Can someone please explain to me what a mutable bitmap is? What advantages/disadvantages or what limitations do mutable and immutable bitmaps have?
It's about the same difference as with String vs StringBuilder - String is immutable so you can't change its content (well at least not without any hacks), while for StringBuilder you can change its content.
In order to convert an immutable bitmap to a mutable one, check out this post: https://stackoverflow.com/a/16314940/878126.