static RGBImage rgbVisualizeRectsZoomed(RGBImage img, L<Rect> rects) {
  int markColor = 0xFF0000;
  int w = img.w(), h = img.h();
  RGBImage img2 = new RGBImage(w*2, h*2);
  for y to h: for x to w: {
    int color = img.getInt(x, y);
    img2.setPixel(x*2, y*2, color);
    img2.setPixel(x*2, y*2+1, color);
    img2.setPixel(x*2+1, y*2+1, color);
    img2.setPixel(x*2+1, y*2+1, color);
  }
  for (Rect r : rects) {
    int x1 = r.x, y1 = r.y, x2 = r.x2(), y2 = r.y2();
    for (int x = x1; x <= x2; x++) {
      img2.setPixel(x*2, y1*2, markColor);
      img2.setPixel(x*2, y2*2, markColor);
    }
    for (int y = y1; y <= y2; y++) {
      img2.setPixel(x1*2, y*2, markColor);
      img2.setPixel(x2*2, y*2, markColor);
    }
  }
  ret img2;
}