Keira Knightley says she is grateful for the challenge that her role in Atonement brings.

The Bend It Like Beckham star told Empire magazine that her role as a star-crossed lover in the Ian McEwan adaptation gave her the opportunity to explore her acting limits.

"This is such a relief," she explained. "Not that I don't enjoy all that Pirates stuff but it's not about my character - it's about Johnny (Depp)'s character. It's not focusing on emotional turmoil. It's been great just to get my brain engaged."