Katy Perry, label to pay $4m for song copy

It was an underdog victory for rapper Marcus Gray, a relatively obscure artist once known as Flame whose 5-year-old lawsuit survived constant court challenges and a trial against top-flight attorneys for Perry and the five other music-industry heavyweights who wrote her song.

But the amount was less than the nearly $US20 million sought by attorneys for Gray and his two co-writers on the 2009 song Joyful Noise but they said they were pleased with the decision.

"These defendants have made millions and millions of dollars from their infringement of the plaintiff's copyright," Gray's attorney, Michael A Kahn, told the jury.

Perry herself was hit for just over $US550,000, with Capitol Records responsible for the vast majority of the money.

Defence attorneys had argued for an award of about $US360,000 after the jury decided earlier this week that Dark Horse copied Joyful Noise.

Perry's attorney, Christine Lepera, said they plan to vigorously fight the decision.

"The writers of Dark Horse consider this a travesty of justice," Lepera said.

Because the rhythmic instrumental riff from Joyful Noise plays through 45 per cent of Dark Horse" Kahn said his clients were entitled to 45 per cent of the entire earnings of Perry's album Prism, where her song appears.

The defence recommended dividing the award money by the number of songs on the album.

At the end of the first phase of the trial Monday, jurors surprised many by finding all six writers of Dark Horse were liable for copying from Joyful Noise, though only a section of the instrumental track was in dispute.

That included Perry, who only co-wrote the lyrics to the song, and Juicy J, who only provided a rap break for it.

All the songwriters testified that they had never heard of Gray or his song before he and co-writers Emanuel Lambert and Chike Ojukwu sued five years ago.

Australian Associated Press