VENICE — Johnny Depp starrer “Black Mass” world premiered to positive response Friday at the Venice Film Festival where a relaxed Depp held court, musing on the challenges of playing Boston gangster James “Whitey” Bulger in a natural fashion. Talking about his dramatically receding hairline in the film, he said he feels risky physical transformations are part of his duty to give audiences “something new each time.”

Director Scott Cooper’s biopic of Bulger, who became an FBI informant and used this status to eliminate criminal competition during the 1970s, ’80s and early ’90s, was greeted with applause at the Venice press screening, and the press conference was packed to the rafters.

Depp downplayed the purely criminal component of Bulger, whom he described as a man of “very proud Irish immigrant stock, who was loyal to his neighborhood. He would help a little old old lady bring groceries into her home and then a few minutes later go bash somebody’s head in.”

Asked whether it had been difficult for him as an actor to tap into the evil side of the Winter Hill gang boss — who has been indicted in connection with 19 murders — Depp quipped: “I found the evil in myself a long time ago. I accept it, we are old friends. But with James Bulger, I think you have to approach him as just a human being.”

Just as important to getting the character right was the physical transformation, which involved latex, contacts and dramatically receding whitish-blond hair.

“I thought it was very important to look as much like Jimmy Bulger as humanly possible,” Depp said. “My eyeballs are black as the ace of spades. So the blue contacts were hand-painted because they need to be piercing; they needed to cut through you.”

He said transformations like these are “very challenging, and I think that’s important as an actor, to test yourself, challenge yourself each time. Take the chance that you may actually fall flat on your face and look like a complete ass. That’s what I do for a living!”

Director Cooper said when Bulger’s longtime attorney visited the set,”I saw him shaking his head. I walked over to him and I said, ‘Did we not get something right?’ He said, ‘No. I have known this man forever and to see him play him the way he does is uncanny, and it’s chilling.”

Warner Bros. will release “Black Mass” on Sept. 18 in the U.S.