Katy Perry is not just "fluff", director Jane Lipsitz has said.

The New York filmmaker - who co-directed the US pop star's concert documentary Katy Perry: Part Of Me with Dan Cutforth - said the biggest misconception people have of the singer is that she's not a serious person.

"I think probably that she's fluff and that she doesn't have a lot of depth, and that she doesn't write her songs. There's a lot more to her than all of those things," she said.

"That is probably what people perceive but this movie is meant to say that that's not true - that Katy is smart, writes beautiful songs, is emotional, connects with her fans and has a lot of business acumen."

The film, which is in cinemas now, was shot during Katy's year-long California Dreams world tour, and Jane said that the tight schedule proved to be the biggest challenge.

"The time frame was incredibly intense. We were on a really accelerated schedule - you want to have the time to nuance it, get the right details and really make it feel special," she admitted.

"Trying to turn the film around in such a short period of time was really hard. It was pretty gruelling: it was around-the-clock, seven days a week for three or four months straight."

:: Katy Perry: Part Of Me is in cinemas now.