Why do it the easy way? Just kidding Nick 
, I didn’t even try that!
LOL!!! 
I wonder why C4D is exporting a png with so much background space around it? Must be a mesh object stray point perhaps?
I actually like to fit my art into the ellipse or rounded corner boxes whenever possible for a couple of reasons
- A round shape can give you more of a base and sides for the sprite to accurately hit the static elements.
- In Hype physics it also has more "slip" and "bounce" capabilities.
- Rounded corner boxes can give you that nice curved edge and still accommodate a taller or wider piece of artwork.
Tip: Design sprite characters so the base of your character will comfortably nest itself in a circle. Or make it so the base (bottom of feet etc) will sit on the base of a rounded rectangle as well.
Download and tear apart my "saucer-sled Psychos" lots of rounded corners and circles.