x 265におけるmotionCompensation()解析(バージョン2.8)

一.運動補償:

動き補償の基本原理は、符号化器が画像シーケンスのN番目のフレームを処理するとき、動き補償の中核技術である動き推定ME(Motion Estimation)を用いて、N番目のフレームの予測フレームN´を得ることである.実際の符号化伝送では、必ずしもNフレーム目を伝送するのではなく、Nフレーム目とその予測フレームN´との差△を伝送する.動き推定が非常に有効である場合、△中得確率は基本的にゼロ付近に分布し、△元の画像のNフレーム目よりもエネルギーがずっと小さく、符号化伝送△に必要なビット数もずっと少ない.

二.ソース注釈分析:

/*
 =============Analysed by: yangxin
 =============Date:        2018.10
 =============Function:    motionCompensation()  
*/
void Predict::motionCompensation(const CUData& cu, const PredictionUnit& pu, Yuv& predYuv, bool bLuma, bool bChroma)
{
    int refIdx0 = cu.m_refIdx[0][pu.puAbsPartIdx];
    int refIdx1 = cu.m_refIdx[1][pu.puAbsPartIdx];

    if (cu.m_slice->isInterP())
    {
        /* P Slice */
        WeightValues wv0[3];

        X265_CHECK(refIdx0 >= 0, "invalid P refidx
");
        X265_CHECK(refIdx0 < cu.m_slice->m_numRefIdx[0], "P refidx out of range
");
        const WeightParam *wp0 = cu.m_slice->m_weightPredTable[0][refIdx0];

        MV mv0 = cu.m_mv[0][pu.puAbsPartIdx];
        cu.clipMv(mv0);//-- mv

        if (cu.m_slice->m_pps->bUseWeightPred && wp0->bPresentFlag) //-- 
        {
            for (int plane = 0; plane < (bChroma ? 3 : 1); plane++)
            {
                wv0[plane].w      = wp0[plane].inputWeight;
                wv0[plane].offset = wp0[plane].inputOffset * (1 << (X265_DEPTH - 8));
                wv0[plane].shift  = wp0[plane].log2WeightDenom;
                wv0[plane].round  = wp0[plane].log2WeightDenom >= 1 ? 1 << (wp0[plane].log2WeightDenom - 1) : 0;
            }

            ShortYuv& shortYuv = m_predShortYuv[0];

            if (bLuma)
                predInterLumaShort(pu, shortYuv, *cu.m_slice->m_refReconPicList[0][refIdx0], mv0);
            if (bChroma)
                predInterChromaShort(pu, shortYuv, *cu.m_slice->m_refReconPicList[0][refIdx0], mv0);

            addWeightUni(pu, predYuv, shortYuv, wv0, bLuma, bChroma);
        }
        else//-- 
        {
            if (bLuma)
                predInterLumaPixel(pu, predYuv, *cu.m_slice->m_refReconPicList[0][refIdx0], mv0);//-- 
            if (bChroma)
                predInterChromaPixel(pu, predYuv, *cu.m_slice->m_refReconPicList[0][refIdx0], mv0);//-- 
        }
    }
    else
    {
        /* B Slice */

        WeightValues wv0[3], wv1[3];
        const WeightParam *pwp0, *pwp1;

        X265_CHECK(refIdx0 < cu.m_slice->m_numRefIdx[0], "bidir refidx0 out of range
");
        X265_CHECK(refIdx1 < cu.m_slice->m_numRefIdx[1], "bidir refidx1 out of range
");

        if (cu.m_slice->m_pps->bUseWeightedBiPred)
        {
            pwp0 = refIdx0 >= 0 ? cu.m_slice->m_weightPredTable[0][refIdx0] : NULL;
            pwp1 = refIdx1 >= 0 ? cu.m_slice->m_weightPredTable[1][refIdx1] : NULL;

            if (pwp0 && pwp1 && (pwp0->bPresentFlag || pwp1->bPresentFlag))
            {
                /* biprediction weighting */
                for (int plane = 0; plane < (bChroma ? 3 : 1); plane++)
                {
                    wv0[plane].w = pwp0[plane].inputWeight;
                    wv0[plane].o = pwp0[plane].inputOffset * (1 << (X265_DEPTH - 8));
                    wv0[plane].shift = pwp0[plane].log2WeightDenom;
                    wv0[plane].round = 1 << pwp0[plane].log2WeightDenom;

                    wv1[plane].w = pwp1[plane].inputWeight;
                    wv1[plane].o = pwp1[plane].inputOffset * (1 << (X265_DEPTH - 8));
                    wv1[plane].shift = wv0[plane].shift;
                    wv1[plane].round = wv0[plane].round;
                }
            }
            else
            {
                /* uniprediction weighting, always outputs to wv0 */
                const WeightParam* pwp = (refIdx0 >= 0) ? pwp0 : pwp1;
                for (int plane = 0; plane < (bChroma ? 3 : 1); plane++)
                {
                    wv0[plane].w = pwp[plane].inputWeight;
                    wv0[plane].offset = pwp[plane].inputOffset * (1 << (X265_DEPTH - 8));
                    wv0[plane].shift = pwp[plane].log2WeightDenom;
                    wv0[plane].round = pwp[plane].log2WeightDenom >= 1 ? 1 << (pwp[plane].log2WeightDenom - 1) : 0;
                }
            }
        }
        else
            pwp0 = pwp1 = NULL;

        if (refIdx0 >= 0 && refIdx1 >= 0)
        {
            MV mv0 = cu.m_mv[0][pu.puAbsPartIdx];
            MV mv1 = cu.m_mv[1][pu.puAbsPartIdx];
            cu.clipMv(mv0);
            cu.clipMv(mv1);

            if (bLuma)
            {
                predInterLumaShort(pu, m_predShortYuv[0], *cu.m_slice->m_refReconPicList[0][refIdx0], mv0);
                predInterLumaShort(pu, m_predShortYuv[1], *cu.m_slice->m_refReconPicList[1][refIdx1], mv1);
            }
            if (bChroma)
            {
                predInterChromaShort(pu, m_predShortYuv[0], *cu.m_slice->m_refReconPicList[0][refIdx0], mv0);
                predInterChromaShort(pu, m_predShortYuv[1], *cu.m_slice->m_refReconPicList[1][refIdx1], mv1);
            }

            if (pwp0 && pwp1 && (pwp0->bPresentFlag || pwp1->bPresentFlag))
                addWeightBi(pu, predYuv, m_predShortYuv[0], m_predShortYuv[1], wv0, wv1, bLuma, bChroma);
            else
                predYuv.addAvg(m_predShortYuv[0], m_predShortYuv[1], pu.puAbsPartIdx, pu.width, pu.height, bLuma, bChroma);
        }
        else if (refIdx0 >= 0)
        {
            MV mv0 = cu.m_mv[0][pu.puAbsPartIdx];
            cu.clipMv(mv0);

            if (pwp0 && pwp0->bPresentFlag)
            {
                ShortYuv& shortYuv = m_predShortYuv[0];

                if (bLuma)
                    predInterLumaShort(pu, shortYuv, *cu.m_slice->m_refReconPicList[0][refIdx0], mv0);
                if (bChroma)
                    predInterChromaShort(pu, shortYuv, *cu.m_slice->m_refReconPicList[0][refIdx0], mv0);

                addWeightUni(pu, predYuv, shortYuv, wv0, bLuma, bChroma);
            }
            else
            {
                if (bLuma)
                    predInterLumaPixel(pu, predYuv, *cu.m_slice->m_refReconPicList[0][refIdx0], mv0);
                if (bChroma)
                    predInterChromaPixel(pu, predYuv, *cu.m_slice->m_refReconPicList[0][refIdx0], mv0);
            }
        }
        else
        {
            MV mv1 = cu.m_mv[1][pu.puAbsPartIdx];
            cu.clipMv(mv1);

            /* uniprediction to L1 */
            X265_CHECK(refIdx1 >= 0, "refidx1 was not positive
");

            if (pwp1 && pwp1->bPresentFlag)
            {
                ShortYuv& shortYuv = m_predShortYuv[0];

                if (bLuma)
                    predInterLumaShort(pu, shortYuv, *cu.m_slice->m_refReconPicList[1][refIdx1], mv1);
                if (bChroma)
                    predInterChromaShort(pu, shortYuv, *cu.m_slice->m_refReconPicList[1][refIdx1], mv1);

                addWeightUni(pu, predYuv, shortYuv, wv0, bLuma, bChroma);
            }
            else
            {
                if (bLuma)
                    predInterLumaPixel(pu, predYuv, *cu.m_slice->m_refReconPicList[1][refIdx1], mv1);
                if (bChroma)
                    predInterChromaPixel(pu, predYuv, *cu.m_slice->m_refReconPicList[1][refIdx1], mv1);
            }
        }
    }
}