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| I have this vague recollection that optical flow technology (e.g. twixtor and reel smart motion blur) was originally developed to help speed up 3D rendering workflows. I think the idea was that 3D animators could render out every 2nd or 3rd frame, and use an optical flow plugin like twixtor to create the in-betweens. Even if that's not strictly correct, the potential is there. Some of the photo-realistic projects I've worked on have had 3D render times of 3 - 5 hours a frame. Rendering every 2nd frame is effectively halving the overall render time, which can be a massive saving. Even a slow After Effects plugin is usually only seconds per frame, not hours. So I was wondering if anyone has actually done this, or tried using other 2D techniques to help speed up 3D rendering. I can think of 3 ways in which slow 3D renders can be compensated for by faster compositing techniques: 1) Up-resing. For example rendering at 720p instead of 1080p and scaling up the finished renders. If compositing multiple passes, only the slow renders need to be smaller and scaled up. 2) De-noising. Forgive me for not knowing the correct terminology, but when rendering with global illumination it seems that there's an overall quality setting that directly determines both the speed of rendering and the noisiness of the image. Rendering with a lower setting can make renders noisier, but a de-noising plugin such as Neat Video can fix this. 3) As stated above, rendering every 2nd or 3rd frame and using something like twixtor to create the missing frames. A motion vector pass would make this more accurate. So I'm familiar with 2 of those 3 approaches - I have worked in situations where 3D passes are rendered at smaller sizes and then scaled up. It works very well and the time savings can be dramatic when dealing with very long renders. 3D renders can be so clean that they scale up very well. I have also worked in situations where the neat video de-noiser was used to compensate for noisy GI renders, and again the savings can be dramatic - in some cases this can almost half 3D rendering times. Neat video seems to be an incredible plugin, so much faster and so much better than the AE equivalent. So that leaves the optical flow technique as the one I haven't tried yet. Has anyone done this? I'd love to hear from real-world examples where people were able to render every 2nd or 3rd frame. Is a motion vector pass essential for it to work properly? Any other thoughts or insight welcome… -Chris |
