'**SUMMARY**
The convex hull of a blob is the shape that would result if you snapped a rubber band around
the blob. So if you had the letter "C" as your blob the convex hull would be the letter "O."
This method returns an image where the source image around the convex hull of the blob is copied
ontop a black background.
**RETURNS**
Returns a SimpleCV Image of the convex hull, cropped to fit.
>>> img = Image("lenna")
>>> blobs = img.findBlobs()
>>> blobs[-1].hullImage().show()'

def hullImage(self):

    return self.mHullImg
