I'm on histogram equalization process. I have quite well understood the math but i don't understand why an histogram on bimodal image fails in image enhancment and what tecniques can i use in this case (some kind of local/adaptive histogram?).

![enter image description here][1]
![enter image description here][2]


  [1]: https://i.sstatic.net/pv76s.png
  [2]: https://i.sstatic.net/VQygg.png