When the band arrived in Mexico to start the film production on the South American leg of the tour, he says, "I'm embarrassed to say I wasn't looking the best. I don't think I'm the most vain of rock 'n' roll stars you'll meet, but I had a panic attack at the thought of a 3-D, 40-foot arse. But by the time we got to Buenos Aires, I was back on track. But some of the shots I can see, I can't help thinking, 'You fat bastard …' "

The movie also has had an effect on band unity, giving them all a clearer perspective on what the others do. Bono marvels at bassist Adam Clayton's renewed prowess, while The Edge says he wondered if Larry Mullen Jr. felt isolated stuck on the top platform of the massive stage with his drums.

"He's very assertive, Adam is, in this," Bono says. "On this last tour, he really came out of himself. He's kind of the 'wise owl' of the band, and he has become a bit of a hermit. He withdraws to his fine art and quite cerebral life, and on this movie, he's a real proper rock star."

Keeping emotions in check

Bono recalls the performance in Sydney during the early 1990s when Clayton "had a terrible turn" struggling with alcoholism and missed a show, threatening the unity of the band. In those days, Bono says, Clayton "was hanging on to his bass for dear life, and he's frightened about what's happening to him. You cut to where he is now, this person who is filled by the music and strength and joy … and he's with his friends, and he's alive and loving being alive. You can never know what that feels like."

Though fans might not notice such nuance, Bono says the movie captures the inner lives of his friends. "I see Edge's frustration. He was going through some tricky things at the start of this tour in Buenos Aires, and there's proper violence in the guitar playing. That is the right arena for your despair."

The Edge adds, "Some of my best shows and indeed probably the worst shows I ever played in U2 were filmed for this 3-D movie. The final show of the tour, for some very sort of personal reasons to do with family and health, what have you — it was the only time I ever played a U2 show where I didn't want to be there. Thankfully, looking at the film I can't see that."