OTSU方法计算图像二值化的自适应阈值

2004年09月02日 10:42:00

int otsu (unsigned char *image, int rows, int cols, int x0, int y0, int dx, int dy, int vvv)
{

  unsigned char *np;      // 图像指针
  int thresholdValue=1; // 阈值
  int ihist[256];             // 图像直方图，256个点

  int i, j, k;          // various counters
  int n, n1, n2, gmin, gmax;
  double m1, m2, sum, csum, fmax, sb;

  // 对直方图置零...
  memset(ihist, 0, sizeof(ihist));

  gmin=255; gmax=0;
  // 生成直方图
  for (i = y0 + 1; i < y0 + dy - 1; i++) {
    np = &image[i*cols+x0+1];
    for (j = x0 + 1; j < x0 + dx - 1; j++) {
      ihist[*np]++;
      if(*np > gmax) gmax=*np;
      if(*np < gmin) gmin=*np;
      np++;
    }
  }

  // set up everything
  sum = csum = 0.0;
  n = 0;

  for (k = 0; k <= 255; k++) {
    sum += (double) k * (double) ihist[k];   
    n   += ihist[k];                                        
  }

  if (!n) {
    // if n has no value, there is problems...
    fprintf (stderr, "NOT NORMAL thresholdValue = 160\n");
    return (160);
  }

  // do the otsu global thresholding method
  fmax = -1.0;
  n1 = 0;
  for (k = 0; k < 255; k++) {
    n1 += ihist[k];
    if (!n1) { continue; }
    n2 = n - n1;
    if (n2 == 0) { break; }
    csum += (double) k *ihist[k];
    m1 = csum / n1;
    m2 = (sum - csum) / n2;
    sb = (double) n1 *(double) n2 *(m1 - m2) * (m1 - m2);
   
    if (sb > fmax) {
      fmax = sb;
      thresholdValue = k;
    }
  }

  // at this point we have our thresholding value

  // debug code to display thresholding values
  if ( vvv & 1 )
  fprintf(stderr,"# OTSU: thresholdValue = %d gmin=%d gmax=%d\n",
     thresholdValue, gmin, gmax);

  return(thresholdValue);
}

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