HM代码阅读5：快速大范围运动估计函数xTZSearch()与xTZ8PointDiaMondSearch()

本文主要是介绍HM代码阅读5：快速大范围运动估计函数xTZSearch()与xTZ8PointDiaMondSearch()，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

上一次讲过了全搜索的做法，主要用于第二次对cost较大的参考图像列表的对应MV做一定范围内的全搜索减小cost。

这次主要讲在第一次做ME时的快速搜索算法，HM中采用TZSearch进行大范围内的ME。HM中提供的算法如下：
一般是采用Diamond搜索，也就是菱形搜索，在进搜索函数之前需要找到左、上、右上的MV，来判断是不是邻居MV更适合做ME的起始点（这里书本中没有详细写明，要注意）

Void TEncSearch::xPatternSearchFast( const TComDataCU* const  pcCU,const TComPattern* const pcPatternKey,const Pel* const         piRefY,const Int                iRefStride,const TComMv* const      pcMvSrchRngLT,const TComMv* const      pcMvSrchRngRB,TComMv&                  rcMv,Distortion&              ruiSAD,const TComMv* const      pIntegerMv2Nx2NPred )
{assert (MD_LEFT < NUM_MV_PREDICTORS);pcCU->getMvPredLeft       ( m_acMvPredictors[MD_LEFT] );assert (MD_ABOVE < NUM_MV_PREDICTORS);pcCU->getMvPredAbove      ( m_acMvPredictors[MD_ABOVE] );assert (MD_ABOVE_RIGHT < NUM_MV_PREDICTORS);pcCU->getMvPredAboveRight ( m_acMvPredictors[MD_ABOVE_RIGHT] );switch ( m_motionEstimationSearchMethod ){case MESEARCH_DIAMOND:xTZSearch( pcCU, pcPatternKey, piRefY, iRefStride, pcMvSrchRngLT, pcMvSrchRngRB, rcMv, ruiSAD, pIntegerMv2Nx2NPred, false );break;case MESEARCH_SELECTIVE:xTZSearchSelective( pcCU, pcPatternKey, piRefY, iRefStride, pcMvSrchRngLT, pcMvSrchRngRB, rcMv, ruiSAD, pIntegerMv2Nx2NPred );break;case MESEARCH_DIAMOND_ENHANCED:xTZSearch( pcCU, pcPatternKey, piRefY, iRefStride, pcMvSrchRngLT, pcMvSrchRngRB, rcMv, ruiSAD, pIntegerMv2Nx2NPred, true );break;case MESEARCH_FULL: // shouldn't get here.default:break;}
}

接下来是菱形搜索的具体过程
1、预先设置搜索的参数，如：逐行搜索还是菱形搜索，精调时选star菱形搜索还是逐行搜索，是否考虑角落等。

2、定义结构体IntTZSearchStruct ，用于存储当前最好的MV以及最小失真，以及重建帧的同位起始地址、步幅等。

3、调用xTZSearchHelp去判断最好的起始位置，需要依次考虑当前最佳MVP、左、上、右上MVP、0运动矢量、若不是2NX2N的块，还需要判断一下2NX2N的块是不是最佳起始位置。

4、开始做菱形搜索，菱形搜索如图所示：
在这里插入图片描述

步长从1 到 64 每次增加2倍。能够得到当前最佳运动矢量。再以0矢量为起始点，再进行同样的搜索，对比两次结果找到最优MV。
如果是在distance=1时找到最优的MV，那还需进行一次两点搜索。
以当前最佳MV进行starRefine，以同样的方式进行8点菱形搜索。
代码如下：

Void TEncSearch::xTZSearch( const TComDataCU* const pcCU,const TComPattern* const pcPatternKey,const Pel* const         piRefY,const Int                iRefStride,const TComMv* const      pcMvSrchRngLT,const TComMv* const      pcMvSrchRngRB,TComMv&                  rcMv,Distortion&              ruiSAD,const TComMv* const      pIntegerMv2Nx2NPred,const Bool               bExtendedSettings)
{const Bool bUseAdaptiveRaster                      = bExtendedSettings;const Int  iRaster                                 = 5;const Bool bTestOtherPredictedMV                   = bExtendedSettings;const Bool bTestZeroVector                         = true;const Bool bTestZeroVectorStart                    = bExtendedSettings;const Bool bTestZeroVectorStop                     = false;const Bool bFirstSearchDiamond                     = true;  // 1 = xTZ8PointDiamondSearch   0 = xTZ8PointSquareSearchconst Bool bFirstCornersForDiamondDist1            = bExtendedSettings;const Bool bFirstSearchStop                        = m_pcEncCfg->getFastMEAssumingSmootherMVEnabled();const UInt uiFirstSearchRounds                     = 3;     // first search stop X rounds after best match (must be >=1)const Bool bEnableRasterSearch                     = true;const Bool bAlwaysRasterSearch                     = bExtendedSettings;  // true: BETTER but factor 2 slowerconst Bool bRasterRefinementEnable                 = false; // enable either raster refinement or star refinementconst Bool bRasterRefinementDiamond                = false; // 1 = xTZ8PointDiamondSearch   0 = xTZ8PointSquareSearchconst Bool bRasterRefinementCornersForDiamondDist1 = bExtendedSettings;const Bool bStarRefinementEnable                   = true;  // enable either star refinement or raster refinementconst Bool bStarRefinementDiamond                  = true;  // 1 = xTZ8PointDiamondSearch   0 = xTZ8PointSquareSearchconst Bool bStarRefinementCornersForDiamondDist1   = bExtendedSettings;const Bool bStarRefinementStop                     = false;const UInt uiStarRefinementRounds                  = 2;  // star refinement stop X rounds after best match (must be >=1)const Bool bNewZeroNeighbourhoodTest               = bExtendedSettings;UInt uiSearchRange = m_iSearchRange;pcCU->clipMv( rcMv );
#if ME_ENABLE_ROUNDING_OF_MVSrcMv.divideByPowerOf2(2);
#elsercMv >>= 2;
#endif// init TZSearchStructIntTZSearchStruct cStruct;cStruct.iYStride    = iRefStride;cStruct.piRefY      = piRefY;cStruct.uiBestSad   = MAX_UINT;// set rcMv (Median predictor) as start point and as best pointxTZSearchHelp( pcPatternKey, cStruct, rcMv.getHor(), rcMv.getVer(), 0, 0 );// test whether one of PRED_A, PRED_B, PRED_C MV is better start point than Median predictorif ( bTestOtherPredictedMV ){for ( UInt index = 0; index < NUM_MV_PREDICTORS; index++ ){TComMv cMv = m_acMvPredictors[index];pcCU->clipMv( cMv );
#if ME_ENABLE_ROUNDING_OF_MVScMv.divideByPowerOf2(2);
#elsecMv >>= 2;
#endifif (cMv != rcMv && (cMv.getHor() != cStruct.iBestX && cMv.getVer() != cStruct.iBestY)){// only test cMV if not obviously previously tested.xTZSearchHelp( pcPatternKey, cStruct, cMv.getHor(), cMv.getVer(),