static int[] ocr_leftProfile(BWImage img, double stopAtRatio) {
  int stopAt = iround(img.getWidth()*stopAtRatio), h = img.getHeight();
  int[] out = new int[h];
  for y to w: {
    int x = 0;
    while (x <= stopAt && img.getPixel(x, y) > 0.5f) ++x;
    out[y] = x;
  }
  ret out;
}