white-out the background:
1) read each polygon and load its corresponding image from the Perl-generated text file of polygon coordinates.
2) cycle through each set of polygon coordinates to find the largest and smallest pair of (x,y). Use these values to specify a bounding-box for each soda can.
3) Using the bounding box from (2), crop out the image within this bounding box (should be a single soda can).
4) Translate all polygon coordinates by subtracting the smaller bounding box coordinate from each (so they are with respect to (0,0) rather than the smaller bounding-box coordinate. This is because a new image was created with the bounding box region.)
5) For each pixel in the subimage, check if it is within the bounding polygon. If not, then set that pixel value to 1.0, which is white. To determine if a pixel is within the polygon, the polygon is translated to a new coordinate system where the pixel in question is at the origin. The edges of the polygon are then checked to see if they intersect the x-axis. If the number of intersections is odd, then the pixel is inside the polygon. If the number of intersections is even, then the pixel is not inside the polygon. More details on this algorithm can be found at the aforementioned website.