Robin Thicke, Pharrell Williams and T.I. have launched an appeal against a court's verdict that 'Blurred Lines' was a copyright infringement.

Pharrell Williams

Pharrell Williams

The trio were sued by the estate of the late Marvin Gaye for the song's similarity to his 1997 hit 'Got To Give It Up' last year and were ordered to pay $7.3 million.

The payout was reduced on appeal, but the singer's estate receives 50 per cent of publishing and songwriting revenues from sale of the track.

Robin, Pharrell and T.I. denied any wrong doing at the time and have now vowed to battle the court's decision.

The trio's lawyers filed an opening brief with the ninth circuit court of appeals on Wednesday (24.08.16).

The lawsuit, which points out several "legal errors" in proceedings, states: "What happened instead was a cascade of legal errors warranting this court's reversal or vacatur for new trial. At summary judgment, the district court entertained expert testimony by musicologists for the Gayes who based their opinions entirely on the sound recording, not the deposit copy. The court correctly filtered out non-deposit copy and generic musical features from their testimony, but then erroneously failed to compare what remained to 'Blurred Lines'.

"At trial, the district court made things worse. While correctly excluding the 'Got to Give It Up' sound recording itself, the court erroneously allowed the Gaye's experts to testify about the sound recording anyway, including by playing their own musical excerpts based on the sound recording. The court then instructed the jury that it could consider all this testimony in its substantial-similarity analysis."

Ed Sheeran is also currently facing a copyright infringement lawsuit from the Gaye's estate for allegedly copying 'Let's Get It On' on his hit 'Thinking Out Loud'.