void filterWind(Img *img, Img *pattern, double att) {

  if (!img->data) return;

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

    double nk = pattern && pattern->data ? imgCubicHCh(pattern, 0, (double)x/img->w*pattern->w, 0) : 1;

    double acc[4] = {};

    double a = 1 - pow(1 - att, nk);

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

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

      for(int c = 0; c < 4; ++c) {

        if (cl[c] < acc[c]) {

          cl[c] = acc[c];

        } else

        if (acc[c] < cl[c]) {

          acc[c] = cl[c];

        }

        acc[c] *= a;

      }

    }

  }

}