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| Fix Tracking Errors Workflow https://forum.ipisoft.com/viewtopic.php?f=6&t=5940 |
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| Author: | absameen [ Wed Apr 04, 2012 7:59 pm ] |
| Post subject: | Fix Tracking Errors Workflow |
I just finished tracking a motion and there are frames where the arm is flipped incorrectly. I have already applied jitter removal but these are tracking errors that I'm not sure how to fix. What is the proper workflow to fix tracking errors using iPi Studio? |
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| Author: | Greenlaw [ Wed Apr 04, 2012 10:44 pm ] |
| Post subject: | Re: Fix Tracking Errors Workflow |
I just wrote about this in another forum so I hope you don't mind the 'cut and paste': :) If you haven't used iPi Studio before, 'supervised' tracking (i.e., error correction) is pretty straightforward. When you see an error occur you can do any of the following to fix it: 1. Go to a good frame and track backward through the error. This is the easiest trick and often it works the best. If it doesn't work... 2. ...position the mis-tracked limb to the middle of the frame range around the error (iPi Studio supports IK and FK), click Refit Pose and then track backward and forward from that frame to correct the surrounding frames. (Be careful not to track through the corrected frame.) Or... 3. ...if Refit Pose fails, just position the limb manually (do not click Refit Pose) and track backward and forward to correct the surrounding frames. Or... 4. ...Reposition the mis-tracked limb and hit Refit Pose, step through manually (< and > keys), and repeat as necessary through the error. Once you get the rhythm for it, the process goes very quickly. When you're done it's a good idea to 'bump' the Trajectory Filtering slider to smooth the transition between fixes. In the very worst cases you may need to manually matchmove through the error but I've never had to do that. Honestly, if the footage is THAT bad, it's much easier to just record the motion again. My typical workflow is to allow iPi Studio to process an entire Take from T-Pose to end frame by itself (unsupervised), and when it's done I'll play through the Take and fix any errors I might see. Typically, if there are errors in a Take, they can all be corrected in a few minutes. When you're all done, you will need to run Configurable Jitter Removal. The 'raw' data can be very jittery if you don't apply at least a little CJR. CJR is run in a layer on top of the mocap data so it's non-destructive. This means, if you feel you've used too aggressive a setting, you can simply dial it down and run it again. Also, using CJR is not cumulative and you can run it as often as you like without worrying about permanently over-smoothing the motion. Typically, I dial in the strongest CJR setting for the legs, a little less for the torso, and the least amount for the arms. If you wish, you can vary the settings at different points in the Take but I usually run one setting for the entire Take unless it's a special situation. If you use varying CJR settings in a Take, you need to 'bump' Trajectory Filtering to smooth out the transitions when you're done, otherwise you may notice a 'twitch' at the frames where you changed CJR settings. And then there is Trajectory Filtering. This is another feature that can 'smooth' your motion data. TF is applied on-the-fly so you can change its strength at anytime. Be careful not to use too strong a setting because it can make your motions look too soft and lifeless. I usually set it at 1 or 2, and only go higher if there is a severe problem with the data. For me, most of my iPi tracks produce very few errors if any. This is because I plan my shots in advance by creating an animatic, and I capture the exact motions I need on a shot by shot basis. This keeps my Takes fairly short and easier to track. 'Happy Box' is a very good example. I haven't posted my animatic online but you can see the original storyboard at my website. The animatic version of the board served as a guide when I recorded the motions and it helped me capture motions for 3 characters for 17 shots in about an hour. Because this shoot had been carefully planned, tracking and error correcting the entire show took me about two evenings. A more difficult case is the motion my daughter and I captured last Sunday right before dinner time. You can see the results here: Mocap Test with Small Child (1 m) This example was the trickiest to track because the motions were very fast and 'poppy' but also because the iPi 'Actor' isn't really proportioned to track a small child. There were more errors generated in this track than usual but using the techniques described above, they were all corrected in about an hour. In spite of these challenges, iPi Studio was still able to produce accurate motion capture results quickly. (Tracking was done after dinner of course.) :) Hope this info is helpful. G. |
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| Author: | absameen [ Thu Apr 05, 2012 1:33 am ] |
| Post subject: | Re: Fix Tracking Errors Workflow |
Thanks a lot, this is very helpful. |
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| Author: | Greenlaw [ Thu Apr 05, 2012 2:17 am ] |
| Post subject: | Re: Fix Tracking Errors Workflow |
If you're curious, there are three errors I missed: - At the very end you might notice that Sienna's left arm is briefly mis-tracked when she lowers it. I fixed this one tonight in a couple of minutes using a combination of the above techniques. - Twice in the middle of this Take, you can see her left knee briefly points inward when it should be pointing out. I think this happens because she leans too close to the sofa and her leg probably 'merges' into the furniture for moment. I haven't tried to fix this yet...maybe tomorrow night. This one should be interesting to fix. BTW, for difficult errors, it does help to have the RGB data in the background as a visual reference. Technically, the RGB data isn't used by the Tracker but in my opinion it's worth recording if your system can handle it. Just for kicks, once I get these last two errors corrected, I'll retarget the motion to a couple of different character types. If I find some time later, I'll record a short video showing how to fix some typical and some not-so-typical errors like these using the Tracker. :) G. |
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| Author: | ppe [ Tue Apr 10, 2012 1:26 am ] |
| Post subject: | Re: Fix Tracking Errors Workflow |
Greenlaw wrote: 3. ...if Refit Pose fails, just position the limb manually (do not click Refit Pose) and track backward and forward to correct the surrounding frames. Or... If you don't mind, I'd like to add: 3.5 Find the nearest acceptable frame, then do "copy pose", go back to the area that needs correction and "paste pose" and then hit retarget. If this was not successful, find another good frame (or just try it to another mis-tracked frame) and try copy-paste again. This doesn't work well, however, if the person has moved a lot (i.e. you cannot find a good frame very nearby). Alternatively, you might want to paste the same pose to several (mis-tracked) frames surrounding the one you are going to retarget. I think 10 frames usually does the trick. I do not know for certain, but it seems to me, that when you hit retarget, iPi checks the frames nearby, too. At least I cannot explain myself why sometimes successfully retargeting in the middle of mis-tracked area is so difficult. Note that retargeting one frame usually does some fine-tuning to the frame(s) before that as well. In my opinion, you need more than one good frame in the middle of mis-tracked area before you can safely assume that you can do successful tracking again. At least in my experience you should have at least 3-4 good frames to both directions from where you start tracking. Sometimes it is just easier to clear the mis-tracked area completely than try to manually correct so many frames (when the Region of Interest is clear, you only need one good frame to start the tracking). BTW, I use PS3 cameras, I do not know if any of what I just wrote is valid for Kinects. |
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