final sclass BWIntegralImage implements MakesBufferedImage, IBWIntegralImage {

  int w, h;

  int[] data; // 1 entry per pixel

  ifdef BWIntegralImage_CountAccesses

    long accesses;

  endifdef

  *() {}

  *(File f) { this(loadImage2(f)); }

  *(MakesBufferedImage img) { this(toBufferedImage(img)); }

  //*(BufferedImage img) { this(BWImage(img)); }

  *(BufferedImage image) ctex {

    alloc(image.getWidth(), image.getHeight());

    // Just grab directly into data array

    PixelGrabber pixelGrabber = new PixelGrabber(image, 0, 0, w, h, data, 0, w);

    if (!pixelGrabber.grabPixels())

      fail("Could not grab pixels");

    int sum = 0;

    for x to w: {

      int packed = data[x];

      int brightness = packedToBrightness(packed);

      data[x] = (sum += brightness);

    }

    ifdef BWIntegralImage_useVectorAPI

      import jdk.incubator.vector.*;

      VectorSpecies<Int> species = IntVector.SPECIES_PREFERRED;

      int upperBound = species.loopBound(w);

    endifdef

    int i = w;

    for (int y = 1; y < h; y++) {

      sum = 0;

      ifdef BWIntegralImage_useVectorAPI

        int x = 0;

        for (; x < upperBound; x += species.length(), i += species.length()) {

          for (int sub = 0; sub < species.length(); sub++) {

            sum += packedToBrightness(data[i+sub]);

            data[i+sub] = sum;

          }

          IntVector v = IntVector.fromArray(species, data, i);

          IntVector v_last = IntVector.fromArray(species, data, i-w);

          v = v.add(v_last);

          v.intoArray(data, i);

        }

        for (; x < w; x++, i++) {

          int packed = data[i];

          int brightness = packedToBrightness(packed);

          sum += brightness;

          data[i] = sum + data[i-w];

        }

      endifdef

      ifndef BWIntegralImage_useVectorAPI

        for x to w: {

          int packed = data[i];

          int brightness = packedToBrightness(packed);

          sum += brightness;

          data[i] = sum + data[i-w];

          i++;

        }

      endifndef

    } // for y

  }

  *(BWImage img) {

    alloc(img.w(), img.h());

    data = new int[w*h];

    int i = 0;

    for y to h: {

      int sum = 0;

      for x to w: {

        sum += img.getByte(x, y) & 0xFF;

        data[i] = y > 0 ? sum + data[i-w] : sum;

        i++;

      }

    }

  }

  private void alloc(int w, int h) {

    this.w = w;

    this.h = h;

    if (w*h > 8*1024*1024)

      fail("Image too large (more than 8 MP): " + w + "*" + h);

    data = new int[w*h];

  }

  // pixels outside of image are considered black

  int get(int x, int y) {

    ifdef BWIntegralImage_CountAccesses

      ++accesses;

    endifdef

    ret x < 0 || y < 0 || x >= w || y >= h ? 0

      : data[min(y, h-1)*w+min(x, w-1)];

  }

  public int getIIValue(int x, int y) { ret get(x, y); }

  public double getPixelAverage(int x1, int y1, int x2, int y2) {

    int area = (x2-x1)*(y2-y1);

    ret doubleRatio(bwIntegralImage_sumRect(this, x1, y1, x2, y2), area);

  }

  int getPixel(int x, int y) {

    ret bwIntegralImage_sumRect(this, x, y, x+1, y+1);

  }

  int getPixel(Pt p) { ret getPixel(p.x, p.y); }

  public int getWidth() { ret w; }

  public int getHeight() { ret h; }

  // unoptimized

  public BufferedImage getBufferedImage() {

    ret scaleDownUsingIntegralImageBW(this, w).getBufferedImage();

  }

  int packedToBrightness(int packed) {

    int b = (packed & 0xFF);

    ifdef BWIntegralImage_brightnessCheat

      ret b;

    endifdef

    ifndef BWIntegralImage_brightnessCheat

      int r = ((packed >> 16) & 0xFF);

      int g = ((packed >> 8) & 0xFF);

      ret (r+g+b+1)/3;

    endifndef

  }

}