vpx/vp8/common/pred_common.c

/*
 *  Copyright (c) 2012 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 "vp8/common/pred_common.h"

// TBD prediction functions for various bitstream signals

// Returns a context number for the given MB prediction signal
unsigned char get_pred_context( VP8_COMMON *const cm,
                                MACROBLOCKD *const xd,
                                PRED_ID pred_id )
{
    int pred_context;
    MODE_INFO *m = xd->mode_info_context;

    // Note:
    // The mode info data structure has a one element border above and to the
    // left of the entries correpsonding to real macroblocks.
    // The prediction flags in these dummy entries are initialised to 0.
    switch (pred_id)
    {
    case PRED_SEG_ID:
        pred_context = (m - 1)->mbmi.seg_id_predicted +
                       (m - cm->mode_info_stride)->mbmi.seg_id_predicted;
        break;


#if CONFIG_COMPRED

    case PRED_REF:
        pred_context = (m - 1)->mbmi.ref_predicted +
                       (m - cm->mode_info_stride)->mbmi.ref_predicted;
        break;
#endif

    default:
        // TODO *** add error trap code.
        pred_context = 0;
        break;
    }

    return pred_context;
}

// This function returns a context probability for coding a given
// prediction signal
vp8_prob get_pred_prob( VP8_COMMON *const cm,
                        MACROBLOCKD *const xd,
                        PRED_ID pred_id )
{
    vp8_prob pred_probability;
    int pred_context;

    // Get the appropriate prediction context
    pred_context = get_pred_context( cm, xd, pred_id );

    switch (pred_id)
    {
    case PRED_SEG_ID:
        pred_probability = cm->segment_pred_probs[pred_context];
        break;

#if CONFIG_COMPRED

    case PRED_REF:
        pred_probability = cm->ref_pred_probs[pred_context];
        break;
#endif

    default:
        // TODO *** add error trap code.
        pred_probability = 128;
        break;
    }

    return pred_probability;
}

// This function returns the status of the given prediction signal.
// I.e. is the predicted value for the given signal correct.
unsigned char get_pred_flag( MACROBLOCKD *const xd,
                             PRED_ID pred_id )
{
    unsigned char pred_flag = 0;

    switch (pred_id)
    {
    case PRED_SEG_ID:
        pred_flag = xd->mode_info_context->mbmi.seg_id_predicted;
        break;

#if CONFIG_COMPRED

    case PRED_REF:
        pred_flag = xd->mode_info_context->mbmi.ref_predicted;
        break;
#endif

    default:
        // TODO *** add error trap code.
        pred_flag = 0;
        break;
}

    return pred_flag;
}

// This function sets the status of the given prediction signal.
// I.e. is the predicted value for the given signal correct.
void set_pred_flag( MACROBLOCKD *const xd,
                    PRED_ID pred_id,
                    unsigned char pred_flag)
{
    switch (pred_id)
    {
    case PRED_SEG_ID:
        xd->mode_info_context->mbmi.seg_id_predicted = pred_flag;
        break;

#if CONFIG_COMPRED

    case PRED_REF:
        xd->mode_info_context->mbmi.ref_predicted = pred_flag;
        break;
#endif

    default:
        // TODO *** add error trap code.
        break;
    }
}


// The following contain the guts of the prediction code used to
// peredict various bitstream signals.

// Macroblock segment id prediction function
unsigned char get_pred_mb_segid( VP8_COMMON *const cm, int MbIndex )
{
    // Currently the prediction for the macroblock segment ID is
    // the value stored for this macroblock in the previous frame.
    return cm->last_frame_seg_map[MbIndex];
}

#if CONFIG_COMPRED
MV_REFERENCE_FRAME get_pred_ref( VP8_COMMON *const cm,
                                 MACROBLOCKD *const xd )
{
    MODE_INFO *m = xd->mode_info_context;

    MV_REFERENCE_FRAME left;
    MV_REFERENCE_FRAME above;
    MV_REFERENCE_FRAME above_left;
    MV_REFERENCE_FRAME pred_ref = LAST_FRAME;

    int segment_id = xd->mode_info_context->mbmi.segment_id;
    int seg_ref_active;
    int i;

    unsigned char frame_allowed[MAX_REF_FRAMES] = {1,1,1,1};
    unsigned char ref_score[MAX_REF_FRAMES];
    unsigned char best_score = 0;
    unsigned char left_in_image;
    unsigned char above_in_image;
    unsigned char above_left_in_image;

    // Is segment coding ennabled
    seg_ref_active = segfeature_active( xd, segment_id, SEG_LVL_REF_FRAME );

    // Special case treatment if segment coding is enabled.
    // Dont allow prediction of a reference frame that the segment
    // does not allow
    if ( seg_ref_active )
    {
        for ( i = 0; i < MAX_REF_FRAMES; i++ )
        {
            frame_allowed[i] =
                check_segref( xd, segment_id, i );

            // Score set to 0 if ref frame not allowed
            ref_score[i] = cm->ref_scores[i] * frame_allowed[i];
        }
    }
    else
        vpx_memcpy( ref_score, cm->ref_scores, sizeof(ref_score) );

    // Reference frames used by neighbours
    left = (m - 1)->mbmi.ref_frame;
    above = (m - cm->mode_info_stride)->mbmi.ref_frame;
    above_left = (m - 1 - cm->mode_info_stride)->mbmi.ref_frame;

    // Are neighbours in image
    left_in_image = (m - 1)->mbmi.mb_in_image;
    above_in_image = (m - cm->mode_info_stride)->mbmi.mb_in_image;
    above_left_in_image = (m - 1 - cm->mode_info_stride)->mbmi.mb_in_image;

    // Adjust scores for candidate reference frames based on neigbours
    if  ( frame_allowed[left] && left_in_image )
    {
        ref_score[left] += 16;
        if ( above_left_in_image && (left == above_left) )
            ref_score[left] += 4;
    }
    if  ( frame_allowed[above] && above_in_image )
    {
        ref_score[above] += 16;
        if ( above_left_in_image && (above == above_left) )
            ref_score[above] += 4;
    }

    // Now choose the candidate with the highest score
    for ( i = 0; i < MAX_REF_FRAMES; i++ )
    {
        if ( ref_score[i] > best_score  )
        {
            pred_ref = i;
            best_score = ref_score[i];
        }
    }

    return pred_ref;
}

// Functions to computes a set of modified reference frame probabilities
// to use when the prediction of the reference frame value fails
void calc_ref_probs( int * count, vp8_prob * probs )
{
    int tot_count;

    tot_count = count[0] + count[1] + count[2] + count[3];
    if ( tot_count )
    {
        probs[0] = (vp8_prob)((count[0] * 255) / tot_count);
        probs[0] += !probs[0];
    }
    else
        probs[0] = 128;

    tot_count -= count[0];
    if ( tot_count )
    {
        probs[1] = (vp8_prob)((count[1] * 255) / tot_count);
        probs[1] += !probs[1];
    }
    else
        probs[1] = 128;

    tot_count -= count[1];
    if ( tot_count )
    {
        probs[2] = (vp8_prob)((count[2] * 255) / tot_count);
        probs[2] += !probs[2];
    }
    else
        probs[2] = 128;

}

// Computes a set of modified conditional probabilities for the reference frame
// Values willbe set to 0 for reference frame options that are not possible
// because wither they were predicted and prediction has failed or because
// they are not allowed for a given segment.
void compute_mod_refprobs( VP8_COMMON *const cm )
{
    int norm_cnt[MAX_REF_FRAMES];
    int intra_count;
    int inter_count;
    int last_count;
    int gfarf_count;
    int gf_count;
    int arf_count;
    int i;

    intra_count = cm->prob_intra_coded;
    inter_count = (255 - intra_count);
    last_count = (inter_count * cm->prob_last_coded)/255;
    gfarf_count = inter_count - last_count;
    gf_count = (gfarf_count * cm->prob_gf_coded)/255;
    arf_count = gfarf_count - gf_count;

    // Work out modified reference frame probabilities to use where prediction
    // of the reference frame fails
    norm_cnt[0] = 0;
    norm_cnt[1] = last_count;
    norm_cnt[2] = gf_count;
    norm_cnt[3] = arf_count;
    calc_ref_probs( norm_cnt, cm->mod_refprobs[INTRA_FRAME] );
    cm->mod_refprobs[INTRA_FRAME][0] = 0;    // This branch implicit

    norm_cnt[0] = intra_count;
    norm_cnt[1] = 0;
    norm_cnt[2] = gf_count;
    norm_cnt[3] = arf_count;
    calc_ref_probs( norm_cnt, cm->mod_refprobs[LAST_FRAME]);
    cm->mod_refprobs[LAST_FRAME][1] = 0;    // This branch implicit

    norm_cnt[0] = intra_count;
    norm_cnt[1] = last_count;
    norm_cnt[2] = 0;
    norm_cnt[3] = arf_count;
    calc_ref_probs( norm_cnt, cm->mod_refprobs[GOLDEN_FRAME] );
    cm->mod_refprobs[GOLDEN_FRAME][2] = 0;  // This branch implicit

    norm_cnt[0] = intra_count;
    norm_cnt[1] = last_count;
    norm_cnt[2] = gf_count;
    norm_cnt[3] = 0;
    calc_ref_probs( norm_cnt, cm->mod_refprobs[ALTREF_FRAME] );
    cm->mod_refprobs[ALTREF_FRAME][2] = 0;  // This branch implicit

    // Score the reference frames based on overal frequency.
    // These scores contribute to the prediction choices.
    // Max score 17 min 1
    cm->ref_scores[INTRA_FRAME] = 1 + (intra_count * 16 / 255);
    cm->ref_scores[LAST_FRAME] = 1 + (last_count * 16 / 255);
    cm->ref_scores[GOLDEN_FRAME] = 1 + (gf_count * 16 / 255);
    cm->ref_scores[ALTREF_FRAME] = 1 + (arf_count * 16 / 255);
}
#endif