python opencv extract multiple images in png spritesheet

Question

I have some spritesheets that are packed with multiple images (with different size) inside separated with transparent spcae.

I want to extract individual images and save them. So far i was able to create this abstraction in red and yellow.

I don't know how to proceed in finding the bounding boxes of all those.

If you can point me to some numpy or opencv methods that can help.