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| I have not used optical flow for speeding up 3D renders specifically but I've used Twixtor for a number of projects over the years with various types of sources that have included some 3D source material. The problem with optical flow is that it's not an automatic solution i.e. set and forget as camera motion, foreground and background layers can confuse and cause subtle or obvious artifacts. On say a two second shot with a lot of camera and subject movement (especially if CGI has handheld or zoom camera simulation), it's likely manual tweaking of the optical flow is going to be necessary even with tweaked motion vectors. If the 3D CGI renders are fairly static and predictable (for the optical flow) it's possible to get settings that will work for a whole shot. But the reason optical flow is simply not a default solution is that ultimately computers and software is still stupid and can't compensate for unexpected situations. And while it's much faster than it used to be, unless the CGI renders are brutal, the renders are still going to be considerable with optical flow required to get artifact free processing. Plus manual labor time. Again - certain controlled scenarios it might work - but unlikely to be a simple plug and play solution. stephen van vuuren 336.202.4777 http://www.insaturnsrings.com/ http://www.sv2dcp.com/ http://www.sv2studios.com/ A film is - or should be - more like music than like fiction. It should be a progression of moods and feelings. The theme, what's behind the emotion, the meaning, all that comes later. -Stanley Kubrick -----Original Message----- From: After Effects Mail List [mailto:AE-List@media-motion.tv] On Behalf Of Chris Zwar Sent: Wednesday, March 05, 2014 6:48 AM To: After Effects Mail List Subject: [AE] Using optical flow to speed up 3D renders 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 +---End of message---+ To unsubscribe send any message to <ae-list-off@media-motion.tv> |
