Called by the base class to determine the output bounds of 2-D transforms.
HRESULT retVal = object.DetermineBnds(Bnds);
Bnds [in, out, ref]
On input, Bnds is equal to the union of the input bounds. On output, the derived method should return the size of the transform's output space.
If the transform does not alter the dimensions of the input to produce the output, the derived class doesn't need to override this method.