Framestore’s New Stereo Triage Process Takes Off with ‘The Martian’

Triage is a process that deals with inaccuracies between the left eye and right eye stereo plates, in both colour and alignment. For ‘The Martian’, the production requested that Framestore handle this work soon after the plates were available, rather than leaving Triage until the final stages of compositing. The result was a more efficient workflow. “Getting all of that work signed off at an early stage really helped,” Bronwyn said. “It saves the rest of the compositing, and the real beauty work, for a later stage, without the fear of needing to go back and take it apart again.’

Maths, Art and Film

The new pipeline was based on The Foundry Ocula software, and the work was carried out by a team of compositors and paint and rotoscope artists. Over time, Bronwyn and the team successfully refined the processes to reach a quality that would stand up to external stereographic standards.

Bronwyn talked to Digital Media World about her own background as a 2D artist, her experience of native stereo projects and how this experience helped her lead the team on ‘The Martian’.

“Maths, art and film are three topics that interest me and what contributed to my decision to become a compositor,” Bronwyn said. “My first native stereo job was at MPC on ‘47 Ronin’. When applying for a job at Framestore, Christian Manz interviewed me and had also been the overall VFX Supervisor for ‘47 Ronin’. This movie was also I learned native stereo compositing - prior to that I had only been involved in stereo for conversion.”

Since ‘Triage’ is the industry standard name for the correction of colour and vertical misalignments between the two eyes of a native stereo shot, Bronwyn likes to think of it as a technical process of understanding vision. She also notes a creative element, which involves making non-quantitative choices about how an image should look in order to invoke a desired response in the viewer.

She said, “Both of these skills are relevant to a 2D artist and 2D supervisor, and the work is about using those skills in relation to the Triage process. In essence, a 2D photoreal image is conveying to the viewer an interpretation of the 3D/4D world - when working in native stereo, having that second eye of the image gives you more to play with in terms of conveying the 3D/4D world. Both of the eyes are 2D images in the same way that each human eye on its own can only see in two dimensions.”

Two-Way Benefit

Apart from perfecting the pipeline for Framestore, the work made a great opportunity for the artists on the team to learn about the structure and effect of 3D stereo images. “Almost everyone on the Paint & Roto and Compositing team worked on the Triage. The process gets everyone up to speed with stereo compositing, which means that by the time we are in creative shot production, the stereo compositing side of things becomes just part of our everyday working life,” Bronwyn said. “Ideally we try and schedule so that the artists get to do the Triage on the shots that they will be taking to final, but this isn’t always practical,” said Bronwyn.

Because native stereo shows are relatively rare compared to stereo conversion shows, it proved to be invaluable to ask each compositing artist to carry out Triage on at least one or two shots each. This benefited both them and the project, as they may have not worked in native stereo for some time, if at all. They found it made their usual compositing work more fluid, requiring them to consider the aesthetic impact as well as the technical elements of what they were doing.

Every single shot requires colour and vertical alignment. All plates are analysed initially by eye to look at what the most challenging aspects of the alignment will be. This informs the scheduling of the shots and if tracking is required before the alignment process begins. A simple shot may take a day, while a complex one can run into weeks of work.

Triage Tools

The Ocula application the team were using for the work is made up of lots of different plug-ins, two or three of which were especially useful on ‘The Martian’. Among these, vertical aligner allows for different types of vertical alignment based on either corner pins or warps, using the incident points identified by the osolver. Most Ocula plugins rely on the incident points tracked by the osolver plug-in, and therefore it is also essential when using Ocula for alignment.

Bronwyn said, “In terms of colour alignment, colour aligner is a very powerful tool that, in most cases, will achieve a 90% match out of the box. However in high end image manipulation, it is the final 5% and 1% that define a very high quality result. Consequently, colour alignment is also done manually in certain scenarios.”

The main cameras on 'The Martian' were the RED Epic and RED Scarlet, both with the Dragon sensor, housed in a 3ality TS5 rig. Both prime and zoom Angenieux Optimo lenses were used. The metadata received from the shoot was excellent, consistent and very comprehensive, according to Bronwyn. “This allowed it to be easily incorporated into our pipeline and workflow. The Triage is only one part of making great stereo images and the metadata was used not only in the Triage process but also in tracking and when creating cameras,” she said.

Stereoscopic Discipline

Once the triage is complete and the actual compositing and beauty work on shots takes off, procedural operations such as colour corrections and filters are carried out correctly in both eyes. Any additional layers and mattes must be placed very accurately relative to the geometry of the scene. Bronwyn emphasized that compositors should periodically check that what they are doing is working correctly in both eyes so that they don’t end up in a situation where a shot is approved in mono and the work on the hero eye will not carry through into the non-hero eye.

“When compositing in stereo, all operations must be done correctly and many of the techniques known as ‘cheats’ will not work on the images,” she explained. “As a basic example, if a roto mask used to grade half of a tree darker, but the mask is not placed in the correct depth relative to the geometry of the scene, a different overall area of the tree will appear to have the darker grade in each eye, resulting in a disparity between the two eyes and, therefore, an uncomfortable viewing experience.

“This means that stereo compositing must be more disciplined than mono compositing. This increase in the compositor's discipline when working the comp can result in a better finished product - that is, a composite that hasn’t been constructed in a technically correct way may work for mono, but not for stereo and it could be argued that something built on firm and correct foundations allows for an improved creative expression.”  www.framestore.com