Published on Tuesday, 13 March 2012
Among the challenges the production crew on ‘Journey 2’ faced was defining the electronic
workflows for six different digital camera platforms. VFX Supervisor Boyd Shermis described
some important considerations for the VFX teams.
|Images show Rising Sun Pictures' work on the bee chase jungle backgrounds, shot with the SI-2K cameras.|
|“The problem for us was that all of the different cameras use different sensors and use or require their own custom colour space conversions or de-bayering to get even marginally close to any of the other cameras in terms of the colour response curve,” Boyd said. “We shot the majority of the movie on Sony F35 or F23 cameras, recording 4:4:4: to HDCam SR. The workflow for these cameras going from 4:4:4 tape to .dpx file format, the industry standard for digital intermediate, has been well established and the resulting colour is pretty much as expected.”
Because a 10-bit log file format can accommodate the overall latitude of these cameras fairly well, delivering usable files to the visual effects vendors and then supplying those VFX-processed files back to the DI was not terribly difficult and gave expected results. Getting colour-matched files into editorial was a challenge at first, however, as the original dailies QuickTime files provided to editorial were processed via Clipster hardware. Boyd explained that the 3D LUTs applied in that hardware don't translate well into industry standard compositing software such as Nuke.
|“But that was a side issue,” he said. “The real challenge was getting the colour space of the Red MX, Phantom HD Gold and SI 2K cameras used on some of the other VFX shoots to match the colour response curve of the Sony F35.The VR Phantom has its own unique de-bayering application, which doesn't really lend itself to getting a colour match. It's really a utility piece of software to get it into a workable format. But the colour curves are completely different to any other camera.
“The Red MX camera has its own colour space and handles exposure data which exceeds the 10-bit log capability. So we started by re-mapping the R3D files into a 16-bit EXR file and then brought all those files into a DI facility in order to neutralise them with respect to each other, and more closely match the look of the Sony F35 colour curves. The resulting .exr files were then sent to the vendors, who in turn gave us 10-bit .dpx files to go into the DI.”
In a similar manner, they took the SI-2K Cineform files, used for two of the sequences – the underwater green screen and the bee chase jungle backgrounds - and remapped those to 16-bit .exr files, neutralized them across their respective sequences and colour matched them to the Sony F35 colour curves, then delivered those files as 16-bit .exr files to the vendors to use. They in turn delivered 10-bit log .dpx files once again, back to the DI.
“It was a bit of a challenge and we had to go outside of more traditional digital workflows in order to get all the various cameras to look close enough to each other to work well in the DI,” Boyd noted.
“I should note that I believe it's time that the post production side of the industry moves beyond the standard 10-bit log, or .dpx, file format. It is a standard that is now over 20 years old that doesn't completely represent the capabilities of today's acquisition formats, including the latest film stocks from Kodak. While I know that the AMPAS scientific committees are currently ratifying the new ACES file format, it will be several years before that truly becomes a standard. In the meantime, I believe that we should be utilizing the more capable .exr file format to maintain the image integrity throughout the post process all the way through the DI, where having greater latitude for exposure and colour can be important.”