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PSEye setup: background noise and tracking precision
https://forum.ipisoft.com/viewtopic.php?f=2&t=6950		 Page 1 of 2
Author:  plang [ Sat Mar 16, 2013 3:22 am ]
Post subject:  PSEye setup: background noise and tracking precision
Hi,

I saw a few images of studios with mocap areas with no office furniture at all, and a uniform background color. On the other side, I know ipisoft is quite robust, and can accept a non-uniform background. Most of the examples on the website show just that. That's my situation at the moment, and I'm pretty happy with that.

I'm hesitating building some kind of movable walls in order to reduce background "noise", but I'm wondering if it would bring a lot to the tracking quality. I'm especially interested in knowing if it brings something in term of "jitter" and "precision", not tracking errors. (You might argue it's more or less the same!)

I know lightning conditions are very important. More important than background "noise"?

Thanks for the tips!

Philippe
Author:  Greenlaw [ Sat Mar 16, 2013 9:55 am ]
Post subject:  Re: PSEye setup: background noise and tracking precision
When I recorded using PS Eye cameras, I recorded my scene on a bare green stage because, well, we just happen to have a green screen stage. It was not set up specially for iPi Mocap Studio. :)

You can actually record mocap in any environment so long as iPi MS2 can 'cancel out' the background. That said, the less 'cluttered' you have in the background, the more effective this process can be.

On the other hand...I believe Mocap Studio may search for visual features in finding the ground plane and solving camera calibration, so you don't want to have a completely blank environment.

So, the ideal environment is probably a little of both: not too cluttered and not too bare. In my case, even though I have an empty stage, the edges are clearly visible and there are a few features visible outside of the stage area. I think this helped in getting perfect calibration results every time as shown in this ancient video: iPi Studio Calibration Video

What's probably more important is room and subject lighting: you want to light the room and performer as evenly as possible and avoid harsh directional lighting that can create dark shadows. Suitable clothing is important too.

G.
Author:  vmaslov [ Sun Mar 17, 2013 12:50 pm ]
Post subject:  Re: PSEye setup: background noise and tracking precision
plang wrote:
I know lightning conditions are very important. More important than background "noise"?

Uniform lighting is more important than any background adjustment. The colors of the actor should look more or less the same from the viewpoints of all the cameras.

Greenlaw wrote:
I believe Mocap Studio may search for visual features in finding the ground plane and solving camera calibration, so you don't want to have a completely blank environment.

Currently calibration algorithm does not extract any visual features, and just detects the light marker. Ground plane is determined by the frames which were specified by the user as having the marker at the ground.
Author:  Greenlaw [ Sun Mar 17, 2013 1:52 pm ]
Post subject:  Re: PSEye setup: background noise and tracking precision
Ah! Of course. Thanks for clarifying. :)

G.
Author:  plang [ Sun Mar 17, 2013 11:52 pm ]
Post subject:  Re: PSEye setup: background noise and tracking precision
Greenlaw, Vmaslov, thanks for your answers.

In order to check if lightning conditions are good, and if the furniture/bookshelf/clutter I have in my office do not cause problems, I wanted to check if the background subtraction is done properly on all of my (PSEye) cameras.

Here is a screenshot:

Image

I cannot say if that's a good result or not. Note that I do not wear the clothes I usually use for mocap: I can see my torso and arms are sometimes recognized as background, when there are green dots on me. Even my hair I can see.
Author:  vmaslov [ Mon Mar 18, 2013 12:10 am ]
Post subject:  Re: PSEye setup: background noise and tracking precision
Looks pretty well I think. Of course, for good mocap results you should use the clothes of colors that are more contrast with your background and between the body parts.
The areas at the floor, which are not detected as background, are caused by the actor's shadows. It will not give you much trouble if you ensure that the actor is contrasting with the floor color.
Author:  plang [ Mon Mar 18, 2013 12:17 am ]
Post subject:  Re: PSEye setup: background noise and tracking precision
Some more results: the previous video was done in the evening. The next one was done just now, in the morning. There is brightness coming from the windows, and I think the results are better:

Image

But I can see the shadows on the floor cause a few problems. I have to light up the floor, as you suggest in your wiki.

Image

I also have to cover the windows: I can see my reflections on them! And next time, I'll have to hide better when doing the background evaluation... :)

On camera 3, I can see my deep green shirt is being recognized as background.
Author:  plang [ Mon Mar 18, 2013 12:33 am ]
Post subject:  Re: PSEye setup: background noise and tracking precision
Again some more results, which are quite interesting. I tried using two big spots to light up the scene:

Image

There are shadows all over the background, and the result is not good at all:

Image

BUT! Tell me if I'm wrong: the rest of the scene (part of the scene with no shadow) seems to be subtracted much better, not to say perfectly. Does that mean I would benefit from a stronger diffuse lightning coming from the ceiling? Maybe I could change my neon lights. What do you think?
Author:  plang [ Mon Mar 18, 2013 12:55 am ]
Post subject:  Re: PSEye setup: background noise and tracking precision
And final results of my light optimization session:

Image

I have directed my spots to the walls, and it diffuses the light in the whole room. No more nasty shadows that do not allow proper background subtraction.

With proper clothes, and my windows covered (you can see my own reflection on camera 1), I think this show that background clutter is not a big problem...
Author:  Greenlaw [ Mon Mar 18, 2013 1:15 am ]
Post subject:  Re: PSEye setup: background noise and tracking precision
I noticed that all of your cameras are set fairly high up, and all are positioned at approximately the same level and downward angle. IMO, you will get much better coverage of the performances if some cameras are placed much lower.

With all the cameras basically sharing similar POV, there may be a greater chance of occlusion. For example, having only 'high views' and the complete lack of any 'side views' may compromise the ability to accurately track a walk cycle. Or if the performer crouched down low, his body will completely occlude his legs.

G.
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