persistable sclass Image2B is IBinaryImage {

  int w, h;

  byte[] pixels;

  *(int *w, int *h, byte[] *pixels) { cleanPixelArray(); }

  *(Image2B img) {

    w = img.getWidth();

    h = img.getHeight();

    pixels = cloneByteArray(img.pixels);

  }

  *(RGBImage img) {

    w = img.getWidth();

    h = img.getHeight();

    pixels = new byte[(w*h+7)/8];

    for y to h: for x to w:

      if (img.getPixel(x, y).getBrightness() >= 0.5f) {

        int i = y*w+x;

        pixels[i/8] |= 1 << (i & 7);

      }

  }

  *(BWImage img) {

    this(img, 128);

  }

  // >= threshold

  *(BWImage img, int threshold) {

    w = img.w(); h = img.h();

    int n = w*h;

    int nOut = (n+7)/8;

    byte[] pixels = this.pixels = new byte[nOut];

    byte[] bwPixels = img.pixels;

    int iIn = 0;

    // do the bulk

    for (int iOut = 0; iOut < nOut-1; iOut++) {

      int value = 0;

      for bit to 8: {

        value >>= 1;

        if (ubyteToInt(bwPixels[iIn++]) >= threshold)

          value |= 0x80;

      }

      pixels[iOut] = (byte) value;

    }

    // do last (up to 7) bits

    for (; iIn < n; iIn++)

      if (ubyteToInt(bwPixels[iIn]) >= threshold)

        pixels[nOut-1] |= 1 << (iIn & 7);

  }

  *(BufferedImage img) {

    this(img, 128);

  }

  *(BufferedImage img, int threshold) {

    this(BWImage(img), threshold);

  }

  // initializes with black

  *(int *w, int *h) {

    pixels = new byte[(w*h+7)/8];

  }

  RGBImage toRGB() {

    RGBImage img = new RGBImage(w, h, Color.black);

    for y to h: for x to w: {

      int i = y*w+x;

      if ((pixels[i/8] & (1 << (i & 7))) != 0)

        img.setPixel(x, y, Color.white);

    }

    ret img;

  }

  BWImage toBW() {

    BWImage img = new BWImage(w, h, 0f);

    for y to h: for x to w: {

      int i = y*w+x;

      if ((pixels[i/8] & (1 << (i & 7))) != 0)

        img.setPixel(x, y, 1f);

    }

    ret img;

  }

  public BufferedImage getBufferedImage() { ret toBW().getBufferedImage(); }

  // x and y must be inside the image

  public bool getPixel aka getBoolPixel(int x, int y) {

    int i = y*w+x;

    ret (pixels[i/8] & (1 << (i & 7))) != 0;

  }

  // defaultColor is color outside of image

  public bool getPixel aka getBoolPixel(int x, int y, bool defaultColor) {

    if (x < 0 || y < 0 || x >= w || y >= h) ret defaultColor;

    ret getPixel(x, y);

  }

  public void setPixel(int x, int y, bool b) {

    int i = y*w+x;

    byte val = pixels[i/8], shifted = (byte) (1 << (i & 7));

    val = (byte) (b ? val | shifted : val & ~shifted);

    pixels[i/8] = val;

  }

  void setPixel(int x, int y) {

    int i = y*w+x;

    pixels[i/8] |= 1 << (i & 7);

  }

  public int getWidth() { ret w; }

  public int getHeight() { ret h; }

  toString {

    ret "Image2B " + str_px(w, h);

  }

  // clear unused bits in pixel array after we received

  // a possibly dirty array

  void cleanPixelArray {

    int n = w*h;

    if ((n & 7) != 0)

      pixels[n/8] &= (1 << (n & 7))-1;

  }

  public double averageBrightness() {

    ret doubleRatio(bitCount(pixels), w*h);

  }

}