经典水印算法qim源码.txt

qim是与扩频水印并列的算法。他有很多特性

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

double quantize(double value, double delta) {
  int q = rint(value / delta);
  if ((value - delta * q) <= (delta * (q + 1) - value))
    return delta * q;
  else
    return delta * (q + 1);
}

void quantize_vector(double s[], double x[], double dither[], double delta, int n) {
  int i;

  for (i = 0; i < n; i++) 
    s[i] = quantize(x[i] + dither[i], delta) - dither[i];
}

void print_vector(double x[], int n) {
  int i;
  
  for (i = 0; i < n; i++)
    printf("%.2f ", x[i]);

  printf("\n");
}

void print_bits(char x[], int n) {
  int i;
  
  for (i = 0; i < n; i++)
    printf("%c", x[i] ? '1' : '0');

  printf("\n");
}

double sqr(double x) {
  return x * x;
}

double distance(double y[], double dither[], double delta, int n) {
  int i;
  double sum = 0.0;

  for (i = 0; i < n; i++) 
    sum += sqr(y[i] - (quantize(y[i] + dither[i], delta) - dither[i]));

  return sum;
}

int decode_vector(double y[], double **dither, double delta, int l) {
  return (distance(y, dither[0], delta, l) < distance(y, dither[1], delta, l)) ? 0 : 1;
}

int main(int argc, char *argv[]) {
  double *s, *x, *y;
  double delta, delta2;
  double **dither;
  int n;
  int i;

  int nbits;
  char *bits, *bits2;
  int l;

  srandom(1234);

  delta = 10.0;
  delta2 = delta / 2.0;

  nbits = 10000;
  bits = malloc(nbits * sizeof(char));
  bits2 = malloc(nbits * sizeof(char));
  for (i = 0; i < nbits; i++) {
    bits[i] = (random() > RAND_MAX / 2) ? 0 : 1;
    bits2[i] = 0;
  }

  printf("original bits\n");
  print_bits(bits, nbits);

  l = 140;
  dither = malloc(2 * sizeof(double *));
  dither[0] = malloc(l * sizeof(double));
  dither[1] = malloc(l * sizeof(double));
  for (i = 0; i < l; i++) {
    dither[0][i] = (random() / (double) RAND_MAX) * delta - delta2;
    if (dither[0][i] < 0.0)
      dither[1][i] = dither[0][i] + delta2;
    else
      dither[1][i] = dither[0][i] - delta2;
  }

  printf("dither 0\n");
  print_vector(dither[0], l);
  printf("dither 1\n");
  print_vector(dither[1], l);

  n = l * nbits;
  s = malloc(n * sizeof(double));
  x = malloc(n * sizeof(double));
  y = malloc(n * sizeof(double));
  for (i = 0; i < n; i++) {
    x[i] = (random() / (double) RAND_MAX) * 255.0;
    s[i] = 0.0;
    y[i] = 0.0;
  }

  printf("original\n");
  print_vector(x, n);

  for (i = 0; i < nbits; i++) {
    int bit = bits[i];
    quantize_vector(s + l*i, x + l*i, dither[bit], delta, l);    
  }

  printf("watermarked\n");
  print_vector(s, n);

  for (i = 0; i < n; i++) {
    y[i] = s[i] + 5 * ((random() / (double) RAND_MAX) - 0.5);
  }

  printf("attacked\n");
  print_vector(y, n);

  for (i = 0; i < n; i++) {
    if (i > 200 && i < 300)
      y[i] = 0;
  }

 printf("zeroed\n");
 print_vector(y, n);

  for (i = 0; i < nbits; i++) {
    bits2[i] = decode_vector(y + l*i, dither, delta, l);    
  }


  printf("decoded bits\n");
  print_bits(bits2, nbits);

  for (i = 0; i < nbits; i++)
    if (bits[i] != bits2[i]) 
      printf("error bit #%d\n", i);

  exit(0);
}