(a) Except as otherwise provided in this chapter, the Department of the Youth Authority and the Youth Authority Board shall keep under continued study a person in their control and shall retain him or her, subject to the limitations of this chapter, under supervision and control so long as in their judgment that control is necessary for the protection of the public.
(b) The board shall discharge that person as soon as in its opinion there is reasonable probability that he or she can be given full liberty without danger to the public.