Keira Knightley thinks "people look down on" actresses like herself.

The British star feels that some leading ladies are often dismissed as "just a pretty face".

But the actress explained that with the right kind of movie role you can alter the public perception.

"I think people really look down particularly on women in big-budget films. It's like you're just a pretty face which is fair," she told British newspaper The Sun. "So a lot of the negative attention is because of that. So all of a sudden you do work where people go, 'Oh, OK, I can see the work' "

Keira is currently promoting new movie A Dangerous Method, which sees her tackle a difficult character.

In the film she portrays Sabina Spielrein, a psychiatric patient who is obsessed with sado-masochistic sexual games and develops an intense relationship with Sigmund Freud.

The Pirates of the Caribbean star insisted she had nothing in common with the troubled young woman and didn't find it difficult to shed her on-screen persona once filming had finished.

"People talk about how infamous the post-job blues are and I think a lot of that has to do with re-finding where you are and getting the other thing off," she explained. "You do find you're suddenly in a mood in the middle of playing something and you think, 'Is that my mood or is that actually nothing to do with me? Is it this other character that I've got living on my shoulder at the moment?' That was not the case with this at all. In fact, quite the reverse."