Remove everything that is alpha channel

Is it somehow possible to remove everything that would belong to alpha in a `.png` while converting into a STL via `numpy2stl`? Currently it produces a flat ground/plane, as can be seen in the picture
<img width="640" alt="screen shot 2018-05-18 at 16 35 50" src="https://user-images.githubusercontent.com/3730888/40240761-9954ac4e-5ab9-11e8-89d4-500c5007bd24.png">

Any help appreciated! 👍 