code: public boolean forall(PixelPredicate predicate) {
          return Arrays.stream(points()).allMatch(p -> predicate.test(p.x, p.y, pixel(p)));
      }
docs: Returns true if the predicate is true for all pixels in the image.
  
  @param predicate a predicate function that accepts 3 parameters - the x,y coordinate and the pixel at that coordinate
  @return true if f holds for at least one pixel