binsort.cpp

/*
histogram sort, from vlfeat/mser.c
*/
 /* -----------------------------------------------------------------
   *                                          Sort pixels by intensity
   * -------------------------------------------------------------- */

  {
    vl_uint buckets [ VL_MSER_PIX_MAXVAL ] ;

    /* clear buckets */
    memset (buckets, 0, sizeof(vl_uint) * VL_MSER_PIX_MAXVAL ) ;

    /* compute bucket size (how many pixels for each intensity
       value) */
    for(i = 0 ; i < (int) nel ; ++i) {
      vl_mser_pix v = im [i] ;
      ++ buckets [v] ;
    }

    /* cumulatively add bucket sizes */
    for(i = 1 ; i < VL_MSER_PIX_MAXVAL ; ++i) {
      buckets [i] += buckets [i-1] ;
    }

    /* empty buckets computing pixel ordering */
    for(i = nel ; i >= 1 ; ) {
      vl_mser_pix v = im [ --i ] ;
      vl_uint j = -- buckets [v] ;
      perm [j] = i ;
    }
}