code: public T subimage(int x0, int y0, int x1, int y1 ) {
  		return subimage(x0,y0,x1,y1,null);
  	}
docs: Same as {@link #subimage(int, int, int, int, ImageBase)}, but sets the storage for the input subimage
  to null.
  
  @param x0 x-coordinate of top-left corner of the sub-image, inclusive.
  @param y0 y-coordinate of top-left corner of the sub-image, inclusive.
  @param x1 x-coordinate of bottom-right corner of the sub-image, exclusive.
  @param y1 y-coordinate of bottom-right corner of the sub-image, exclusive.
  @return A sub-image of 'this' image.