git.sesse.net Git - x264/blob - doc/dct.txt

   1 /****************************************************************************
   2  * DCT/IDCT functions
   3  ****************************************************************************/
   4 /* be carefull that "dct" could be equal to "luma" (ie dct_4x4(dct,dct) )*/
   5 static void dct_2x2_dc( int16_t dct[2][2], int16_t chroma[2][2] )
   6 {
   7     int tmp[2][2];
   8
   9     tmp[0][0] = chroma[0][0] + chroma[0][1];
  10     tmp[1][0] = chroma[0][0] - chroma[0][1];
  11     tmp[0][1] = chroma[1][0] + chroma[1][1];
  12     tmp[1][1] = chroma[1][0] - chroma[1][1];
  13
  14     dct[0][0] = tmp[0][0] + tmp[0][1];
  15     dct[0][1] = tmp[1][0] + tmp[1][1];
  16     dct[1][0] = tmp[0][0] - tmp[0][1];
  17     dct[1][1] = tmp[1][0] - tmp[1][1];
  18 }
  19
  20 static void idct_2x2_dc( int16_t dct[2][2], int16_t chroma[2][2] )
  21 {
  22     dct_2x2_dc( chroma, dct );
  23 }
  24
  25 static void dct_4x4_dc( int16_t dct[4][4], int16_t luma[4][4] )
  26 {
  27     int16_t tmp[4][4];
  28     int i;
  29
  30     for( i = 0; i < 4; i++ )
  31     {
  32         tmp[0][i] = luma[i][0] + luma[i][1] + luma[i][2] + luma[i][3];
  33         tmp[1][i] = luma[i][0] + luma[i][1] - luma[i][2] - luma[i][3];
  34         tmp[2][i] = luma[i][0] - luma[i][1] - luma[i][2] + luma[i][3];
  35         tmp[3][i] = luma[i][0] - luma[i][1] + luma[i][2] - luma[i][3];
  36     }
  37
  38     for( i = 0; i < 4; i++ )
  39     {
  40         dct[0][i] = ( tmp[i][0] + tmp[i][1] + tmp[i][2] + tmp[i][3] + 1) / 2;
  41         dct[1][i] = ( tmp[i][0] + tmp[i][1] - tmp[i][2] - tmp[i][3] + 1) / 2;
  42         dct[2][i] = ( tmp[i][0] - tmp[i][1] - tmp[i][2] + tmp[i][3] + 1) / 2;
  43         dct[3][i] = ( tmp[i][0] - tmp[i][1] + tmp[i][2] - tmp[i][3] + 1) / 2;
  44     }
  45 }
  46
  47 static void dct_4x4( int16_t dct[4][4], int16_t luma[4][4] )
  48 {
  49     int16_t tmp[4][4];
  50     int i;
  51
  52     for( i = 0; i < 4; i++ )
  53     {
  54         tmp[0][i] =   luma[i][0] +   luma[i][1] +   luma[i][2] +   luma[i][3];
  55         tmp[1][i] = 2*luma[i][0] +   luma[i][1] -   luma[i][2] - 2*luma[i][3];
  56         tmp[2][i] =   luma[i][0] -   luma[i][1] -   luma[i][2] +   luma[i][3];
  57         tmp[3][i] =   luma[i][0] - 2*luma[i][1] + 2*luma[i][2] -   luma[i][3];
  58     }
  59
  60     for( i = 0; i < 4; i++ )
  61     {
  62         dct[0][i] =   tmp[i][0] +   tmp[i][1] +   tmp[i][2] +   tmp[i][3];
  63         dct[1][i] = 2*tmp[i][0] +   tmp[i][1] -   tmp[i][2] - 2*tmp[i][3];
  64         dct[2][i] =   tmp[i][0] -   tmp[i][1] -   tmp[i][2] +   tmp[i][3];
  65         dct[3][i] =   tmp[i][0] - 2*tmp[i][1] + 2*tmp[i][2] -   tmp[i][3];
  66     }
  67 }
  68
  69 static void idct_4x4( int16_t dct[4][4], int16_t luma[4][4] )
  70 {
  71     int16_t tmp[4][4];
  72     int i;
  73
  74     for( i = 0; i < 4; i++ )
  75     {
  76         tmp[0][i] = dct[0][i]   +  dct[1][i]     + dct[2][i]   + (dct[3][i]>>1);
  77         tmp[1][i] = dct[0][i]   + (dct[1][i]>>1) - dct[2][i]   -  dct[3][i];
  78         tmp[2][i] = dct[0][i]   - (dct[1][i]>>1) - dct[2][i]   +  dct[3][i];
  79         tmp[3][i] = dct[0][i]   -  dct[1][i]     + dct[2][i]   - (dct[3][i]>>1);
  80     }
  81
  82     for( i = 0; i < 4; i++ )
  83     {
  84         /* XXX XXX use >> 6 and not / 64 -> doesn't give the same result :((((((((( */
  85         luma[i][0] = ( tmp[i][0] +  tmp[i][1]     + tmp[i][2] + (tmp[i][3]>>1) + 32 ) >> 6;
  86         luma[i][1] = ( tmp[i][0] + (tmp[i][1]>>1) - tmp[i][2] -  tmp[i][3]     + 32 ) >> 6;
  87         luma[i][2] = ( tmp[i][0] - (tmp[i][1]>>1) - tmp[i][2] +  tmp[i][3]     + 32 ) >> 6;
  88         luma[i][3] = ( tmp[i][0] -  tmp[i][1]     + tmp[i][2] - (tmp[i][3]>>1) + 32 ) >> 6;
  89     }
  90 }
  91 static void idct_4x4_dc( int16_t dct[4][4], int16_t luma[4][4] )
  92 {
  93     int16_t tmp[4][4];
  94     int i;
  95
  96     for( i = 0; i < 4; i++ )
  97     {
  98         tmp[0][i] = dct[0][i] + dct[1][i] + dct[2][i] + dct[3][i];
  99         tmp[1][i] = dct[0][i] + dct[1][i] - dct[2][i] - dct[3][i];
 100         tmp[2][i] = dct[0][i] - dct[1][i] - dct[2][i] + dct[3][i];
 101         tmp[3][i] = dct[0][i] - dct[1][i] + dct[2][i] - dct[3][i];
 102     }
 103
 104     for( i = 0; i < 4; i++ )
 105     {
 106         luma[i][0] = ( tmp[i][0] + tmp[i][1] + tmp[i][2] + tmp[i][3] ) ;
 107         luma[i][1] = ( tmp[i][0] + tmp[i][1] - tmp[i][2] - tmp[i][3] ) ;
 108         luma[i][2] = ( tmp[i][0] - tmp[i][1] - tmp[i][2] + tmp[i][3] ) ;
 109         luma[i][3] = ( tmp[i][0] - tmp[i][1] + tmp[i][2] - tmp[i][3] ) ;
 110     }
 111 }