title: using a loop to change color of pixels according to calculations
body: <p>I am just starting to learn jython, and just have a question which I cannot seem to get right.</p>
  
  <p>From my text, I am to create a picture that is 640 x 480 pixels, and then, using a loop, pixel by pixel set the color to a calculation for r, g, b which we have already been given.
  I can create a picture, I can set variables, however I cannot seem to go any further in creating a loop to set each pixel colour.
  I know its only simple, but just wandering if anyone can help me out here.</p>