1. PImage P1, P2;
   int bg = 0x00;
   int fg = 0xFF;
   int len1, len2;
   void setup()
   {
       size(512, 512, P3D);
       noLoop();
       noStroke();
       len1 = (8 * width / 13);
   }
   void draw()
   {
       //Layer 1
       background(bg);
       fill(fg);
       ellipse(width / 3, height / 2, len1, len1);
       P1 = get();
       //Layer 2
       background(bg);
       fill(fg);
       ellipse(2 * width / 3, height / 2, len1, len1);
       P2 = get();
       imageXOR(P1, P2);
       image(P1,0,0);
   }
   void imageXOR(PImage I1, PImage I2)
   {
       for (int i = 0; i < min(I1.width, I2.width); i++)
           for (int j = 0; j < min(I1.height, I2.height); j++)
               I1.set(i, j, I1.get(i, j) ^ I2.get(i, j));
   }

I have this book teaching me processing and it has this section on bitwise operators, but I can't get any of them to work correctly. Here is the XOR one, for example. The expected output is on the following image:



But the actual output is:



I have copied everything correctly, as far as I can tell. Processing 2.0b7. I can include the other examples' (namely AND and OR) images if things aren't clear enough. Thanks in advance.