best way to downsample then upsample with ofxCv?

[batchku]

I'm working on an application where i need to find contours in the image from a live camera feed, and then use those contours to process the image.

I'd like to do the contour finding on a downsampled version of the image to save CPU, then up sample; i can easy apply .resize() to the input ofImage for the downsampling; but once i have the contourFinder.getPolylines, what's the best way to scale them back up to match with the size of my live feed?