The Redraw region is a 2D region that define the portion of the image (in "Frm" space) that need to be redrawn.  If your module change the values of a pixel, it then need to add this pixel to the region to be redrawn if you want your change to be visible on the screen.  You also need to set the general "Redraw" flag and the one associated with the frame to the correct value. The next time sliceOmatic does an actual redraw, it will refresh the designated region and reset it for the next redraw.