// result image is as large as the region's bounds
// with black pixels inside and white pixels outside the region
srecord noeq RegionToImage2B(IPixelSet region) {
  settable Rect bounds;
  Image2B image;
  
  run {
    bounds if null = region.bounds();
    int x1 = bounds.x, y1 = bounds.y, w = bounds.w, h = bounds.h, i = 0;
    byte[] pixels = new[(w*h+7)/8];
    for y to h:
      for x to w: {
        if (!region.contains(x1+x, y1+y))
          pixels[i/8] |= 1 << (i & 7);
        i++;
      }
      
    image = new Image2B(w, h, pixels);
  }
  
  Image2B get() {
    if (image == null) run();
    ret image;
  }
}

Began life as a copy of #1034574