static BWImage removeGrayBorder(BWImage image) {

  float threshold = 0.9f;

  int w = image.getWidth(), h = image.getHeight();

  int x1 = w, x2 = 0, y1 = h, y2 = 0;

  // haha, slow algorithm :)

  for (int y = 0; y < h; y++)

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

      float f = image.getPixel(x, y);

      if (f < threshold || f == 1) {

        x1 = Math.min(x1, x);

        x2 = Math.max(x2, x);

        y1 = Math.min(y1, y);

        y2 = Math.max(y2, y);

      }

    }

  if (x1 == 0 && y1 == 0 && x2 == w-1 && y2 == h-1)

    return image;

  else

    if (x2 < x1 || y2 < y1)

      null;

    else

      return image.clip(x1, y1, x2 - x1 + 1, y2 - y1 + 1);

}