When Harry Gregson-Williams attended the premiere of Michael Mann’s “Blackhat,” he was stunned to find very little of his 90 minutes of score left in the movie. He joins an ever-growing list of celebrated composers who have had all or part of their scores tossed by directors over the years, including Henry Mancini (Hitchcock’s “Frenzy”), Alex North (Kubrick’s “2001”) and Jerry Goldsmith (Ridley Scott’s “Legend”).

Gregson-Williams (“Kingdom of Heaven,” the “Shrek” films) was one of at least six composers who worked on “Blackhat” over the course of a year, and he is one of the two main credited composers. Atticus Ross (“Gone Girl,” “The Social Network”) is the other.

After attending the premiere, Gregson-Williams posted on Facebook that “the ‘score’ for ‘Blackhat’ may be credited to me but contains almost none of my compositions. … I was not the author of most of what is now in the movie.”

He added: “I therefore reluctantly join the long list of composers who have had their scores either sliced and diced mercilessly or ignored completely by Michael Mann. This is his film and these are his decisions, and I do respect that, but see no reason to have people mistake this score for one that I composed, or in any way approved of musically.”

Gregson-Williams later told Variety that he simply didn’t want his fans, seeing the film, to mistake the music in “Blackhat” as his. “I knew going into it that (Mann) would mix and match his favorite tracks. He would get a composer who he felt was good at certain things to do one thing, and another composer to do another.

“That’s not to say that I would approve of how he goes about that. But I have no complaints about it. I respect his way of doing things.” But, as he said in his original Facebook post, the movie contained music that “shocked and surprised” him and, because “my name is right there listed as the lead composer, one would expect that to mean something, but it doesn’t. And I do care about that.”

Gregson-Williams declined further comment, and deleted his Facebook post after a day. Ross also declined comment.

In a statement, Mann responded: “Harry’s a talented composer whose music needed editing and remixing to fit the contemporary subject and ambitions of our picture. He was one of four composers who contributed to the score, along with Atticus and Leo Ross, Ryan Amon and Mike Dean. It would have been preferable to me, too, if the delivered music could have been used as it was.”

Mann is well known for using multiple composers on his films, dating back to 1981’s “Thief,” for which Craig Safan was called in to augment the work of Tangerine Dream, and to 1992’s “The Last of the Mohicans,” for which Randy Edelman was asked to supplement and complement Trevor Jones’ original score.

Composer Elliot Goldenthal, who initially scored for Mann on “Heat,” said after working with him a second time on “Public Enemies”: “Michael has a propensity to change his mind the whole time. For some people it can be very frustrating. You think you’ve accomplished something, but you never know. It’s Kafkaesque.”

Adds another composer who has collaborated with Mann, and who asked for anonymity: “He gets all this music from loads of people and then puts it together in a way that he likes. He’s not a musician, and sometimes it’s led to something great, and sometimes it hasn’t. I would have dinner with him any night of the week. I just wouldn’t work for him again.”