Feet and Leg Jitters

Greenlaw · **Posted:** Mon Nov 15, 2010 6:09 pm

Hi,

I was wondering if other iPi users were seeing more or less jittering in the legs and feet when using the latest build of iPi DMC? I'm not completely certain about this, but it seems like I was getting better stability in the feet and legs a few months ago than I am now.

I guess a fair test would be to track the same footage from last summer in the current version of iPi DMC and compare the results, but I'd still like to hear what other iPi users think.

G.

Greenlaw · **Posted:** Tue Nov 16, 2010 11:33 am

I haven't had a chance revisit this problem yet (I'm back at work this week but I'm also pretty sick too...ugh!) but I've been thinking about it.

Now I'm wondering if this is not actually a tracking issue but instead it's an IK problem. When I get back to this, I'll try scaling the rig to different sizes and see if refitting the joints to different locations helps reduce the jitters at all.

Question: when you use Refit Pose in iPi DMC, does it move the joints in the rig to account for different body proportions? What I mean is, does it modify the default rig to fit the proportions of the performer, or is it just shoehorning the default rig into the calculated volume space? I'm thinking it does the latter but I wanted to be sure.

Thanks in advance for any helpful info!

G.

andrew · **Joined:** Wed Apr 07, 2010 4:33 am **Posts:** 468

Hello!

Greenlaw wrote:

I'm thinking it does the latter but I wanted to be sure.

As usual you are absolutely correct!

Greenlaw · **Posted:** Thu Nov 18, 2010 3:58 pm

This morning, I shot new capture video designed to test my rigs and mesh deformations, and also to investigate the feet jitter issue I've been having that I didn't seem to have with earlier sessions.

While setting up the T-Pose in iPi DMC for the first test, I noticed that the tracker was putting extra effort into fitting the rig's feet. When I clicked the button repeatedly, the rest of the body quickly settled in place but it never quite gets the feet exactly in position. My guess is that in the video, my feet may be closer together than what iPi DMC wants, and it's struggling with that. I took a closer look at my video, and it appears my feet have about three or four inches of space between them, but I think iPi DMC is looking for five to six inches for the rig T-Pose, maybe more even. Is this a good assumption, and could it be the cause for excessive feet jitter?

I'll check my old videos, when I got steadier results, and compare the feet positions in it later today. I'll also try experimenting with different actor scales today.

G.

Greenlaw · **Posted:** Thu Nov 18, 2010 4:19 pm

Oh, one more thing I was wondering about: does video compression increase the likelihood of jitter? The footage I shot recently that had a lot of jitter was shot with compression set at about 65% Best quality.

Part of the test footage I shot today involved making sample 'clean video' clips at different compression levels, including no compression. I'll check the channels in each clip for video artifacts and compare the differences.

I don't recall what my old footage was captured at, but the rig test footage I shot this morning was all captured at the compression level '100% Best Quality'.

FYI, for those wondering about the file sizes:

No Compression: 976 MB
Medium (50% BQ): 47MB
Medium High (75% BQ): 246 MB
Best Quality (100% BQ): 72 MB

The video clips range between 11 and 13 secs each. I'll post more accurate data when I have time to trim the clips properly.

G.

Greenlaw · **Posted:** Thu Nov 18, 2010 4:50 pm

Okay, now that I'm really thinking about it, I guess the feet should be positioned so that your legs are as vertical as possible, and the feet themselves need to be parallel. In other words, the performer should try to mimic the actor rig as closely as possible.

This might sound silly but I'm going to practice the pose in front of a full body mirror. :)

G.

Greenlaw · **Posted:** Sun Nov 21, 2010 5:16 pm

I'm back. :)

I did a series of tests a few days ago, with my feet spaced at different widths. I found that the feet should be spaced at least as wide as the feet spacing of the rig (i.e., ideally, the legs should be perfectly vertical.) If you're stance is wider though, this doesn't hurt the tracking. If your feet are too close together however, the results can be shaky.

What seems to help reduce jittering is to carefully tweak the shape of the actor. Use the morph controls to match the actor as closely to the body shape of the performer in the video or just slightly larger. (Maybe. Still testing this the 'larger' idea.) Also, adjust the rig to be taller than actual size, but not so tall that you start to have IK issues (i.e., incorrectly bending or popping limbs.)

I'm still having some random jittering in all joints even when the performer is standing perfectly still. I'm coming to accept that this is normal for the system, but I'm hoping there will continue to be improvements here. For now, I'm able to fix or cheat around the jitter in my 3D app.

(FYI, I'm going allow some jittering for our film because it kinda looks cool for this project.) :)

G.

Michael Nikonov · **Joined:** Tue Mar 31, 2009 9:13 pm **Posts:** 805

We did change many internal configuration parameters in latest versions, so it is possible that we introduced some bug that causes jitter. We will need a couple of weeks to come up with a solution to this problem. It is not easy to fix this without breaking something else, and we need to do a lot of testing after possible fix. Sorry for being so slow, but this is a kind of fix that cannot be done quickly.

Greenlaw · **Posted:** Tue Nov 23, 2010 12:05 am

Hi Michael,

Thanks for looking into this. I can certainly imagine how difficult this is to fix internally based on what it's taking me to fix this problem manually in post. I can't exactly quantify how much more jittery my tracking has been, but it seems to take a lot more effort to stabilize the rig now than before. Also, while the new Jitter Removal seems to be doing a good job with the feet, it's also hammering out motions that I want to keep elsewhere in the body; for now I've stopped using the Jitter Removal button.

Best of luck coming up with a solution; I'll be looking forward to it.

In other areas, iPi DMC is working better than ever for me. Calibration has been very fast (under 10 minutes) and I'm getting 100% green results every time. Tracking has been very good too (except for the jitters.)

I did set of motions the other day specifically designed for testing rig limits and deformations for my own characters. The motions included various stretches, twisting, bending, squatting, walking around in a circle, and standing still with arms crossed. All the motions tracked better than I expected.

The most noticeable problem I saw (besides excessive jittering,) was that during body twists, the feet will rotate when they should be locked.

What worked surprisingly well was walking around in a tight circle. Somebody else did a similar video several months ago, and I think this latest version shows a lot of improvement in iPi DMC's hips tracking.

The arms crossing motion was meant to be a tricky test and, while it did have penetration issues, the result was still better than I expected. I think the penetration problem here is perfectly fixable in another 3D package and possibly from within iPi DMC even.

I'll post a video rendered out of iPi DMC using the default rig tonight, and I'll re-track this video with future iPi DMC updates to compare the results.

Update: I'm finding that I cannot export a playable video out of the current version iPi DMC. Even with the Uncompressed option the video will not open in any media players I use (MPC, VLC, QT Player, etc.,) or Sony Vegas Pro 10. Exporting with other codecs are also resulting in corrupted video or crashing iPi DMC. I'm running iPi DMC with Windows 7 Professional on a Quad Core computer and a GTX 260 card.

G.

Greenlaw · **Posted:** Tue Nov 23, 2010 12:47 am

I copied the uncompressed version of the video to another computer and it's not playable there either. Here's the error I get with Media Player Classic:

--

Media Player Classic could not render some of the pins in the graph, you may not have the needed codecs or filters installed on the system.

The following pin(s) failed to find a connectable filter:

C:\Users\Greenlaw\Downloads\video.avi::Output

Media Type 0:
--------------------------
Unknown

AM_MEDIA_TYPE:
majortype: MEDIATYPE_Stream {E436EB83-524F-11CE-9F53-0020AF0BA770}
subtype: MEDIASUBTYPE_Avi {E436EB88-524F-11CE-9F53-0020AF0BA770}
formattype: TIME_FORMAT_NONE {00000000-0000-0000-0000-000000000000}
bFixedSizeSamples: 1
bTemporalCompression: 0
lSampleSize: 1
cbFormat: 0

Media Type 1:
--------------------------
Unknown

AM_MEDIA_TYPE:
majortype: MEDIATYPE_Stream {E436EB83-524F-11CE-9F53-0020AF0BA770}
subtype: TIME_FORMAT_NONE {00000000-0000-0000-0000-000000000000}
formattype: TIME_FORMAT_NONE {00000000-0000-0000-0000-000000000000}
bFixedSizeSamples: 1
bTemporalCompression: 0
lSampleSize: 1
cbFormat: 0

--
The file is an uncompressed .avi and its total size is about 3GB. It was exported using the 'Export Video...' command from iPi DMC's File menu. iPi DMC version 1.1.0.111.

Hope this info is helpful.

G.

Feet and Leg Jitters

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