Prime Focus lost a key battle over 3D conversion technology last week when the U.S. Patent and Trademark Office (USPTO) invalidated a patent that Prime Focus Creative Services Canada said protected its proprietary techniques for converting 2D footage to stereo. The VFX and post-production giant had claimed that 3D specialist Legend 3D was infringing its patented process.

U.S. Patent no. 8,922,628 was issued to Prime Focus in December 2014. It was followed three months later by a Prime Focus lawsuit alleging patent infringement by Legend. Rather than paying up, Legend punched back, filing a petition for an inter partes review challenging the validity of Prime Focus’s patent. Now, more than two years later, the USPTO’s Patent Trial and Appeal Board has ruled that all 18 claims made by the Prime Focus patent are “unpatentable.”

Prime Focus had asked to amend those claims in hopes of strengthening them against the re-examination, but that motion was denied by the board, which said that the substitute claims were no stronger relative to earlier patents that covered some of the same technology. They included patent 7,573,475, originally assigned to ILM back in 2009, and patents 8,213,711 and 8,488,868, originally assigned to the Canadian government’s Communications Research Centre in 2012 and 2013, respectively.

Expert witnesses Carlos Vazquez, Ph.D., of the University of Quebec’s École de Technologie Supérieure and David Forsyth, Ph.D., Fulton-Watson-Copp Professor of Computer Science at the University of Illinois at Urbana-Champaign, testified in the case.

“The Board’s decision invalidated all of the claims of the subject patent, gutting Prime’s lawsuit and completely vindicating Legend,” said Daniel Yannuzzi of Sheppard Mullin, one of the attorneys representing Legend in the case.

Attorneys for Prime Focus did not respond immediately to a request for comment.