中當DM借用的亮度角度模式與前四種模式相同時，會將與DM重複的模式換爲角度66模式。
其中調用的重要函數有：getIntraChromaCandModes（獲取色度幀內候選），xGetLumaRecPixels（獲取亮度重構像素值，填充LM預測的參考像素），predIntraChromaLM（色度LM預測），predIntraAng（角度預測）。
色度候選列表如下：
modeList[ 0 ] = PLANAR_IDX;
modeList[ 1 ] = VER_IDX;
modeList[ 2 ] = HOR_IDX;
modeList[ 3 ] = DC_IDX;
modeList[4] = LM_CHROMA_IDX;
modeList[5] = MDLM_L_IDX;
modeList[6] = MDLM_T_IDX;
modeList[7] = DM_CHROMA_IDX;
//其中當DM借用的亮度角度模式與前四種模式相同時，會與DM重複的模式換爲角度66模式。
代碼分析：
void IntraSearch::estIntraPredChromaQT(CodingUnit &cu, Partitioner &partitioner)
{
const ChromaFormat format = cu.chromaFormat;
const uint32_t numberValidComponents = getNumberValidComponents(format);
CodingStructure &cs = *cu.cs;
const TempCtx ctxStart ( m_CtxCache, m_CABACEstimator->getCtx() );
cs.setDecomp( cs.area.Cb(), false );
auto &pu = *cu.firstPU;
{
uint32_t uiBestMode = 0;
Distortion uiBestDist = 0;
double dBestCost = MAX_DOUBLE;
//----- init mode list ----
{
uint32_t uiMinMode = 0;
uint32_t uiMaxMode = NUM_CHROMA_MODE;
//----- check chroma modes -----
uint32_t chromaCandModes[ NUM_CHROMA_MODE ];
PU::getIntraChromaCandModes( pu, chromaCandModes ); //獲取色度候選模式
// create a temporary CS
CodingStructure &saveCS = *m_pSaveCS[0];
saveCS.pcv = cs.pcv;
saveCS.picture = cs.picture;
saveCS.area.repositionTo( cs.area );
saveCS.clearTUs();
if( CS::isDualITree( cs ) )
{
if( partitioner.canSplit( TU_MAX_TR_SPLIT, cs ) )
{
partitioner.splitCurrArea( TU_MAX_TR_SPLIT, cs );
do
{
cs.addTU( CS::getArea( cs, partitioner.currArea(), partitioner.chType ), partitioner.chType ).depth = partitioner.currTrDepth;
} while( partitioner.nextPart( cs ) );
partitioner.exitCurrSplit();
}
else
cs.addTU( CS::getArea( cs, partitioner.currArea(), partitioner.chType ), partitioner.chType );
}
std::vector<TransformUnit*> orgTUs;
// create a store for the TUs
for( const auto &ptu : cs.tus )
{
// for split TUs in HEVC, add the TUs without Chroma parts for correct setting of Cbfs
if( pu.contains( *ptu, CHANNEL_TYPE_CHROMA ) || ( !cs.pcv->noRQT && !ptu->Cb().valid() && !ptu->Cr().valid() ) )
{
saveCS.addTU( *ptu, partitioner.chType );
orgTUs.push_back( ptu );
}
}
#if JVET_L0338_MDLM
// SATD pre-selecting.
int satdModeList[NUM_CHROMA_MODE];
int64_t satdSortedCost[NUM_CHROMA_MODE];
for (int i = 0; i < NUM_CHROMA_MODE; i++)
{
satdSortedCost[i] = 0; // for the mode not pre-select by SATD, do RDO by default, so set the initial value 0.
satdModeList[i] = 0;
}
bool modeIsEnable[NUM_INTRA_MODE + 1]; // use intra mode idx to check whether enable
for (int i = 0; i < NUM_INTRA_MODE + 1; i++)
{
modeIsEnable[i] = 1;
}
DistParam distParam;
const bool useHadamard = true;
pu.intraDir[1] = MDLM_L_IDX; // temporary assigned, just to indicate this is a MDLM mode. for luma down-sampling operation.
initIntraPatternChType(cu, pu.Cb());
initIntraPatternChType(cu, pu.Cr());
xGetLumaRecPixels(pu, pu.Cb()); //獲取亮度重構值，填充參考像素
/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
/////////////////////粗選階段：按DC、Ver、Hor、LM_L、LM_T進行預測，按SATD排序，去掉兩個SATD最大的模式。
for (int idx = uiMinMode; idx <= uiMaxMode - 1; idx++)
{
int mode = chromaCandModes[idx];
satdModeList[idx] = mode;
if (PU::isLMCMode(mode) && !PU::isLMCModeEnabled(pu, mode))
{
continue;
}
if ((mode == LM_CHROMA_IDX) || (mode == PLANAR_IDX) || (mode == DM_CHROMA_IDX)) // only pre-check regular modes and MDLM modes, not including DM ,Planar, and LM
{
continue;
}
pu.intraDir[1] = mode; // temporary assigned, for SATD checking.
int64_t sad = 0;
CodingStructure& cs = *(pu.cs);
CompArea areaCb = pu.Cb();
PelBuf orgCb = cs.getOrgBuf(areaCb);
PelBuf predCb = cs.getPredBuf(areaCb);
m_pcRdCost->setDistParam(distParam, orgCb, predCb, pu.cs->sps->getBitDepth(CHANNEL_TYPE_CHROMA), COMPONENT_Cb, useHadamard);
distParam.applyWeight = false;
if (PU::isLMCMode(mode))
{
predIntraChromaLM(COMPONENT_Cb, predCb, pu, areaCb, mode);
}
else
{
predIntraAng(COMPONENT_Cb, predCb, pu, false);
}
sad += distParam.distFunc(distParam);
CompArea areaCr = pu.Cr();
PelBuf orgCr = cs.getOrgBuf(areaCr);
PelBuf predCr = cs.getPredBuf(areaCr);
m_pcRdCost->setDistParam(distParam, orgCr, predCr, pu.cs->sps->getBitDepth(CHANNEL_TYPE_CHROMA), COMPONENT_Cr, useHadamard);
distParam.applyWeight = false;
if (PU::isLMCMode(mode))
{
predIntraChromaLM(COMPONENT_Cr, predCr, pu, areaCr, mode); //LM預測
}
else
{
predIntraAng(COMPONENT_Cr, predCr, pu, false); //角度預測
}
sad += distParam.distFunc(distParam);
satdSortedCost[idx] = sad;
}
// sort the mode based on the cost from small to large.
int tempIdx = 0;
int64_t tempCost = 0;
for (int i = uiMinMode; i <= uiMaxMode - 1; i++) //按SATD排序
{
for (int j = i + 1; j <= uiMaxMode - 1; j++)
{
if (satdSortedCost[j] < satdSortedCost[i])
{
tempIdx = satdModeList[i];
satdModeList[i] = satdModeList[j];
satdModeList[j] = tempIdx;
tempCost = satdSortedCost[i];
satdSortedCost[i] = satdSortedCost[j];
satdSortedCost[j] = tempCost;
}
}
}
int reducedModeNumber = 2; // reduce the number of chroma modes
for (int i = 0; i < reducedModeNumber; i++) //刪除兩個SATD大的
{
modeIsEnable[satdModeList[uiMaxMode - 1 - i]] = 0; // disable the last reducedModeNumber modes
}
#endif
// save the dist
Distortion baseDist = cs.dist;
/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
/////////////////////細選階段：粗選剩下三個模式和Planar、LM、DM（共六種）進行RD檢測選最優。其中當DM借用的亮度角度模式與前四種模式相同時，會將DM換爲角度66模式。
for (uint32_t uiMode = uiMinMode; uiMode < uiMaxMode; uiMode++)
{
const int chromaIntraMode = chromaCandModes[uiMode];
if( PU::isLMCMode( chromaIntraMode ) && ! PU::isLMCModeEnabled( pu, chromaIntraMode ) )
{
continue;
}
#if JVET_L0338_MDLM
if (!modeIsEnable[chromaIntraMode] && PU::isLMCModeEnabled(pu, chromaIntraMode)) // when CCLM is disable, then MDLM is disable. not use satd checking
{
continue;
}
#endif
cs.setDecomp( pu.Cb(), false );
cs.dist = baseDist;
//----- restore context models -----
m_CABACEstimator->getCtx() = ctxStart;
//----- chroma coding -----
pu.intraDir[1] = chromaIntraMode;
xRecurIntraChromaCodingQT( cs, partitioner ); //重構色度
if (cs.pps->getUseTransformSkip())
{
m_CABACEstimator->getCtx() = ctxStart;
}
uint64_t fracBits = xGetIntraFracBitsQT( cs, partitioner, false, true );
Distortion uiDist = cs.dist;
double dCost = m_pcRdCost->calcRdCost( fracBits, uiDist - baseDist );
//----- compare -----
if( dCost < dBestCost ) //和最優模式比較
{
for( uint32_t i = getFirstComponentOfChannel( CHANNEL_TYPE_CHROMA ); i < numberValidComponents; i++ )
{
const CompArea &area = pu.blocks[i];
saveCS.getRecoBuf ( area ).copyFrom( cs.getRecoBuf ( area ) );
#if KEEP_PRED_AND_RESI_SIGNALS
saveCS.getPredBuf ( area ).copyFrom( cs.getPredBuf ( area ) );
saveCS.getResiBuf ( area ).copyFrom( cs.getResiBuf ( area ) );
#endif
cs.picture->getRecoBuf( area ).copyFrom( cs.getRecoBuf( area ) );
for( uint32_t j = 0; j < saveCS.tus.size(); j++ )
{
saveCS.tus[j]->copyComponentFrom( *orgTUs[j], area.compID );
}
}
dBestCost = dCost;
uiBestDist = uiDist;
uiBestMode = chromaIntraMode;
}
}
for( uint32_t i = getFirstComponentOfChannel( CHANNEL_TYPE_CHROMA ); i < numberValidComponents; i++ )
{
const CompArea &area = pu.blocks[i];
cs.getRecoBuf ( area ).copyFrom( saveCS.getRecoBuf( area ) );
#if KEEP_PRED_AND_RESI_SIGNALS
cs.getPredBuf ( area ).copyFrom( saveCS.getPredBuf( area ) );
cs.getResiBuf ( area ).copyFrom( saveCS.getResiBuf( area ) );
#endif
cs.picture->getRecoBuf( area ).copyFrom( cs. getRecoBuf( area ) );
for( uint32_t j = 0; j < saveCS.tus.size(); j++ )
{
orgTUs[ j ]->copyComponentFrom( *saveCS.tus[ j ], area.compID );
}
}
}
pu.intraDir[1] = uiBestMode;
cs.dist = uiBestDist;
}
//----- restore context models -----
m_CABACEstimator->getCtx() = ctxStart;
}