SIGGRAPH 2016 : OpenDCX, des extensions pour le deep compositing

OpenDCX

DreamWorks Animation annonce la mise à disposition en open source d’OpenDCX, leur projet d’extensions pour le deep compositing.
Développé par Jonathan Egstad et Mark Davis, OpenDCX avait été présenté l’an passé à la conférence DigiPro, avec un accueil très positif.

OpenDCX est une librairie C++ qui étend les possibilités d’OpenEXR. Le système permet par exemple de faire du compositing avec anti-aliasing de fichiers deep image, lorsqu’il y a un mélange d’éléments solides et volumétriques, tout en minimisant l’impact en mémoire.

Autrement dit, OpenDCX permet par exemple de résoudre de nombreux problèmes liés au travail en deep image lorsqu’une scène comporte des intersections de géométries solides et des objets tels que le hair/fur. Le projet est d’ailleurs fortement lié à la production de Kung-Fu Panda 3.

Le site officiel donne de nombreux détails techniques, et permet de télécharger OpenDCX. DreamWorks espère à terme qu’OpenDCX puisse être inclus dans OpenEXR.

Voici l’annonce complète :

DreamWorks Animation Announces Deep Compositing Extensions (DCX) Open Source Project

Glendale, Calif. – July 21, 2016 – DreamWorks Animation (Nasdaq: DWA) today announced their Deep Compositing Extensions are available as an open source project, OpenDCX (opendcx.org). The technology developed by engineers Jonathan Egstad, and Mark Davis was enthusiastically received at the 2015 Digital Production Symposium (dp2015.digiproconf.org), and DreamWorks is pleased to respond with this open source effort to encourage industry adoption of the technique.

DreamWorks Deep Compositing Extensions allow anti-aliased compositing of OpenEXR (openexr.com) deep image files with a mixture of solid and volumetric elements, while keeping the memory requirements to a minimum. The addition of subpixel masks to each sample allows for coverage and opacity to be treated separately, without an excessive increase in memory consumption, and with the use of the new “hard surface” flag, the included flattening algorithm allows for any combination of volumetric and solid elements to be merged with plausible anti-aliasing. Furthermore, the extensions provide the ability to apply affine image-space transforms to the deep image data, taking advantage of the sub-pixel information within each sample. Finally, a sub-pixel accurate pixel filtering method is provided to allow higher quality image reconstruction.

“FX at DreamWorks has utilized deep images for many years; however, Kung Fu Panda 3 was the first feature where Lighting fully embraced the technology. Previously, deep pixel information proved problematic in reconciling high-frequency features like hair and fur with intersecting hard-surface geometry, and flattening a deep image did not produce the same image as a full render,” said Jeff Budsberg, Head of FX on Croods 2. “With deep subpixel masks, an efficient EXR channel encoding, and a custom deep image flattener, the DCX technology yields a production-friendly solution for full deep compositing that resolves previous visual artifacts, while only requiring a small increase in disk footprint.”

“Adding subpixel Mask support allowed us to jump between a deep image workflow and the old workflow without a noticeable loss of image quality.” said Matt Titus, FX Lead on Kung Fu Panda 3.

“Our digital production requirements continue to drive industry-leading innovation in our technology,” said Andrew Pearce, Director of Technical Strategies at DreamWorks Animation. “We are honored by the recognition of the technique, and pleased to continue to work with industry to extend our collective capabilities.”

OpenDCX is available immediately at opendcx.org.”

Full use of the technology requires simultaneous changes to all three of a studio’s renderer, compositor, and file format. To that end the open source package contains reference implementations for those three components;

1) Pseudo-code for Renderers, as written for DreamWorks Animations’ Moonlight renderer, and substantially implemented in Houdini’s Mantra renderer (SideFX.com)
2) Nuke (thefoundry.co.uk) plug-ins to execute deep compositing extensions
3) OpenEXR (openexr.com) extension to support the modified deep image format as a separate layer that sits on top of the file format, supplying the logic to interpret the OpenEXR channel data.

If community feedback is positive, DreamWorks will work with OpenEXR to find a suitable implementation and then lobby for full inclusion in the OpenEXR standard.

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