void filterNoise(Img *img) {

  if (!img->data) return;

  for(double *p = img->data, *e = p + 4*img->w*img->h; p < e; p += 4) {

    p[0] = randomFloat();

    p[1] = randomFloat();

    p[2] = randomFloat();

    p[3] = randomFloat();

  }

}

void filterMulNoise(Img *img, int w, int h, double vmin, double vmax) {

  if (!img->data || w <= 0 || h <= 0) return;

  Img imgC = {};

  imgInit(&imgC, w, h);

  filterNoise(&imgC);

  for(int y = 0; y < img->h; ++y) {

    for(int x = 0; x < img->w; ++x) {

      double pn[4];

      imgCubic(&imgC, (double)x/img->w*w, (double)y/img->h*h, pn);

      double *p = imgPixel(img, x, y);

      p[0] *= vmin + (vmax - vmin)*pn[0];

      p[1] *= vmin + (vmax - vmin)*pn[1];

      p[2] *= vmin + (vmax - vmin)*pn[2];

      p[3] *= vmin + (vmax - vmin)*pn[3];

    }

  }

  imgDestroy(&imgC);

}

void filterMulNoiseGray(Img *img, int w, int h, double vmin, double vmax) {

  if (!img->data || w <= 0 || h <= 0) return;

  Img imgC = {};

  imgInit(&imgC, w, h);

  filterNoise(&imgC);

  for(int y = 0; y < img->h; ++y) {

    for(int x = 0; x < img->w; ++x) {

      double pn = vmin + (vmax - vmin)*imgCubicCh(&imgC, 0, (double)x/img->w*w, (double)y/img->h*h);

      double *p = imgPixel(img, x, y);

      p[0] *= pn;

      p[1] *= pn;

      p[2] *= pn;

      //p[3] *= pn;

    }

  }

  imgDestroy(&imgC);

}