media/libvpx/vp8/encoder/quantize.c
author Jan Gerber <j@mailb.org>
Mon, 29 Jun 2015 23:07:20 +0200
changeset 273771 2f025dfee1f4455057b21e7053d87b4f92849129
parent 273666 ad7b4c50532ef7e22a1e0e715e2c21959c9a04ea
permissions -rw-r--r--
Bug 1178215 - Update libvpx. r=rillian, a=lmandel Update libvpx to e67d45d4ce92468ba193288b59093fef0a502662

/*
 *  Copyright (c) 2010 The WebM project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */


#include <math.h>
#include "vpx_mem/vpx_mem.h"

#include "onyx_int.h"
#include "quantize.h"
#include "vp8/common/quant_common.h"

void vp8_fast_quantize_b_c(BLOCK *b, BLOCKD *d)
{
    int i, rc, eob;
    int x, y, z, sz;
    short *coeff_ptr   = b->coeff;
    short *round_ptr   = b->round;
    short *quant_ptr   = b->quant_fast;
    short *qcoeff_ptr  = d->qcoeff;
    short *dqcoeff_ptr = d->dqcoeff;
    short *dequant_ptr = d->dequant;

    eob = -1;
    for (i = 0; i < 16; i++)
    {
        rc   = vp8_default_zig_zag1d[i];
        z    = coeff_ptr[rc];

        sz = (z >> 31);                              /* sign of z */
        x  = (z ^ sz) - sz;                          /* x = abs(z) */

        y  = ((x + round_ptr[rc]) * quant_ptr[rc]) >> 16; /* quantize (x) */
        x  = (y ^ sz) - sz;                          /* get the sign back */
        qcoeff_ptr[rc] = x;                          /* write to destination */
        dqcoeff_ptr[rc] = x * dequant_ptr[rc];       /* dequantized value */

        if (y)
        {
            eob = i;                                 /* last nonzero coeffs */
        }
    }
    *d->eob = (char)(eob + 1);
}

void vp8_regular_quantize_b_c(BLOCK *b, BLOCKD *d)
{
    int i, rc, eob;
    int zbin;
    int x, y, z, sz;
    short *zbin_boost_ptr  = b->zrun_zbin_boost;
    short *coeff_ptr       = b->coeff;
    short *zbin_ptr        = b->zbin;
    short *round_ptr       = b->round;
    short *quant_ptr       = b->quant;
    short *quant_shift_ptr = b->quant_shift;
    short *qcoeff_ptr      = d->qcoeff;
    short *dqcoeff_ptr     = d->dqcoeff;
    short *dequant_ptr     = d->dequant;
    short zbin_oq_value    = b->zbin_extra;

    memset(qcoeff_ptr, 0, 32);
    memset(dqcoeff_ptr, 0, 32);

    eob = -1;

    for (i = 0; i < 16; i++)
    {
        rc   = vp8_default_zig_zag1d[i];
        z    = coeff_ptr[rc];

        zbin = zbin_ptr[rc] + *zbin_boost_ptr + zbin_oq_value;

        zbin_boost_ptr ++;
        sz = (z >> 31);                              /* sign of z */
        x  = (z ^ sz) - sz;                          /* x = abs(z) */

        if (x >= zbin)
        {
            x += round_ptr[rc];
            y  = ((((x * quant_ptr[rc]) >> 16) + x)
                 * quant_shift_ptr[rc]) >> 16;       /* quantize (x) */
            x  = (y ^ sz) - sz;                      /* get the sign back */
            qcoeff_ptr[rc]  = x;                     /* write to destination */
            dqcoeff_ptr[rc] = x * dequant_ptr[rc];   /* dequantized value */

            if (y)
            {
                eob = i;                             /* last nonzero coeffs */
                zbin_boost_ptr = b->zrun_zbin_boost; /* reset zero runlength */
            }
        }
    }

    *d->eob = (char)(eob + 1);
}

void vp8_quantize_mby(MACROBLOCK *x)
{
    int i;
    int has_2nd_order = (x->e_mbd.mode_info_context->mbmi.mode != B_PRED
        && x->e_mbd.mode_info_context->mbmi.mode != SPLITMV);

    for (i = 0; i < 16; i++)
        x->quantize_b(&x->block[i], &x->e_mbd.block[i]);

    if(has_2nd_order)
        x->quantize_b(&x->block[24], &x->e_mbd.block[24]);
}

void vp8_quantize_mb(MACROBLOCK *x)
{
    int i;
    int has_2nd_order=(x->e_mbd.mode_info_context->mbmi.mode != B_PRED
        && x->e_mbd.mode_info_context->mbmi.mode != SPLITMV);

    for (i = 0; i < 24+has_2nd_order; i++)
        x->quantize_b(&x->block[i], &x->e_mbd.block[i]);
}


void vp8_quantize_mbuv(MACROBLOCK *x)
{
    int i;

    for (i = 16; i < 24; i++)
        x->quantize_b(&x->block[i], &x->e_mbd.block[i]);
}

static const int qrounding_factors[129] =
{
    48, 48, 48, 48, 48, 48, 48, 48,
    48, 48, 48, 48, 48, 48, 48, 48,
    48, 48, 48, 48, 48, 48, 48, 48,
    48, 48, 48, 48, 48, 48, 48, 48,
    48, 48, 48, 48, 48, 48, 48, 48,
    48, 48, 48, 48, 48, 48, 48, 48,
    48, 48, 48, 48, 48, 48, 48, 48,
    48, 48, 48, 48, 48, 48, 48, 48,
    48, 48, 48, 48, 48, 48, 48, 48,
    48, 48, 48, 48, 48, 48, 48, 48,
    48, 48, 48, 48, 48, 48, 48, 48,
    48, 48, 48, 48, 48, 48, 48, 48,
    48, 48, 48, 48, 48, 48, 48, 48,
    48, 48, 48, 48, 48, 48, 48, 48,
    48, 48, 48, 48, 48, 48, 48, 48,
    48, 48, 48, 48, 48, 48, 48, 48,
    48
};


static const int qzbin_factors[129] =
{
    84, 84, 84, 84, 84, 84, 84, 84,
    84, 84, 84, 84, 84, 84, 84, 84,
    84, 84, 84, 84, 84, 84, 84, 84,
    84, 84, 84, 84, 84, 84, 84, 84,
    84, 84, 84, 84, 84, 84, 84, 84,
    84, 84, 84, 84, 84, 84, 84, 84,
    80, 80, 80, 80, 80, 80, 80, 80,
    80, 80, 80, 80, 80, 80, 80, 80,
    80, 80, 80, 80, 80, 80, 80, 80,
    80, 80, 80, 80, 80, 80, 80, 80,
    80, 80, 80, 80, 80, 80, 80, 80,
    80, 80, 80, 80, 80, 80, 80, 80,
    80, 80, 80, 80, 80, 80, 80, 80,
    80, 80, 80, 80, 80, 80, 80, 80,
    80, 80, 80, 80, 80, 80, 80, 80,
    80, 80, 80, 80, 80, 80, 80, 80,
    80
};


static const int qrounding_factors_y2[129] =
{
    48, 48, 48, 48, 48, 48, 48, 48,
    48, 48, 48, 48, 48, 48, 48, 48,
    48, 48, 48, 48, 48, 48, 48, 48,
    48, 48, 48, 48, 48, 48, 48, 48,
    48, 48, 48, 48, 48, 48, 48, 48,
    48, 48, 48, 48, 48, 48, 48, 48,
    48, 48, 48, 48, 48, 48, 48, 48,
    48, 48, 48, 48, 48, 48, 48, 48,
    48, 48, 48, 48, 48, 48, 48, 48,
    48, 48, 48, 48, 48, 48, 48, 48,
    48, 48, 48, 48, 48, 48, 48, 48,
    48, 48, 48, 48, 48, 48, 48, 48,
    48, 48, 48, 48, 48, 48, 48, 48,
    48, 48, 48, 48, 48, 48, 48, 48,
    48, 48, 48, 48, 48, 48, 48, 48,
    48, 48, 48, 48, 48, 48, 48, 48,
    48
};


static const int qzbin_factors_y2[129] =
{
    84, 84, 84, 84, 84, 84, 84, 84,
    84, 84, 84, 84, 84, 84, 84, 84,
    84, 84, 84, 84, 84, 84, 84, 84,
    84, 84, 84, 84, 84, 84, 84, 84,
    84, 84, 84, 84, 84, 84, 84, 84,
    84, 84, 84, 84, 84, 84, 84, 84,
    80, 80, 80, 80, 80, 80, 80, 80,
    80, 80, 80, 80, 80, 80, 80, 80,
    80, 80, 80, 80, 80, 80, 80, 80,
    80, 80, 80, 80, 80, 80, 80, 80,
    80, 80, 80, 80, 80, 80, 80, 80,
    80, 80, 80, 80, 80, 80, 80, 80,
    80, 80, 80, 80, 80, 80, 80, 80,
    80, 80, 80, 80, 80, 80, 80, 80,
    80, 80, 80, 80, 80, 80, 80, 80,
    80, 80, 80, 80, 80, 80, 80, 80,
    80
};


static void invert_quant(int improved_quant, short *quant,
                         short *shift, short d)
{
    if(improved_quant)
    {
        unsigned t;
        int l;
        t = d;
        for(l = 0; t > 1; l++)
            t>>=1;
        t = 1 + (1<<(16+l))/d;
        *quant = (short)(t - (1<<16));
        *shift = l;
        /* use multiplication and constant shift by 16 */
        *shift = 1 << (16 - *shift);
    }
    else
    {
        *quant = (1 << 16) / d;
        *shift = 0;
        /* use multiplication and constant shift by 16 */
        *shift = 1 << (16 - *shift);
    }
}


void vp8cx_init_quantizer(VP8_COMP *cpi)
{
    int i;
    int quant_val;
    int Q;

    int zbin_boost[16] = {0, 0, 8, 10, 12, 14, 16, 20, 24, 28, 32, 36, 40, 44,
                          44, 44};

    for (Q = 0; Q < QINDEX_RANGE; Q++)
    {
        /* dc values */
        quant_val = vp8_dc_quant(Q, cpi->common.y1dc_delta_q);
        cpi->Y1quant_fast[Q][0] = (1 << 16) / quant_val;
        invert_quant(cpi->sf.improved_quant, cpi->Y1quant[Q] + 0,
                     cpi->Y1quant_shift[Q] + 0, quant_val);
        cpi->Y1zbin[Q][0] = ((qzbin_factors[Q] * quant_val) + 64) >> 7;
        cpi->Y1round[Q][0] = (qrounding_factors[Q] * quant_val) >> 7;
        cpi->common.Y1dequant[Q][0] = quant_val;
        cpi->zrun_zbin_boost_y1[Q][0] = (quant_val * zbin_boost[0]) >> 7;

        quant_val = vp8_dc2quant(Q, cpi->common.y2dc_delta_q);
        cpi->Y2quant_fast[Q][0] = (1 << 16) / quant_val;
        invert_quant(cpi->sf.improved_quant, cpi->Y2quant[Q] + 0,
                     cpi->Y2quant_shift[Q] + 0, quant_val);
        cpi->Y2zbin[Q][0] = ((qzbin_factors_y2[Q] * quant_val) + 64) >> 7;
        cpi->Y2round[Q][0] = (qrounding_factors_y2[Q] * quant_val) >> 7;
        cpi->common.Y2dequant[Q][0] = quant_val;
        cpi->zrun_zbin_boost_y2[Q][0] = (quant_val * zbin_boost[0]) >> 7;

        quant_val = vp8_dc_uv_quant(Q, cpi->common.uvdc_delta_q);
        cpi->UVquant_fast[Q][0] = (1 << 16) / quant_val;
        invert_quant(cpi->sf.improved_quant, cpi->UVquant[Q] + 0,
                     cpi->UVquant_shift[Q] + 0, quant_val);
        cpi->UVzbin[Q][0] = ((qzbin_factors[Q] * quant_val) + 64) >> 7;;
        cpi->UVround[Q][0] = (qrounding_factors[Q] * quant_val) >> 7;
        cpi->common.UVdequant[Q][0] = quant_val;
        cpi->zrun_zbin_boost_uv[Q][0] = (quant_val * zbin_boost[0]) >> 7;

        /* all the ac values = ; */
        quant_val = vp8_ac_yquant(Q);
        cpi->Y1quant_fast[Q][1] = (1 << 16) / quant_val;
        invert_quant(cpi->sf.improved_quant, cpi->Y1quant[Q] + 1,
                     cpi->Y1quant_shift[Q] + 1, quant_val);
        cpi->Y1zbin[Q][1] = ((qzbin_factors[Q] * quant_val) + 64) >> 7;
        cpi->Y1round[Q][1] = (qrounding_factors[Q] * quant_val) >> 7;
        cpi->common.Y1dequant[Q][1] = quant_val;
        cpi->zrun_zbin_boost_y1[Q][1] = (quant_val * zbin_boost[1]) >> 7;

        quant_val = vp8_ac2quant(Q, cpi->common.y2ac_delta_q);
        cpi->Y2quant_fast[Q][1] = (1 << 16) / quant_val;
        invert_quant(cpi->sf.improved_quant, cpi->Y2quant[Q] + 1,
                     cpi->Y2quant_shift[Q] + 1, quant_val);
        cpi->Y2zbin[Q][1] = ((qzbin_factors_y2[Q] * quant_val) + 64) >> 7;
        cpi->Y2round[Q][1] = (qrounding_factors_y2[Q] * quant_val) >> 7;
        cpi->common.Y2dequant[Q][1] = quant_val;
        cpi->zrun_zbin_boost_y2[Q][1] = (quant_val * zbin_boost[1]) >> 7;

        quant_val = vp8_ac_uv_quant(Q, cpi->common.uvac_delta_q);
        cpi->UVquant_fast[Q][1] = (1 << 16) / quant_val;
        invert_quant(cpi->sf.improved_quant, cpi->UVquant[Q] + 1,
                     cpi->UVquant_shift[Q] + 1, quant_val);
        cpi->UVzbin[Q][1] = ((qzbin_factors[Q] * quant_val) + 64) >> 7;
        cpi->UVround[Q][1] = (qrounding_factors[Q] * quant_val) >> 7;
        cpi->common.UVdequant[Q][1] = quant_val;
        cpi->zrun_zbin_boost_uv[Q][1] = (quant_val * zbin_boost[1]) >> 7;

        for (i = 2; i < 16; i++)
        {
            cpi->Y1quant_fast[Q][i] = cpi->Y1quant_fast[Q][1];
            cpi->Y1quant[Q][i] = cpi->Y1quant[Q][1];
            cpi->Y1quant_shift[Q][i] = cpi->Y1quant_shift[Q][1];
            cpi->Y1zbin[Q][i] = cpi->Y1zbin[Q][1];
            cpi->Y1round[Q][i] = cpi->Y1round[Q][1];
            cpi->zrun_zbin_boost_y1[Q][i] = (cpi->common.Y1dequant[Q][1] *
                                             zbin_boost[i]) >> 7;

            cpi->Y2quant_fast[Q][i] = cpi->Y2quant_fast[Q][1];
            cpi->Y2quant[Q][i] = cpi->Y2quant[Q][1];
            cpi->Y2quant_shift[Q][i] = cpi->Y2quant_shift[Q][1];
            cpi->Y2zbin[Q][i] = cpi->Y2zbin[Q][1];
            cpi->Y2round[Q][i] = cpi->Y2round[Q][1];
            cpi->zrun_zbin_boost_y2[Q][i] = (cpi->common.Y2dequant[Q][1] *
                                             zbin_boost[i]) >> 7;

            cpi->UVquant_fast[Q][i] = cpi->UVquant_fast[Q][1];
            cpi->UVquant[Q][i] = cpi->UVquant[Q][1];
            cpi->UVquant_shift[Q][i] = cpi->UVquant_shift[Q][1];
            cpi->UVzbin[Q][i] = cpi->UVzbin[Q][1];
            cpi->UVround[Q][i] = cpi->UVround[Q][1];
            cpi->zrun_zbin_boost_uv[Q][i] = (cpi->common.UVdequant[Q][1] *
                                             zbin_boost[i]) >> 7;
        }
    }
}

#define ZBIN_EXTRA_Y \
    (( cpi->common.Y1dequant[QIndex][1] *  \
    ( x->zbin_over_quant +  \
      x->zbin_mode_boost +  \
      x->act_zbin_adj ) ) >> 7)

#define ZBIN_EXTRA_UV \
    (( cpi->common.UVdequant[QIndex][1] *  \
    ( x->zbin_over_quant +  \
      x->zbin_mode_boost +  \
      x->act_zbin_adj ) ) >> 7)

#define ZBIN_EXTRA_Y2 \
    (( cpi->common.Y2dequant[QIndex][1] *  \
    ( (x->zbin_over_quant / 2) +  \
       x->zbin_mode_boost +  \
       x->act_zbin_adj ) ) >> 7)

void vp8cx_mb_init_quantizer(VP8_COMP *cpi, MACROBLOCK *x, int ok_to_skip)
{
    int i;
    int QIndex;
    MACROBLOCKD *xd = &x->e_mbd;
    int zbin_extra;

    /* Select the baseline MB Q index. */
    if (xd->segmentation_enabled)
    {
        /* Abs Value */
        if (xd->mb_segement_abs_delta == SEGMENT_ABSDATA)
            QIndex = xd->segment_feature_data[MB_LVL_ALT_Q][xd->mode_info_context->mbmi.segment_id];
        /* Delta Value */
        else
        {
            QIndex = cpi->common.base_qindex + xd->segment_feature_data[MB_LVL_ALT_Q][xd->mode_info_context->mbmi.segment_id];
            /* Clamp to valid range */
            QIndex = (QIndex >= 0) ? ((QIndex <= MAXQ) ? QIndex : MAXQ) : 0;
        }
    }
    else
        QIndex = cpi->common.base_qindex;

    /* This initialization should be called at least once. Use ok_to_skip to
     * decide if it is ok to skip.
     * Before encoding a frame, this function is always called with ok_to_skip
     * =0, which means no skiping of calculations. The "last" values are
     * initialized at that time.
     */
    if (!ok_to_skip || QIndex != x->q_index)
    {

        xd->dequant_y1_dc[0] = 1;
        xd->dequant_y1[0] = cpi->common.Y1dequant[QIndex][0];
        xd->dequant_y2[0] = cpi->common.Y2dequant[QIndex][0];
        xd->dequant_uv[0] = cpi->common.UVdequant[QIndex][0];

        for (i = 1; i < 16; i++)
        {
            xd->dequant_y1_dc[i] =
            xd->dequant_y1[i] = cpi->common.Y1dequant[QIndex][1];
            xd->dequant_y2[i] = cpi->common.Y2dequant[QIndex][1];
            xd->dequant_uv[i] = cpi->common.UVdequant[QIndex][1];
        }
#if 1
        /*TODO:  Remove dequant from BLOCKD.  This is a temporary solution until
         * the quantizer code uses a passed in pointer to the dequant constants.
         * This will also require modifications to the x86 and neon assembly.
         * */
        for (i = 0; i < 16; i++)
            x->e_mbd.block[i].dequant = xd->dequant_y1;
        for (i = 16; i < 24; i++)
            x->e_mbd.block[i].dequant = xd->dequant_uv;
        x->e_mbd.block[24].dequant = xd->dequant_y2;
#endif

        /* Y */
        zbin_extra = ZBIN_EXTRA_Y;

        for (i = 0; i < 16; i++)
        {
            x->block[i].quant = cpi->Y1quant[QIndex];
            x->block[i].quant_fast = cpi->Y1quant_fast[QIndex];
            x->block[i].quant_shift = cpi->Y1quant_shift[QIndex];
            x->block[i].zbin = cpi->Y1zbin[QIndex];
            x->block[i].round = cpi->Y1round[QIndex];
            x->block[i].zrun_zbin_boost = cpi->zrun_zbin_boost_y1[QIndex];
            x->block[i].zbin_extra = (short)zbin_extra;
        }

        /* UV */
        zbin_extra = ZBIN_EXTRA_UV;

        for (i = 16; i < 24; i++)
        {
            x->block[i].quant = cpi->UVquant[QIndex];
            x->block[i].quant_fast = cpi->UVquant_fast[QIndex];
            x->block[i].quant_shift = cpi->UVquant_shift[QIndex];
            x->block[i].zbin = cpi->UVzbin[QIndex];
            x->block[i].round = cpi->UVround[QIndex];
            x->block[i].zrun_zbin_boost = cpi->zrun_zbin_boost_uv[QIndex];
            x->block[i].zbin_extra = (short)zbin_extra;
        }

        /* Y2 */
        zbin_extra = ZBIN_EXTRA_Y2;

        x->block[24].quant_fast = cpi->Y2quant_fast[QIndex];
        x->block[24].quant = cpi->Y2quant[QIndex];
        x->block[24].quant_shift = cpi->Y2quant_shift[QIndex];
        x->block[24].zbin = cpi->Y2zbin[QIndex];
        x->block[24].round = cpi->Y2round[QIndex];
        x->block[24].zrun_zbin_boost = cpi->zrun_zbin_boost_y2[QIndex];
        x->block[24].zbin_extra = (short)zbin_extra;

        /* save this macroblock QIndex for vp8_update_zbin_extra() */
        x->q_index = QIndex;

        x->last_zbin_over_quant = x->zbin_over_quant;
        x->last_zbin_mode_boost = x->zbin_mode_boost;
        x->last_act_zbin_adj = x->act_zbin_adj;



    }
    else if(x->last_zbin_over_quant != x->zbin_over_quant
            || x->last_zbin_mode_boost != x->zbin_mode_boost
            || x->last_act_zbin_adj != x->act_zbin_adj)
    {
        /* Y */
        zbin_extra = ZBIN_EXTRA_Y;

        for (i = 0; i < 16; i++)
            x->block[i].zbin_extra = (short)zbin_extra;

        /* UV */
        zbin_extra = ZBIN_EXTRA_UV;

        for (i = 16; i < 24; i++)
            x->block[i].zbin_extra = (short)zbin_extra;

        /* Y2 */
        zbin_extra = ZBIN_EXTRA_Y2;
        x->block[24].zbin_extra = (short)zbin_extra;

        x->last_zbin_over_quant = x->zbin_over_quant;
        x->last_zbin_mode_boost = x->zbin_mode_boost;
        x->last_act_zbin_adj = x->act_zbin_adj;
    }
}

void vp8_update_zbin_extra(VP8_COMP *cpi, MACROBLOCK *x)
{
    int i;
    int QIndex = x->q_index;
    int zbin_extra;

    /* Y */
    zbin_extra = ZBIN_EXTRA_Y;

    for (i = 0; i < 16; i++)
        x->block[i].zbin_extra = (short)zbin_extra;

    /* UV */
    zbin_extra = ZBIN_EXTRA_UV;

    for (i = 16; i < 24; i++)
        x->block[i].zbin_extra = (short)zbin_extra;

    /* Y2 */
    zbin_extra = ZBIN_EXTRA_Y2;
    x->block[24].zbin_extra = (short)zbin_extra;
}
#undef ZBIN_EXTRA_Y
#undef ZBIN_EXTRA_UV
#undef ZBIN_EXTRA_Y2

void vp8cx_frame_init_quantizer(VP8_COMP *cpi)
{
    /* Clear Zbin mode boost for default case */
    cpi->mb.zbin_mode_boost = 0;

    /* MB level quantizer setup */
    vp8cx_mb_init_quantizer(cpi, &cpi->mb, 0);
}


void vp8_set_quantizer(struct VP8_COMP *cpi, int Q)
{
    VP8_COMMON *cm = &cpi->common;
    MACROBLOCKD *mbd = &cpi->mb.e_mbd;
    int update = 0;
    int new_delta_q;
    int new_uv_delta_q;
    cm->base_qindex = Q;

    /* if any of the delta_q values are changing update flag has to be set */
    /* currently only y2dc_delta_q may change */

    cm->y1dc_delta_q = 0;
    cm->y2ac_delta_q = 0;

    if (Q < 4)
    {
        new_delta_q = 4-Q;
    }
    else
        new_delta_q = 0;

    update |= cm->y2dc_delta_q != new_delta_q;
    cm->y2dc_delta_q = new_delta_q;

    new_uv_delta_q = 0;
    // For screen content, lower the q value for UV channel. For now, select
    // conservative delta; same delta for dc and ac, and decrease it with lower
    // Q, and set to 0 below some threshold. May want to condition this in
    // future on the variance/energy in UV channel.
    if (cpi->oxcf.screen_content_mode && Q > 40) {
      new_uv_delta_q = -(int)(0.15 * Q);
      // Check range: magnitude of delta is 4 bits.
      if (new_uv_delta_q < -15) {
        new_uv_delta_q = -15;
      }
    }
    update |= cm->uvdc_delta_q != new_uv_delta_q;
    cm->uvdc_delta_q = new_uv_delta_q;
    cm->uvac_delta_q = new_uv_delta_q;

    /* Set Segment specific quatizers */
    mbd->segment_feature_data[MB_LVL_ALT_Q][0] = cpi->segment_feature_data[MB_LVL_ALT_Q][0];
    mbd->segment_feature_data[MB_LVL_ALT_Q][1] = cpi->segment_feature_data[MB_LVL_ALT_Q][1];
    mbd->segment_feature_data[MB_LVL_ALT_Q][2] = cpi->segment_feature_data[MB_LVL_ALT_Q][2];
    mbd->segment_feature_data[MB_LVL_ALT_Q][3] = cpi->segment_feature_data[MB_LVL_ALT_Q][3];

    /* quantizer has to be reinitialized for any delta_q changes */
    if(update)
        vp8cx_init_quantizer(cpi);

}