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PostPosted: Thu Nov 05, 2009 11:51 pm 

Joined: Tue Nov 03, 2009 10:19 pm
Posts: 18
I'm really pleased with this software, but I have lots of questions. My setup is as follows: I have two Logitech Webcam Pro 9000 cams right now; a fast Vista 64 PC; nVidia GTX 295 with 1.7G video RAM. I'm having no trouble recording video with two cameras, and I'm prepared to buy one or two more. I have a room that is about 18' x 15' (6m x 5m); there is some furniture, but I have managed to clear away a fairly large performance area right in the middle. Anyway, my questions:

1. Why do we need a codex at all? What if I just want to capture video in uncompressed DIB form? Sure, I get 1GB sized files, but I only plan to capture 30 seconds at a time anyway, and I can store the vids on an external HD. Must I use a codex to capture the video? Does it make iPi more accurate or fast or something?

2. What's the optimal way to set up two cameras? 90 degrees apart? 75 degrees? How far off the floor?

3. Will it be easier to calibrate 3 (or 4) cams than two? I'm having lots of trouble calibrating 2.

4. One problem I have is that I'm confused about which is cam #1. Is it the one showing on the left side of iPi recorder, or the right? Is cam #1 the right one?

5. What do you use to hold cams up, anyway? Should I buy some cheap photo tripods? I don't understand how the "clip" on the cam holds it onto anything securely.

6. I'm having trouble getting a sufficiently wide field of view because my cam's USB cords are only about 5' long. I think I read somewhere that iPi recommends a USB powered extender cable. I'm not quite sure what this is -- can anyone point me to a link of an example? Something like this? http://www.amazon.com/Tripp-Lite-U026-0 ... B0002D6QJO Do you guys use such things?

Thanks!

Thanks!


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PostPosted: Sat Nov 07, 2009 8:27 am 

Joined: Tue Nov 03, 2009 10:19 pm
Posts: 18
Anyone? I'm particularly curious about whether I really need to use a codec. I'm getting 30 FPS at 320x240 with two cams when I record to uncompressed DIB. I have a fast SATA hard disk, a fast quad-core PC with 64-bit Vista, and a fast video card with 1.7G of video RAM. The only downside is file size, but once I'm done with the recorded video, I can just move it onto an external hard drive. Maybe my framerate will slow down once I add a third cam; I'm about to do that today, so we'll see. But for now I have no problem getting 30 FPS. I don't see any dropped frames when recording unless I turn exposure up pretty high.

I resist using a codec for a couple reasons. One, when I try to switch to DivX, iPi Recorder crashes, which makes me nervous. Two, I generally hate installing codecs on my PC; they invariably seem to screw up something else.

So is there any reason other than framerate to use a codec with iPi Recorder? Does iPi Studio work better or faster with compressed video? E.g., if compressed video would reduce the processing time to generate mocap files, then indeed I would consider downloading MJPEG. (I gather I want Mainconcept MJPEG for Vista 64.)


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PostPosted: Sat Nov 07, 2009 11:53 am 

Joined: Mon Aug 03, 2009 1:34 pm
Posts: 2354
Location: Los Angeles
I have a few minutes to answer some of your questions, but you can actually find most of your answers elsewhere in the forum, in the docs, and the on-screen pop-ups, as these are very common questions. (I've asked many myself.)

Groot wrote:
I have a room that is about 18' x 15' (6m x 5m); there is some furniture, but I have managed to clear away a fairly large performance area right in the middle.


That should be big enough depending on where you place the cameras. In my experience, your actual performance space will be fairly small though. (Well, I'm basing in on min. three cameras; with two, your performance space may be a little bigger. I find that with more cameras, you need more space.)

Groot wrote:
Why do we need a codex at all?...Sure, I get 1GB sized files, but I only plan to capture 30 seconds at a time anyway.


The reason for a codec is to conserve diskspace. Also, you want to use a codec that records whole frames, like MJPEG. You'll probably find that capturing only 30 seconds isn't very practical considering the amount of setup time required. After setting up my sessions, I usually let the camera run for many minutes. Calibration alone, will take couple of minutes. Action sessions much longer, since I will do many takes and variations. If I captured all this uncompressed, I would run out of diskspace pretty quickly. You can always cut the footage down to more manageable clips later.

FWIW, I use Morgan MJPEG. I do my capture on a laptop with XP Pro x32, and Morgan works great. It reads fine on my workstation with Vista x64. I've been told there are issues with capturing video to Morgan on Vista x64, but I haven't experienced this. Early on I capture video to Morgan on my workstation with no problem. FWIW, I also often resave edited videos shot in Morgan (from my laptop) in Vegas or Fusion (on my workstation.) I thought maybe was okay only because I was doing straight cuts and no recompression was required, but lately I've done some compositing and processing with did require recompression, and this seemed to work okay.

Recently, I asked if iPi Studio could support frames as this would make a lot this kind of video manipulation much easier, and they said they will look into it.

Groot wrote:
What's the optimal way to set up two cameras? 90 degrees apart? 75 degrees? How far off the floor?


I've only done three and four camera setups, but my guess would be to place them to the sides in front of the subject. 90 degress apart might be appropriate. When you do the T-Pose, you will want to face one camera directly I imagine. Bear in mind, these are just guesses based on what I've done with more cameras.

Groot wrote:
Will it be easier to calibrate 3 (or 4) cams than two? I'm having lots of trouble calibrating 2.


Three or four cameras give the tracker a lot more spatial data. Processing this data is slower, but far more accurate. Also, be advised that calibration is probably the most important step. If iPiSoft fails with your calibration footage, then all your action footage is wasted.

Groot wrote:
One problem I have is that I'm confused about which is cam #1. Is it the one showing on the left side of iPi recorder, or the right? Is cam #1 the right one?


You can drag the panels around to any position. The one on the left would be camera #1, but any camera can be #1.

Groot wrote:
What do you use to hold cams up, anyway?


Since one moved camera can ruin an entire session, you want to be sure the cameras are very secure. I like to use gaffers tape. It's expensive, but it's strong and doesn't leave a residue. You can actually reuse it too--I stick used strips on the plastic cover of the box I carry my mocap gear in to reuse for later sessions.

When it's convienent, I may leave one camera clipped to the laptop, but even then I'll put some gaffer's tape on it to secure it.

Another user recommended these clips you can buy at B&H. You'll have to search the forums for that info.

Groot wrote:
I'm having trouble getting a sufficiently wide field of view because my cam's USB cords are only about 5' long.


I own several of these. You can daisy-chain up to five of them, they're cheap, and they're awesome:

http://www.newegg.com/Product/Product.a ... 6812224004

Greenlaw

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PostPosted: Sat Nov 07, 2009 12:04 pm 

Joined: Mon Aug 03, 2009 1:34 pm
Posts: 2354
Location: Los Angeles
After all that, I should also mention that using iPi Studio is still very experimental and we're all making stuff up as we go along. Michael has been very good with providing information, but new information shared by other users has been just a helpful. If you make some interesting discoveries or come up better techniques, by all means please post the info. :)

Greenlaw

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PostPosted: Sat Nov 07, 2009 12:14 pm 

Joined: Tue Nov 03, 2009 10:19 pm
Posts: 18
I very much appreciate your replies! I have spent several hours reading these forums and the documentation, but I still found your reply especially helpful.

I just got a third cam, and I'm about to give it a go. I take your point about the importance of calibration. One issue I've had with calibration, with two cams, is that whenever I mark three ground points, the cam position is suddenly shifted in very strange ways. If I undo the ground points, the cams go back to looking more or less right. Maybe this will work easier with 3 cams. Also, maybe I need to make a larger "triangle" of ground points, as the docs say.

Incidentally, one of my first efforts was surprisingly good -- a mocap of me doing a club dance. The only glitch was that the right arm went "backwards" for about 7 seconds, but that was easily fixed in Poser. The quality of the motion capture was far superior to the quality of the dancing. :)


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PostPosted: Sat Nov 07, 2009 5:07 pm 

Joined: Tue Nov 03, 2009 10:19 pm
Posts: 18
Well, I got MJPEG, and it does make file sizes smaller, but of course the video quality is somewhat lower. And consequently I'm not sure the tracking is as good, even using 3 cams. I've read here that it doesn't help to record video at 640x480; is that still the consensus? I'm still wondering whether recording uncompressed, with higher quality resulting video, might give better tracking results.


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PostPosted: Sun Nov 08, 2009 9:18 am 

Joined: Tue Nov 03, 2009 10:19 pm
Posts: 18
One more question: does the cam order matter? Does iPi studio expect cams 1, 2 and 3 to be arranged in clockwise order? I have a semicircle, and by default iPi recorder selects the middle cam as cam 1, and the outer cams as cam 2 and 3. Is that OK?

I'm sorry I'm so full of questions! I know it's beta and all, so I appreciate any answers.


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PostPosted: Sun Nov 08, 2009 2:37 pm 

Joined: Mon Aug 03, 2009 1:34 pm
Posts: 2354
Location: Los Angeles
From what I was told, yes, keeping the cameras in sequence is important. I don't think it matters if it's clockwise or counter, just that they follow a circular pattern. I think this helps the tracker. I was also told that your 'main' camera should be camera one.

Be careful when dragging the panels in order--I found that it's easy to get turned around and get the order completely mixed up from I thought I was doing.

Once recorded, the camera panels are set, but you can fix this in a compositing program. I use Fusion to correct this, but AE will work fine too. You can actually do this in Photoshop too using an Action, but you are then dealing with frames of course, which means another conversion to video again before iPi Studio can use the data.

Actually, this would be a great feature for a future version of iPi Studio: the ability to rearrange the order of pre-recorded video panels in DMC. Please, Michael? :)

Greenlaw

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PostPosted: Sun Nov 08, 2009 7:42 pm 

Joined: Tue Nov 03, 2009 10:19 pm
Posts: 18
Thanks. I guess mine are in clockwise order, and "main" is indeed #1. The center "main" cam is 1; 80 degrees to the right of that, #2; and across the room from that, #3. In other words, I have a semicircle, but my #1 cam is the midpoint of the semicircle, #2 is the rightmost point, and #3 is the leftmost point. It seems to be working very well now, so I'm not going to tamper with success unless I have unforeseen problems.

Indeed, today I've had some of my best tracking results yet. I've been wearing a dark green T-shirt over a bright red long-sleeved shirt, dark tight thermal leggings, and red socks (!). That outfit seems to have improved my results; previously I had on all black. My background is white/beige. I might even try bright yellow gloves yet, though I read here that for a fair-skinned person like me, that may not be necessary. I also think I've gotten better at calibration; now when I load a new video, and then load my calibration scene, I don't have to adjust the scene as much to fit the T-pose.

In some ways, the biggest flaws in my .bvh files stem from the actor (me), not the tracking. I need to hire someone with more talent. :)


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PostPosted: Sun Nov 08, 2009 8:01 pm 

Joined: Mon Aug 03, 2009 1:34 pm
Posts: 2354
Location: Los Angeles
Glad to hear it's working out! By the way, they recommend a black T-Shirt over red or green long sleeves. The reason is because black will not show shadows cast by your arms on your torso, which may confuse the tracker. (All black clothing will confuse the tracker even more for obvious reasons.) :)

Greenlaw

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