remove brown spots

https://www.youtube.com/watch?v=BDZSZh6ikYA
https://www.youtube.com/watch?v=x_MMalaAXg4
https://www.youtube.com/watch?v=hAUjqXDirgg
https://www.youtube.com/watch?v=0PHepWwFvD4
https://www.youtube.com/watch?v=pOUO4qvbjT0