Blue and green-screen effects pioneer Petro Vlahos dies

The visual effects industry has paid tribute to Petro Vlahos - the pioneer of blue- and green-screen systems.

The techniques allow filmmakers to superimpose actors and other objects against separately filmed backgrounds.

He developed the procedure for 1959's Ben-Hur and then went on to win an Oscar in 1964 after creating a related process for Disney's Mary Poppins.

The death of the 96-year-old was announced by the company he founded, Ultimatte.

His innovations continue to be used and developed by the television, film, computer games and advertising industries.

"Our industry has lost a giant," Everett Burrell, senior visual effects supervisor at Los Angeles-based studio Look Effects. told the BBC.

"It's hard to even conceive of how we would do what we do without the amazing number of processes and techniques he pioneered. All visual effects professionals and movie fans owe him a debt of gratitude."

Look Effects has built on Mr Vlahos' achievements to create work for the movies Avatar, The Life of Pi and the upcoming Superman film, Man of Steel.

Mr Vlahos was not the first to use a blue-screens - earlier versions of the technique can be seen in films including The Thief of Bagdad, and The Ten Commandments.

But he is credited with developing a way to use it that minimised some objects appearing to have a strange looking glow as a side-effect.

He called his invention the colour-difference travelling matte scheme.

Like pre-existing blue-screen techniques it involves filming a scene against an aquamarine blue-coloured background.

This is used to generate a matte - which is transparent wherever the blue-colour features on the original film, and opaque elsewhere. This can then be used to superimpose a separately filmed scene or visual effects to create a composite.

Mr Vlahos's breakthrough was to create a complicated laboratory process which involved separating the blue, green and red parts of each frame before combining them back together in a certain order.

He also noted in a patent filing, external that the process allowed the blue-screen procedure to cope with glassware, cigarette smoke, blowing hair and motion blur which had all caused problems for earlier efforts.

Movie studio MGM had commissioned him to invent it. Mr Vlahos later noted that it had taken him six months of thought to come up with the idea, much of it spent staring out onto Hollywood Boulevard.

He later created a "black box" - which he called Ultimatte - to handle the process, first for film and then electronically for video.

Mr Vlahos was also awarded a patent for his work on a related technique called sodium vapour illumination, external, which he developed for Disney.

This involved filming the actors' scenes against a white backdrop using sodium-powered lamps which caused a yellow glow to bounce off the background.

The camera featured two film stocks shot simultaneously, and a prism on its lens.

The prism split the yellow sodium light away from the other colours, sending it to a black-and-white-based film stock which was then used to create the matte.

Meanwhile, the other film stock recorded the scenes in colour without the sodium's yellow cast being visible.

The advantage was that this created an even cleaner effect than Mr Vlahos' original blue-screen efforts.

Disney used Mr Vlahos's version of the technique to make Mary Poppins, Bedknobs and Broomsticks, and Pete's Dragon - among other movies - letting its actors appear to interact with cartoons.

Alfred Hitchcock also borrowed the technique for The Birds, and Warren Beatty later used it in Dick Tracy.

However, it has since fallen out of favour because the equipment involved is more expensive and cumbersome to operate, and the quality of blue- and green-screen techniques has improved.

Mr Vlahos ultimately racked up more than 35 movie-related patents and went on to co-found his company, Ultimatte Corp, with his son Paul in 1976.

It now focuses its efforts on making AdvantEdge, a compositing software plug-in.

Robin Shenfield, chief executive of visual effects studio The Mill, recalls meeting Petro Vlahos several times in the 1980s and says he came across as "unassuming", despite his many achievements.

"I remember him being rather quiet," he told the BBC.

"He was a scientist - he wasn't a showman, although I think he rather liked the involvement of his technology in the world of entertainment. Ultimatte had a bit of razzmatazz about it as a company."

The Mill has since used blue- and green-screen technologies to create visual effects for the film Gladiator, the BBC's Dr Who television series and director Guy Ritchie's Call of Duty: Black Ops 2 trailer, external among other works.

"It's the absolute building block of all the visual effects that you see in television and movies," added Mr Shenfield.

"It's significance is extraordinary. Everything people like us and others are still built on that fundamental ability to take lots of elements from lots of places and seamlessly mesh them into a new convincing reality.

"Mr Petro - and his family - were pioneers in our industry for which he should be remembered."