基于线性相关检测的数字水印与隐藏算法源代码详解

/*--------------------------------------------------------------------------*
 | E_BLIND -- embed a watermark by simply adding a message pattern          |
 |                                                                          |
 | Arguments:                                                               |
 |   c -- image to be watermarked (changed in place)                        |
 |   width -- width of img                                                  |
 |   height -- height of img                                                |
 |   m -- one-bit message to embed                                          |
 |   alpha -- embedding strength                                            |
 |   wr -- reference pattern (width x height array of doubles)              |
 |                                                                          |
 | Return value:                                                            |
 |   none                                                                   |
 *--------------------------------------------------------------------------*/

void E_BLIND( unsigned char *c, int width, int height,
              int m, double alpha, double *wr )
{
  static double wm[ MAX_IMG_SIZE ];    /* pattern that encodes m */

  /* Encode the message in a pattern */
  ModulateOneBit( m, wr, wm, width, height );

  /* Scale and add pattern to image (with clipping and rounding) */
  AddScaledPattern( c, width, height, alpha, wm );
}

/*--------------------------------------------------------------------------*
 | D_LC -- detect watermarks using linear correlation                       |
 |                                                                          |

 | Arguments:                                                               |
 |   c -- image                                                             |
 |   width -- width of img                                                  |
 |   height -- height of img                                                |
 |   tlc -- detection threshold                                             |
 |   wr -- reference pattern (width by height array of doubles)             |
 |                                                                          |
 | Return value:                                                            |
 |   decoded message (0 or 1), or NO_WMK if no watermark is found           |
 *--------------------------------------------------------------------------*/

int D_LC( unsigned char *c, int width, int height,
          double tlc, double *wr )
{
  double lc;                           /* linear correlation */
  int m;                               /* decoded message (or NO_WMK) */

  /* Find the linear correlation between the image and the reference
     pattern */
  lc = ImgPatInnerProduct( c, wr, width, height ) / (width * height);

  /* Decode the message */
  if( lc > tlc )
    m = 1;
  else if( lc < -tlc )
    m = 0;
  else
    m = NO_WMK;

  return m;