How do I add a spotlights to an image
<p>I have an image that I want to show some 'spotlights' on, like they do on TV.  The rest of the image should be darker than the original, and the person that I'm spotlighting should be normal.  I have the x,y and radius of the spotlight, but I'm not sure how to change the brightness at that location.  </p>

<p>Also, if I have two spotlights and they intersect, the intersection should be brighter than either of the spotlights.  </p>
