title: matlab: correct approach to add geometrical objects to image
body: <p>please help with Matlab beginner challenge
  i need to create an image with few geometrical objects (circles,
  ellipses) and then to apply some projective transforms
  my problem is that i cant understand how to actually "draw" on image</p>
  
  <p>image is AFAIU generally  defined as [X;Y;3] matrix,
  functions as SCIRCLE1 can compute/return collection of points
  representing circle, but the problem is that points are not discrete ,
  coordinates are real numbers and not pixels</p>
  
  <p>how can i recompute the scircle output to be valid in image
  coordinates system ? i.e. how can i "pixelize" it?</p>
  
  <p>thanks for your attention, i really missing some basic concept and
  will appreciate your help</p>
  
  <p>John </p>