block.c

包含了从MPEG4的视频解码到H.264的视频编码部分的源代码

/*
***********************************************************************
* COPYRIGHT AND WARRANTY INFORMATION
*
* Copyright 2001, International Telecommunications Union, Geneva
*
* DISCLAIMER OF WARRANTY
*
* These software programs are available to the user without any
* license fee or royalty on an "as is" basis. The ITU disclaims
* any and all warranties, whether express, implied, or
* statutory, including any implied warranties of merchantability
* or of fitness for a particular purpose.  In no event shall the
* contributor or the ITU be liable for any incidental, punitive, or
* consequential damages of any kind whatsoever arising from the
* use of these programs.
*
* This disclaimer of warranty extends to the user of these programs
* and user's customers, employees, agents, transferees, successors,
* and assigns.
*
* The ITU does not represent or warrant that the programs furnished
* hereunder are free of infringement of any third-party patents.
* Commercial implementations of ITU-T Recommendations, including
* shareware, may be subject to royalty fees to patent holders.
* Information regarding the ITU-T patent policy is available from
* the ITU Web site at http://www.itu.int.
*
* THIS IS NOT A GRANT OF PATENT RIGHTS - SEE THE ITU-T PATENT POLICY.
************************************************************************
*/

/*!
 *************************************************************************************
 * \file block.c
 *
 * \brief
 *    Process one block
 *
 * \author
 *    Main contributors (see contributors.h for copyright, address and affiliation details)
 *    - Inge Lille-Lang鴜               <[e-mail]>
 *    - Rickard Sjoberg                 <[e-mail]>
 *    - Stephan Wenger                  <[e-mail]>
 *    - Jani Lainema                    <[e-mail]>
 *    - Detlev Marpe                    <[e-mail]>
 *    - Thomas Wedi                     <[e-mail]>
 *    - Ragip Kurceren                  <[e-mail]>
 *    - Greg Conklin                    <[e-mail]>
 *************************************************************************************
 */

#include "contributors.h"


#include <math.h>
#include <stdlib.h>
#include <assert.h>

#include "block.h"
#include "refbuf.h"
#include "vlc.h"


#define Q_BITS          15
#define DQ_BITS         6
#define DQ_ROUND        (1<<(DQ_BITS-1))


static const _int16 quant_coef[6][4][4] = {
  {{13107, 8066,13107, 8066},{ 8066, 5243, 8066, 5243},{13107, 8066,13107, 8066},{ 8066, 5243, 8066, 5243}},
  {{11916, 7490,11916, 7490},{ 7490, 4660, 7490, 4660},{11916, 7490,11916, 7490},{ 7490, 4660, 7490, 4660}},
  {{10082, 6554,10082, 6554},{ 6554, 4194, 6554, 4194},{10082, 6554,10082, 6554},{ 6554, 4194, 6554, 4194}},
  {{ 9362, 5825, 9362, 5825},{ 5825, 3647, 5825, 3647},{ 9362, 5825, 9362, 5825},{ 5825, 3647, 5825, 3647}},
  {{ 8192, 5243, 8192, 5243},{ 5243, 3355, 5243, 3355},{ 8192, 5243, 8192, 5243},{ 5243, 3355, 5243, 3355}},
  {{ 7282, 4559, 7282, 4559},{ 4559, 2893, 4559, 2893},{ 7282, 4559, 7282, 4559},{ 4559, 2893, 4559, 2893}}
};

static const _int16 dequant_coef[6][4][4] = {
  {{10, 13, 10, 13},{ 13, 16, 13, 16},{10, 13, 10, 13},{ 13, 16, 13, 16}},
  {{11, 14, 11, 14},{ 14, 18, 14, 18},{11, 14, 11, 14},{ 14, 18, 14, 18}},
  {{13, 16, 13, 16},{ 16, 20, 16, 20},{13, 16, 13, 16},{ 16, 20, 16, 20}},
  {{14, 18, 14, 18},{ 18, 23, 18, 23},{14, 18, 14, 18},{ 18, 23, 18, 23}},
  {{16, 20, 16, 20},{ 20, 25, 20, 25},{16, 20, 16, 20},{ 20, 25, 20, 25}},
  {{18, 23, 18, 23},{ 23, 29, 23, 29},{18, 23, 18, 23},{ 23, 29, 23, 29}}
};
static const int A[4][4] = {
  { 16, 20, 16, 20},
  { 20, 25, 20, 25},
  { 16, 20, 16, 20},
  { 20, 25, 20, 25}
};


// Notation for comments regarding prediction and predictors.
// The pels of the 4x4 block are labelled a..p. The predictor pels above
// are labelled A..H, from the left I..P, and from above left X, as follows:
//
//  X A B C D E F G H
//  I a b c d
//  J e f g h
//  K i j k l
//  L m n o p
//

// Predictor array index definitions
#define P_X (PredPel[0])
#define P_A (PredPel[1])
#define P_B (PredPel[2])
#define P_C (PredPel[3])
#define P_D (PredPel[4])
#define P_E (PredPel[5])
#define P_F (PredPel[6])
#define P_G (PredPel[7])
#define P_H (PredPel[8])
#define P_I (PredPel[9])
#define P_J (PredPel[10])
#define P_K (PredPel[11])
#define P_L (PredPel[12])

/*!
 ************************************************************************
 * \brief
 *    Make intra 4x4 prediction according to all 9 prediction modes.
 *    The routine uses left and upper neighbouring points from
 *    previous coded blocks to do this (if available). Notice that
 *    inaccessible neighbouring points are signalled with a negative
 *    value in the predmode array .
 *
 *  \para Input:
 *     Starting point of current 4x4 block image posision
 *
 *  \para Output:
 *      none
 ************************************************************************
 */
void intrapred_luma(int img_x,int img_y)
{
  int i,j;
  int s0;
  int PredPel[13];  // array of predictor pels
  byte **imgY_pred = imgY;  // For MB level frame/field coding tools -- set default to imgY

  int block_available_up        = (img->ipredmode[img_x/BLOCK_SIZE+1][img_y/BLOCK_SIZE] >=0);
  int block_available_up_right  = (img->ipredmode[img_x/BLOCK_SIZE+2][img_y/BLOCK_SIZE] >=0);
  int block_available_left      = (img->ipredmode[img_x/BLOCK_SIZE][img_y/BLOCK_SIZE+1] >=0);
  int block_available_up_left   = (img->ipredmode[img_x/BLOCK_SIZE][img_y/BLOCK_SIZE] >=0);

  if(input->InterlaceCodingOption >= MB_CODING && mb_adaptive && img->field_mode)
  {
    imgY_pred     = img->top_field ? imgY_top:imgY_bot;
    if(img->top_field)
    {
      block_available_up        = (img->ipredmode_top[img_x/BLOCK_SIZE+1][img_y/BLOCK_SIZE] >=0);
      block_available_up_right  = (img->ipredmode_top[img_x/BLOCK_SIZE+2][img_y/BLOCK_SIZE] >=0);
      block_available_left      = (img->ipredmode_top[img_x/BLOCK_SIZE][img_y/BLOCK_SIZE+1] >=0);
      block_available_up_left   = (img->ipredmode_top[img_x/BLOCK_SIZE][img_y/BLOCK_SIZE] >=0);
    }
    else
    {
      block_available_up        = (img->ipredmode_bot[img_x/BLOCK_SIZE+1][img_y/BLOCK_SIZE] >=0);
      block_available_up_right  = (img->ipredmode_bot[img_x/BLOCK_SIZE+2][img_y/BLOCK_SIZE] >=0);
      block_available_left      = (img->ipredmode_bot[img_x/BLOCK_SIZE][img_y/BLOCK_SIZE+1] >=0);
      block_available_up_left   = (img->ipredmode_bot[img_x/BLOCK_SIZE][img_y/BLOCK_SIZE] >=0);
    }
  }
  
  if(input->InterlaceCodingOption >= MB_CODING && mb_adaptive)
  {
    if(img->field_mode)
    {
      if(img_x%MB_BLOCK_SIZE == 12 && img_y%MB_BLOCK_SIZE )
        block_available_up_right = 0; // for MB pairs some blocks will not have block available up right  
    }
    else
    {
      if(img_x%MB_BLOCK_SIZE == 12 && img_y%(2*MB_BLOCK_SIZE) )
        block_available_up_right = 0; // for MB pairs some blocks will not have block available up right  
    }

    /*
    if(img_x%MB_BLOCK_SIZE == 12)   
      block_available_up_right = 0; // for MB pairs some blocks will not have block available up right  
      */
  }
  i = (img_x & 15);
  j = (img_y & 15);
  if (block_available_up_right)
  {
    if ((i == 4  && j == 4) ||
        (i == 12 && j == 4) ||
        (i == 12 && j == 8) ||
        (i == 4  && j == 12) ||
        (i == 12 && j == 12))
    {
      block_available_up_right = 0;
    }
  }

  // form predictor pels
  if (block_available_up)
  {
    P_A = imgY_pred[img_y-1][img_x+0];
    P_B = imgY_pred[img_y-1][img_x+1];
    P_C = imgY_pred[img_y-1][img_x+2];
    P_D = imgY_pred[img_y-1][img_x+3];

    if (block_available_up_right)
    {
      P_E = imgY_pred[img_y-1][img_x+4];
      P_F = imgY_pred[img_y-1][img_x+5];
      P_G = imgY_pred[img_y-1][img_x+6];
      P_H = imgY_pred[img_y-1][img_x+7];
    }
    else
    {
      P_E = P_F = P_G = P_H = P_D;
    }
  }
  else
  {
    P_A = P_B = P_C = P_D = P_E = P_F = P_G = P_H = 128;
  }

  if (block_available_left)
  {
    P_I = imgY_pred[img_y+0][img_x-1];
    P_J = imgY_pred[img_y+1][img_x-1];
    P_K = imgY_pred[img_y+2][img_x-1];
    P_L = imgY_pred[img_y+3][img_x-1];
  }
  else
  {
    P_I = P_J = P_K = P_L = 128;
  }

  if (block_available_up_left)
  {
    P_X = imgY_pred[img_y-1][img_x-1];
  }
  else
  {
    P_X = 128;
  }

  for(i=0;i<9;i++)
    img->mprr[i][0][0]=-1;

  ///////////////////////////////
  // make DC prediction
  ///////////////////////////////
  s0 = 0;
  if (block_available_up && block_available_left)
  {   
    // no edge
    s0 = (P_A + P_B + P_C + P_D + P_I + P_J + P_K + P_L + 4)/(2*BLOCK_SIZE);
  }
  else if (!block_available_up && block_available_left)
  {
    // upper edge
    s0 = (P_I + P_J + P_K + P_L + 2)/BLOCK_SIZE;             
  }
  else if (block_available_up && !block_available_left)
  {
    // left edge
    s0 = (P_A + P_B + P_C + P_D + 2)/BLOCK_SIZE;             
  }
  else //if (!block_available_up && !block_available_left)
  {
    // top left corner, nothing to predict from
    s0 = 128;                           
  }

  for (j=0; j < BLOCK_SIZE; j++)
  {
    for (i=0; i < BLOCK_SIZE; i++)
    {
      // store DC prediction
      img->mprr[DC_PRED][i][j] = s0;
    }
  }

  ///////////////////////////////
  // make horiz and vert prediction
  ///////////////////////////////

  for (i=0; i < BLOCK_SIZE; i++)
  {
    img->mprr[VERT_PRED][0][i] = 
    img->mprr[VERT_PRED][1][i] = 
    img->mprr[VERT_PRED][2][i] = 
    img->mprr[VERT_PRED][3][i] = (&P_A)[i];
    img->mprr[HOR_PRED][i][0]  = 
    img->mprr[HOR_PRED][i][1]  = 
    img->mprr[HOR_PRED][i][2]  = 
    img->mprr[HOR_PRED][i][3]  = (&P_I)[i];
  }

  if(!block_available_up)img->mprr[VERT_PRED][0][0]=-1;
  if(!block_available_left)img->mprr[HOR_PRED][0][0]=-1;

  if (block_available_up) 
  {
    // Mode DIAG_DOWN_LEFT_PRED
    img->mprr[DIAG_DOWN_LEFT_PRED][0][0] = (P_A + P_C + 2*(P_B) + 2) / 4;
    img->mprr[DIAG_DOWN_LEFT_PRED][0][1] = 
    img->mprr[DIAG_DOWN_LEFT_PRED][1][0] = (P_B + P_D + 2*(P_C) + 2) / 4;
    img->mprr[DIAG_DOWN_LEFT_PRED][0][2] =
    img->mprr[DIAG_DOWN_LEFT_PRED][1][1] =
    img->mprr[DIAG_DOWN_LEFT_PRED][2][0] = (P_C + P_E + 2*(P_D) + 2) / 4;
    img->mprr[DIAG_DOWN_LEFT_PRED][0][3] = 
    img->mprr[DIAG_DOWN_LEFT_PRED][1][2] = 
    img->mprr[DIAG_DOWN_LEFT_PRED][2][1] = 
    img->mprr[DIAG_DOWN_LEFT_PRED][3][0] = (P_D + P_F + 2*(P_E) + 2) / 4;
    img->mprr[DIAG_DOWN_LEFT_PRED][1][3] = 
    img->mprr[DIAG_DOWN_LEFT_PRED][2][2] = 
    img->mprr[DIAG_DOWN_LEFT_PRED][3][1] = (P_E + P_G + 2*(P_F) + 2) / 4;
    img->mprr[DIAG_DOWN_LEFT_PRED][2][3] = 
    img->mprr[DIAG_DOWN_LEFT_PRED][3][2] = (P_F + P_H + 2*(P_G) + 2) / 4;
    img->mprr[DIAG_DOWN_LEFT_PRED][3][3] = (P_G + 3*(P_H) + 2) / 4;

    // Mode VERT_LEFT_PRED
    img->mprr[VERT_LEFT_PRED][0][0] = (P_A + P_B + 1) / 2;
    img->mprr[VERT_LEFT_PRED][0][1] = 
    img->mprr[VERT_LEFT_PRED][2][0] = (P_B + P_C + 1) / 2;
    img->mprr[VERT_LEFT_PRED][0][2] = 
    img->mprr[VERT_LEFT_PRED][2][1] = (P_C + P_D + 1) / 2;
    img->mprr[VERT_LEFT_PRED][0][3] = 
    img->mprr[VERT_LEFT_PRED][2][2] = (P_D + P_E + 1) / 2;
    img->mprr[VERT_LEFT_PRED][2][3] = (P_E + P_F + 1) / 2;
    img->mprr[VERT_LEFT_PRED][1][0] = (P_A + 2*P_B + P_C + 2) / 4;
    img->mprr[VERT_LEFT_PRED][1][1] = 
    img->mprr[VERT_LEFT_PRED][3][0] = (P_B + 2*P_C + P_D + 2) / 4;
    img->mprr[VERT_LEFT_PRED][1][2] = 
    img->mprr[VERT_LEFT_PRED][3][1] = (P_C + 2*P_D + P_E + 2) / 4;
    img->mprr[VERT_LEFT_PRED][1][3] = 
    img->mprr[VERT_LEFT_PRED][3][2] = (P_D + 2*P_E + P_F + 2) / 4;
    img->mprr[VERT_LEFT_PRED][3][3] = (P_E + 2*P_F + P_G + 2) / 4;

  }

  /*  Prediction according to 'diagonal' modes */
  if (block_available_left) 
  {
    // Mode HOR_UP_PRED
    img->mprr[HOR_UP_PRED][0][0] = (P_I + P_J + 1) / 2;
    img->mprr[HOR_UP_PRED][0][1] = (P_I + 2*P_J + P_K + 2) / 4;
    img->mprr[HOR_UP_PRED][0][2] = 
    img->mprr[HOR_UP_PRED][1][0] = (P_J + P_K + 1) / 2;
    img->mprr[HOR_UP_PRED][0][3] = 
    img->mprr[HOR_UP_PRED][1][1] = (P_J + 2*P_K + P_L + 2) / 4;
    img->mprr[HOR_UP_PRED][1][2] = 
    img->mprr[HOR_UP_PRED][2][0] = (P_K + P_L + 1) / 2;
    img->mprr[HOR_UP_PRED][1][3] = 
    img->mprr[HOR_UP_PRED][2][1] = (P_K + 2*P_L + P_L + 2) / 4;
    img->mprr[HOR_UP_PRED][3][0] = 
    img->mprr[HOR_UP_PRED][2][2] = 
    img->mprr[HOR_UP_PRED][2][3] = 
    img->mprr[HOR_UP_PRED][3][1] = 
    img->mprr[HOR_UP_PRED][3][2] = 
    img->mprr[HOR_UP_PRED][3][3] = P_L;
  }

  /*  Prediction according to 'diagonal' modes */
  if (block_available_up && block_available_left && block_available_up_left) 
  {
    // Mode DIAG_DOWN_RIGHT_PRED
    img->mprr[DIAG_DOWN_RIGHT_PRED][3][0] = (P_L + 2*P_K + P_J + 2) / 4; 
    img->mprr[DIAG_DOWN_RIGHT_PRED][2][0] =
    img->mprr[DIAG_DOWN_RIGHT_PRED][3][1] = (P_K + 2*P_J + P_I + 2) / 4; 
    img->mprr[DIAG_DOWN_RIGHT_PRED][1][0] =
    img->mprr[DIAG_DOWN_RIGHT_PRED][2][1] = 
    img->mprr[DIAG_DOWN_RIGHT_PRED][3][2] = (P_J + 2*P_I + P_X + 2) / 4; 
    img->mprr[DIAG_DOWN_RIGHT_PRED][0][0] =
    img->mprr[DIAG_DOWN_RIGHT_PRED][1][1] =
    img->mprr[DIAG_DOWN_RIGHT_PRED][2][2] =
    img->mprr[DIAG_DOWN_RIGHT_PRED][3][3] = (P_I + 2*P_X + P_A + 2) / 4; 
    img->mprr[DIAG_DOWN_RIGHT_PRED][0][1] =
    img->mprr[DIAG_DOWN_RIGHT_PRED][1][2] =
    img->mprr[DIAG_DOWN_RIGHT_PRED][2][3] = (P_X + 2*P_A + P_B + 2) / 4;
    img->mprr[DIAG_DOWN_RIGHT_PRED][0][2] =
    img->mprr[DIAG_DOWN_RIGHT_PRED][1][3] = (P_A + 2*P_B + P_C + 2) / 4;
    img->mprr[DIAG_DOWN_RIGHT_PRED][0][3] = (P_B + 2*P_C + P_D + 2) / 4;

     // Mode VERT_RIGHT_PRED
    img->mprr[VERT_RIGHT_PRED][0][0] = 
    img->mprr[VERT_RIGHT_PRED][2][1] = (P_X + P_A + 1) / 2;
    img->mprr[VERT_RIGHT_PRED][0][1] = 
    img->mprr[VERT_RIGHT_PRED][2][2] = (P_A + P_B + 1) / 2;
    img->mprr[VERT_RIGHT_PRED][0][2] = 
    img->mprr[VERT_RIGHT_PRED][2][3] = (P_B + P_C + 1) / 2;
    img->mprr[VERT_RIGHT_PRED][0][3] = (P_C + P_D + 1) / 2;
    img->mprr[VERT_RIGHT_PRED][1][0] = 
    img->mprr[VERT_RIGHT_PRED][3][1] = (P_I + 2*P_X + P_A + 2) / 4;
    img->mprr[VERT_RIGHT_PRED][1][1] = 
    img->mprr[VERT_RIGHT_PRED][3][2] = (P_X + 2*P_A + P_B + 2) / 4;
    img->mprr[VERT_RIGHT_PRED][1][2] = 
    img->mprr[VERT_RIGHT_PRED][3][3] = (P_A + 2*P_B + P_C + 2) / 4;
    img->mprr[VERT_RIGHT_PRED][1][3] = (P_B + 2*P_C + P_D + 2) / 4;
    img->mprr[VERT_RIGHT_PRED][2][0] = (P_X + 2*P_I + P_J + 2) / 4;
    img->mprr[VERT_RIGHT_PRED][3][0] = (P_I + 2*P_J + P_K + 2) / 4;

    // Mode HOR_DOWN_PRED
    img->mprr[HOR_DOWN_PRED][0][0] = 
    img->mprr[HOR_DOWN_PRED][1][2] = (P_X + P_I + 1) / 2;
    img->mprr[HOR_DOWN_PRED][0][1] = 
    img->mprr[HOR_DOWN_PRED][1][3] = (P_I + 2*P_X + P_A + 2) / 4;
    img->mprr[HOR_DOWN_PRED][0][2] = (P_X + 2*P_A + P_B + 2) / 4;
    img->mprr[HOR_DOWN_PRED][0][3] = (P_A + 2*P_B + P_C + 2) / 4;
    img->mprr[HOR_DOWN_PRED][1][0] = 
    img->mprr[HOR_DOWN_PRED][2][2] = (P_I + P_J + 1) / 2;
    img->mprr[HOR_DOWN_PRED][1][1] = 
    img->mprr[HOR_DOWN_PRED][2][3] = (P_X + 2*P_I + P_J + 2) / 4;
    img->mprr[HOR_DOWN_PRED][2][0] = 
    img->mprr[HOR_DOWN_PRED][3][2] = (P_J + P_K + 1) / 2;
    img->mprr[HOR_DOWN_PRED][2][1] = 
    img->mprr[HOR_DOWN_PRED][3][3] = (P_I + 2*P_J + P_K + 2) / 4;
    img->mprr[HOR_DOWN_PRED][3][0] = (P_K + P_L + 1) / 2;
    img->mprr[HOR_DOWN_PRED][3][1] = (P_J + 2*P_K + P_L + 2) / 4;
  }
}

/*!
 ************************************************************************
 * \brief
 *    16x16 based luma prediction
 *
 * \para Input:
 *    Image parameters
 *
 * \para Output:
 *    none
 ************************************************************************
 */
void intrapred_luma_16x16()
{
  int s0=0,s1,s2;
  int i,j;
  int s[16][2];

  int ih,iv;
  int ib,ic,iaa;
  byte **imgY_pred = imgY;  // For Mb level field/frame coding tools -- default to frame pred
  int pix_y = img->pix_y; // For MB level field/frame coding tools


  int mb_nr = img->current_mb_nr;
  int mb_width = img->width/16;
  int mb_available_left = (img->mb_x == 0) ? 0 : (img->mb_data[mb_nr].slice_nr == img->mb_data[mb_nr-1].slice_nr);
  int mb_available_up = (img->mb_y == 0) ? 0 : (img->mb_data[mb_nr].slice_nr == img->mb_data[mb_nr-mb_width].slice_nr);
  int mb_available_up_left = (img->mb_x==0 || img->mb_y==0) ? 0 : (img->mb_data[mb_nr].slice_nr == img->mb_data[mb_nr-mb_width-1].slice_nr);

  if(input->UseConstrainedIntraPred)
  {
    if (mb_available_up   && (img->intra_block[mb_nr-mb_width][2]==0 || img->intra_block[mb_nr-mb_width][3]==0))
      mb_available_up   = 0;
    if (mb_available_left && (img->intra_block[mb_nr-       1][1]==0 || img->intra_block[mb_nr       -1][3]==0))
      mb_available_left = 0;
    if (mb_available_up_left && (img->intra_block[mb_nr-mb_width-1][3]==0))
      mb_available_left = 0;
  }

  if(input->InterlaceCodingOption >= MB_CODING && mb_adaptive && img->field_mode)
  {
    if(img->top_field)
    {
      mb_available_up = (img->mb_y/2 == 0) ? 0 : (img->mb_data[mb_nr].slice_nr == img->mb_data[mb_nr-mb_width].slice_nr);
      mb_available_up_left = (img->mb_y/2 == 0 || img->mb_x==0) ? 0 : (img->mb_data[mb_nr].slice_nr == img->mb_data[mb_nr-mb_width-1].slice_nr);
      pix_y   = img->field_pix_y; // set pix_y to field pix_y
      imgY_pred = imgY_top; // set the prediction image to top field
    }
    else
    {
      mb_available_up = ((img->mb_y-1)/2 == 0) ? 0 : (img->mb_data[mb_nr].slice_nr == img->mb_data[mb_nr-mb_width].slice_nr);
      mb_available_up_left = ((img->mb_y-1)/2 == 0 || img->mb_x==0) ? 0 : (img->mb_data[mb_nr].slice_nr == img->mb_data[mb_nr-mb_width-1].slice_nr);
      imgY_pred = imgY_bot;
      pix_y   = img->field_pix_y; // set pix_y to field pix_y
    }
  }

  
  s1=s2=0;
  // make DC prediction
  for (i=0; i < MB_BLOCK_SIZE; i++)
  {
    if (mb_available_up)
      s1 += imgY_pred[pix_y-1][img->pix_x+i];    // sum hor pix
    if (mb_available_left)
      s2 += imgY_pred[pix_y+i][img->pix_x-1];    // sum vert pix
  }
  if (mb_available_up && mb_available_left)
    s0=(s1+s2+16)/(2*MB_BLOCK_SIZE);             // no edge
  if (!mb_available_up && mb_available_left)
    s0=(s2+8)/MB_BLOCK_SIZE;                     // upper edge
  if (mb_available_up && !mb_available_left)
    s0=(s1+8)/MB_BLOCK_SIZE;                     // left edge
  if (!mb_available_up && !mb_available_left)
    s0=128;                                      // top left corner, nothing to predict from

  for (i=0; i < MB_BLOCK_SIZE; i++)
  {
    // vertical prediction
    if (mb_available_up)
      s[i][0]=imgY_pred[pix_y-1][img->pix_x+i];