Pits or Piles?

I was shooting a group of gravel piles with the drone; moving around; rotating; hooting at different angles and positions,. When I reviewed the images for the day I had two images of the piles that were of the same area, but 180 degrees different in orientation. Curiously one shot looked like piles of gravel while the other looked like pits in the ground and they were shot just about a minute apart, so the lighting had nothing to do with this interesting optical illusion. What made the images transform from positive to negative space? I decided to do a mirror image of the same shot and lo and behold you see it both ways …. a transformative vision.