Can you suggest some image pre-processing technique for 3-D shape detection?

We are actually working on 3-D shape detection of shapes like cube,cuboid,pyramid and sphere. And we are considering the top view of the objects so as the shape appears to be 2-dimentional. The shapes viewed by the camera in top view are not exactly circle,square or triangle. The edges of these 3-D shapes are creating little bit distortion and problem in shape detection.Can you suggest some good image pre-processing techniques to avoid edge distortion.