static BufferedImage blendBufferedImages(BufferedImage bi1, BufferedImage bi2) {
  ret blendBufferedImages(bi1, bi2, 0.5);
}

static BufferedImage blendBufferedImages(BufferedImage bi1, BufferedImage bi2, double weight2) {
 double weight = 1-weight2;
 
 int width = bi1.getWidth ();
 if (width != bi2.getWidth ())
   fail("widths not equal");

 int height = bi1.getHeight ();
 if (height != bi2.getHeight ())
   fail("heights not equal");

 BufferedImage bi3 = new BufferedImage (width, height,
                     BufferedImage.TYPE_INT_RGB);
 int [] rgbim1 = new int [width];
 int [] rgbim2 = new int [width];
 int [] rgbim3 = new int [width];

 for (int row = 0; row < height; row++)
 {
    bi1.getRGB (0, row, width, 1, rgbim1, 0, width);
    bi2.getRGB (0, row, width, 1, rgbim2, 0, width);

    for (int col = 0; col < width; col++)
    {
      int rgb1 = rgbim1 [col];
      int r1 = (rgb1 >> 16) & 255;
      int g1 = (rgb1 >> 8) & 255;
      int b1 = rgb1 & 255;

      int rgb2 = rgbim2 [col];
      int r2 = (rgb2 >> 16) & 255;
      int g2 = (rgb2 >> 8) & 255;
      int b2 = rgb2 & 255;

      int r3 = (int) (r1*weight+r2*(1.0-weight));
      int g3 = (int) (g1*weight+g2*(1.0-weight));
      int b3 = (int) (b1*weight+b2*(1.0-weight));
      rgbim3 [col] = (r3 << 16) | (g3 << 8) | b3;
    }

    bi3.setRGB (0, row, width, 1, rgbim3, 0, width);
 }

 return bi3;
}