Does the emission of semen during sleep or upon waking necessitate ghusl?

If a person who has experienced a wet dream sees semen after waking up, ghusl (ritual bath) becomes obligatory for him, whether the semen is alone or accompanied by urine. The emission of semen during sleep, whether with or without lust, is, by consensus, one of the things that necessitate ghusl. The same applies to when it occurs in a waking state, if accompanied by lust.