Skeltrack: A Free Software library for skeleton tracking (GUADEC 2012)
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Skeltrack: A Free Software library for skeleton tracking (GUADEC 2012)



By Joaquim Rocha. ...

By Joaquim Rocha.

With the release of the Kinect device, there was finally an affordable camera capable of giving depth information. This, together with the Kinect's open USB connection, led to a lot of innovative projects.

Still, the Kinect just gives raw signals and the only way to obtain more complex information, such as skeleton tracking was to use either the Microsoft SDK or the OpenNI framework. Both of these solutions are closed, proprietary and, in the case of Microsoft's, only for non-commercial work.

To solve the issue above, Igalia developed Skeltrack, a Free and Open Source library published under LGPL that performs human skeleton tracking and identifies a number of skeleton joints.
It is a more atomic solution than the other commercial counterparts because it does not connect directly to the Kinect nor to any other depth camera, instead it expects to be given the buffer corresponding to the depth buffer.

In this talk Joaquim will present how Skeltrack was developed and show a demo of it working.



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Skeltrack: A Free Software library for skeleton tracking (GUADEC 2012) Skeltrack: A Free Software library for skeleton tracking (GUADEC 2012) Presentation Transcript

  • Skeltrack - Open Source Skeleton Tracking Joaquim Rocha, Igalia GUADEC 2012 - A Coruña
  • Igalia's Interactivity Team was on to investigate immersive applications using FOSS
  • These applications represent new/different ways of interaction for users
  • Those can go from entertainment to more serious applications
  • The Kinect
  • Microsoft's Kinect was the first camera with a price affordable to the public
  • The USB connection is open and thus hackable
  • This originated Open Source projects like the libfreenect, a library to control the Kinect device and get its information
  • We created a GLib wrapper for libfreenect called GFreenect
  • GFreenect offers asynchronous functions (and some synchronous as well) and makes it easy to use with other GNOME technologies
  • GObject Introspection opens these technologies for users of Python, Javascript, Vala, etc.
  • The Kinect has a structured light camera which gives depth information
  • But that's raw information... values from 0-2048
  • libfreenect/GFreenect can give those values in mm
  • Still...
  • It does NOT tell you there is a person in the picture
  • Or a cow
  • Or a monkey
  • Let alone a skeleton and where its joints are!
  • For this you need a skeleton tracking solution
  • Skeleton Tracking
  • Three proprietary/closed solutions exist:
  • Microsoft Kinect SDK: non-commercial only
  • OpenNI: commercial compatible
  • Kinect for Windows: commercial use allowed but incompatible with the XBox's Kinect
  • Conclusion: There were no Free solutions to perform skeleton tracking... :(
  • So Igalia built one!
  • Enter Skeltrack
  • What we wanted: ✩ A shared library, no fancy SDK ✩ Modular (do one thing) ✩ Device independent ✩ No pattern matching, no databases ✩ Easy to use (everybody wants that!)
  • Not as easy as it sounds!
  • The current version tracks up to 7 joints: ✩ Head; ✩ Shoulders; ✩ Elbows; ✩ Hands.
  • Smoothing is implemented using Holt's Double Exponential formulas
  • Smoothing and heuristics used can be tweaked using GObject properties
  • There are still some things missing...
  • Future work
  • Hands from elbows: If one of the extremas is an elbow, we need to infer where the hand is
  • Robustness: Use restrictions to ignore objects that are not the user
  • Multi-user: Track more than one person at a time
  • And of course, get the rest of the joints: hips, knees, etc.
  • How to use it?
  • First reduce the depth buffer's dimension Reducing the buffer's dimension will make things faster
  • While at it, it's wise to also apply a depth threshold
  • Asynchronous API
  • SkeltrackSkeleton *skeleton = SKELTRACK_SKELETON (skeltrack_skeleton_new ()); skeltrack_skeleton_track_joints (skeleton, depth_buffer, buffer_width, buffer_height, NULL, on_track_joints, NULL);
  • Synchronous API
  • SkeltrackJointList list; list = skeltrack_skeleton_track_joints_sync (skeleton, depth_buffer, buffer_width, buffer_height, NULL, NULL);
  • Skeleton Joint: ID: HEAD, LEFT_ELBOW, RIGHT_HAND, ... x: X coordinate in real world (in mm) y: Y coordinate in real world (in mm) screen_x: X coordinate in the screen (in pixels) screen_y: Y coordinate in the screen (in pixels)
  • Join us!
  • Nifty Tools for Development: GFreenect: GFreenect Utils:
  • GFreenect Python Example
  • Tool: depth-file-viewer
  • Tool: record-depth-file
  • Demo? Warning: Might go wrong!
  • Questions?
  • Creative Commons pictures from flickr: Kinect: Monkey: nothingtosay Kid Playing: Rob Welsh Skeleton: Dark Botxy Other non CC images: Doctor: Minority Report: